aes/tg/10-08 bunter reservoir quality for geothermal

AES/TG/10-08 Bunter Reservoir Quality for Geothermal Applications in the

Zuid Holland Area

June 2010 Olakunle Bukola Ogunjimi

ii

Bunter Reservoir Quality for Geothermal Applications

MSc Graduation Thesis of Olakunle Bukola OGUNJIMI. June, 2010.

Title : Bunter Reservoir Quality for Geothermal Applications in the

Zuid Holland Area

Author(s) : Olakunle Bukola Ogunjimi

Date : June 2010

Professor(s) : Dr. Gert Jan Weltje

Supervisor(s) : Dr. Bert Dijksman, Dr. Gert Jan Weltje

TA Report number : AES/TG/10-08

Postal Address : Section for Petroleum Geosciences

Department of Applied Earth Sciences

Delft University of Technology

P.O. Box 5028

The Netherlands

Telephone : (31) 15 2781328 (secretary)

Telefax : (31) 15 2781189

Copyright ©2010 Section for Petroleum Geosciences

All rights reserved.

No parts of this publication may be reproduced,

Stored in a retrieval system, or transmitted,

In any form or by any means, electronic,

Mechanical, photocopying, recording, or otherwise,

Without the prior written permission of the

Section for Petroleum Geosciences

iii



Acknowledgement

This project has been carried out during a graduation thesis position created by the

Exploration and Appraisal Unit of the Subsurface Evaluation Department at Panterra

Geoconsultants B.V. in Leiderdorp, The Netherlands. I am very grateful, not only for the

opportunity to carry out this project in this company but also for the opportunity to gain a

much needed industrial work experience while the project lasted.

I would like to thank my external supervisor, Dr. Bert Dijksman for his guidance and

mentorship through out the period of the project and to all staff members of the Exploration

and Appraisal Unit. They were always ready to assist me when ever the need arose.

My University supervisor, Dr. Gert Jan Weltje, was of great help and guidance in the

achievement of this project. He was instrumental to the easy facilitation and coordination

between TU Delft and Panterra Geoconsultants B.V., without which the graduation thesis will

not have been possible. I appreciate your constructive comments and criticism.

Lastly, I will like to appreciate all my lecturers and colleagues from the Faculty of

Civil Engineering and Geosciences for all their input into my academic and professional

development.

Olakunle Bukola Ogunjimi

June, 2010.

iv



Abstract

With the continued growth of world population comes the need for more energy resources to

quench the thirst of the energy insatiable world we live in. Geothermal energy is green and is a

sustainable way of providing our energy needs. Formation water at depths greater than 3,000m

in the Netherlands is a potential source of energy to generate electricity. Over the study area

observed formations are buried deep enough to reach water temperatures in excess of 1000C,

and this could conceivably be used for the generation of electricity with very low CO2

emissions.

Four seismic surveys L3NAM1985P (146.6km2), L3NAM1991A (414.5km

2), Z3NAM1990D

(762.2km2) and Z3AMC1989A (544.6km

2) were interpreted and integrated with well data

including well tops to help in this evaluation.

The Detfurth and Volpriehausen (Triassic) of the West Netherlands Basin in the Zuid Holland

area are established to be potentially good reservoirs for geothermal development. This is due

to the fact that stratigraphically, they are the deepest sandstones and consequently most likely

to reach sufficient depths. These objectives are too deep to be visible and adequately

interpretable on seismic due to the low impedance contrast and because it is overlain by the

strong reflectors of the evaporates of the Upper Germanic Triassic. Therefore, surfaces for

these objectives were generated based on formation markers in the wells that intersected the

Triassic using 3D gridding in Jewel Suite.

Generally, the reservoir interval from the top of the Detfurth to the base of the Volpriehausen

contains enough thick sequences of porous sands. The gross thickness ranges from 95m in

well VAL-01 to 163m in P15-14. Two porosity/permeability relationships have been used for

calculating N/G at various permeability cut-offs of 0.1mD, 1mD, 10mD and 100mD. Net sand

ranges from 0.14m to 58.04m for 10mD and 0.1mD permeability cut-offs respectively.

The zone in and around Wells MON-03, P18-A-02, P15-01 and P15-14 show the best

reservoir intervals based on average porosity and N/G values. Based on different scenarios the

average porosity ranges from 6.5% to 16.2% and N/G ranges from 0.6% to 30.8%. Primary

porosity and permeability are generally low in the mapped area, but it is expected that

permeability and connectivity are enhanced locally through fracturing. The objective is highly

faulted, and hence this will serve as conduit for water leading to a higher level of connectivity

and water production. Heterogeneity remains an issue of concern due the high level of Vcl in

some of the intervals. But it is believed that they will generally not serve as a barrier or baffle

to flow, i.e. it will reduce the vertical permeability but not the important horizontal

permeability.

The objectives in the mapped area suggest that aeolian and fluvial facies occupy more than

50% of the rock unit. Aeolian sandstones are known for their excellent reservoir qualities.

They are well sorted with good porosity and permeability. This means that a larger part of the

rock unit within the mapped area is of good reservoir quality.

The focus of the oil industry is on the structural highs. Prospective areas for geothermal

exploitation occur in lows. The lows have no well penetrations and are usually considerably

deeper than the much shallower oil fields. It is, however, suspected that structuration and

formation of highs and lows is relatively late and that diagenesis predates structuration. This

would imply that the shallow oil fields have porosities representative of much greater depths.

This is borne out by the fact that there is hardly any relationship of porosity against depth.

When this proves to be accurate it would have a very positive effect on the development of

geothermal energy, since this reduces the uncertainties involved in a project like this.

v



Table of Contents Acknowledgements.................................................................................................................................................iii

Abstract...................................................................................................................................................................iv

Table of Contents.....................................................................................................................................................v

List of Figures.........................................................................................................................................................vi

List of Tables..........................................................................................................................................................vii

1. INTRODUCTION ........................................................................................................................................... 1

1.1 Project Plan: ......................................................................................................................................... 3 1.2 Deliverables: ......................................................................................................................................... 3

2. REGIONAL GEOLOGY ................................................................................................................................. 7

2.1 Overview of the Triassic Stratigraphy .................................................................................................. 9 2.1.1 Lower Germanic Triassic Group ............................................................................................. 10 2.1.1.2 Main Buntsandstein Subgroup ................................................................................................. 10 2.1.1.2.3 Hardegsen Formation ..................................................................................................... 11

3. AVAILABLE DATA AND METHODS USED ............................................................................................ 13

3.1 Coordinate System .............................................................................................................................. 13 3.2 Seismic Data ....................................................................................................................................... 13 3.3 Well Data ............................................................................................................................................ 14

4 INTERPRETATION AND RESULTS .......................................................................................................... 16

4.1 Seismic Interpretation ......................................................................................................................... 16 4.2 Mapping in Time ................................................................................................................................ 20 4.3 Velocity Model ................................................................................................................................... 22 4.4 Mapping in Depth ............................................................................................................................... 23

4.4.1 3D Gridding............................................................................................................................. 23 4.4.2 Depth and Thickness Maps of the Detfurth and Volpriehausen .............................................. 25 4.4.3 Geothermal Gradient/Temperature Maps ................................................................................ 27

4.5 Petrophysical Interpretation of reservoir levels .................................................................................. 29 4.6 Mapping of Reservoir Quality ............................................................................................................ 37

4.6.1 Thickness ................................................................................................................................. 37 4.6.2 Net/Gross ................................................................................................................................. 39 4.6.3 Porosity ................................................................................................................................... 40

4.7 Compilation of Core Data ................................................................................................................... 40 4.7.1 Porosity and Permeability trends and relationships ................................................................. 40 4.7.2 Environment of Deposition ..................................................................................................... 42

4.8 Areas Suitable for Geothermal Exploitation ....................................................................................... 43 4.9 Risks and possible means to reduce risks ........................................................................................... 44 4.10 Volumetrics Reporting ........................................................................................................................ 46

5.0 CONCLUSIONS AND RECOMMENDATIONS ......................................................................................... 47

Reference................................................................................................................................................................48 Appendixes.............................................................................................................................................................50

vi



List of Figures

Figure 1.1: Depth in m to the base of the Triassic section in the Netherlands..........................................................1

Figure 1.2: Licences for geothermal energy as at January 1st, 2010 in the Netherlands...........................................4

Figure 1.3a: The study area showing the four seismic surveys interpreted...............................................................5

Figure 1.3b: The study area showing the four seismic surveys............................................................................... ..6

Figure 2.1: Structural elements map of the Netherlands……………………………………………………………8

Figure 2.2: Seismic section running from SW flank of the West Netherlands Basin into the inverted basin...........8

Figure 2.3: Regional cross-section passing through the Central Netherlands Basin.................................................9

