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1

WHOC11-571

WHOC, Edmonton 2011 Theme: Striking the Balance: Economics, Environment,

and Energy Mix Session 15– Reservoir Monitoring I

Integrated Use of NMR, Petrel and Modflow in the Modeling

of SAGD Produced Water Re-injection

CAMPBELL, K1 1MISWACO, FORMERLY SWS CALGARY, CANADA

PHAIR, C2

2 MNEME CORP, CALGARY

ALLOISIO, S3 3SWS VANCOUVER, CANADA

NOVOTNY, M4

4SWS DENVER, USA

RAVEN, S5 5OILSANDS QUEST INC, CALGARY, CANADA

This paper has been selected for presentation and/or publication in the proceedings for the 2011 World Heavy Oil Congress

[WHOC11]. The authors of this material have been cleared by all interested companies/employers/clients to authorize dmg

events (Canada) inc., the congress producer, to make this material available to the attendees of WHOC11 and other relevant

industry personnel.

14 March 2011 Page | 2 Schlumberger Water Services

ABSTRACT A key element of a successful SAGD operation and a typical regulatory requirement for production water disposal is the ability to ensure that the re-injected production water will not adversely affect the quality of the surrounding fresh groundwater. A local-scale characterization of the geometry and hydraulic properties of the aquifers located in the area of re-injection is required to assess accurately the flow path and mixing potential of the re-injected water with groundwater. This paper presents a study conducted to estimate the flow path and the time that produced water from a proposed re-injection well near a SAGD field in western Canada would take to reach an adjacent freshwater aquifer. The approach was based on the use of PETREL, a petroleum reservoir engineering software package, to integrate existing site data and to create a static (conceptual) hydrogeological model of the injection setting. . NMR logs were used to provide a detailed evaluation of the vertical and hotizontal distribution of hydraulic conductivity in the Dina Water Sands. The static hydrogeological model developed within PETREL was exported to MODFLOW, a widely used groundwater flow simulation program, for simulation of injection scenarios.The iterative workflow executed for this project includes three elements of innovation:

(a) it is based on a non-conventional application of PETREL (typically used for oil reservoir modelling) in hydrogeologic characterization, and

(b) it demonstrates the advantages offered by a conceptual modeling tool such as PETREL, which can integrate different types of digital geophysical data, in the development of a groundwater flow simulation for the oil industry. The ability to integrate and process digital subsurface data offers a huge saving in manpower commonly associated with conventional hydrogeological modelling

(c) it demonstrates the application of NMR logs to provide upscaled quantification of the vertical permeability distribution of permeability in the injection zone

The MODFLOW simulation provided the following estimates: - flow path of the water after re-injection into a low-bitumen sand; and - time required by the re-injected water to reach the freshwater Quaternary aquifer. These estimates provided both the SAGD operator and the Regulatory Authority with information required to assess the feasibility of the SAGD pilot project currently under consideration.


INTRODUCTION

Oilsands Quest Sask. Inc. (OQI) is planning to undertake a water circulation and steam injection test program in a horizontal well pair at their Axe Lake Test Site 1 (TS1) in the winter 2010-2011. A key element of the test program is the ability to dispose of up to 60 m3/day of produced water. The produced water will consist of condensed steam that was injected into the bitumen bearing zones and connate water that was incorporated into the bitumen bearing zones at the time of deposition. The zone selected for disposal of the produced fluids is an inter-bitumen aquifer (Water Sands) within the Dina Formation. SWS has been requested to update the computer modeling previously undertaken to reflect the proposed injection requirements of the current reservoir test program and to provide a more precise particle tracking estimate that reflects an upgraded determination of the permeability distribution in the vertical profile of the injection zone.. This paper presents the updated modeling information and results of the numerical groundwater flow model that was used to simulate the injection of produced fluids into the Water Sands. The model incorporates a non-traditional methodology for creating the static hydrogeological model, using PETREL, and determining physical aquifer properties using NMR geophysical logs. This paper describes the following:

Creation of a conceptual hydrogeological (static) model using PETREL to maximize utilization of digital oilfield data

Review of the application of NMR logs to provide an understanding of the permeability distribution in the Water Sands

Review of the numerical flow model (e.g., domain, grid, boundaries, hydraulic parameters)

Results of the flow model simulations, and a comparison to results of previous simulations based on

Scope of Work

The specific questions that Schlumberger Water Services (SWS) was asked to address by OQI were:

What would be the injected fluids profile assuming an injection rate of 60 m3/day for a period of six months up to one year? How will the injected fluids penetrate into the formation 10 years post the injection period?

What significance does the heterogeneity in the Dina Water Sands have in determining the ultimate migration of the injected fluids?

General Site Location

The Axe Lake Area is located in northwestern Saskatchewan, along the Alberta-Saskatchewan border, approximately 90 km northwest of La Loche, SK (Figure 1.0). The well 4-21-94-25 W3M is to be used for the injection of produced fluids from the SAGD test conducted at TS1. The Injection Well is located in the south-western portion of the Axe Lake Area (Figure 2.0). The modeled area is an 8 km X 8 km region around the Injection Well. Background on Steam Injection Pilot Project

An integral component of the pilot testing is the ability to dispose of produced water. As part of the development of a subsurface disposal capability, a number of engineering programs have been executed, and computer simulations run to evaluate the feasibility of injection scenarios that are being proposed as part of pilot testing. Through the application of more advanced techniques and improved geological data, the computer modeling conducted as part of this project upgrades computer modeling previously conducted as part of other pilot testing conducted in 2009.


Figure 1 Axe Lake Site Location HYDREOGEOLOGICAL SETTING

The Axe Lake Discovery Area lies near the north-eastern limit of the Western Canada Sedimentary Basin

(WCSB). The neighbouring Canadian Shield is just tens of kilometres to the northeast. Geology in the study area

includes the extreme north-eastern extensions of several units from the WCSB, but is influenced by the close

proximity of the Canadian Shield (Figure3).

