Wastewater Disposal in the Maturing Montney Play Fairway, Northeastern (NTS 093P, 094A, B, G, H)

B.J. Hayes, Petrel Robertson Consulting Ltd., Calgary, , [email protected] J.H. Anderson, Reservoir Engineering Consultant, Calgary, Alberta M. Cooper, Sherwood Geological Consulting, Calgary, Alberta P.J. McLellan, McLellan Energy Advisors Inc., Calgary, Alberta B. Rostron, University of Alberta, Edmonton, Alberta J. Clarke, Petrel Robertson Consulting Ltd., Calgary, Alberta

Hayes, B.J., Anderson, J.H., Cooper, M., McLellan, P.J., Rostron, B. and Clarke, J. (2021): Wastewater disposal in the maturing Montney play fairway, northeastern British Columbia (NTS 093P, 094A, B, G, H); in Geoscience BC Summary of Activities 2020: Energy and Wa- ter, Geoscience BC, Report 2021-02, p. 91–102.

Introduction tainment risks, and to help understand disposal reservoir geomechanical settings; In 2019, British Columbia’s Scientific Hydraulic Fractur- 5) integrate well test, production and reservoir pressure ing Review Panel (2019) identified knowledge gaps in the data with geomechanical data to characterize in situ understanding of water disposal in deep saline aquifers in stresses and rock properties, which can influence dis- the Montney play fairway in northeastern British Columbia posal aquifer compartmentalization and containment (BC). The Petrel Robertson Consulting Ltd. (PRCL) team risks; has undertaken a project for Geoscience BC to address 6) undertake targeted laboratory work to address critical these knowledge gaps, consistent with Geoscience BC’s data gaps; and strategic objective to support development of the Montney 7) develop practical conclusions and recommendations to play through technical studies that aid safe oil and gas guide operators and BCOGC in decisions around devel- production and waste fluid disposal. opment and regulation of disposal capacity and contain- Study Methodology ment across the entire Montney play fairway. Wastewater disposal is a complex issue, and presents vary- Consultation Findings ing challenges across the huge Montney play fairway (Fig- ure 1). Recognizing the scope of these challenges, the Seventeen companies, including wastewater disposal workplan for this project builds on the experience of firms, operating in the BC Montney play fairway were con- Montney play operators, service companies and the British sulted. Key points resulting from these consultations Columbia Oil and Gas Commission (BCOGC), and in- include · cludes the following elements: many operators manage their own water resources, 1) consult with operators, service companies and BCOGC some in co-operation with other operators in order to staff to best understand disposal requirements and oper- maximize recycling and disposal efficiencies; · ational experiences; recycling is a very important strategy to minimize dis- 2) interpret performance of existing disposal wells, paying posal needs but most companies must dispose of particular attention to information around regulator-im- wastewater at least periodically; posed restrictions or shutdowns; · most disposal is into regional aquifers; few companies 3) build on existing aquifer characterization work to com- target depleted oil and gas reservoirs, although some are plete updated maps on disposal aquifer distribution, looking at the option; quality and fluid composition; · limited disposal reservoir capacity in close proximity to 4) map and assess structural elements across the Montney operations is an important issue for many operators; play fairway to identify discontinuities related to con- · seismicity induced by wastewater injection is uncom- mon but has resulted in curtailment or modification of operations in at least 11 wells to date; · This publication is also available, free of charge, as colour digital fluid compatibilities and rock-fluid interactions are crit- files in Adobe Acrobat® PDF format from the Geoscience BC web- ically important in minimizing degradation of injection site: http://geosciencebc.com/updates/summary-of-activities/. zone quality; they are managed primarily by careful

Geoscience BC Report 2021-02 91 Figure 1. Location of study area within the Montney play fairway of northeastern British Columbia and northwestern Alberta.

monitoring of the water chemistries in fluid batches to port the analysis of each aquifer interval across the study be disposed; area. · wellbore integrity is not a major issue but operators gen- erally avoid re-entering older wellbores, or those with Disposal Aquifer Mapping and suspected integrity issues, for disposal purposes. Characterization