Figure 2.4: Characteristic trap situation in the WNB…………………………………………………………….....9

Figure 2.5: Stratigraphy of the Triassic in the Netherlands....................................................................................12

Figure 3.1: The seventy-nine (79) wells in the study area......................................................................................15

Figure 3.2: The thirty (30) wells that intersected the Triassic in the study area.....................................................15

Figure 4.1: Inline 1004 (L3NAM1991A)...............................................................................................................17

Figure 4.2: Inline 1627 (Z3NAM1990D).............................................................................................. .................17

Figure 4.3a: A regional view of the four levels mapped showing the complex faulting system in the WNB.........18

Figure 4.3b: A regional view of the TM, BP and TT............................................................................................. 18

Figure 4.3c: A regional view of the BP and TT............................................................................................... .......19

Figure 4.3d: A regional view of the TT.............................................................................. ....................................19

Figure 4.4a: Base Tertiary time structural map............................................................................................ ..........20

Figure 4.4b: Texel Marl time structural map..........................................................................................................20

Figure 4.4c: Base Posidonia time structural map.............................................................................................. ......21

Figure 4.4d: Top Triassic time structural map.................................................................................................... ....21

Figure 4.5a: Base Tertiary Velocity Model................................................................................... .........................22

Figure 4.5b: Top Triassic Velocity Model.............................................................................................. ...............23

Figure 4.6: Model Layer Definition........................................................................................................................24

Figure 4.7a: Area used for gridding with lateral and vertical dimensions..............................................................24

Figure 4.7b: 3D Grid of the modelled area............................................................................................................ .25

Figure 4.8a: Detfurth depth map with wells for location...................................................................................... ..26

Figure 4.8b: Volpriehausen depth map with wells for location..............................................................................26

Figure 4.8c: Top Detfurth to Base Volpriehausen thickness map with wells for location......................................27

Figure 4.9a: Detfurth Temperature map with wells for location.............................................................................28

Figure 4.9b: Volpriehausen Temperature map with wells for location...................................................................28

Figure 4.10: Wells used for Correlation and Petrophysical Interpretation.............................................................29

Figure 4.11a: Graph of Poro-Perm of Wells of interest..........................................................................................30

Figure 4.11b: Graph of Poro-Perm of Wells of interest giving more weight to the good values............................31

Figure 4.12: Correlation Panel 1............................................................................................................................32

Figure 4.13: Correlation Panel 2.............................................................................................. ..............................33

Figure 4.14: Correlation Panel 3...................................................................................................... ......................34

Figure 4.15: Correlation Panel 4.......................................................................... ..................................................35

Figure 4.16: Correlation Panel 5.............................................................................................. ..............................36

Figure 4.17: Correlation Panel 6............................................................................................................................38

Figure 4.18: Por-Perm Detfurth for Wells Q16-08 and VAL-01............................................................................41

Figure 4.19: Por-Perm Volpriehausen for Wells Q13-04, Q13-07-S2, Q16-02, Q16-08 and VAL-01..................41

Figure 4.20: Depositional model for the Lower Buntsandstein and Volpriehausen formations in the southern

Netherlands.............................................................................................................................................................42

Figure 4.21: Area suitable for geothermal exploitation in the Detfurth..................................................................43

Figure 4.22: Area suitable for geothermal exploitation in the Volpriehausen........................................................44

Figure 4.23: Depth Vs Porosity for Wells that intersected the Triassic..................................................................45

vii



List of Tables

Table 2.1. Stratigraphic framework of the Triassic in the Netherlands..................................................................10

Table 3.1: Parameters of each of the four seismic surveys interpreted in the project.............................................14

Table 4.1: Gross reservoir thickness for each Well................................................................................................29

Table 4.2a: Gross and Net Thickness of the reservoir intervals in the Wells.........................................................37

Table 4.2b: Gross and Net Thickness of the reservoir intervals in the Wells based on the second scenario..........37

Table 4.3a: N/G, Average Porosity, and Average Volume of Clay calculated in the reservoir intervals in the

Wells........................................................................................................................ ..............................................39

Table 4.3b: N/G, Average Porosity, and Average Volume of Clay calculated in the reservoir intervals in the

Wells based on the second scenario which gives more weight to the good values.................................................39

Figure 4.4a: Volumetrics Report using Sw of 100%..............................................................................................46

Figure 4.4b: Volumetrics Report using Sw of 80%................................................................................................46

Figure 4.4c: Volumetrics Report using Sw of 60%................................................................................................46

1. INTRODUCTION

With the continued growth of world population comes the need for more energy

resources to quench the thirst of the energy insatiable world we live in. In 2009, Prof. John

Beddington, the UK government chief scientist said, “ growing world population will cause a

“perfect storm” of food, energy and water shortages by 2030”. Demand for food and energy

will jump 50% by 2030 and for fresh water by 30%, as the population tops 8.3 billion, he told

the Sustainable Development UK 09 conference in London. Climate change will exacerbate

matters in unpredictable ways, he added.1

Figure 1.1: Depth in m to the base of the Triassic section in the Netherlands.(Mulder et al., 2003)15

2



As a result of the above, other forms of sustainable energy solutions are needed for energy

production. Geothermal energy which is a green source of energy does not burn fuel to

generate electricity, so their emission levels are very low. They release less than 1% of the

carbon dioxide emissions of a fossil fuel plant. Geothermal plants use scrubber systems to

clean the air of hydrogen sulphide that is naturally found in the steam and hot water.

Geothermal plants emit 97% less acid rain-causing sulphur compounds than are emitted by

fossil fuel plants. After the steam and water from a geothermal reservoir has been used, they

are injected back to the earth.2

Therefore, in many ways this source of energy is not only renewable but it is also

“green”, i.e. friendly to the environment. If the trend in worldwide energy demand which

triggered the oil price to rise to around US $ 140 per barrel in July 2008 is anything to go by,

then other forms of sustainable energy resources need to be developed aggressively.

Groundwater at greater depths in the Netherlands is a potential source of energy.

Generally it can be stated that a permeable layer at a depth of 3000 m or more contains water

in excess of 1000C. This implies that the generation of electricity could be considered. The

distribution of the Triassic is shown in Figure 1.1. It occurs over large parts of the

Netherlands. Locally it is buried deep enough ( >3000 m) to have formation water temperature

in excess of 1000C, and this could conceivably be used for the generation of electricity with

very low CO2 emissions. Aquifers that are of potential interest for the heating purposes occur

at depths of less than 100 m to more than 3000 m in Permian, Lower Triassic and Lower

Cretaceous sandstones and in two Tertiary sand units. In total, ca. 90 1018

J (equivalent to

2400 109 m

3 natural gas, i.e. the equivalent of the Groningen Gas Field) of heat in place

(HIP) may be present in these deep reservoirs. The fraction of this energy that may eventually

be produced successfully, however, depends strongly on location-specific reservoir

properties.3

There has been renewed efforts in the recent past by the Delft University of Technology to

produce hot water for heating purposes (Delft Geothermal Project, DAP), but the target

reservoir (Delft Sandstone) is shallow and the water that will be produced is below 1000C,

making it not suitable for electricity generation.14

This project therefore is targeting the

Triassic where it is believed water above 1000C will be present for electricity generation.

This project is aimed at studying the spatial variations of the reservoir quality of the

Bunter sandstone (Triassic) in the Zuid Holland area of the Netherlands. Issues like

environment of deposition, reservoir thickness, net/gross, porosity, permeability will be

3



addressed. The results can be used to advise on possibilities for the application of geothermal

energy. The project plan and deliverables are highlighted below.

1.1 Project Plan:

Create an inventory of wells which have intersected the Bunter Section (Location;

Projection System; Deviation data; Well velocity surveys; Log data/interpretations).

Interpretation (Interpretation of four levels: Base Tertiary (BT), Texel Marl (TM),

Base Posidonia (BP), and Top Triassic (TT)); Mapping in time; Velocity modelling;

Mapping in depth; Isopach mapping.

Reservoir Modelling (Petrophysical interpretation of reservoir levels; Porosity and

permeability trends and relationships; Environment of deposition; Thickness;

Net/Gross, Porosity).

1.2 Deliverables:

Identification of areas suitable for geothermal exploitation.

Identification of risks.

Groundwater at greater depths in the Netherlands is a potential source of energy. Based on

subsurface temperature data, several evaluation projects were carried out in the 1980s,

ultimately resulting in a number of inventory and feasibility studies. In 2005 the first

exploration licence was granted and a number of projects are being evaluated presently.4

Figure 1.2 shows the licences for geothermal energy issued by the Dutch Ministry of

Economic Affairs as at January 1st, 2010. Figures 1.3 (a & b) shows the present study area and

a zoomed in view.

