report on leaching tests and insolubles profile of...

DEEP. Underground Engineering - Eyhauser Allee 2a - D-26160 Bad Zwischenahn Tel: (04403) 9322-10 - Fax: (04403) 9322-11 - E-Mail: [email protected] - Website: www.deep.de

Report on Leaching Tests and

Insolubles Profile of

Exploration Well Carnduff #01

for:

Gaelectric Energy Storage Ltd.

Portview House, Thorncastle Street, Ringsend

Dublin 4

Ireland

KBB/DEEP. Project No.: 6407-880834

Author/s: Lars Dittert

Daniel Albes

Date: 17. March 2014

Report No. SPIRE20140930.2 Provided by Gaelectric Energy Storage Ltd to University of Ulster September 2014. Project SPIRE. University Ref project_13574. This report constitutes Commercially Sensitive Information and Confidential Information as defined in the contract between University of Ulster and Gaelectric Energy Storage Ltd dated 30th September 2013.

Content

140304_GES_C01_Report_LeachingTests_InsolublesProfile_rev00.docx Page 1 of 12

Content

Tables ....................................................................................................................... 2

1 Introduction ..................................................................................... 3

2 Core Samples .................................................................................. 4

3 Lab Work and Results .................................................................... 5

3.1 Bulk Density and Insolubles Content ...................................................... 6

3.2 Loosening Factor ....................................................................................... 6

3.3 Leaching Velocities ................................................................................... 8

4 GES C01 Insolubles Log ................................................................ 8

5 Executive Summary ...................................................................... 10

References ............................................................................................................. 11

List of Enclosures .................................................................................................. 12


Tables


Tables

Table 1: List of samples ............................................................................................. 5

Table 2: Leaching test programme for the samples from well GES C01 ................... 5


1 Introduction


1 Introduction

Gaelectric Energy Storage Ltd. (GES) is planning the construction of a CAES

caverns south of Larne, Northern Ireland. Two exploration wells have been drilled to

confirm suitable thickness and depths of the Larne Halite Member (LHM; a sub-unit

of the Triassic Mercia Mudstone Group) in the target area for the construction of

compressed air storage caverns. The vertical well Carnduff #01 (C01) drilled from

July to December 2013 was continuously cored and exposed the LHM from 556.8 m

to total depth at 922.7 m MD (see [1]). The cores have a diameter of 84 mm (PQ

size). Amongst others, the wireline logging programme covered formation density,

gamma-ray and caliper run.

Altogether, twelve samples have been selected for analyses in the leaching test

laboratory of DEEP. Underground Engineering (Bad Zwischenahn/Germany) from

nine core boxes covering the depth section of approx. 693 – 878 m. The samples

have been analysed for their insolubles content and the bulking factor of the

insolubles. Furthermore, three samples have been tested for the leaching velocities.

The test results serve as input for the initial cavern leaching simulation and are used

as a basis for a generic insolubles log, which can be developed, if geophysical

logging data of good quality for the rock density and natural gamma ray log are

present.


2 Core Samples


2 Core Samples

After visual inspection at the DEEP. core store, the samples were selected

considering the following requirements: The sampled sections should have to be as

representative as possible for the entire deposit (largely distributed within the target

section, different insoluble contents). They must not have alterations or artefacts

from drilling/coring activities, undersaturated mud, handling or storage. They have to

feature the full gauge and no dissolution effects and no breakage or structural

shattering.

The selected core samples could not completely satisfy the above specified as large

sections of the cores have been altered due to large or small rock break outs. Many

of those voids are filled with mud (presumably drilling mud). Examples are shown in

Figure 1 and Enclosure 1 (samples #7 and #10). A thin mud ‘coating’ was present

even on core sections with full gauge and cylindrical shape which appeared to be

clean. The coating was firstly detected during further testing and can also be seen in

the leaching test movies, as the coating detaches from the samples during the initial

stage of the dissolution tests (see CD-ROM).

Thus, for upcoming exploration and cavern wells a better core quality is desirable

(i.e. undamaged and carefully cleaned from drilling mud).

Figure 1: Example for break outs and pits on core material


3 Lab Work and Results


A total amount of 12 samples has been identified and cut for further analyses

(Table 1). Each specimen has a length of 18 to 20 cm with the exception of sample

#7 (15 cm). All samples have been photographed prior to testing.

