The five articles in this month’s issue were assembled to provide a summary of the current status of development of the Saleski, Alberta area Grosmont carbonate bitumen resource. The selection includes a previously published overview article to provide background, two articles discussing a thermal pilot that is underway, and two discussions of proposed new thermal process variations. It is encouraging to see the increased activity related to the development of commercial exploitation processes for this extensive resource.
Prospects for Commercial Bitumen Recovery from the Grosmont Carbonate, Alberta is a ‘legacy’ JCPT article that has been included to provide background information for discussion of this resource.
Recent Pilot Results
Thermal Recovery of Bitumen From the Grosmont Carbonate Formation—Part 1: The Saleski Pilot discusses a pilot initiated in late 2010 to evaluate steam-injection recovery in both the Grosmont C and D units. The initial operating strategy was conventional steam-assisted-gravity drainage (SAGD), which demonstrated that that sufficient injectivity to steam was present because of the fracture system, and that drilling and completion practices strongly influences performance. The steam/oil ratio for SAGD was disappointing, although this is partially attributed by the authors to facility constraints; therefore, the production strategy was switched to cyclic steam stimulation (CSS), resulting in far better performance. Two other interesting observations were that well length did not exert the strongest influence on production, and that well-to-well communication was established quickly. Pilot production data for this pilot will become publically available this year.
Thermal Recovery of Bitumen From the Grosmont Carbonate Formation—Part 2: Pilot Interpretation and Development Strategy expands on the information in Part 1 by adding an in-depth analysis of the production mechanisms. Solution-gas drive was excluded from the analysis “because of the current lack of sufficient bitumen characterization,” a situation that will hopefully be overcome in the near future. Thermal effects and spontaneous imbibition were described as likely to mobilize bitumen by forcing fluids out of the matrix caused by fluid expansion and a wettability change from oil wet to water wet caused by steam injection, but the authors felt the strongest production mechanism should be gravity drainage because of the dominant vertical fracture orientation. On the basis of the pilot data and the production mechanism studies, the proposed operating strategy for the next, larger, field project is CSS using horizontal wells low in the pay targeting the bitumen in fractures and vugs, followed by conversion to steamdrive from horizontal wells high in the pay to achieve SAGD production targeting the bitumen in the matrix.
Proposed Thermal Processes
Recovery of Bitumen From a Carbonate Reservoir by Thermal-Assisted Gravity Drainage (TAGD) contains a description and discussion of an exploitation process designed for bitumen recovery from heterogeneous carbonate reservoirs by conduction heating from electrically heated cables. The target is the Leduc formation rather than the Grosmont. Important differences of TAGD from steam processes include a lower 120 to 160°C final temperature and a slower heating rate. Electromagnetic heating and radiofrequency heating were not selected because of concerns about the ability to vapourize some connate water but leaving enough behind to be the conductive medium, and the need for an additional energy conversion process and the associated efficiency loss, respectively. Scoping economic runs were used to determine the optimum pattern layout. It should be noted that the findings in this article are based entirely on nonhistory-matched numerical simulation.
Modelling Development of a Thermal-Gas-Oil-Gravity-Drainage Process in an Extraheavy-Oil Fractured Reservoir describes proposed application to a bitumen-bearing fractured reservoir of the Thermal-Gas-Oil-Gravity-Drainage (T-GOGD) steam-injection process currently in use in a carbonate reservoir in Oman. The authors note that the process works best in reservoirs that are intensely fractured to provide a path for the steam, and that have high vertical flow potential in the matrix to provide a separate path for the oil; therefore, both of these properties need to be present. Steam stimulation is recommended at the start to provide injector-to-producer communication. Similar to the article discussed previously, the basis of this study is nonhistory-matched numerical simulation runs.
Karl A. Miller, PhD, P.Eng
About the Issue Coordinator
Karl Miller has worked for the last 32 years to improve heavy-oil- and bitumen-recovery processes, including assignments in Canada, the US, Argentina, Colombia, and Brazil as both an employee of several oil companies, and as an independent consultant. He is currently a Reservoir Engineering Specialist in Husky Energy’s Heavy Oil Thermal Assets Group. Miller’s diverse areas of work have included cold production with vertical wells and horizontal wells, post-cold production using both solvent and in-situ-combustion processes, waterflooding, surface transport of produced heavy oil, and CSS, steamdrive, and SAGD processes using various combinations of vertical and horizontal wells. Much of this work has been documented in more than 30 papers and articles that have emphasized field results and technical innovations. He holds BES and PhD degrees in chemical engineering, and has also worked and published in diverse technical areas, including diamond synthesis, explosives research, and manufacture of glass containers. Miller was an active volunteer with the Canadian Petroleum Society for 12 years, including serving on the Board of Directors and as the Student Affairs Director. He has worked on a number of CIPC Technical Committees, including serving as Chairman for 2005. Miller has also worked on 10 Slugging It Out conference committees, including 7 years as cochair, as the Canadian Petroleum Society and SPE Chairman of the Heavy Oil and Horizontal Well Special Interest Group for 11 years, and as the cochair of the 2012 SPE Thermal Horizontal Well Sand Control Workshop. He is a member of SPE, The Association of Professional Engineers and Geoscientists of Alberta, and the Canadian Heavy Oil Association.
Thermal Recovery of Bitumen From the Grosmont Carbonate Formation—Part 1: The Saleski Pilot is the first public overview of data from the Saleski steam pilot in the Grosmont carbonate reservoir containing bitumen. The background for operational decisions is provided, data from injectors, producers and observation wells are outlined, and analyses of the observations are discussed. This paper also creates the basis for a second paper (Part 2), with the interpretation of the results.
Thermal Recovery of Bitumen From the Grosmont Carbonate Formation—Part 2: Pilot Interpretation and Development Strategy discusses interpretations of data from the Saleski steam pilot in the Grosmont carbonate reservoir containing bitumen, presented in Part 1. Recovery mechanisms in the fractured reservoir are linked to the pilot heat and material balance. On the basis of pilot performance, expectations for a planned expansion project are outlined, including reserve evaluation. A concept for future optimization of recovery from the Grosmont reservoir is presented.
Recovery of Bitumen From a Carbonate Reservoir by Thermal-Assisted Gravity Drainage (TAGD) discusses a new recovery process that specifically targets bitumen-bearing carbonate reservoirs of Alberta. The TAGD process uses a pattern of horizontal heater wells to heat the reservoir by conduction, which results in gravity drainage of mobile oil to a producer placed at the base of the reservoirs. Key recovery mechanisms that impact bitumen-production rate, recovery efficiency, and energy usage as identified by reservoir simulations are discussed. A strategy to optimize pattern configuration, well spacing , and heater power is presented. The advantages of TAGD over steam-based thermal processes for the production of bitumen in carbonates are highlighted.
Modelling Development of a Thermal-Gas-Oil-Gravity-Drainage Process in an Extraheavy-Oil Fractured Reservoir discusses a case study for application of thermal gas-oil gravity drainage using steam injection in a naturally-fractured carbonate bitumen reservoir. The paper shows how this recovery process differs from SAGD in clastic reservoirs and presents a feasible optimized geometrical well configuration and operating schedule.