4



Figure 1.2: Licences for geothermal energy as at January 1st, 2010 in the Netherlands. Source: TNO.

5



Figure 1.3a: The study area showing the four seismic surveys interpreted.

N

6



Figure 1.3b: The study area showing the four seismic surveys.

N

7



2. REGIONAL GEOLOGY

This project is situated in the West Netherlands Basin (WNB). The boundaries of the

WNB are the Zandvoort ridge and the IJmuiden high to the north, the London-Brabant Massif

to the south and it merges with the Roer-Valley Graben towards the south-east (Figure 2.1).

The WNB was formed on the Campine basin and existed from Late Permian till Late

Cretaceous. During the middle and late Triassic tectonic movement, large-scale half-graben

structures were formed. The strongest rifting occurred during the Late Jurassic to Early

Cretaceous.5

During this rifting event tilted faults blocks have been formed and thick fluvial sediment

packages were deposited in the half-grabens. During this formation of the half-grabens, NW-

SE faults patterns were formed. The Late Cretaceous compressive forces (Alpine

compression) reactivated the earlier faults. This resulted in the formation of complex

inversion structures and NNW-SSE fault patterns (Figure 2.2, 2.3). In these structures most of

the oil and gas fields of the WNB (Figure 2.4) are found.6,7

For the purpose of geothermal energy, three main intervals are identified as promising zones:

the Permian Rotliegendes sandstones, the Lower Triassic sandstones and the Lower

Cretaceous sandstones.3 For this study, however, the Lower Triassic sandstones are the target

reservoir. (Figure 1). In the lower Triassic (Lower Germanic Triassic), the Detfurth and

Volpriehausen intervals are best suited for geothermal exploitation. Table 2.1. Further

description of the Triassic and especially this two intervals are given in Chapter 2.1

8



Figure 2.1: Structural elements map of the Netherlands. (De Jager, 2007)6

Figure 2.2: Seismic section running from SW flank of the West Netherlands Basin into the inverted basin.

See Fig. 2.1 for location.(De Jager, 2007)6

9



Figure 2.3: Regional cross-section passing through the Central Netherlands Basin. See Fig. 2.1 for

location.(De Jager, 2007)6

Figure 2.4: Characteristic trap situation in the WNB: gas occurs in a tilted fault-block structure. The oil is

situated in the overlying anticline.(Van Balen, 2002)5

2.1 Overview of the Triassic Stratigraphy

The Triassic section consists mainly of an alternation of varicoloured, but mainly

reddish sandstone and claystone with greyish limestone, marls and evaporites. See Figure 2.5.

The sequence was deposited under continental conditions.

Two groups have been defined: the Lower and Upper Germanic Trias, separated by an

unconformity. This unconformity is known as the Base Solling or Hardegsen unconformity.

Triassic rock outcrop locally in the Eastern part of the Netherlands (Achterhoek). The Lower

Germanic group is deposited and preserved over large parts of the Netherlands whereas the

10



upper Germanic group is preserved in the Mesozoic basins. The Triassic lies conformably

over the Zechstein group (Permian) and then unconformably overlain by younger sequences of

the Altena, Nedersaksen, Rijnland and North Sea Groups. The stratigraphic framework of the

Triassic in the Netherlands is shown in Table 2.1. Best reservoirs occur in the Lower

Germanic Trias, which is described in more detail below.

Table 2.1. Stratigraphic framework of the Triassic in the Netherlands. The intervals best suited for

geothermal exploitation are marked in yellow.

2.1.1 Lower Germanic Triassic Group

The sediments of the lower Germanic Triassic Group date from the Early Triassic

(Scythien). Within this group four formations have been defined: The Lower Buntsandstein,

The Volpriehausen, the Detfurth and the Hardegsen Formation. The upper three are also

referred to the the Main Buntsandstein Group.

2.1.1.1 Lower-Buntsandstein Formation

The Lower Buntsanstein Formation consists of a cyclic alternation of fining upward

sequences, from fine grained sandstone to claystone/siltstone. This cyclicity is caused by

periodic changes in the climate. The individual cycles are between 20 and 40 m thick and

show a large geographic extent. The lower Buntsandstein is very constant in thickness and

composition and is because of its transparant character very well correlatable on seismic data.

It is underlain by the Permian carbonates/clastics. Permian evaporites do not occur over the

study area

2.1.1.2 Main Buntsandstein Subgroup

This subgroup consists of three, fining upward formations: the Volpriehausen, the

Detfurth and the Hardegsen Formations. Over the southern part of the Netherlands this

Formation Lithology Thickness m Depth Range m

Sleen Grey Shales and Brown Limestone 45 40-4450

Keuper Evaporites and Claystone >1000 850-3900

Muschelkalk Limestone and Evaporites 500 outcrop-3950

Roet Evaporites, Clay- and Siltstone 300 outcrop-4200

Solling Sand- and Claystone 125 90-4250

Hardegsen Sand- and Claystone 200 680-4350

Detfurth Sand- and Claystone 100 270-4500

Volpriehausen Sand- and Claystone 200 125-4750

Lower Buntsandstein Varicoloured Sand- and Claystone 400 80-5000

Up

pe

r

Ge

rma

nic

Tri

as

Lo

we

r

Ge

rma

nic

Tri

as

11



subgroup consists of mainly sands. In contrast with the underlying Lower Buntsandstein

Formation the thicknes can vary considerably. This subgroup overlies the Lower

Buntsandstein with a sharp boundary (minor unconformity) and is unconformably overlain by

the Upper Germanic Trias Group-North Sea Super Group. This subgroup contains the best

reservoir intervals, the Volpriehausen Formation and the Detfurth Formation.

2.1.1.2.1 Volpriehausen Formation

The Volpriehausen Formation occurs widely in the Dutch subsurface. The

Volpriehausen Formation displays its greatest thickness, over 200 m, in the Dutch Central

Graben and the Broad Fourteens Basin. It reaches 100 m in the Ems Low and 150 m in the

Roer Valley Graben. The Volpriehausen Unconformity at the base of the formation locally

cuts up to several tens of meters into the Lower Buntsandstein Formation. It consists of

arkosic sandstones with a quartz content slightly below 50%. It is cemented by high

percentages of calcite and dolomite, especially in its lower part.

2.1.1.2.2 Detfurth Formation

The occurrence of the Detfurth Formation is restricted to the Early Triassic lows as a

result of uplift and erosion prior to deposition of the Solling Formation. The depositional

thickness of the formation displays considerable variation: 60–100 m in the Dutch Central

Graben, 50–80 m in the Ems Low and 20–40 m in the West Netherlands Basin, Roer Valley

Graben and Broad Fourteens Basin. In the West Netherlands Basin and Roer Valley Graben

the formation consists entirely of sandstones.

2.1.1.2.3 Hardegsen Formation

The Hardegsen Formation consists predominantly of siltstones, with subordinate, thin

sandstone beds. Significant amounts of sandstone occur only in the basin-margin area. The

present-day thickness of the formation was strongly influenced by the pre-Solling erosion and

displays strong variations. Only erosional remnants remain; e.g in Ems Low and in the Dutch

Central Graben (well F9-3) up to 200 m occur. In the Broad Fourteens Basin, the West

Netherlands Basin and the Roer Valley Graben, the thickness reaches up to 70 m. During

deposition of the formation, syn-rift subsidence occurred in the Dutch Central Graben, as is

evident from the thickening of individual sequences. In other earlier depocentres, such as the

12



Broad Fourteens Basin, the West Netherlands Basin and the Roer Valley Graben, differential

subsidence had ceased.

Figure 2.5: Stratigraphy of the Triassic in the Netherlands. (Source: Stratigraphic Nomenclature of the

Netherlands) 8

13



3. AVAILABLE DATA AND METHODS USED

3.1 Coordinate System

The coordinate system used is the Rijksdriehoekstelsel New (RD New), the Dutch

national projection system. Datum is the Netherlands datum. The onshore data were available

in RD while the offshore data were available in UTM (ED50). They UTM (ED50) coordinates

were transformed to RD new (Netherlands datum) for consistency. The transformation was

done in Geographix. The Bessel-ellipsoid (1841) is used and this ellipsoid is projected on

plane with the Double Stereographic projection (first to a sphere with the Gauss-projection

and then to the plane). Note: In Geographix the Netherlands (Molodensky) datum should be

used and not the Amersfoort (Bursa-Wolff) datum.

To transform the old RD system to the new RD system:

X = + 155.000 m

Y = + 463.000 m

Details of the projection systems used are presented in the Appendix under Coordinate

System.

3.2 Seismic Data

Four 3D seismic surveys were interpreted. They were all supplied by TNO in segy format.

