Unconventional reservoirs through hydraulic fracturing produce higher initial volumes of oil while the decline rates are very high with low recovery factors. Enhanced oil recovery through cyclic gas injection has increased recovery factors in Eagle Ford. This paper focuses on multiple realistic conceptual models representing different areas in Eagle Ford resulting in different stimulated reservoir volumes (SRV) and well performances. Different areas in Eagle Ford are characterized by depth and fluid type. The main objective of this study is to provide operational ranges such as compressor rate and discharge pressure requirements for a successful cyclic injection in different areas of Eagle Ford. The analysis takes into account different parameters including Injection rates and corresponding pressures, cyclic durations, fill up timing and the total duration of huff and puff periods, completion practices and well spacing.
This physics based approach has been successfully applied to various field studies. In this paper to demonstrate the methodology a dual-porosity reservoir simulation model with multiple horizontal wells is utilized. The methodology used in this study integrates the hydraulic fracturing process, multi-phase flow and geo-mechanics within the reservoir simulation. In this approach, the change in mean stress for each grid block is implicitly solved together with pressure and the other flow variables using poro-elastic information. Multiple models representing different areas of Eagle Ford are studied. The reservoir and geomechanical properties are same across the models. Planar weakness planes with different intensity which are often observed in Eagle Ford are incorporated as sensitivity in the models. Different cyclic gas injection scenarios were performed using these models.
This paper provides better understanding of operational parameters involved in designing a successful cyclic gas injection process in different areas of Eagle Ford. The efficiency of gas injection operation highly depends on the complexity (matrix access) generated and the communication paths established during hydraulic fracturing. Higher gas injection rates lead to higher oil recovery but the return is diminished after a certain rate for each area. Determining the most beneficial rate is critical in designing the compressor, gas purchase and surface facilities. It was observed that the wells with more complexity have higher gas injectivity and lower discharge pressures. Blow down timing after the cyclic gas injection is found to be an impacting parameter on recovery. The results show that the understanding of SRV characteristics and gas communication pathways is critical in designing a successful cyclic gas injection by utilizing available wells in the DSU. Design of the injection/production scheduling has an impact on oil recovery and net gas purchase. Proper cyclic injection design is required to have an economically feasible project.