Consultation with staff at the BCOGC was very productive The BCOGC regulations dictate that deep disposal aquifers in understanding their strategies in regulating disposal must lie below the base of usable groundwater, which is de- wells, and in accessing online databases and matters related fined as between 300 and 600 m below ground surface, and to induced seismicity. below the Base of Fish Scales stratigraphic marker (BC Oil and Gas Commission, 2020d). Eight formations were iden- Review of Existing Disposal Wells tified that offer widespread disposal capacity and have been Atotal of 162 active, suspended and abandoned wastewater used as disposal zones in the Montney play area: Peace disposal wells were found in the study area by inspecting River (Paddy/Cadotte members), Bluesky, , Bu- well data files hosted by geoSCOUT (geoLOGIC systems ick Creek /Nikanassin, Baldonnel, Halfway, ltd., 2020) and the BCOGC, including 139 in BC and 23 in Belloy and Debolt (Figure 3). Asmall number of wells have Alberta (Figure 2). Acid gas disposal wells were not in- disposed of fluids into the Charlie Lake and Spirit River cluded, nor were water injection wells that provide pressure formations, but these wells are very isolated, and regional support in oil fields. Twenty wells tested and/or injected characterization of the formations would not have been into two disposal zones, and one well tested and/or injected useful in defining additional potential. into three disposal zones. Each disposal formation has been mapped and character- Each disposal zone was assigned to the appropriate strati- ized regionally, building on studies in the public domain graphic interval(s), and relevant data were tabulated to sup- (e.g., Petrel Robertson Consulting Ltd., 2011, 2015), pro-

92 Geoscience BC Summary of Activities 2020: Energy and Water Figure 2. Distribution of existing wastewater disposal wells in the study area, northeastern British Columbia and northwestern Alberta (well data from British Columbia Oil and Gas Commission and geoLOGIC Systems ltd., 2020). Background shows – bedrock outcrops (modified from Cui et al., 2017). prietary PRCL studies, and new work. Gross thickness, net east, which feature better reservoir quality and most of the porous reservoir thickness and depth-to-top formation Cadomin Formation disposal wells. maps have been prepared as warranted by available data. Most disposal formations exhibit depositional and/or ero- Structural Geology Review sional limits that sharply define their distribution and utility. To provide a structural framework for the study, data from various sources were compiled on a summary map of struc- Figure 4 shows the gross thickness of the Cadomin Forma- tural elements (Figure 5). It is particularly striking that the tion, one of the major disposal aquifers. The Fox Creek Es- extrapolation of the Hay River shear zone (HRSZ) carpment defines a sharp northern depositional limit, con- southwestwards into the Rocky Mountain fold-and-thrust fining Cadomin Formation disposal zone potential to the belt (FTB; yellow chevrons on Figure 5), coincides with southern part of the Montney play fairway. Depth to top of significant shifts to the southwest in the eastern limits of the the formation and net porous reservoir mapping (not shown outcrop edge of the FTB, the subsurface eastern limit of the here) demonstrate that the disposal potential of the FTB and the eastern limit of the subsurface inversion. To Cadomin Formation is best in shallower updip areas in the the north of the HRSZ, the edge of the deformed belt is

Geoscience BC Report 2021-02 93 Belloy thick. There is also an eastward shift in the eastern limit of overpressure in the south of the HRSZ.