They were supplied as different file collections and then merged in Geographix before being

loaded in Tigress Workstation for interpretation. The merged segy files were also later

exported to Jewel Suite for fault interpretation. Each individual survey has been interpreted

and the interpretation was exported and merged during the mapping. They include;

1. L3NAM1985P

2. L3NAM1991A

3. Z3NAM1990D

4. Z3AMC1989A

The seismic parameters of each of the surveys is shown in Table 3.1 and the summary of

parameters used to process each survey and a picture denoting both the SEG and Non SEG

polarities can be seen in the Appendix under Seismic Data.

Seismic data polarity follows the SEGY acquisition convention for L3NAM1985P,

L3NAM1991A, and Z3NAM1990D i.e. an increase in impedance is recorded as an increase in

14



pressure for a hydrophone or an upwards movement of the Geophone and is recorded as a

negative number. This polarity has been maintained through processing and display, resulting

in a Reverse SEGY display (normal European display convention).This implies that an

increase in impedance is represented by a negative loop. The data is assumed to be (close to)

zero phase.

However, seismic display polarity follows the Normal SEGY convention for

Z3AMC1989A i.e. an increase in impedance is displayed as a positive loop (normal American

display convention). The data is also assumed to be (close to) zero phase. The shifts applied

can be seen in Table 3.1

No reprocessing has been carried out, i.e. the data is according to the original initial

processing. No processing reports were available. Quality of the data is good i.e. the seismic

resolution is clear enough to help in the interpretation of faults and distinguish important

horizons.

Table 3.1: Parameters of each of the four seismic surveys interpreted in the project.

3.3 Well Data

There were seventy-nine (79) wells in the study area (Figure 3.1 and Appendix under

Well Data). For each well a set of data (Well ID, coordinates, location, KB, status, class, total

depth, completion well logs, reports, velocity information, pressure etc), digital logs,

formation tops, deviation surveys and core data were available from the TNO website

www.nlog.nl

Out of the seventy-nine (79) wells in the study area, only thirty (30) intersected the

Triassic (Figure 3.2 and Appendix under Well Data), but not all of them had the complete

suite of logs needed for petrophysical interpretations.

Minimum Maximum Minimum Maximum Minimum Maximum

L3NAM1985P 245 980 1 567 0s 5s 189 193 No clip applied 10ms Non SEG

L3NAM1991A 700 1440 720 2125 0s 5s 189 193 Clipped at 15000 60ms Non SEG

Z3NAM1990D 1001 1989 68 1736 0s 5s 189 193 Clipped at 6000 60ms Non SEG

Z3AMC1989A 2 1406 1 1641 0s 3.5s 189 193 No clip applied 40ms SEG

INLINE XLINE

3D SEISMIC SURVEYS XLINE BYTE LOCATION

TIME

AMPLITUDES TIMESHIFT POLARITYINLINE BYTE LOCATION

http://www.nlog.nl/

15



Figure 3.1: The seventy-nine (79) wells in the study area.

Figure 3.2: The thirty (30) wells that intersected the Triassic in the study area.

N

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4 INTERPRETATION AND RESULTS

4.1 Seismic Interpretation

The TNO provided seismic data volumes that were loaded into Tigress software for

horizon interpretation and then later Jewel Suite for fault interpretation. Four seismic surveys

were provided (See area in Figure 3.1b) and in each of the surveys, four levels were mapped.

The levels are; Base Tertiary (BT), Texel Marl (TM), Base Posidonia (BP) and Top

Triassic (TT). The L3NAM1985P, L3NAM1991A and Z3NAM1990D surveys which

covered 146.6 km2, 414.5 km

2 and 767.2 km

2 respectively, were acquired by NAM.

However, the Z3AMC1989A survey which covers an area of 544.6 km2 was initially acquired

by AMOCO and was later taken over by BP.

In this interpretation, all the wells intersecting the Triassic (including well tops) were

integrated with the seismic data to help in interpretation. The Base Tertiary, Texel Marl and

Base Posidonia were interpreted to give a view of the overall structure of the subsurface and

to serve as reference points. The target horizons, which were the Detfurth and Volpriehausen

were too deep to be visible and adequately interpretable on Seismic due to the noisy

reflections at that level (due to the low impedance contrast and because it is overlain by the

strong reflectors of the evaporites of the Upper Germanic Triassic). Therefore, the Top

Triassic was mapped from Seismic and based on the formation markers of the target horizons

in the wells that intersected the Triassic, surfaces for this levels were generated using 3D

gridding in Jewel Suite. Inline 1004 in survey L3NAM1991A shows the geometry of the

levels mapped. Here the TT is offset by normal and reverse faults that have resulted in a series

of highs and lows for this interval. The intense faulting occurs over the entire mapped area

(Figures 4.1 - 4.3) . Also, see Inline 1627 in Survey Z3NAM1990D. In the appendix under

Seismic Interpretation, a more general overview and geometry of the horizons and faults

mapped in this area can be seen. This interpretation is consistent with previous work done in

this area. The occurrence of the Detfurth Formation is restricted to the Early Triassic lows as a

result of uplift and erosion prior to deposition of the Solling Formation. The depositional

thickness of the formation displays considerable variation: 20-40 m in the West Netherlands

Basin. In the WNB the formation consists entirely of sandstones.9

Figures 4.3a – 4.3d gives a

regional view of the four levels mapped in this project. All the various intervals were merged

for all the four surveys and displayed as a single surface. The faulting system is displayed as

well in these pictures.

17



Figure 4.1: Inline 1004 (L3NAM1991A). The Top Triassic (TT) is seen here in a series of highs and lows

between fault blocks just like in all the area of the project mapped. This area is between the onshore/coast

line. See Fig. 1.3b for location of survey.

Figure 4.2: Inline 1627 (Z3NAM1990D). The Top Triassic (TT) is seen here in a series of highs and lows

between fault blocks just like in all the area of the project mapped. This area is offshore. See Fig. 1.3b for

location of survey.

BTTM

BP

TT

BTTM

BP

TT

BT

TM

BP

TT

BT

TM

BP

TT

18



Figure 4.3a: A regional view of the four levels mapped showing the complex faulting system in the WNB.

For Figures 4.3a-d, the polygons are faults.

Figure 4.3b: A regional view of the TM, BP and TT.

BT

TM

BP

TT

TM

BP

TT

19



Figure 4.3c: A regional view of the BP and TT.

Figure 4.3d: A regional view of the TT.

BP

TT

TT

20



4.2 Mapping in Time

Based on the seismic interpretation, a time structural map of the four levels mapped

were generated and they are shown in Figures 4.4a – 4.4d

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Figure 4.4a: Base Tertiary time structural map.

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Figure 4.4b: Texel Marl time structural map.

21



Figure 4.4c: Base Posidonia time structural map.

Figure 4.4d: Top Triassic time structural map.

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4.3 Velocity Model

In order to convert the faults and horizons mapped in time to depth, a velocity model

was generated based on “Vint from marker depth and horizon time”. The marker depths were

obtained from well tops supplied by TNO and the horizon time generated from the seismic

interpreted horizons. For the interpolation type, a “distance weighted” approach was used with

an interpolator option of power 5 and an underburden velocity of 4000 m/s. Two velocity

models were generated for both the Base Tertiary and Top Triassic for the domain conversion.

The Base Tertiary model looks fine, but the Top Triassic model shows some rather dramatic

changes from 2500 to over 3000 m/s. The higher velocities in general are seen over the deeper

parts and the lower velocities over the shallow fault blocks. In order to solve this problem,

some dummy wells next to the bull‟s eyes were introduced which resulted in a velocity field in

line with the horst and graben pattern.. Figures 4.5a – 4.5b shows the two models used.

Figure 4.5a: Base Tertiary Velocity Model.

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Figure 4.5b: Top Triassic Velocity Model.

4.4 Mapping in Depth

A 3D grid of the area was generated using the Jewel Suite Gridding software and from

this Grid isopach/thickness and depth maps of the target levels, Detfurth and Volpriehausen

were generated. Also, a temperature map for this two levels were generated by using a simple

geothermal gradient formula (See Paragraph 4.4.3). The results are presented below.

4.4.1 3D Gridding

To generate a grid, a model layer definition was set up and an area that covered the

mapped area and this were used as an input. The model layer definition consists of five levels

i.e Levels 0 – 4. In Level 4 as can be seen in Figure 4.6. The Detfurth and Volpriehausen

formations were further divided into members. Volpriehausen was divided into the Lower and

Upper Volpriehausen Sandstone (Reservoir) and the Volpriehausen Clay Siltstone (Non

Reservoir). Detfurth was divided into the Lower and Upper Detfurth Sandstone (Reservoir)

and the Detfurth Claystone (Non reservoir). Figure 4.7a shows the area used for the gridding

purpose with the lateral and vertical dimensions, while Figure 4.7b shows the 3D grid

generated.