Table 1: List of samples

Sample Well Core Box

Depth from [m MD/TVD]

Depth to [m MD/TVD]

1 Carnduff01 375 693.24 693.42

2 Carnduff01 391 721.46 721.65

3 Carnduff01 421 777.02 777.20

4 Carnduff01 440 811.70 811.88

5 Carnduff01 449 827.47 827.65

6 Carnduff01 449 827.85 828.03

7 Carnduff01 449 828.24 828.39

8 Carnduff01 454 836.35 836.53

9 Carnduff01 464 856.29 856.47

10 Carnduff01 469 863.40 863.60

11 Carnduff01 476 875.76 875.94

12 Carnduff01 476 877.23 877.41


The leaching test programme determines the parameters given in Table 2. The

leaching test results are listed in Enclosure 2. The time lapse movies of the

dissolution rate tests are provided on the enclosed CD-ROM (Enclosure 4).

Table 2: Leaching test programme for the samples from well GES C01

Sample #

Core Box

Depth from [m MD/TVD]

Depth to[m MD/TVD]

Bulk Density

Insolubles Content

Loosening Factor

Leaching Velocity

1 375 693.24 693.42 x x x

2 391 721.46 721.65 x x x

3 421 777.02 777.20 x x x

4 440 811.70 811.88 x x x x

5 449 827.47 827.65 x x x

6 449 827.85 828.03 x x x

7 449 828.24 828.39 x x x

8 454 836.35 836.53 x x x x

9 464 856.29 856.47 x x x

10 469 863.40 863.60 x x x

11 476 875.76 875.94 x x x

12 476 877.23 877.41 x x x x




3.1 Bulk Density and Insolubles Content

The bulk density (i.e. rock density) is a basic parameter for the calculation of a

continuous insolubles log. It is calculated by determining the mass and the volume

of each sample. The sample volume is measured by hydrostatic weighing.

To determine the insoluble fraction for each specimen the salt portion of each

sample is completely dissolved in fresh water. The remaining insoluble components

are carefully collected. The volume of the insolubles is measured by gas

pycnometry. The density is calculated by dividing the mass by the volume. The

volume percentage of the insoluble content is then measured on the basis of the

insoluble volume and the initially determined sample volume.

The bulk densities of the samples range between 2.18 and 2.37 g/cm³. Their

insolubles content was determined to be 2.0 – 48.4 vol-%. Both parameters

correlate very well. The coefficient of determination of the linear relationship is very

good (R² = 0.976). The insoluble fraction consists dominantly of mud stone,

sometimes with minor portions of anhydrite. The true density of this fraction is

2.58 - 2.77 g/cm³. This result fits well with the finding of the correlation equation (see

diagram in Enclosure 2), whereas a sample with 100 vol-% of insolubles should

have a theoretical density of 2.61 g/cm³.

3.2 Loosening Factor

For the determination of the bulk volume of the particles (the bulking) the remaining

insolubles portion of each leaching test sample is put into beakers, and completely

covered with water. The bulking factor is the ratio of the bulked volume and the pure

material volume as it derives from the true insolubles density. Together with the

insolubles profile (see Chapter 4) this ratio allows for an initial estimation on the

sump development within the cavern.

Due to the lab scale the sump compaction is not considered as it happens in real

scale caverns. This depends on some issues:

- The effective size of the particles that may be released from a certain cavern

wall section will very likely exceed the scale of the core sample and cannot

be considered during laboratory testing.

- The successively increasing sump level in the cavern achieves higher

burden pressures which cannot be realized in the laboratory. The resulting

compaction is efficient to a lesser degree in the lab.




- The time scales are of the lab test and the cavern is different. The lab test

will be conducted within hours to days, while the development and

consolidation time of the sump takes months to years.

Subsequently under laboratory conditions high loosening factors are observed

especially for samples with low insolubles contents, as there is no ‘additional’

material that compresses the loosely dumped material. Thus, the bulking factor has

to be adapted to the conditions in the intended cavern, if the mentioned effects apply

to the insolubles.