The regional stratigraphy (Figure 4) comprises the following, in ascending order:

1. Precambrian basement;

2. Devonian carbonates and shales;

3. Cretaceous clastic marine or fluvial sediments; and,

4. 4Unconsolidated Quaternary sediments Precambrian

Regionally, the Precambrian basement is known to dip gently to the southwest at a slope of 4 to 5 m/km (Bachu

et al., 1993). The Canadian Shield consists of Precambrian aged igneous and metamorphic rocks that either

outcrop at surface or are covered by a thin veneer of soil. As a result these rocks outcrop in the Canadian Shield

just tens of kilometres to the northeast.

The Precambrian granites and gneisses are considered a regional aquiclude (e.g., Ozoray et al., 1980; Bachu et

al., 1993; AMEC, 2007). Their surface forms the base of the HRSA as groundwater flow through this unit is

insignificant relative to the amount of groundwater flow that occurs in overlying sediments.


Figure 3 Axe Lake Bedrock Geology Devonian

Five geologic units have been identified locally within the Devonian from oldest to youngest:

La Loche Formation consisting of mudstones, red beds, siltstones, sand or sandstones,

sedimentary breccia and conglomerate;

Contact Rapids Formation consisting of clay, shale, mudstone and siltstone;

Winnepegosis Formation consisting primarily of dolostone and some dolomitic limestone;

Prairie Evaporite sediments consisting of various types of karst breccia; and,

An upper Paleosol, directly underlying the Cretaceous that is generally clay or mud, and may be

calcareous or dolomitic, or may be silty.

In the topmost portion of the Paleozoic, near the unconformity, all units are weathered with features such as rubble, fractures, and karsts. As a consequence, the Paleozoic will tend to show different porosity and permeabilities than the same stratigraphic interval more deeply buried underneath the unconformity. All zones show porosity and oil occurrences within the analysed interval.

Water quality of the Devonian carbonates is expected to be relatively good. Mineralization as total dissolved

solids (TDS) concentration from groundwater in the EnCana Borealis area (EnCana, 2007) was 482 ppm, The

hydrochemical type of this water was mixed cation-bicarbonate and the laboratory pH was 8.18.

Cretaceous

The uppermost bedrock units in the Axe Lake Area consist of the Dina Formation. The Dina Formation is used on

the Saskatchewan to describe the formation referred to as the McMurray Formation in Alberta, and the terms are

used interchangeably.


Figure 4 Axe Lake Stratigraphic Column The Clearwater Formation overlies the Dina Formation. However, borehole data from Axe Lake field studies suggest it may not be present within the local or regional study areas

The Cretaceous Dina Formation has been divided into two distinct zones:

Sand-dominated channel zone, and

Basal mud-dominated continental floodplain zone.

Dina Bitumen Impregnated Sections

The Channel Zone is predominantly sand ranging in particle size from fine-grained with thin beds of mud or silt, to

coarse-grained intermixed with pebble-sized gravels. Channel breccia consisting of sands with abundant matrix

supported mud clasts were also present, as was a calcite or other cemented sandstone. The Channel Zone is the

main target for oil sands exploration. Lean oil sands with little or no bitumen, or ‗water sands‘, are also present

within this zone.

Voids within the Dina Formation can be saturated with either water and/or bitumen. In general, the bitumen impregnated sections of the Dina Formation oil sands and the underlying Basal Mud Zone act as aquitards. Ironically, the best aquitard is the Dina oil sand itself—it is the most continuous body in the property and has no relative permeability to water. The sands are at irreducible water conditions and the oil sands themselves contain extremely viscous oil.


In northeast Alberta, the hydraulic conductivity of oil sands varies between 10-5 and 10-8 m/s (Hackbarth and

Nastasa, 1979). At EnCana Borealis, lateral hydraulic conductivity used for modelling was on the order of 10-8 m/s

(EnCana, 2007).

Dina Water Sands Regionally, the continuity, position relative to oil sands, thicknesses, and lateral extent of Dina water-sands are not well defined; thus, potential yields and hydraulic connection with adjacent portions of the Dina and with adjacent formations are uncertain. Once the Dina gets over 18 metres thick, there is a likelihood of encountering a lean oil or water zone. Where the Dina gets up to 40 metres in thickness, it is almost invariably contains significant lean oil and/or water zones. Locally however water sands exist in mappable units within the Dina, especially in the extreme south-west portion of the Axe Lake property where thicknesses of Water Sands in the range of 20 - 40 m have been documented. This is illustrated in north-south cross-section Figure 7 and 8) . Delineation of the position of water sands within and overlying the Dina oil sand has been determined through a combination of core analysis, petrophysics, and analysis of seismic data, and subsequent manipulation within PETREL. Estimates of hydraulic conductivity within the range from 1.2 x 10-8 to 3.2 x 10-6 m/s, but tended toward the higher end of the range. As with the Devonian wells, groundwater levels within the Dina were well above the screened interval showing 150 to 200 m of hydraulic head. Mineralization of groundwater within the water-bearing sands of the Dina is relatively low (Hackbarth and Nastasa, 1979; Bachu et al., 1993; EnCana, 2007). Field pH of Dina groundwater samples ranged from 10.1 to 11.8 and EC from 451 to 2,850 μS/cm. Groundwater ranged from hard to very hard (150 to 590 mg/L as CaCO3) and TDS ranged from 255 to 711. Hydrochemical types were calcium-sodium / carbonate-sulphate and calcium-sodium / hydroxide. Basal Mud Zone

The Basal Mud Zone directly overlies the Devonian and consists of overbank deposits, pond and marsh deposits ranging from muds to sands, and coal swamp deposits

The basal zone is a mixture of shales and sands with poorer reservoir quality (lower porosity, permeability, and oil

saturation) than the Dina zone. The Basal zone is discontinuous and covers a minority of the Axe Lake study

area. In the zone, there are also oil and water sands in proportions similar to the main Dina zone. It is possible

that water sands in the Basal zone can be in hydraulic connection with overlying Dina water zones

Quaternary

Quaternary sediments in the Axe Lake area range in thickness from approximately 140 to 290 m. Quaternary

thickness correlates well with topography; thicker deposits are noted in areas that are topographically elevated.

