The three papers in this issue cover different types of reservoirs and production mechanisms, but there are certain commonalities. The first two papers are related to recovery processes in heavy-oil reservoirs, while the first and third paper deal with fractures, and geomodelling techniques are covered in the second and third paper. These papers, all authored by university researchers in Alberta, offer useful insights in the recovery processes for heavy oil and for fractured reservoirs.
Many papers have been written on in-situ combustion (ISC) or air injection in heavy-oil reservoirs and in light oil fractured reservoirs. Field pilots indicated that great challenges remain in the application of high-temperature oxidation (HTO) or low-temperature oxidation (LTO) to recover heavy oil in clastic reservoirs, never mind in the more complex naturally-fractured-heavy-oil reservoirs. In the paper Low-Temperature Air/Solvent Injection for Heavy-Oil Recovery in Naturally Fractured Reservoirs, Mayorquin-Ruiz and Babadagli provide a new concept of adding a small amount of propane solvent in an ai- injection process applied to such type of reservoirs. Experiments were conducted to search for optimum operating conditions, soaking time, and fluid injection sequence. This could lead to a commercial process for the development of heavy-oil carbonates in Alberta and other parts of the world.
The second paper, Assimilation of Time-Lapse Temperature Observations and 4D-Seismic Data With the EnKF in SAGD Petroleum Reservoirs, authored by Zagayevskiy and Deutsch, describe an inverse-modelling technique to petroleum-reservoir characterization of steam-assisted-gravity-drainage (SAGD) projects. Rather than using only the geologic model developed from the static properties based on core and log data and, of course, the interpretation of the geoscientists, data from temperature observation wells and 4D seismic attributes are assimilated to improve the quality of the model for better prediction of future performance. A short-cut approach for both 2D and 3D cases is also presented to reduce the computational cost.
A reasonable production forecast is essential to establish the economics of tight oil reservoirs after stimulation. In the last paper of this issue, Effect of Fracture Geometry on Well Production in Hydraulic-Fractured Tight Oil Reservoirs, authors Lin, Chen, Ding, Chen, and Xu identify the pitfalls of using a simple planar fractures geometry in the numerical simulation model for tight oil reservoirs with hydraulic fractures from multistage hydraulic fracture and a horizontal well. It can overestimate the oil rate and recovery as compared with the model with a complex fracture network. The impact of conductivity of the main fractures and secondary fractures are investigated such that the operators could use to develop a stimulation strategy to optimize production.
About the Issue Coordinator
KC Yeung is Chief Advisor, Technology & Petroleum Engineering at Brion Energy in Calgary, Alberta. He has worked in the heavy-oil industry for more than 38 years, primarily in the area of reservoir and technology development. Yeung has been involved in various in-situ field projects, including cyclic steam stimulation, steamflood, ISC, cold heavy-oil production with sand, and SAGD. He was a Distinguished Lecturer for the Petroleum Society of CIM. Yeung has given lectures and training courses on heavy-oil recovery and SAGD in Canada, the United States, South America, China, Europe, and the Middle East to promote Canada’s in-situ heavy-oil technology. He was also a member of the evaluation committee on the SPE Reprint Series No. 61, Heavy Oil Recovery. Yeung holds BSc (with distinction) and MSc degrees in mechanical engineering, both from the University of Hawaii. He was the 2005–2006 president of the Canadian Heavy Oil Association and the 2007 chairman of the Petroleum Society of CIM. Yeung received the Lifetime Achievement Award from the Petroleum Society of Canada in 2009 and the SPE Regional Services Award from SPE Canada in 2011.
Low-Temperature Air/Solvent Injection for Heavy-Oil Recovery in Naturally Fractured Reservoirs discusses the experimental results of a new approach for air injection at nonthermal conditions in heavy-oil fractured reservoirs in which air and solvent are injected alternately. A description of the laboratory setup is outlined as well as the experimental procedure and results. Static diffusion experiments are conducted at different temperatures by soaking a heavy-oil saturated core into different gas mixtures of propane and air at different oxygen concentrations in a huff ‘n’ puff fashion. Critical parameters in the oil recovery and the oxygen concentration in produced gas are identified.
The paper Assimilation of Time-Lapse Temperature Observations and 4D-Seismic Data With the EnKF in SAGD Petroleum Reservoirs describes application of the ensemble Kalman filter (EnKF) continuous data assimilation technique to the characterization of heavy-oil reservoirs operated by SAGD thermal oil extraction method. The theoretical framework is developed for integration of core data, continuous temperature observations, and exhaustively sampled time-lapse seismic attributes into a geological model for static properties estimation and dynamic properties prediction. Various implementation aspects of the EnKF are demonstrated with case studies. Several options for computational time reduction are stressed, which is necessary for the algorithm to be applied to real reservoir characterization problems.
Effect of Fracture Geometry on Well Production in Hydraulic Fractured Tight Oil Reservoir discusses how fracture geometry impacts a horizontal well after stimulation production in unconventional tight oil reservoirs. A geological model for the Cardium formation is built and history-matched with the field-production data. Three hydraulic fracture scenarios, including symmetrical biwing planar fractures, branched fractures, and a complex fracture network are generated and all three scenarios are confined by the microseismic mapping data. Well after stimulation, productions of the three scenarios are predicted and compared. Effects of fracture geometry, half-length and conductivity of the biwing fractures, and conductivity of the secondary fractures on the cumulative production of the wells are highlighted. Flow regimes of a hydraulic fractured well with three different fracture geometries are finally analyzed and compared.