A series of seven regional cross-sections is being con- structed;theCameroncross-sectionisshowninFigure6. The cross-sections have been constructed using surficial geology, well data within a ±5 km corridor of each section (usually 150–250 wells per section) and limited seismic data. Formation tops for the wells were obtained from the BCOGC website (BC Oil and Gas Commission, 2020b) and validated against formation tops picked by PRCL. Where available, well deviation surveys and dip data have been included. The location of structural highs and lows, stratigraphic erosional and depositional edges, structural and overpressure limits and the HRSZ are shown on the Cameron section (Figure 5). In addition, the locations of oil and gas pools based on the BCOGC shapefiles of pools are also indicated. The cross-section shows a combination of thick- and thin-skinned compressional deformation at the western end of the section with a notable detachment within the Besa River Formation shales. Close to the outcrop edge of the FTB, a major inverted extensional fault creates a broad anticline at Cameron River. Further east there are some low amplitude thin-skinned compressional structures and deeper rooted extensional faults that influence strati- graphic thickness changes from the Devonian to Early Cre- taceous and also act as triggers for thin-skinned structures to develop, for example at the Blueberry field (Figure 6). Reservoir Engineering The goals of the reservoir engineering work are to evaluate injection efficiency (injectivity index and reservoir storage capacity), as well as comparing and contrasting disposal performance of horizontal with vertical wells, the different disposal formations and their variations across the basin, and deterioration or enhancement of disposal performance with time and injection volumes. The terms injection and disposal are used interchangeably and refer only to waste- water disposal, not to waterflooding or pressure mainte- nance operations.

Figure 3. Stratigraphic column for northeastern British Columbia The relevant data, including disposal rates versus time, in- (NEBC), highlighting disposal zone aquifers addressed in this pa- jection wellhead pressures and reservoir pressures, were per (modified from BC Ministry of Energy, Mines and Low Carbon gathered. The first two types of data are in the production/ Innovation, 2011). Abbreviations: S., south; SS, sandstone. injection databases (geoLOGIC systems ltd., 2020), but reservoir pressures are more difficult to determine and are found in a variety of sources. much more diffuse, forming a broad zone extending east of the outcrop edge of the FTB. South of the HRSZ, the sur- Firstly, the injectivity index, defined as injection rate per face and subsurface eastern limits of the FTB are essen- pressure gradient from sandface to reservoir (units of tially coincident. The southwest extension of the HRSZ bbl/day/psi or m3/day/kilopascal), was estimated. To do into the FTB also appears to coincide with the western limit this, sandface pressure was estimated using recorded sur- of the Fort St. John graben and the northern edge of the face pressure plus vertical pressure head to the mid-point of Arch and with three structural lows: the Hud- perforations minus frictional pressure losses, using a fric- son Hope low, the Hudson Hope Embayment and the tion factor derived from commonly used pipeflow correla-

94 Geoscience BC Summary of Activities 2020: Energy and Water Figure 4. Gross thickness of Cadomin Formation in the study area. Well data accessed through geoSCOUT (geo- LOGIC systems ltd., 2020). tions. For reservoir pressure, data recorded by the well op- horizontal wells), and for both early and late times for 75 erator was used, which included drill-stem test results, wells (13 horizontal wells). Pressure measurement timing static gradients, buildups, falloffs and diagnostic fracture varied with operator practice, and so time intervals could injection test (DFIT) results, judiciously examining the not be standardized for these calculations. Obvious anoma- conditions and shut-in times of the tests, and discarding any lies are being evaluated in a handful of wells, but early re- data that were erroneous or not deemed reasonable. sults indicate that about 30% of the wells showed improved Wellbore pressure calculations were carefully made using data from the same month as the reservoir pressures were injectivity over time, about 10% stayed the same, and about taken. Injectivity index estimates were not normalized to 60% lost injectivity over time. Not all wells are on the same formation thickness, although this will be reviewed for the time scale or have received the same injection. Focusing on final report. the Cadomin Formation as an example, where there are 25 vertical and 6 horizontal disposal wells, the horizontal An injectivity index was obtained for shortly after the start wells on average showed approximately four times the of injection for 86 wells (13 of which were horizontal), for injectivity index of the vertical wells, and deteriorated less near the end of injection (or present day) for 101 wells (14 with time: 6% versus 23% (Figure 7).