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Figure 4.6: Model Layer Definition.

Figure 4.7a: Area used for gridding with lateral and vertical dimensions.

25



Figure 4.7b: 3D Grid of the modelled area.

4.4.2 Depth and Thickness Maps of the Detfurth and Volpriehausen

Based on the 3D grid generated, depth and thickness map of the Detfurth and

Volpriehausen Formations were plotted. The map of these levels were arrived at as a result of

the markers that was input into the model layer definition in the Jewel Suite Gridding process.

The gridder interpolated (using triangulated interpolation, see Appendix on 3D Gridding)

between this various marker points in the wells and created a surface out of them. Figures 4.8a

– 4.8b shows the Detfurth and Volpriehausen depth maps respectively, while Figure 4.8c

shows the thickness map of Top Detfurth to Base Volpriehausen. The region close to and

around Well Q16-02 and especially at the middle of the mapped area shows depths that are

greater than 3,000m. This are the kind of reservoir depths required to have formation waters in

excess of 1000C. A general regional trend shows that this reservoir level of interest increases

in thickness towards the offshore realm. This and the reservoir thickness and quality will be

discussed in more detail later in this report.

26



Figure 4.8a: Detfurth depth map with wells for location. These wells were used for correlation purposes as

well.

Figure 4.8b: Volpriehausen depth map with wells for location. These wells were used for correlation

purposes as well.

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Figure 4.8c: Top Detfurth to Base Volpriehausen thickness map with wells for location. The overall trend

shows that the reservoir thickens as you go towards the offshore realm.

4.4.3 Geothermal Gradient/Temperature Maps

Also as an input to the static model, the temperature in the WNB is estimated. Because

this is a regional interpretation, the normal geothermal gradient of 310C/km is used. However,

the average geothermal gradient in the Netherlands is ca. 3 to 40C/100 m down to 2000 m

depth.3

The property calculator is used in Jewel Suite. A new property is created for each depth

surface with an expression:

10+0.031*h i.e. 10+0.031*$Depth$

See appendix on Geothermal Gradient for property calculator.

Updating the property in Jewel Property calculator then generates a temperature map. Figures

4.9a – 4.9b shows the Detfurth and Volpriehausen temperature maps respectively. From these

maps it can be seen that a larger area shows great interest especially at the area in and around

the Q16-02 Well. The temperature estimate at the middle block in the central part of the

survey area and close to the Q16-02 Well is expected to exceed 1400C. This is well above the

required temperature to generate electricity.

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Figure 4.9a: Detfurth Temperature map with wells for location. The centre of the mapped area shows very

good prospects.

Figure 4.9b: Volpriehausen Temperature map with wells for location. The centre of the mapped area

shows very good prospects.

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4.5 Petrophysical Interpretation of reservoir levels

About 30 wells intersected the Triassic (Detfurth and Volpriehausen Formations which

are the target levels) in the study area. Only nine wells had sufficient data for correlation and

petrophysical interpretation purposes because they were the only wells that have core data

(porosity and permeability), GR log, NPHI log, and RHOB log. These wells are evenly spread

over the project area and therefore serve as a good representation of the conditions in the

entire area (Figure 4.10). For the petrophysical interpretation, there was a focus on the interval

of interest which is the Top Detfurth to the Base Volpriehausen for each of the Wells and

calculated the reservoir thickness in each (Table 4.1).

Figure 4.10: Wells used for Correlation and Petrophysical Interpretation.

Table 4.1: Gross reservoir thickness for each Well.

Well Top Detfurth (m) Base Volpriehausen (m) Gross Thickness (m)

MON-03 2966 3097 131

P18-A-02 4165 4309 144

P15-01 2725 2884 159

P15-14 3186 3349 163

KDZ-02-S1 3285 3408 123

Q16-02 3530 3649 119

WAS-23-S2 2662 2788 126

VAL-01 2826 2921 95

Q13-07-S2 3157 3300 143

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The Volume of clay, Vcl was calculated in Tigress software using Equation (i), while

the Porosity, PHI, was calculated using the Density method from the PHOB log using

Equation (ii). The Permeability was calculated by making a cross plot of Porosity Vs

Permeability and fitting an exponential trend line as seen in the graph in Figure 4.11a. The

trend line equation generated is:

y = 0.0025e59.279x

Where y is permeability (k) and x is porosity ()

The equation is therefore re-written as k = 0.0025e59.279

This equation was also used to generate values of 0.1mD, 1mD and 10mD permeability cut-

offs. These are plotted in a track on the correlation panels and will be used in describing N/G

later.

.........................................................Equation (i)

......................Equation (ii)

Figure 4.11a: Graph of Poro-Perm of Wells of interest.

minmax

minlog

GRGR

GRGRVClay

mfma

clma

clay

mfma

ma

density V

log

31



In order to be able to correlate the reservoir and also investigate the Vcl, PHI and K

values in the level of interest, some correlation panels are shown below (Figure 4.12 - 4.16).

An explanation and description of reservoir geometry and quality is given at the base of each

of the correlation panels. More on reservoir quality is presented in a later chapter. For each of

the panels, the Solling Formation was chosen as the datum. The line of correlation is shown as

the inset map below each correlation panel.

To look at a different scenario to arriving at N/G values, an alternative to the above

graph is considered. One which gives more weight to the good values. The problem here is

that many point occur in the low porosity/permeability range. Poor porosities give poor

permeability measurements, not only low values but also low confidence values, whereas the

higher porosities give better higher confidence permeability values. Therefore, a higher

confidence will be given to the higher porosity points, by eyeballing a relationship which

gives more credit to the higher porosity. The resulting graph is seen in Figure 4.11b. The new

equation is thus:

y = 0.0002e102.78x

Values of 0.1, 1, 10 and 100mD permeability cut-offs were generated. While the

values for 0.1mD cut-off remained the same for the two scenarios, there was a marked

difference in the others. More on this in the N/G section.

Figure 4.11b: Graph of Poro-Perm of Wells of interest giving more weight to the good values.

Figure 4.12: Correlation Panel 1.

The level of interest is from the top Detfurth to the base Volpriehausen. Here the top of the shaly Rogenstein Formation is chosen as the base of the Volpriehausen.

The Triassic is believed to have been deposited in a quiet environment, hence, the thickness does not vary too much throughout the areas correlated. i.e. there is no

sudden change in thickness. A general trend however noticed is that the reservoir thickens as you move from onshore to the offshore parts. See Figures 4.8c,

4.14 and 4.15. As can be seen from the PHI and K plots, the porosity are not that good, but the levels that are porous seem to have an excellent permeability.

This is very crucial for water production. Another good thing that will enhance connectivity here is the faulting pattern. Therefore, even if there are lower

porosities, the high level of faulting will enhance connectivity and hence good water production. MON-03 and Q16-02 have higher porosities and good permeable

levels compared to KDZ-02-S1 and Q13-07-S2 in this correlation panel. Therefore, in the region especially around Q13-07-S2, it is believed that the reservoir

quality will not be very good. This is also visible from the Vcl which is relatively high throughout the objective interval.

SSE N

33



Figure 4.13: Correlation Panel 2. This correlation panel also illustrates the fact that as you go offshore, the reservoir level

thickens. The P18-A-02 is in a region were the reservoir is dipping downwards as a result of faulting. One trend that is also

noticed throughout the area correlated is that, the upper portion of the reservoir shows good porosity and permeability values.

Hence, the Detfurth is believed will have a better connectivity and higher water production values and be of better reservoir

quality than the Volpriehausen. The region that falls within and around Wells MON-03, P18-A-02, P15-01 and P15-14, which

is roughly SE of the mapped area, also appear to have better quality when compared to the other parts. More on this will be

explained in the chapter of reservoir quality below.

SE NW

34



Figure 4.14: Correlation Panel 3. This correlation panel also illustrates the fact that as , the reservoir interval thickens.

ESE NW

35



Figure 4.15: Correlation Panel 4. This correlation panel also illustrates the fact that as you go offshore, the reservoir level thickens.

The reservoir in Well P15-01 is exceptionally good here (good porosity and permeability values, especially in the upper part of the reservoir)

when compared to the other wells.

ESE NW

36



Figure 4.16: Correlation Panel 5. This is a regional correlation of the mapped area and once again it can be seen that as you go offshore, the reservoir

thickens and as you get back towards the coast it thins again. The individual levels show no sudden change in thickness and almost appear sheet like in

geometry. Generally, it is believed that, as also seen here, that the Triassic deposits are sheet-like/sheet-sands. This is the reason why the using of an

object-based modelling approach may be difficult in modelling them.

4.6 Mapping of Reservoir Quality

Based on the correlation panels, the thickness map and the petrophysical interpretation of

the reservoir levels, the reservoir quality of the Bunter sandstone in the Zuid Holland area will

be mapped.

