Improving CO2 Vertical Sweep Efficiency in Tinsley Field with Dedicated Injectors

Abstract

Lower oil production rate, conformance, and poor sweep efficiency are major concerns in an enhanced oil recovery (EOR) flood when implemented across multiple intervals. Oil recovery and flood performance in reservoirs with multiple lobes characterized by heterogeneous rock properties suffer greatly when the lobes are commingled. Tinsley Field is a reservoir with two distinct lobes. Initial development of the EOR flood commenced by commingling injection in the same wellbore and production from the two lobes to decrease the capital cost and boost oil production. Reservoir management of the CO2 flood indicated good sweep was taking place in one lobe. Concerns about the possibility of early breakthrough of CO2 in the dominate lobe, leaving stranded oil in the other lobe, prompted the initiation of a dedicated injection program. Early breakthrough could lead to filling up our compressors more quickly than anticipated, which could increase our capital requirements. Dedicated injection into individual lobes was initiated to improve the sweep efficiency. The team devised a methodology to select prospective wells and quantify the feasibility of adding new dedicated injectors in some of the existing patterns at Tinsley field. The methodology utilized a combination of geological cross sections to identify areas that are characterized by two lobes separated by a shale barrier or baffle, injection profiles to identify the current CO2 allocation, and an estimation of remaining oil in place. A sector model was constructed to simulate the recovery process and aid in understanding the impact of dedicated injection on oil production rate and recovery from individual lobes. The study revealed that only two of the three fault blocks can be characterized with an upper and lower lobe. Within those two fault blocks, several producers were identified as having poor conformance with a high remaining oil in place. Numerical results of the simulation model show that without dedicated injectors, the two lobes will be flooded at two different injection rates leaving substantial oil unrecovered because of the different injectivity of each zone. Candidate dedicated injectors were selected and ranked for execution based on our methodology. The early results from the dedicated injection program indicate it will lead to a higher recovery factor in the lower lobe because of dedicated injection into the lower lobe resulting in higher processing rate of CO2. The methodology presented in this paper provides a logical workflow that can identify areas with stranded oil in a reservoir with multiple zones. Following this process could lead to opportunities to drill dedicated injectors to improve oil production rate, conformance, and recovery factor.