Quaternary sediments include:

Glacial meltwater channels consisting of sand, gravel and boulders and little to no clay;

Thinly bedded glacial outwash deposits ranging from clay to fine sand;

Clay and silt glaciolacustrine deposits;

Silty and sandy clay with pebbles, rocks or boulders;

Reworked or glacially displaced Dina; and,

Recent sediments include eolian sands, loess, peat, and lacustrine deposits. Glacial deposits in the Axe Lake area are expected to be the major source of groundwater as thicknesses are

substantial (local boreholes show thicknesses upwards of 200 m in places) and composition is dominantly sand.

Ozoray et al. (1980) Projected yields from Quaternary sediments are to be 120-480 L/min in sand and gravel

deposits and 6-24 L/min in sand deposits.


Based on drilling and seismic data, a system of erosional channels at the base of the Quaternary have been identified that locally penetrate through the Dina into the Devonian, or in some cases through both the Dina and Devonian, and into the Precambrian basement. Thus there are sections of the Quaternary that are in direct contact with both the Paleozoic and PreCambrian zones. Quaternary sediments within the channels vary in grain size and composition from mixtures of sand and clay to boulders. The system of channels is several kilometres long. (Figure 4 ) The Quaternary sediments constitute an extensive system of sand and gravel aquifers with discontinuous confining units. Estimates of hydraulic conductivity at most wells ranged from 1.5 x 10-6 m/s to 7.4 x 10-5 m/s, which is typical of sands and gravels. Depending on interaction between the sand and gravel deposits through the full thickness of the Quaternary, potential groundwater yield could be very high. Results suggest the highest yielding aquifers will be Quaternary sands and gravels given the measured hydraulic conductivity and thickness of the deposits. Vertical gradients indicate generally downward movement of groundwater. This suggests the majority of the Axe Lake Discovery Area may be a groundwater recharge area. This is logical as the area is a regional topographic high and straddles a watershed divide. The low vertical gradients given the relatively large vertical spacing between well screens suggest there is hydraulic connection between the sand and gravel units at different depths. The pH of Quaternary groundwater samples ranged from 8.9 to 11.5, EC ranged from 213 to 1919 μS/cm, hardness was generally soft to medium (53 to 82 mg/L as CaCO3) with the exception of P5-3-95-25Q which was very hard (190 mg/L as CaCO3). Total dissolved solids ranged from 121 to 447 mg/L. Groundwater hydrochemical types showed calcium and sodium dominated the cations in all samples, while anions were generally dominated by a mix of bicarbonate, carbonate and hydroxide, depending on the pH

Inter-Aquifer Groundwater Flow

Groundwater flow between aquifers in different formations was evaluated by considering groundwater levels, vertical hydraulic gradients, and water chemistry. It should be noted that the degree of interconnection between different aquifers can vary depending on location. Generally, groundwater level within the Dina was below that of the Quaternary, suggesting continuous downward vertical gradients and downward groundwater flow. This is consistent with a continuous Quaternary – Dina Water Sand conceptual model, where groundwater is recharged by atmospheric water at surface and percolates downwards. Differences in groundwater chemistries between aquifers were subtle. This suggests that either the Quaternary, Dina, and Devonian deposits are hydraulically connected to some degree, or that the water in these deposits has undergone a similar evolution. Physically, there is the potential for hydraulic connection between formations where both Dina and Devonian deposits have been eroded away to the Precambrian in places; connecting all potential aquifers via Quaternary sand and gravels in these ―paleo-channels‖. The results of analysis of water samples suggest that Quaternary waters are ―flushing‖ the Dina water zone. It is likely that wherever the Quaternary overlies any water bearing zone (Dina, Basal, or Paleozoic), hydraulic continuity exists.


Figure 4 Configuration of Main Glacial Channels

Baseline Summary

Overall, Quaternary sands and gravels are expected to be the main aquifers within the study area given the sandy composition and overall extensive thickness. Hydraulic connection over such a large vertical depth (over 200 m in some cases) is possible if confining beds within the Quaternary are discontinuous. Generally, there is evidence for hydraulic connection between all groundwater bearing formations in the Quaternary, Cretaceous, and Devonian considering groundwater elevations and chemistries. Hydraulic connection from the Quaternary to Devonian is apparent where well-saturated Dina oil sands are absent, as in the southwest of the Axe Lake property. Also, erosional channels through the Dina and Devonian and subsequent deposition of sands and gravels to the top of the Precambrian may act as hydraulic pathways connecting all aquifers. Any zone chosen as a target disposal zone is likely to be in hydraulic continuity with the Quaternary. The Quaternary scours every unit at Axe Lake. There are places at Axe Lake where the Quaternary will be in direct contact with all Paleozoic zones and the PreCambrian. Where a Quaternary sand or gravel zone sits on a water-bearing unit in the Dina or Paleozoic, there is the potential for flow across the boundary between the two zones. Vertical groundwater gradients within the Quaternary and the position of the site at the headwaters of two watersheds suggest groundwater recharge is prevalent in this area. PETREL BASED INPUT PETREL is a software application used to build 3D reservoir geomodels. It has the capability to integrate information from many petroleum disciplines, including seismic, borehole geophysics, geostatistics, and reservoir