4.6.1 Thickness

The gross and net thickness of the reservoir in each of the well intervals studied using

the standard from Figure 4.11a is calculated and shown in the Table 4.2a. Also see Figure

4.8c. The net thickness were calculated based on the 0.1mD, 1mD and 10mD cut-off values of

the N/G. This shows an optimistic to pessimistic case. Generally, the level contains enough

thick sequences to be able to contain large quantities of water needed for daily production.

Table 4.2a: Gross and Net Thickness of the reservoir intervals in the Wells.

Also, based on the second scenario where more weight is given to the good values (Figure

4.11b), the gross and net thicknesses were calculated (Table 4.2b). The 0.1mD cut-off values

remained the same for the two scenarios. The 1 and 10mD cut-off‟s showed an increase in

N/G for each Well. A last cut-off of 100mD for the second scenario also showed that some

wells still had fairly good N/G values. There is also a permeability increase in Scenario 2

which is good for connectivity and more water production. See Correlation Panel 6 (Figure

4.17). Check the appendix on Petrophysical interpretation of reservoir levels for all the other

correlation panels for a comparison between old and new N/G and K values.

Table 4.2b: Gross and Net Thickness of the reservoir intervals in the Wells based on the second scenario.

0.1mD cut-off 1mD cut-off 10mD cut-off

Well Top Detfurth (m) Base Volpriehausen (m) Gross Thickness (m) Net Thickness (m) Net thickness (m) Net thickness (m)

MON-03 2966 3097 131 40.35 9.30 1.05

P18-A-02 4165 4309 144 20.74 4.75 0.14

P15-01 2725 2884 159 58.04 25.28 0.16

P15-14 3186 3349 163 14.67 1.30

KDZ-02-S1 3285 3408 123 8.36

Q16-02 3530 3649 119 26.42

WAS-23-S2 2662 2788 126 3.78

VAL-01 2826 2921 95 4.75

Q13-07-S2 3157 3300 143 3.15

1mD cut-off 10mD cut-off 100mD cut-off

Well Top Detfurth (m) Base Volpriehausen (m) Gross Thickness (m) Net Thickness (m) Net thickness (m) Net thickness (m)

MON-03 2966 3097 131 19.91 7.34 1.97

P18-A-02 4165 4309 144 13.10 4.03 1.87

P15-01 2725 2884 159 38.16 18.92 10.02

P15-14 3186 3349 163 5.22 0.98

KDZ-02-S1 3285 3408 123 1.23

Q16-02 3530 3649 119 1.67

WAS-23-S2 2662 2788 126

VAL-01 2826 2921 95

Q13-07-S2 3157 3300 143

Figure 4.17: Correlation Panel 6. This panel shows the comparison between the base case and the second scenario which gives more weight to the good

values. The second scenario includes K*, 1mD*, 10mD* and 100mD*. Comparing this with K, 1mD and 10mD of the base case immediately shows that there is

an increase in N/G and K values. This therefore shows that given more weight to the higher porosity and permeability values leads to a more optimistic view.

See the appendix on Petrophysical Interpretation of Reservoir Levels for all the other correlation panels for a comparison between old and new N/G and K

values.

SE NW

4.6.2 Net/Gross

See the correlation panel tracks on 0.1mD, 1mD, and 10mD cut-offs to see the actual

reservoir level where there is the net reservoir. It should however be noted that the Wells

MON-03, P18-A-02, P15-01, and P15-14 show the best reservoir intervals based on the Av

Porosity and N/G values as can be seen in Table 4.3a. Therefore, the zone in and around these

wells in the mapped area is believed will have the best reservoir quality. Correlation Panel 2

shows a correlation between MON-02, P18-A-02 and P15-14. There the general trend is that

the level of interest thickens towards the offshore realm. Table 4.3b shows the results for the

second scenario where more weight is given to higher porosity and permeability values.

Table 4.3a: N/G, Average Porosity, and Average Volume of Clay calculated in the reservoir intervals in

the Wells.

Table 4.3b: N/G, Average Porosity, and Average Volume of Clay calculated in the reservoir intervals in

the Wells based on the second scenario which gives more weight to the good values. NB 0.1mD cut-off is

not repeated because they are the same values for the two scenarios.

Av VCl Av Por N/G Av VCl Av Por N/G Av VCl Av Por N/G

MON-03 10.80% 8.60% 30.80% 9.70% 12.20% 7.10% 0% 16.20% 0.80%

P18-A-02 7.80% 9.00% 14.40% 2.60% 12.40% 3.30% 0.80% 15.10% 0.10%

P15-01 15.40% 9.80% 36.50% 8.60% 12.60% 15.90% 2.90% 15.00% 0.10%

P15-14 9.50% 7.90% 9.00% 2.10% 11.40% 0.80%

KDZ-02-S1 7.50% 7.10% 6.80%

Q16-02 5.50% 6.90% 22.20%

WAS-23-S2 6.80% 6.60% 3.00%

VAL-01 0.50% 6.70% 5.00%

Q13-07-S2 9.50% 6.50% 2.20%

0.1mD cutt-off 1mD cut-off 10mD cut-offWell

Av VCl Av Por N/G Av VCl Av Por N/G Av VCl Av Por N/G

MON-03 10.80% 10.50% 15.20% 10.20% 12.60% 5.60% 10.70% 14.90% 1.50%

P18-A-02 6.60% 10.20% 9.10% 2.30% 12.80% 2.80% 1.20% 13.70% 1.30%

P15-01 11.90% 11.40% 24.00% 7.10% 13.30% 11.90% 3.50% 14.50% 6.30%

P15-14 3.80% 9.50% 3.20% 1.50% 11.90% 0.60%

KDZ-02-S1 4.70% 8.50% 1.00%

Q16-02 2.80% 8.20% 1.40%

WAS-23-S2

VAL-01

Q13-07-S2

Well1mD cutt-off 10mD cut-off 100mD cut-off

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4.6.3 Porosity

Primary porosity and permeability are generally low in the mapped area, but it is

expected that permeability and connectivity are enhanced locally through fracturing. The

objective level is highly faulted, and hence this will serve as conduit for water and hence a

higher level of connectivity and more water production. Heterogeneity remains an issue of

concern due to the high level of Vcl in some of the intervals. But it is believed that they will

generally not serve as barrier or baffle to flow, i.e. it will reduce the vertical permeability but

not the more important horizontal permeability

Tables 4.3a and 4.3b shows the average porosity on each level for the two scenarios and this

can also be seen in the PHI track on the correlation panels. Generally, porosity is higher at the

upper part of the reservoir interval. This indicates that the Detfurth will generally have a better

reservoir quality than the Volpriehausen.

4.7 Compilation of Core Data

TNO provided core data which included porosity, permeability and grain density. The

porosity were plotted against permeability and the trends are shown below. Note that only

very few Wells in the study area have core data that reached the Triassic. For this Por-Perm

trend maps, core data from Wells Q13-04, Q13-07-S2, Q16-02, Q16-08, and VAL-01 were

used.

4.7.1 Porosity and Permeability trends and relationships

The Por-Perm trend maps of the Detfurth and Volpriehausen are shown in Figures 4.18

and 4.19. Well Q16-08 has the best values for Detfurth while Well Q16-08 has the best values

for the Volpriehausen. However, there is hardly any relationship in a plot of porosity against

depth (Figure 4.23).

41



Figure 4.18: Por-Perm Detfurth for Wells Q16-08 and VAL-01.

Figure 4.19: Por-Perm Volpriehausen for Wells Q13-04, Q13-07-S2, Q16-02, Q16-08 and VAL-01.

