Wastewater Disposal in the Maturing Montney Play Fairway, Northeastern British Columbia (NTS 093P, 094A, B, G, H) B.J. Hayes, Petrel Robertson Consulting Ltd., Calgary, Alberta, [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, Cadomin, Bu- well data files hosted by geoSCOUT (geoLOGIC systems ick Creek sandstone/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 Devonian–Jurassic 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 Montney Formation 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