engineering. 3D geomodels created in Petrel are regularly used to simulate hydrocarbon flow in reservoir settings. By virtue of the nature of SAGD projects, they require a detailed understanding of subsurface conditions and therefore large amounts of subsurface data is generated., often in digital form. Digitally recorded data does make manual processing and interpretation of large data sets time consuming, and expensive The process of evaluating the geological, reservoir and hydrogeological conditions at the Axe Lake site has been accomplished, through an iterative process of ongoing integration of data into a static model created in response to the emerging needs of the project within the framework of the software PETREL. The inherent power and flexibility of PETREL, allowed for geological reservoir, seismic, hydrogeological and geostatistical frameworks to be developed within a single computer package. A key benefit of this integration is the cost effective interpretation of large digital data sets; and the optimization of the utilization of existing data. PETREL Axe Lake Reservoir Model The first PETREL model to be developed of the Axe Lake site was initially used to assist in the design and development of 3 steam injectors and associate observation wells. In the course of the development of the Axe Lake property, several hundred boreholes were drilled as part of the evaluation of bitumen bearing Dina Formation. Commonly casing was installed at the top of the bedrock, and the hole was drilled several meters below the base of the Dina formation. The entire bedrock section was cored and wireline logs run over the bedrock section. The logging suite normally consisted of gamma, porosity and resistivity. In addition, several kilometers of 2D and 3D seismic had been run, providing an opportunity to correlate borehole information to core analysis and seismic results. The PETREL based reservoir model has been used extensively for identification of prospective Pilot Steam Injection site selection and the evaluation of reservoir development scenarios The reservoir model is updated on an ongoing basis to include additional data acquired through ongoing exploration drilling. While an excellent model, this version was designed for the evaluation of the Dina potential reservoir zone and did not incorporate all relevant hydrogeological data. PETREL Injection Screening Model As part of an initiative to conduct a comprehensive evaluation of potential injection zones in the Axe Lake area, the original reservoir focussed Petrel model was upgraded to include hydrogeological data from the Quaternary and underlying Paleozoic .The utilization of existing, wireline and core data allowed for the creation of a static model far more cost effectively than if a separate hydrogeological program had been executed separately from the reservoir characterization data. As the stratigraphic separation between the quaternary deposits and the Dina Water Sands was minimal, wireline logs of the stratigraphic section of interest were available by virtue of the exploration conducted for the purposes of reservoir characterization. Reservoir and aquifer parameters were screened using a variety of 1D, 2D, and 3D techniques to rank the zones based on the criteria of porosity, permeability, and continuous nature. Identification of confining aquitards was done to help assess the ability of a zone to contain pressure A detailed petrophysical analysis was performed to estimate facies, porosity, and water saturation. While this early static hydrogeological model provided essential insight into the hydraulic and reservoir characteristics focussing on the ability of the various permeable units to provide vertical and horizontal containment; it was not used at this stage to conduct simulations. The results of the Injection Zone Screening were incorporated into a series of 15 digitally generated maps and cross sections. From the PETREL Injection Screening Model a target injection zone was identified in the south west portion of the Axe Lake property where an inter-bitumen Water Sands exhibited initial characteristics conducive to the development of an injection capability PETREL 4-21 Injection Model

The third PETREL model provided a static hydrogeological model that was imported to Modflow for simulations of injection into the mid Dina water Sands. The static model developed for the simulation of injection covered and 8 km by 8 km area surrounding the proposed 4-21 Injection Well. The 4-21 Injection model focussed on the


characterization of the nature and extent of the inter-bitumen Water Sands that were being targeted as a potential injection zone, the containment capability of overlying and underlying bitumen zones, and the sub-crop of the Water Sands into the Quaternary channels

The 2009 aquifer analysis focused on bringing all available information relevant to the study of aquifers and aquitards into a single model, maximizing the utilization of existing data sets. An iterative approach was used to update the model and improve the quality of the results. Improved petrophysical analyses were received at three points: at each point the model was rebuilt which, in turn, uncovered new observations that impacted the petrophysical analysis. With each model iteration, the understanding of the aquifer was improved. The biggest piece of new work was to construct a new structural framework to include the Quaternary and Paleozoic zones. The modelling conducted in 2009 consisted of seven layers, but relied on sparse permeability data including values extracted from publically available literature, and core testing and in-situ tests. A single permeability and porosity value was assigned to the Water Sand Unit. This assumption predetermined that the simulation of injection would result in a uniform flow front radially from the injection point. The 2009 numerical modelling, conducted with MODFLOW 2000 with MODPATH, simulated an injection rate of 300m3/day for a period of 6 months followed by monitoring drift of the injected water particles for a period of 10 years. The main input values of the PETREL 4-21 Injection Model are compared to the input parameters of the 2010 PETREL 4-21 Upgraded Injection Model in Table 1 PETREL 4-21 Upgraded Injection Model

Recognizing that heterogeneities in the permeability distribution were certain to exist at some scale within the Dina Water Sands; and that these heterogeneities would influence the flowpath of injected water particles, there was a need to simulate injection in a model framework that incorporated these heterogeneities.

A fourth model, the PETREL 4- 21 Upgraded Injection Model was subsequently prepared that integrated detailed permeabilities for the Dina Water Sands extracted from NMR logs, and a clearer understanding of the bedrock surface and Quaternary deposits derived from seismic data available The upgraded static model was exported to MODFLOW-SURFACT for simulation of injection scenarios The PETREL 4-21 Upgraded Injection Model is the subject of this paper.

Geologic interpretation

A 3D model was constructed from geologic surfaces of the following formation tops:

Ground Surface

Dina Formation (also called Dina Formation)

Devonian (also called Paleozoic)

PreCambrian

4-21 Injection Well

The location of the Injection Well was selected by OQI based on the results of a seismic survey which indicated the presence of a Water Sand unit of approximately 30 m thickness ( Figure 5). In February 2009, the Injection Well was drilled to a depth of 222.6 m below ground surface (bgs) . The static (or conceptual model) model was centred on the OBS 4-21 Injection Well and extended 4 km in all directions. The model used a 50x50m grid cell size. The Dina Formation zone was further subdivided into two subzones: Water Sands and oil sands. Lastly, the water zones and oil zones were further split into thin cells of approximately 1m thickness. At the well OBS 4-21, the Dina zone contains 3 fluid zones: an upper oil zone (12 metres), a Water Sands (23 metres), and a lower oil zone (5 metres). The Water Sands at OBS 4-21 can be locally correlated to surrounding