The observed loosening factors of all samples range between 2.5 and 3.4

(Enclosure 2). These unusual high values are presumably exaggerated as indicated

by an additional indicative test, which gave reason for considerable compaction on a

week scale: Within three weeks the loosening factor decreased from 2.8 to 2.3. This

test is still running at this time and the compaction process has been slowed down.

However, it is not clear whether the compaction process came to an end. It can be

presumed that the compaction velocity is influenced by the amount of insolubles

within a sample, i.e. low insoluble contents lead to slow compaction.

Compaction is also influenced by the type of insolubles, i.e. by the mineralogy and

by the rock structure. When getting into contact with water the mudstone rich parts

tend to disintegrate into smaller parts, which in turn decay into tinier parts

themselves.

Additionally, swelling of clay minerals under water/brine seems to be an issue, which

should be subject to further investigations.

All these aspects (decay into small grained components, presence of clay minerals,

swelling, no/less compaction) are responsible for the observed high value range.

The highest values can be found below 10 vol.-% insolubles (loosening factor >3).

These values are considered to be too high, especially as the artificial mud coating

has the highest impact in these samples (see Chapter 2).

From the present lab data and knowledge of the material the loosening factor is 2.6

ignoring substantial compaction effects.

Finally, it should be kept in mind that the rock eventually may have been structurally

altered during coring/drilling with the consequence that the observed disintegration

behavior was affected by artificial ‘micro-fractures’.


4 GES C01 Insolubles Log


3.3 Leaching Velocities

The samples are placed for approx. 50 – 60 min in a fresh water filled basin at

standard conditions (20°C, stagnant water). Subsequently, they are removed from

the water, dried and weighed again. The volume is determined again by hydrostatic

weighing. From the differences of the masses and volumes before and after the

leaching test the horizontal and the vertical dissolution rate is calculated.

The test runs are photographed to produce time lapse movies. Additionally, the

samples are visually inspected after dissolution rate testing and before complete

dissolution for subsequent insolubles content determination. Observed structures

and features are journalised.

Altogether three samples have been analyzed for their leaching velocities. The

velocities average to 12.5 mm/h in vertical direction and 7.3 mm/h in horizontal

direction. However, the dissolution rate is somewhat lower than experienced in

similar deposits. This is presumably connected to the thin mud coating that prevents

effective salt dissolution during the test.


In general, there is a close linear relationship between the insolubles content and

the bulk density within the deposit. This applies if the rock represents a simple two

phase system, i.e. there is only one soluble and one insoluble mineral and both

minerals have different densities (e.g. halite and anhydrite).

This relation can also be observed for the investigated deposit (Enclosure 2),

although the insoluble fraction represents obviously a mixture of different minerals

(clay minerals, anhydrite, etc.). Like described in Chapter 3.1 there is a very close

correlation of the insoluble fraction and the bulk density.

Usually, this relation serves as a basis for further calculations, if there are reliable

data from geophysical bore hole logging, especially density, caliper and natural

gamma. This is not given for the exploration well GES C01 as there are many wash

outs that affect particularly the quality of the density log. Furthermore, there are no

reliable logging data available for the well section below approx. 860 m. However,

the section below 860 m is an important depth range as it might serve for initial

cavern leaching, due to its apparent low insoluble content as visually detected and

measured in sample #11 and #12 (Enclosure 2). This part was roughly estimated by

the visual findings. Despite of the quite low amount of insolubles (≤3 vol%) of




sample #11 and #12, the insolubles log was set to more conservative values due to

the lack of reliable geophysical data.

Consequently, the insoluble profile was constructed by considering three different

logs:

- the density log (where the density log seemed to be reliable),

- the natural gamma log (where the density log seemed to be not reliable),

- the visual lithology from the cores (where reliable data from geophysical log

are generally missed).

The average value for the insoluble content within the initially planned cavern

section (880 - 760 m) is considered to be 25 %.

The insolubles log calculation presented here is the best possible estimation/result

which can be provided on the basis of moderate quality of the available geophysical

logging data.

High insoluble contents can be deduced from the gamma ray log where high log

readings occur (this coincides often with the major wash outs). Depending on the

lithological consolidation of the mudstone and the halite distribution the investigated

well section can show different characteristics during the leaching process: The

beds will either decay slowly into more fine grained particles with a higher bulking or

suddenly disintegrate into thicker chunks which settle immediately. In the latter case,

incapsulated portions of halite will be accompanied into the sump, which in turn

have to be considered as insoluble as they will not be dissolved within the saturated

brine of the sump.