Geoscience BC Report 2021-02 95 - e inferred location of the Hay River shear zone projected into the reef trend of the Peace River Arch (PRA) are from Davies (1997) and (thin black lines) are named; the Cameron cross-section is shown in Fig ed on BC Geological Survey digital bedrock geology (Cui et al., 2017). . (2018). Enlighten Geoscience Ltd. kindly provided some of the data as based on BC Oil and Gas Commission pool (BC Oil and Gas Commission, 2020c) on Hope Embayment; HHL, Hudson Hope low; N, north. Summary map of structural elements in the study area. Locations of structural highs and lows, top and base of the Montney Formation ure 6. Abbreviations: BT, Belloy thick; E, east; HHE, Huds Figure 5. subcrop edge, eastern limit ofDavies Montney et Formation al. overpressure (2018). andSubsurface Outcrop limits Leduc edge of the of FTB the andand fold-and-thrust inversion well have belt data been (BC (FTB) interpreted Oil isFTB. and bas The Gas North Commission, Pine 2020e). Charlie Theshapefiles Lake yellow (Fox Formation chevrons and salt Watson, show 2019). basin th Lines is of seven from structural Davies cross-sections et al

96 Geoscience BC Summary of Activities 2020: Energy and Water - eland basin beyond the northeast ut all of the faults and edges shown on lt; N, north; S, south; W, west. ion from the Front Ranges in the southwest to the for igure 5. Well data used to construct the section are omitted for clarity b c age of the reservoir. Abbreviations: E, east; FTB, fold-and-thrust be oss-section showing the structural configurat . A simplified version of the Cameron structural cr Figure 5 are indicated as are all oil and gas pools arranged by the stratigraphi ern edge of the Hay River shear zone (HRSZ). Location of the section is shown on F Figure 6

Geoscience BC Report 2021-02 97 reactivation due to high pressure injec- tion. In situ stress investigations for ap- plication to wastewater disposal wells have not previously been presented or published, except for an examination of injection potential in the Debolt and Belloy formations in northeastern BC, prepared by Canadian Discovery Ltd. (2015). Considerably more in situ stress data exists for producing oil and gas res- ervoirs in northeastern BC, such as the Montney play (e.g., McLellan, 2016); however, the scope for stress magni- tudes in this project has been limited to data from the disposal formations only. Orientations of maximum and minimum horizontal stresses (SHmax and SHmin)in this part of the Western Sedi- mentary Basin have typically been de- termined from borehole breakouts, which are elongations of a drilled bore- hole cross-section parallel to SHmin and perpendicular to SHmax. Elongation of Figure 7. A bubble map showing early and late injectivity indices for Cadomin Formation the borehole is usually due to shear fail- horizontal and vertical disposal wells in the Fort St. John area. Size of the bubbles is pro- ure occurring at the highest concentra- portional to the injectivity index. Horizontal wells (in magenta) generally show higher injectivity indices than vertical wells, and many of the wells show decreased injectivity over tion of stress around the borehole, which time. Well data accessed through geoSCOUT (geoLOGIC systems ltd., 2020). extends for some distance into the bore- hole wall, and creates a ‘breakout angle’ Reservoir pressure change was tabulated as a function of on opposite sides of the borehole wall. water injected over the life of the well. This was intended as Weaker rocks like shale host most breakouts, with break- a proxy for material balance, a difficult problem because outs being less common in hard stiff carbonate and clastic original reservoir saturations prior to injection have not rocks. been quantified consistently. One would expect reservoir The S legacy data for northeastern BC were compiled pressures to rise with continued injection, and the authors Hmax in the in situ stress chapter of the Geological Atlas of West- expected to compare pressure increases with volumes in- ern Canada (Bell et al., 1994). These same data are also jected to get a proxy for reservoir size. However, of the 92 shown for the project study area on the World Stress Map wells in this dataset, 15 wells showed a pressure decrease (Heidbach et al., 2016), along with more recent horizontal with injection, and several more showed no change at all. stress determinations using other techniques such as earth- Some of the wells exhibiting a negative pressure response quake focal mechanism inversion, sonic log anisotropy and had been converted from production in the same zone, so it drilling-induced fractures. Haug and Bell (2016) also pub- is possible that continued production from offset wells has lished a digital file with some additional horizontal stress contributed to this anomaly. Other possibilities include in- determinations for Alberta and northeastern BC. The most consistent pressure measurement procedures or formation recent publicly available datasets for horizontal in situ fracturing; more work is needed in this aspect of the study. stresses will be compiled on a map and in rose diagrams to The horizontal wells, with only one exception, behaved as be included in the final report for this project. A limited expected, with pressures rising as injection progressed. number of new stress determinations have been made for Geomechanical Analysis this project.