Water Disposal Information

Subsurface

Formation DepthFluids

Type

m

Dina171.3 -179.6

8.3 Bitumen

Dina179.6-207.0

27.4 Water

Dina207.0-214.0

7.0 Bitumen

Devonian 214.0-below Water

Perforation

Interval

202.2-207.2

5.0 Water

Figure 5 Injection Zone 4-21- 94-25-W3M boreholes. Cross sections through the Injection Well were created to aid in the development of the conceptual model of the stratigraphy. Cross sections created from wireline logs are map-located in Figure 6 and presented in Figures 7and 8,demonstrating the thickness and porosity of the the Dina Water Sands in the 4-21 area. The Dina Water Sands were confirmed to be present at the 4-21 site (Figure 5, 7and 8)) and contain 27.6 metres of clean Water Sand in the interval 179.7 to 207.0 mbgl. Although areally extensive the upper potions of the Dina have been removed by glacial processes, and subsequent deposition has left Quaternary deposits in direct contact with the Water Sands (Figures 9 and 10) in three directions surrounding the 4-21 Injection Well (Figure 11). The presence of the Quaternary erosional channels introduces the possibility that fluids injected into the Water Sands at the 4-21 Injection Well may ultimately migrate to the unconformity between the Dina Water Sands and the Quaternary deposits a distance estimate to be in the order of several hundred meters. As the Quaternary deposits are considered to be an environmentally sensitive receptor, the consideration of injection into the mid Dina Water Sands NMR ESTIMATES OF PERMEABILITY

The definition of the heterogeneity of the permeability in a vertical stratigraphic profile can be accomplished through comprehensive analysis of continuous core cut from the vertical profile of interest, or through insitu testing of short sections of the profile such that a near continuous understanding of the entire stratigraphic profile would be generated. Both of these methods are costly and time consuming, and suffer from limitations (poor core recovery, unstable borehole conditions, etc) that make them unattractive for generating the data density desirable for detailed modelling. Fortuitously, Nuclear Magnetic Resonance (NMR) logging had been conducted on several, but not all boreholes at the Axe Lake site. One of the boreholes logged using NMR tools was the 4-21 Injection Well. The availability of the NMR logs and the ability to integrate the digital data NMR into the PETREL static model allowed for a more


detailed understanding of the heterogeneity in permeability distribution to be defined both vertically and horizontally.

Disposal Well

Figure 6 Cross Section Location Map NMR Background NMR logging has proven to be an invaluable tool in oil and gas exploration, but the size, weight, and high cost of oilfield NMR has limited its use in hydrogeological environment investigations. NMR logging has a number of applications for groundwater investigations. Estimates of permeability and hydraulic conductivity can be obtained from the NMR total porosity and T2 distributions using empirically established relationships (Fig.9). Nuclear magnetic resonance (NMR) logging provides a measure of the total fluid-filled porosity and pore-size distribution of a formation, from which the bound and moveable water distribution and hydraulic conductivity are estimated. Current NMR logging techniques are discussed by Kenyon et al. (1995), Coates et al. (1999), Allen et al. (2000), Henderson (2004) and Freedman (2006).


Figure 7 South to North Wireline Cross Section

Figure 8 Northeast to Southwest Wireline Cross Section 1 Unlike other standard log porosity measurements, the NMR total water filled porosity measurement is lithology-independent. Pore volumes are represented by fractions of the total area. The empirical algorithms used to interpret the T2 distribution are based on NMR measurements of thousands of core samples from around the world. Figure 12 shows a typical T2 distribution. A value of .33 ms is commonly used for sandstones. General lithology based cutoff values can be used to estimate pore size distribution. However, for best results NMR analyses should be performed on cores from the local study area to calibrate the T2 distribution cut-offs. The primary advantage of borehole geophysical logs is that they can provide a near-continuous high-resolution record of in situ formation properties, which is not practicably possible or cost-effectively obtained by other means. Of particular value, advanced borehole geophysical logging can be used to elucidate porosity types and distribution, and fine-scale variations in aquifer hydraulic conductivity and aquifer composition. Such data can be imported directly into geological data management or workflow software and, in turn, groundwater flow and solute transport models.


Figure 9 T2 Distribution for Various Porosities NMR Application Axe Lake During the 2009-2010 drilling program, Nuclear Magnetic Resonance Tool well logs were run on 14 different wells. Ten of these wells had petrophysical analysis which could then be added into the PETREL geomodel. The analysis includes key estimates of:

NMR porosity (MPHI).

Moveable pore water volume called the free fluid index (FF)

Permeability (MPERM)

The Dina Water Sand Section of the NMR log run on the 4-21-94 -25 W3M well is shown in Figure 13. Water Sands are identified, where the FFI pore volume forms the majority of the MPHI porosity. For each MPHI measurement in water sands, an estimate of permeability (MPERM) was made on a 0.125m depth increment. The detailed vertical resolution of the analysis resulted in a corresponding vertically-detailed estimate of permeability in the geomodel. The NMR analyses are shown in Figures 14, 15, and 16.

Estimate of NMR Permeability.

The 3D geomodel generated with PETREL has a large number of wells (several hundred) with porosity estimates, but only 10 wells with NMR permeability estimates. A permeability to porosity regression in the Water Sands of 10 wells was performed, as there is a significant correlation of permeability to porosity. The permeability regression was then applied to the porosity in the rest of the wells to create a detailed estimate of permeability.


Figure 10 North – South PETREL Generated Cross Section

Figure 11 West -East PETREL Generated Cross Section 1 Regression Crossplot between Porosity and Permeability.

The cross plot between porosity and permeability in Figure 14 a shows the correlation between the two parameters in the Water Sands. The displayed values come from the Water Sands in the 10 wells using the original analysis. Key points illustrated by the crossplot are:

The water sands sample a wide range of porosities (0-36%) and permeabilities (0.001 to 50,000 millidarcies)

The bulk of the porosity measurements occur at the high range of porosities (24% and higher)

There is a significant correlation between porosity and permeability. The crossplot required editing in order for it to be used to stochastically estimate permeability. Edits to the crossplot are:


Figure 12 Subcropping Dina and Dina Water Sand

Divided porosity into discrete classes, or intervals, using an increment of 3 porosity units.

Required a minimum number of 25 data pairs in each class — if fewer existed, then additional points were randomly added using the mean and standard deviation of the class.