For initial cavern simulation the insolubles profile was averaged every 5 m. The

basic logging data, the calculated insolubles profile and the 5 m averages are shown

in Enclosure 3 together.


5 Executive Summary


5 Executive Summary

Leaching tests have been performed on twelve samples from exploration well

GES C01 to gain results on the densities, leaching velocities, insolubles contents

and the bulking factors of the insolubles fractions.

The insolubles content of the specimen range between 2.0 – 48.4 vol-% and the

bulk densities range have been determined to be 2.18 - 2.37 g/cm³. There is a very

high correlation of both parameters.

The first estimate of the general loosening factor is 2.6. However, this value is

considered to be too high to assume it directly for the situation in the cavern sump,

as compaction is not fully effective in lab scale within usual testing durations (hours

to day scale). An additional supporting test with extended duration (> three weeks)

indicates that the loosening factor decreases significantly with time. Yet, it remains

finally unclear if alterations of the original rock structure during coring/drilling had

contributed to enable an easier decay.

Based on the lab results and the geophysical logging data a continuous insoluble

profile was established. This profile suffers from density logging data of low quality.

In the lowermost part there are no reliable geophysical logging data at all. Thus,

additional efforts had to be done (calculations based on gamma log data and visual

logging data) to estimate the amount of insolubles in the deposit. The initially

planned cavern section (760 – 880 m) has an average insolubles content of

25 vol%.

For further drillings and upcoming investigations the following items should be

addressed:

- Care has to be taken on-site directly after core recovery to clean the cores

carefully, but efficiently to avoid mud coatings.

- High quality data of the geophysical logging are needed that are not affected

by the borehole geometry.

- Additional testing on the insolubles should be performed in terms of

compaction and clay mineral swelling.


References


References

[1] SLR: Daily geological reports for Carnduff #1. 31/07/2013 to 06/01/2014



List of Enclosures

Enclosure 1: Sample photographs

Enclosure 2: Lab results

Enclosure 3: Insoluble profile, logging data and lab results

Enclosure 4: CD-ROM


Leaching Test Samples GES C01

PN: 6407

Encl. 1: Sample photographs

PN6407 140304_GES_C01_Samples_Encl1.docx/LD

Sample 1 (693.24 – 693.42 m):



PN: 6407





PN: 6407



Sample 2 (721.46 – 721.65 m):



PN: 6407





PN: 6407



Sample 3 (777.02 – 777.20 m):



PN: 6407





PN: 6407



Sample 4 (811.70 – 811.88 m):



PN: 6407





PN: 6407



Sample 5 (827.47– 827.65 m):



PN: 6407





PN: 6407



Sample 6 (827.85 – 828.03 m):



PN: 6407





PN: 6407



Sample 7 (828.24 – 828.39 m):



PN: 6407





PN: 6407



Sample 8 (836.35 – 836.53 m):



PN: 6407





PN: 6407



Sample 9 (856.29 – 856.47 m):



PN: 6407





PN: 6407



Sample 10 (863.40 – 863.60 m):



PN: 6407





PN: 6407



Sample 11 (875.76 – 875.94 m):



PN: 6407





PN: 6407



Sample 12 (877.23 – 877.41 m):



PN: 6407




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Depth[m TVD]

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Leaching Velocity[mm/h]

horizontalvertical

100

7550250

Insoluble Content[Vol-%]

5m averageavg. in cavern section

100

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Insoluble Content[Vol-%]

calculated,measurement

Co

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Caliper Log[mm]

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806040200

Gamma Ray Log[API]

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Exploration Well GES Carnduff 01

Encl. 3: Insoluble profile with leaching test results and log data140303_GES_Carnduff01_InsolublesProfile_rev00.sdg/LD


Content on the CD-ROM

Gaelectric Energy Storage Exploration Well Carnduff 01

KBB/DEEP. PN: 6407

Encl. 4: CD-ROM

PN6407

140311_GES_C01_CDROM_Encl4.docx

- Report on Leaching Tests and Insolubles Profile of

Exploration Well GES Carnduff 01

- Sample Photographs

- Time Lapse Movies of the Dissolution Tests


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