Basic geomechanical data on horizontal in situ stress orien- The SHmax determinations from earthquake focal mecha- tations and in situ stress magnitudes in wastewater disposal nism inversion have received attention lately, especially in reservoirs are being compiled, analyzed and interpreted. the Septimus region of northeastern BC, where a magni- These data are needed for assessing maximum injection tude 4.6 earthquake in November 2018 was caused by hy- pressures to preclude hydraulic fracturing in vertical and draulic fracturing (Babaie Mahani, 2020). Interestingly, horizontal wells, and to conduct risk assessments for fault there appears to be a systematic difference between SHmax

98 Geoscience BC Summary of Activities 2020: Energy and Water determinations from focal mechanism inversion in this re- an SRT, surface injection pressure and rate are increased in gion, compared to the orientation of local borehole break- a series of steps, designed to find a breakpoint or ‘parting outs. Possible reasons for this will be offered in the final pressure’ where a hydraulic fracture is created, thereby in- report. creasing the injectivity. Subsequent injection pressures are then maintained below the parting pressure. The surface Of high interest in disposal reservoirs of the study area is pressure from this crude test is related to the minimum hori- the original S magnitude, which is confidently mea- Hmin zontal in situ stress, SHmin, which must be overcome to initi- sured only with a small volume mini-fracture test, often ate a hydraulic fracture. High injection rates and accompa- called a Diagnostic Fracture Injection Test (DFIT). How- nying uncertain pipe and perforation friction losses render ever, in the review of disposal well files in the study area it SRTs less accurate for stress determinations than DFITs. was found that the term DFIT was used loosely by some op- erators and service companies to describe a variety of injec- tion tests, some of which did not require the creation of a As shown in Table 1, DFIT and SRT data have been com- small hydraulic fracture. Only DFITs where a hydraulic piled for the study area from a total of 10 well licenses, fracture was created and an instantaneous shut-in pressure which represented 12 formation intervals and one co- (ISIP) and a fracture closure pressure (FCP) were recorded mingled disposal interval with two formations. The avail- were used in this geomechanical analysis. Reservoir falloff ability of ISIP, FCP, reservoir pressure (Pr), permeability to pressure tests, typically performed to determine reservoir water (kw) and SRT data are noted. The DFITs were per- pressure and permeability, are being analyzed in the reser- formed in two horizontal disposal wells; the rest were in voir engineering part of the project. vertical wells. In a few cases, data from a small propped hy- draulic fracture treatment in what is now a disposal well Step rate tests (SRT) have been performed by operators in a were noted in the well records, and ISIPand 15-minute shut few disposal wells, but they are surprisingly uncommon. In in pressure (SIP) data have also been extracted. The final

Table 1. Diagnostic fracture injection test (DFIT) and step rate test (SRT) data for the part of the study area in northeastern British Columbia, from British Columbia Oil and Gas Commission files.