The resultant modified crossplot shown in Figure 15 was used to model permeability using a bivariate, or cloud, transform. The porosity value for each cell in the model was plotted in the transform crossplot to locate its position in one of the porosity classes. Once the class of the porosity value was established, a permeability value was randomly selected from the class and assigned to the cell. Resultant Crossplot Transform

The final crossplot shown in Figure 16 shows the resultant model estimates of permeability. The model permeabilities conform to the bivariate transform correlation Benefits of this transform include:

The preservation of variability of permeability within a porosity class

Ensures that permeability trends match porosity trend


Figure 13 NMR Log 4-21 Injection Well

On the final crossplot, another series of porosity intervals, or classes have been drawn. These classes represent equal distributions of porosity values; in the crossplot, the porosity is divided into 10 intervals of equal points. A key observation from these intervals is that only 10% of the Dina Water Sands have porosity values below 25


porosity units. Therefore, the resultant permeabilities derived from porosity will also reflect this trend with only about 10% of Dina Water Sands have permeabilities below 100 millidarcies.

Figure 14 Relationship Between Permeability and Porosity in Dina Water Sands Outputs for study

The outputs from the model were a series of 13-digitized layers showing the distribution of the following zones:

Ground Surface

Dina Oil Zone

Dina Water Sand Zone

Devonian

PreCambrian To model the vertical variability of reservoir porosity and permeability, 10 of the layer maps were used to represent the Dina Water Sand and oil zone intervals. In each layer, porosity values were estimated for Dina oil and Water Sand zones; permeability values were estimated for Dina Water Sand zones.


Figure-15 Relationship Between Permeability and Porosity in Dina Water Sands (Water ----- Used in Bi-Variate or Cloud Transform)

Figure 16 Relationship between Permeability and Porosity in Dina Water Sands (Final Model, Post Transforms, All Cells)


NUMERICAL GROUNDWATER FLOW MODEL The general approach to modeling was:

Development of a conceptual model of the stratigraphy and flow field based on an interpretation of the geology provided through the application of Petrel and background information available on the flow conditions at the site.

Development of a numerical groundwater model based on the conceptual model. The inputs to the numerical model were based on a variety of hydrogeologic field measurements (e.g. subsurface geology, groundwater elevations, aquifer hydraulic parameters from wireline logs and field tests, observed flow characteristics, etc.).

Calibration of the numerical groundwater flow model using a steady state simulation. The model inputs (e.g., recharge and hydraulic conductivity) were varied until a satisfactory match was found between the modeled hydraulic heads and the observed heads (e.g., water levels) in the field.

Completion of two transient simulations based on a 6 months and 12 months of injection using an injection rate of 60 m3/d.

Conceptual Model Development

The modeled area is within the southwestern portion of the Axe Lake area as shown on Figure--. The topography of the ground surface within the modeled area is generally flat. The elevation varies from about 580 masl in the northern portion of the modeled area to about 525 masl to the south. Streams and wetlands in the southern portion of the modeled area were observed based on maps of the area. The geology within the modeled area was represented by the following sequence of hydrostratigraphic units (from the top down):

Unconsolidated Quaternary sediments;

Cretaceous Dina Formation which includes the Oil Sands, Lean Oil Sands and the Water Sand units;

Devonian carbonates; and

PreCambrian rock.

For the purposes of the modeling, the Lean Oil Sands were combined with the Water Sands. The Water Sand unit is approximately 20 to 25 m thick across the modeled area. The aquifer units within the modeled area are the Quaternary and Water Sands. The hydraulic erosion of the Dina and Devonian deposits results in a potential connection between the aquifers through the Quaternary sand and gravels that fill the eroded channels. Based on an interpretation of the geology using Petrel, Oil Sands overlie the Water Sands at the injection site. Contact between the Water Sands unit that is to be used for the injection and the Quaternary deposit is the closest to the southeast of the Injection Well at a distance of approximately 350 m. The perimeter of the Water Sands unit in the other radial directions is interpreted as generally being in contact with Oil Sands with some potential for Quaternary/Water Sand contact ranging from about 350 - 1000 m away from the Injection Well. The interpretation of the stratigraphy is discussed in further detail in Section 3 (Petrel Model Description). Code Selection

The MODFLOW-SURFACT numerical groundwater model was used to simulate groundwater flow at the Axe Lake project. MODFLOW-SURFACT is a 3D finite-difference code based on the popular MODFLOW code, is compatible with the many modular packages of MODFLOW, and is more numerically stable than the basic MODFLOW code when solving for groundwater flow in aquifers with large differences in permeability across short distances, such as that seen at the interface of the Oil Sands. The particle tracking post-processing package MODPATH version 3 was used to compute three-dimensional flow-paths based on the hydraulic head distribution calculated using MODFLOW-SURFACT. To visualize the three-dimensional flow-paths using MODPATH, simulated ―particles‖ of water were modeled.


Model Development

The lateral boundaries of the model were chosen to be large enough to minimize bias in the results and small enough to keep the model manageable. A uniform finite difference grid consisting of square grid cells of 50 m by 50 m was overlain on the modeled area. The model area (e.g., domain) encompasses a total area of about 64 km2 (Figure 4.2). The numerical groundwater model was constructed using 13 layers. These layers were defined using a simplified conceptual model of the geology in the study area (Figure 17). The layering system provided a method to incorporate the key geological features and potential flow interaction between the formations. Surface topography was assigned to the top of layer 1 using a 1:50,000 DEM (GeoBase). The bottoms of the layers were defined as follows: Layer 1: Elevation of upper contact between Quaternary and Dina Layer 2: Intermediate layer bottom Layer 3: Intermediate layer bottom Layer 4: Elevation of bottom of oil sand unit (where present) Layer 5: Intermediate layer bottom Layer 6: Elevation of contact between Quaternary valleys and Devonian Layer 7: Intermediate layer bottom Layer 8: Intermediate layer bottom Layer 9: Elevation of bottom of upper lean/Water Sand unit Layer 10: Intermediate layer bottom Layer 11: Elevation of contact between Dina paleovalley and Devonian Layer 12: Elevation of contact between Devonian and Pre-Cambrian basement Layer 13: Defined as 0 masl. Boundary Conditions and Aquifer Properties

Boundary conditions are used to specify groundwater sources and sinks in the model domain. Boundary conditions assigned to the model were constant heads, drains and meteoric recharge. The aquifer properties assigned to the model were hydraulic conductivity, storage and porosity.