Poro-Perm Triassic Detfurth

0.0100

0.1000

1.0000

10.0000

100.0000

1000.0000

0.0000 0.0200 0.0400 0.0600 0.0800 0.1000 0.1200 0.1400 0.1600

Porosity

Perm

eab

ilit

y

Q16-08 Upper DetfurthSandstone

Q16-08 Lower DetfurthSandstone

VAL-01 DetfurthClaystone Member

VAL-01 Lower DetfurthSandstone Member

Well MD (m)

Q16-08 3877-3913

VAL-01 2826-2855

Poro-Perm Triassic Volpriehausen

0.01

0.1

1

10

100

0.0000 0.0200 0.0400 0.0600 0.0800 0.1000 0.1200

Porosity

Perm

eab

ilit

y

Q13-04 Volpriehausen Clay-Siltstone Member (No K Values)

Q13-07-S2 VolpriehausenClaystone

Q16-02 VolpriehausenClaystone

Q16-02 Lower VolpriehausenSandstone

Q13-04 Volpriehausen Clay-Siltstone Member (No K Values)

Q16-08 Upper VolpriehausenSandstone

VAL-01 Volpriehausen Clay-Siltstone Member

VAL-01 Lower VolpriehausenSandstone Member

Well MD (m)

Q13-04 2785-2800

Q13-07-S2 3170-3188

Q16-02 3570-3635

Q16-08 3930-3947

VAL-01 2855-2881

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4.7.2 Environment of Deposition

The Triassic formation was deposited in a semi-arid continental basin. Sediments

reached the P and Q quadrants (which forms a larger part of the studied area in this project) in

braided stream complexes from a hinterland to the southeast. The braided stream complexes

were flanked by Aeolian, interdune, flood-plain and crevasse-splay environments and

terminated in playa lakes.11

In central parts of the basin, redeposition of fluvial sands into dune fields occurred on

a wide scale during dry periods. During low clastic influx, the playa lake expanded again

towards the margin of the basin. The repetition of this processes caused the cyclic alternation

in the Main Buntsandstein subgroup. The larger cycles, represented, for example, by the

Volpriehausen and Detfurth formations, are tectonically driven. The depositional model for

the Lower Buntsandstein and Volpriehausen formations in the southern Netherlands is shown

in Figure 4.20. The yellowish colour indicates predominantly sandstones, while the greenish

colour predominantly siltstones.9

Figure 4.20: Depositional model for the Lower Buntsandstein and Volpriehausen formations in the

southern Netherlands. (Geluk, 2007)9

The Detfurth and Volpriehausen formations in the mapped area suggests that Aeolian

and fluvial facies occupy more than 50% of the rock unit, while the interdune, flood plain,

crevasse splay and playa lake facies occupy the remaining of the rock unit. Aeolian sandstones

are known for their excellent reservoir qualities. They are well sorted with good porosity and

permeability. This means that a larger part of the rock unit within the mapped area is of good

reservoir quality. The percentage of other facies present is believed will not serve as an

obstruction to flow.

Study area

43



4.8 Areas Suitable for Geothermal Exploitation

Based on the interpretation and an estimate of temperature, a large part of the mapped

area looks promising and is up to depths of more than 3,000m which is believed will contain

water that is above 1000C needed to produce electricity. The area right around the coast and

the region of the P and Q quadrants looks exceptionally suitable as can be seen from the

temperature estimates in the temperature maps in Figures 4.21 and 4.22. The reservoir quality

here is good as well based on the fact that most of the area within the polygon also falls within

the part of the WNB where it is believed the Detfurth and Volpriehausen Formations have

Aeolian facies that occupy more than 50% of the rock unit.

Figure 4.21: Area suitable for geothermal exploitation in the Detfurth is highlighted in the red polygon

based on expected water temperatures.

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Figure 4.22: Area suitable for geothermal exploitation in the Volpriehausen is highlighted in the red

polygon based on expected water temperatures.

4.9 Risks and possible means to reduce risks

As with any new development effort, there are risks and drawbacks associated with it.

A few drawbacks can be foreseen in the Dutch situation. The aquifers, suitable for geothermal

exploitation are the same as the oil and gas-bearing reservoirs, implying considerable overlap.

A deep-seated geothermal project positioned close to a producing oil or gas field or a gas or

CO2 storage facility, therefore may cause subsurface interference. The extraction of

geothermal energy may affect the pressure distribution in or around the oil or gas field or the

storage facility. A recent simulation study (Brouwer et al., 2005) concerning the effects of

overpressure and temperature changes in the Lower Cretaceous IJsselmonde Sandstone

Member, however, shows that, if re-injection of water takes place under overpressure

conditions, the pressure changes in the direct vicinity of the wells due to the extraction of

geothermal energy are limited, i.e. no more than 1 bar at a distance of 1 km. The simulation

also shows that thermo-elastic effects may occur as well, depending on the temperature of the

injected water.13

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These may amount to 50 bar if the formation is cooled by more than 500C, which

would locally cause a compaction of 2 to 3 cm at reservoir level (ca. 1100 m); the effects at

surface would be negligible. Such investigations are important in the Netherlands, where

public concern about soil subsidence and seismicity due to gas production plays an important

role in discussions on the use of the underground.3

Another important risk is that the prospective lows have very little well penetration

and are usually considerably deeper than the much shallower oil fields. It is however

suspected that structuration and formation of highs and lows is relatively late and that

diagenesis predates structuration. This would imply that the shallow oil fields have porosities

representative of much greater depths. This is borne out by the fact that there is hardly any

relationship of porosity against depth (Figure 4.23).

Figure 4.23: Depth Vs Porosity for Wells that intersected the Triassic. The porosities are both core and log

derived as illustrated in the legend. They all fit properly apart from VAL-01 log derived porosity which

has some lower values as a result of an high Vcl at the beginning of the reservoir interval in this particular

well. Note that only Wells Q16-02, Q16-08 and VAL-01 had core porosities, all the other well porosities

were derived from logs.

46



4.10 Volumetrics Reporting

To determine the volume of water in place in these reservoirs; the N/G, porosity,

reservoir volume and water saturation were all multiplied together using Volumetrics

Reporting in Jewel Suite. To come up with different saturation scenarios, water saturations in

the reservoir were varied at 100%, 80% and 60%. The N/G derived from the 0.1mD cut-off

was used. The volumes of water in place in the reservoirs are presented as volumetric reports

in Tables 4.4a-4.4c. This shows that there is enough water in the reservoir to support daily

water production that is needed for a project like this. Note that in all the tables below, GRV

is Gross Rock Volume, NRV is Net Rock Volume, NPV is Net Pore Volume, and NWPV is

Net Water Pore Volume.

Figure 4.4a: Volumetrics Report using Sw of 100%.

Figure 4.4b: Volumetrics Report using Sw of 80%.

Figure 4.4c: Volumetrics Report using Sw of 60%.

GRV NRV NPV NWPV

m3 m3 m3 m3

Detfurth 4.69E+10 1.07E+10 4.97E+08 4.97E+08

Volpriehausen 1.55E+11 1.90E+10 5.05E+08 5.05E+08

TOTAL 2.02E+11 2.98E+10 1.00E+09 1.00E+09

GRV NRV NPV NWPV

m3 m3 m3 m3

Detfurth 4.69E+10 1.07E+10 4.97E+08 3.98E+08


TOTAL 2.02E+11 2.98E+10 1.00E+09 8.02E+08

GRV NRV NPV NWPV

m3 m3 m3 m3

Detfurth 4.69E+10 1.07E+10 4.97E+08 2.98E+08


TOTAL 2.02E+11 2.98E+10 1.00E+09 6.01E+08

47



5.0 CONCLUSIONS AND RECOMMENDATIONS

From regional geology and the study carried out in this project, the Detfurth and

Volpriehausen formations are established to be potentially good reservoirs for

geothermal development.

The target horizons, which were the Detfurth and Volpriehausen were too deep to be

visible and adequately interpretable on Seismic due to the noisy reflections at that level

(due to the low impedance contrast and because it is overlain by the strong reflectors

of the evaporites of the Upper Germanic Triassic). Therefore, the Top Triassic was

mapped from Seismic and based on the formation markers of the target horizons in the

wells that intersected the Triassic, surfaces for this levels were generated using 3D

gridding in Jewel Suite.

The net thickness were calculated based on the 0.1mD, 1mD and 10mD cut-off values

of the N/G. This shows an optimistic to pessimistic case. Generally, the level contains

enough thick sequences to be able to contain large quantities of water needed for daily

production.

Wells MON-03, P18-A-02, P15-01, and P15-14 show the best reservoir intervals

based on the Av Porosity and N/G values. Therefore, the zone in and around these

wells in the mapped area is believed will have the best reservoir quality.

Primary porosity and permeability are generally low in the mapped area, but it is

expected that permeability and connectivity are enhanced locally through fracturing.

The objective level is highly faulted, and hence this will serve as conduit for water

and hence a higher level of connectivity and more water production. Heterogeneity

remains an issue of concern due to the high level of Vcl in some of the intervals. But it

is believed that they will generally not serve as barrier or baffle to flow, i.e. it will

reduce the vertical permeability but not the more important horizontal permeability.

The Detfurth and Volpriehausen formations in the mapped area suggests that Aeolian

and fluvial facies occupy more than 50% of the rock unit, while the interdune, flood

plain, crevasse splay and playa lake facies occupy the remaining of the rock unit.

Aeolian sandstones are known for their excellent reservoir qualities. They are well

sorted with good porosity and permeability. This means that a larger part of the rock

unit within the mapped area is of good reservoir quality.

48



Based on the interpretation and an estimate of temperature, a large part of the mapped

area looks promising and is up to depths of more than 3,000m which is believed will

contain water that is above 1000C needed to produce electricity.