Geoscience BC Report 2021-02 99 report will include an appendix showing all the DFIT, SRT Incidents of wastewater injection–induced seismicity in the and stimulation-fracture-treatment–derived data, along study area have been compiled by the BCOGC. The com- with other useful calculated metrics and comments on the mon learnings from these cases, based on the injection met- analyses that were undertaken by service companies, rics, geological and geomechanical setting, including the operators and engineering consulting firms. proximity to major faults, will be examined. The BC Oil and Gas Commission (2020a) cited 11 wells known to have

Trends in the FCP (a proxy for the SHmin magnitude) and the produced high levels of seismicity that resulted in their op- reservoir pressure will be analyzed for different parts of the erations being curtailed or modified by the BCOGC. Only 3 study area, and in different formations, especially where of these 11 wells had DFITs where FCP (i.e., SHmin)data they relate to a well’s production and injection history. were obtained. As such it was not deemed a priority in this Given the relatively small number of quality FCP tests ob- study to undertake fault reactivation predictions, given the tainable from DFITs and SRTs, it is not possible to prepare paucity of quality in situ stress magnitude and rock me- maps to show spatial trends by geological unit. The DFIT- chanical property data. derived reservoir pressures for disposal wells represent a small subset of the reservoir pressure tests examined in the Future Work reservoir engineering part of this study. Two components of the project are in the early stages: re- gional assessment of aquifer fluid properties and pressure Vertical stress gradients have not yet been calculated for the regimes, and supplemental lab work to address data gaps top of any of the key disposal reservoirs at the time of writ- regarding geomechanical properties. The authors are cur- ing. This is usually a straightforward calculation, based on rently engaged in both areas, guided by the progress to date integrating corrected bulk density logs to determine the in consistently defining distribution and characteristics of weight of the overburden to a depth of interest. For the final disposal aquifers and the relevant datasets. report, the plan is to produce one illustrative example map of the vertical stress gradient at the top of one disposal unit, Work will conclude with compilation of information from likely the Cadomin Formation. all the study components, assessment and comparison of the performance of each major disposal aquifer, and discus- An open-hole completion would be required to obtain an sion of future disposal potential in the context of maximiz- SHmax determination from a sequence of small hydraulic ing efficiency and minimizing containment risks. fractures pumped into a short interval, isolated with pack- ers, or below a bridge plug. No such data were obtained by Acknowledgments any operator, according to the records examined. Typically The authors thank N. Harris for his review of the paper, other methods are used to calculate a SHmax magnitude value clarifying a number of points. The authors also acknowl- using a DFIT-derived SHmin and assumptions regarding the creation of borehole breakouts or fault reactivation using edge M. Perra and L. Sears for their graphics and editorial the stress polygon method (Zoback, 2010). Such estimates work. were not performed for this project, largely because of the lack of quality data, and the focus on in situ measurements. References Babaie Mahani, A. (2020): Systematic study of earthquake source Similarly, datasets of high quality laboratory-derived static mechanism and regional stress field in the southern or dynamic elastic or strength property tests for water dis- Montney unconventional play of northeastern British Co- lumbia (NTS 093P/09, 10, 15, 16, 094A/01, 02, 07, 08); in posal units were not found. In a few cases compressional Geoscience BC Summary of Activities 2019: Energy and and shear sonic log data were identified in some disposal Water, Geoscience BC, Report 2020-02, p. 13–18, URL wells, which could be used to make first order predictions [October 2020]. BC Ministry of Energy, Mines and Low Carbon Innovation (2011): Stratigraphic correlation chart northeastern British On the other hand, a petrophysical property called pore vol- Columbia and adjacent parts of Alberta, Yukon and North- ume compressibility (PVC) is used in some well test analy- west Territories; BC Ministry of Energy, Mines and Low ses and reservoir simulation. It can be a particularly sensi- Carbon Innovation, URL [Novem- ber 2020]. are currently considering a laboratory program with one of BC Oil and Gas Commission (2020a): Approvals; BC Oil and Gas the project partners to evaluate the range of stress-depend- Commission, URL [October formations in this project. 2020].

100 Geoscience BC Summary of Activities 2020: Energy and Water BC Oil and Gas Commission (2020b): Drilling data for all wells in Davies, G., Watson, N., Moslow, T. and MacEachern, J. (2018): BC [BCOGC 41984]; BC Oil and Gas Commission, Data Regional subdivisions, sequences, correlations and facies Centre, URL

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