Hydraulic Conductivity

Hydraulic conductivity values for the stratigraphic units were based on site specific data when available and literature describing the general properties of these deposits regionally (Figures 4.9a – 4.9m). The Quaternary and units were assigned a ratio of horizontal to vertical conductivity equal to 100. The Devonian and Pre-Cambrian units were assigned a ratio of horizontal to vertical conductivity equal to 1.

AMEC (2008) described the Quaternary deposit as an extensive system of sand and gravel aquifers with discontinuous confining units. A hydraulic conductivity value of 3 x 10-5 m/s was assigned to the Quaternary deposit based on the results of six hydraulic tests carried out by AMEC (2008).

The Oil Sands generally act as an aquitard. In northeast Alberta, the hydraulic conductivity of Oil Sands can vary between 10-8 and 10-5 m/s (Hackbarth and Nastasa 1979). At EnCana, now Cenovus Borealis, the horizontal hydraulic conductivity used for modeling was on the order of 10-8 m/s (EnCana 2007). Although a lower hydraulic conductivity value of 1 x 10-10 m/s was assigned for this model, given the relatively low hydraulic conductivity value of the Oil Sands unit, the unit should behave similarly.

The Water Sands are typically coarse grained and low in bitumen. This unit forms an aquifer with typical transmissivity in the range of 6 x 10-4 to 1 x 10-3 m2/s (K. Baxter, CH2M HILL). For this study the analysis of NMR logs using Petrel software was completed and a realization of the spatial distribution of permeability in this unit was chosen to calculate the Water Sands hydraulic conductivity assuming a formation temperature of 10°C. The permeabilities calculated from the NMR logs ranged from 6 x 10-8 m/d to 6 x 101 m/d The arithmetic mean of the realized conductivity values is 1.2 x 10-4 m/s.

Of the 13 layers in the 4-21Upgraded Injection Model, 10 of the layers contained a horizontal slice of the Water Sands. The permeability in the Water sands in each layer was assigned over the range of


permeabilities extracted from the NMR logs. This provided a representation of the permeability heterogeneity in the horizontal plane (Figures 18 and 19). The stacking of the layers with the horizontal distribution of permeabilities imbedded provided the representation of the vertical heterogeneity.

Porosity and Storage

Total porosity describes the fraction of void space in the material. Effective porosity refers to the fraction of the total volume in which fluid flow is effectively taking place (this excludes dead-end pores or non-connected cavities). The specific yield is the fraction of the total volume which will drain from the material. For this modeling study, the total porosity, effective porosity and specific yield are assumed to be equal. Specific storage, the volume of water an aquifer will release from compressible storage per unit volume per change in head, was specified based on typical values for each of the deposits.

The range in hydraulic conductivity from the field tests carried out in the Devonian unit by AMEC (2008) covered 4 orders of magnitude, from 3.4 x 10-9 to 2.4 x 10-6 m/s. The Alberta Geological Survey (Bulletin 59) provided estimates of the hydraulic conductivity between 3 x 10-8 to 1 x 10-7 m/s for the Devonian. A value of 1 x 10-7 m/s was assigned to the Devonian.

The Pre-Cambrian granites and gneisses are considered a regional aquiclude (Ozoray et al.,1980; Bachu et al., 1993; AMEC 2008). A relatively impermeable hydraulic conductivity of 1 x 10-10 m/s was assigned to the Pre-Cambrian. The initial hydraulic conductivity values applied over the modeled area for each of the 13 model layers are summarized in Figure 17.

Site data was not available to characterize the porosity of the Quaternary deposit; and, therefore, a value of 0.15 was used, which is within the range for sand (Domenico and Schwartz).

A typical value for the total porosity of the Dina is 0.3 based on porosity measurements from samples collected within the Axe Lake Area . For this study, the analysis of NMR logs using Petrel software was completed and a realization of the spatial distribution of porosity in this unit was chosen to represent the water sands porosity. The arithmetic mean of the realized porosity values is 0.30.

Since the voids of the Oil Sands are filled with bitumen, a lower porosity of 0.01 was assigned to this unit.

Porosity values of 0.02 and 0.01 were assigned to the Devonian and Pre-Cambrian, which were also based on typical values for these materials.

Steady State Flow Model

A steady-state model was developed to simulate the natural groundwater gradient and provide a check for the reasonableness of the conceptual and numerical models. Due to the remote nature of the site, calibration data was limited to a group of four co-located piezometers that are within the model area and comparison of calculated heads with a map of interpolated groundwater levels. Two of the piezometers are screened in the Quaternary, one piezometer is screened in the Dina and one in the Devonian. Model Simulation Scenarios

A transient model was developed based on the steady-state model. The transient model simulates a total of 10 years. Two separate scenarios were run with injection occurring for 6 months and for 12 months, followed by a period of recovery of 9.5 and 9 years, respectively. Injection was simulated by a well boundary condition


Figure 17 Conceptual Hydrogeological Model1 assigned to Layer 8 at the location of the Injection Well. The injection rate for both injection scenarios was set equal to 60 m3/d. In order to evaluate the fate of injected water, particle tracking was employed. A total of 50 particles were released around the simulated Injection Well in the model at the beginning of the simulation. Five sets of 10 particles were released in a circle within the injection model cell at levels equivalent to 0.0, 0.25. 0.50, 0.75 and 1.0 of that cell thickness. The paths of these particles were computed for each month during the 10 year injection scenarios.