The aquifers, suitable for geothermal exploitation here in the Netherlands, are the same

as the oil and gas-bearing reservoirs, implying considerable overlap. A deep-seated

geothermal project positioned close to a producing oil or gas field or a gas or CO2

storage facility, therefore may cause subsurface interference.

As with any new development effort, there are risks and drawbacks associated with it.

The extraction of geothermal energy may affect the pressure distribution in or around

the oil or gas field or the storage facility.

Improvements that can be done to verify some assumptions and also reduce

uncertainties include the provision of cores and FMI/FMS. With these, the modelling

of heterogeneities can be done thereby helping in the understanding of the reservoir

architecture. FMI/FMS will show grain size trends, changes in facies as well as

dipping angle of the layers. This will tell the kind of sedimentary structures that were

formed when the sandstone bodies were deposited.

Renewed interest in geothermal energy, driven by concerns about the sustainability of

the environment and the security of energy supply, shows that with the knowledge from the oil

and gas industry geothermal development can be enhanced. Seismic combined with well data

acquired originally for oil and gas purposes is again becoming of great use for geothermal

projects in the Netherlands.

Another problem is the focus of the oil and gas industry on the structural highs. This is

where the oil and gas is found since it migrates to the surface until it is trapped. For

geothermal purposes the structural lows are the most interesting: this is where the highest

temperatures are found. Therefore to be able to predict the fluid behaviour in the structural

low the reservoir properties are extrapolated from the structural highs. When this proves to be

accurate it would have a very positive effect on the development of geothermal energy, since

this reduces the uncertainties involved with such a project.14

As the governments the world over explore the use of renewables due to a dramatic

increase in gas and oil prices and the need to stay green and avoid worsening climate change,

it is sure that geothermal energy will be a key source of energy to contribute to a future

sustainable society.

49



References:

1 Christine McGourty, Science correspondent, BBC News in Global crises „to strike by 2030‟.

Thursday, 19 March 2009. http://news.bbc.co.uk/2/hi/uk_news/7951838.stm

2 US Energy Information Administration energy KIDS, Renewable Geothermal,

http://tonto.eia.doe.gov/kids/energy.cfm?page=geothermal_home-basics-k.cfm

3 Lokhorst, A & Wong, Th. E., 2007: “Geothermal Energy”. In: Wong, Th. E., Batjes, D.A.J.

& De Jager, J., Geology of the Netherlands, Royal Netherlands Academy of Arts and

Sciences, p. 341-346.

4 Geothermal Energy section of the NL Oil and Gas Portal.

http://www.nlog.nl/en/home/geothermy.html

5Van Balen, R.T., et al., 2002: “Modelling the hydrocarbon generation and migration in the

West Netherlands Basin, The Netherlands”. In: Netherlands Journal of Geosciences 79, p. 29-

44.

6 De Jager, J., 2007: “Geological development”. In: Wong, Th. E., Batjes, D.A.J. & De Jager,

J., Geology of the Netherlands, Royal Netherlands Academy of Arts and Sciences, p. 5-26.

7 Den Hartog Jager, D.G., 1996: “Fluviomarine sequences in the Lower Cretaceous of the

West Netherlands Basin: correlation and seismic expression”. In: Rondeel, et al. (eds),

Geology of gas and oil under the Netherlands, Kluwer Academic Publishers, p. 229-241.

8 Van Adrichem Boogaert, H.A. & Kouwe, W.F.P., 1993: “Stratigraphic nomenclature of the

Netherlands, revision and update by RGD and NOGEPA”. In: Mededelingen Rijks

Geologische Dienst (RGD), nr 50.

9 Geluk, M.C., 2007: “Triassic”. In: Wong, Th. E., Batjes, D.A.J. & De Jager, J., Geology of

the Netherlands, Royal Netherlands Academy of Arts and Sciences, p. 85-106.

10 Schlumberger Log Interpretation, Volume 1-Principles. 1972 Edition.

11 Ames R. & Farfan P.F., 1996: “The environments of deposition of the Triassic Main

Buntsandstein Formation in the P and Q quadrants, offshore the Netherlands”. In: Rondeel, et

al. (eds), Geology of gas and oil under the Netherlands, Kluwer Academic Publishers, p. 167-

178.

12 G. Diephuis, 2006: Basic and Advanced Geophysics, Geophysical Education & Advice.

13Brouwer, G.K., Lokhorst, A. & Orlic, B., 2005. Geothermal heat and abandoned gas

reservoirs in the Netherlands. Proceedings World Geothermal Congress 2005, Antalya, Turkey

(24–29 April). International Geothermal Association, CD-ROM, art. 1177.

http://news.bbc.co.uk/2/hi/uk_news/7951838.stm

http://tonto.eia.doe.gov/kids/energy.cfm?page=geothermal_home-basics-k.cfm

http://www.nlog.nl/en/home/geothermy.html

50



14Smits, P.F., 2008: “MSc Thesis: Construction of an integrated reservoir model using the

Moerkapelle field for geothermal development of the Delft sandstone”. TU Delft.

15Mulder, E. de, Geluk, M.C., Ritsema, I., Westerhoff, W.E., Wong, T.E. (Eds), 2003. De

ondergrond van Nederland, Geologie van Nederland, deel 7; Peeters, Herent, België; 379 pp.

51



Appendixes:

1. Introduction

Please note that this appendix contains a full description of the methods used and reported in

this research work. This appendix should be used as an additional resource to the main paper

if more details are required.

2. Coordinate System

The coordinate system used is the Rijksdriehoekstelsel New (RD New), The Dutch national

projection system. To transform the old RD system to the new RD system:

X = + 155.000 m

Y = + 463.000 m

Figure 1: RD New Projection System Parameters

52



Figure 2: Parameters datum ‘Amersfoort’ (Molodensky). This datum is called ‘Netherlands’ in

Geographix.

Figure 3: Parameters datum ED50.

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3. Seismic Data

Four 3D seismic surveys were interpreted. They were all supplied by TNO in segy format.

They were supplied as different file collections and then merged in Geographic before being

loaded in Tigress Workstation for interpretation. Figures 4-7 shows a summary of parameters

used to process data from each survey.

Figure 4: Summary of parameters used to process data from survey L3NAM1985P.

Figure 5: Summary of parameters used to process data from survey L3NAM1991A.

54



Figure 6: Summary of parameters used to process data from survey Z3NAM1990D.

Figure 7: Summary of parameters used to process data from survey Z3AMC1989A.

55



Figure 8: Polarity Convections

4. Well Data

There were seventy-nine (79) wells in the study area. For each well a set of data (Well

ID, coordinates, location, KB, status, class, total depth, completion well logs, reports, velocity

information, pressure etc), digital logs, formation tops, deviation surveys and core data were

available from the TNO website www.nlog.nl

http://www.nlog.nl/

56



Table 1: List of wells in the study area showing Well ID, Coordinates, Location, Class, Status, Total

Depth, Available Well Data etc.

57



5 Seismic Interpretation

A general overview and geometry of the horizons and faults mapped in this area can be

seen from Figures 9-12. This interpretation is consistent with previous work done in this area.

Figure 9: A general overview and geometry of the horizons and faults mapped in survey L3NAM1985P.

Figure 10: A general overview and geometry of the horizons and faults mapped in survey L3NAM1991A.

58



Figure 11: A general overview and geometry of the horizons and faults mapped in survey Z3NAM1990D.

Figure 12: A general overview and geometry of the horizons and faults mapped in survey Z3AMC1989A.

59



5 3D Gridding

In the Jewel gridding process, there are three ways in which interpolation between data

points are done. They include Triangulated Interpolation, Distance weighted, and Ordinary

Kriging. Figure 13 shows the Jewel surface gridding workflow settings.

Figure 13: A picture showing the Jewel gridding surface workflow settings. The interpolation types are

shown in the red rectangular box.

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5 Geothermal Gradient

Also as an input to the static model, the temperature in the WNB is estimated. Because

this is a regional interpretation, the normal geothermal gradient of 310C/km is used. However,

the average geothermal gradient in the Netherlands is ca. 3 to 40C/100 m down to 2000 m

depth.3 The property calculator is used in Jewel Suite (Figure 14). A new property is created

for each depth surface with an expression:

10+0.031*h i.e. 10+0.031*$Depth$

Figure 14: Jewel property calculator used to generate a temperature map for the various levels.

5 Petrophysical Interpretation of reservoir levels

Based on the second scenario where more weight is given to the good values, the gross

and net thicknesses were calculated. The 0.1mD cut-off values remained the same for the two

scenarios. The 1mD and 10mD cut-off‟s showed an increase in N/G for each Well. These

comparisons can be seen for all the correlation Panels. See Figures 15-20.

Figure 15: Correlation Panel 6.

SSE N

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SE NW

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ESE NW

65




ESE NW

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NE NNW

aes/tg/10-08 bunter reservoir quality for geothermal

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