RESULTS Six Month Injection

Results of the six month injection scenario are presented on Figure 20. The particles indicate radial flow away from the Injection Well during injection to an average distance of 16 m. After injection was terminated at 6 months, the flow of the particles was influenced by the natural groundwater gradient and moved toward the south-southwest. At the end of 10 years, the maximum distance of the particle path was 46 m. Twelve Month Injection

Results of the twelve month injection scenario are presented on Figure 21. The particles indicate radial flow away from the Injection Well during injection to an average distance of about 28 m. After injection was terminated at 12 months, the flow of the particles was influenced by the natural groundwater gradient and moved toward the south-southwest. At the end of 10 years, the maximum distance of the particle path was 73 m. CONCLUSIONS The conclusions reached, (beyond the answers to the technical questions originally posed regarding the potential migration of injected water into the Dina Water Sands) include:

Advanced technologies beyond classical hydrogeological techniques must be applied to advance our understanding of hydrogeological issues in scenarios that are deemed high financial or environmental risk

Through the use of PETREL, or PETREL-like-software, large sets of oilfield data can be effectively integrated into geomodels being developed for hydrogeological purposes

Selected oilfield technologies including seismic, wireline (case in point being NMR logs) can be adapted for hydrogeological purposes

Cost savings and efficiencies in the development of hydrogeological insight (whether for the determination of EIA, water sourcing, or disposal purposes) can be realized through the integration of the data needs of these programs into the exploration being conducted for


Figure 18 NMR Based Permeability in Layer 8


Figure 19 Blow Up of Permeability Dina Water Sands in Layer 8


Figure 20 Particle Movement -6-Month Injection Periods 1


Figure 21 Particle Movement 12 month Injection Period


2009 Initial 4-21Injection Model 2010 Upgraded 4-21 Injection Model

InjectionRate (m3/day)

300 60

Injection Duration Months

Inject 6 months

Monitor 10 years

Inject 6 and 12 months

Monitor 10 years

Layers 7 13

Hydraulic Conductivity

5x10-5 m/s 6x10-8 to 6 x 101 m/d

Kh/Kv 1 100

Specific Storage 5 x 10-4 5 x 10-4

Porosity % 30 2 - 37

Specific Yield 0.3 .002 to 0.37

Max distance of travel of injected particle (m)

6 months injection- 35m

10 years post injection– 80m

6 months injection– 16m

10 years post injection- 46m

12 months injection – 28m

10 years post injection– 73m

Table 1 Comparison of Simulation Results From 2009 Initial 4-21 Injection Model With The 4-21 Upgraded Injection Modelling REFERENCES Allen D, Flaum C, Ramakrishnan TS, Bedford J, Castelijns K, Fairhurst D, Gubelin G, Heaton N, Minh CC, Norville MA, Seim MR, Pritchard T, Ramamoorthy R (2000) Trends in NMR logging. Oilfield Rev 12(3):2–19 Alberta Geological Survey. 1989. Hydrogeological and geothermal regimes in the Phanerozoic succession, Cold Lake area, Alberta and Saskatchewan. AMEC (2009), Proposed Injection Well 4-21-94-25 W3M Completion and Testing Results Axe Lake Discovery Area, Oilsands Quest Inc April 2009. AMEC (2008) Oilsands Quest Inc. Environmental Baseline Report Axe Lake Discovery Area, Saskatchewan , March 2008,. Baxter (CH2M HILL Canada Limited). 2002. Management of the Basal Dina Water Sand During Bitumen and Heavy Oil Extraction; 75th Anniversary of Cspg Convention (June 3-7, 2002).


Bachu, S., J.R. Underschultz, B. Hitchon, and D. Cotteril. 1993. Regional-Scale Subsurface Hydrogeology in Northeast Alberta, Alberta Geological Survey, Alberta Research Council Bulletin No. 61. Coates GR, Xiao L, Prammer MG (1999) NMR logging, principle and applications. Halliburton, Houston, TX Domencio P. A., and F. W.Schwartz. 1998. Physical and Chemical Hydrogeology (2nd edition). John Wiley and Sons, New York, NY. Encana Corporation (Encana). 2007. Borealis Thermal Project. Environmental Impact Assessment. Report filed with the Energy of Utilites Board. Calgary AB. Freedman R (2006) Advances in NMR logging. J Petrol Technol 58(1):60–66 GeoBase http://www.geobase.ca/. Last Updated 2009-03-05. Hackbarth, D. and N. Nastasa. 1979. Hydrogeology of the Athabasca Oil Sands Area, Alberta. Alberta Research Council Bulletin 38. Henderson S (2004) Nuclear magnetic resonance logging. In: Asquith G, Krygowski D (eds) Basic well log analysis. Am Assoc Petrol Geol Methods Explor 16:103–113 Kenyon B, Kleinberg R, Straley C, Gubelin G, Morriss C (1995) Nuclear magnetic resonance imaging: technology for the 21st century. Oilfield Rev 7(3):19–33 Keys WS (1989) Borehole geophysics applied to ground-water investigations. National Water Well Assoc., Dublin, Ohio Keys WS (1990) Borehole geophysics applied to ground-water investigations. US Geol Surv Tech Water-Resour Invest, book 2, chapter E2 Keys WS, MacCary LM (1971) Application of borehole geophysics to water resources investigations. US Geol Survey Tech Water-Resources Invest, book 2, chapter E1 Maliva, R.G, Clayton, E.A, Missimer, T.M, 2009, ―Application of advanced borehole geophysic al logging to managed aquifer recharge investigations, Hydrogeology Journal Ozoray G., D. Hackbarth, A.T. Lytviak. 1980. Hydrogeology of the Bitumount-Namur Lake Area, Alberta. Alberta Research Council. Earth Sciences Report 78-6. Schlumberger Water Services (SWS), (2008) Quaternary Permeability Study in Oilsands Quest Inc Axe Lake Discovery Area, Unpublished Presentation,. Schlumberger Data and Consulting Services (DCS). April 2008. Axe Lake Test Site Reservoir Simulation Modelling, Unpublished Presentation. Schlumberger Water Services (SWS), 2008 Characterization of Potential Fluid Disposal Zones in Oilsands Quest Inc Axe Lake Discovery Area, Unpublished Report prepared for Oilsands Quest. Schlumberger Water Services (SWS), 2009, Numerical Groundwater Modelling of Injection of Produced Water Into the Dina Formation Water Sands at 4-21-94-25 W3M – Axe Lake, Saskatchewan, Unpublished report prepared for Oilsands Quest. Schlumberger Water Services (SWS), 2010, Evaluation of Hydrogeological Implications of Pre-Documentation Disposal of Produced Water in Injection Well at 4-21-94-25 W3M Axe Lake, Saskatchewan, Unpublished report prepared for Oilsands Quest.

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