Foam Flood in Yates Reservoir for Improving Oil Recovery

Summary The Yates reservoir is a major, multibillion-barrel legacy oil reservoir in west Texas, USA, discovered in 1926. Oil production mainly comes from the San Andres formation, which is a highly fractured dolomite rock. The fractures in the reservoir provide preferential pathways for fluid flow, leading to early breakthrough of injected fluids and reduced sweep efficiency. As a result, even though a number of secondary and tertiary injection techniques have been implemented over the field’s history to improve the sweep, only a third of the original oil in place has been recovered thus far. The majority of the bypassed oil is believed to remain in the matrix. In this paper, we describe a foam flood that has been implemented at Yates to sweep the bypassed oil in the matrix rock. Foam flooding in the Yates reservoir involves injecting a surfactant, along with the produced gas (PG) into the reservoir. The surfactant reduces the surface tension between the gas and liquid phases, creating a stable foam. This foam is then injected into the reservoir to improve oil recovery. In the case of the Yates reservoir, foam flooding can address several challenges specific to fractured carbonate reservoirs. Foam flooding helps mitigate poor sweep efficiency issue by reducing the mobility of the injected gas, forcing it to contact and displace more oil within the matrix. An extensive laboratory program was implemented to select suitable surfactants that produce stable foam in Yates’ fluids and rock system. Several corefloods were also conducted at the reservoir conditions to evaluate the benefits of a foam flood at Yates. The coreflood results indicate that an incremental oil recovery of 13–16% can be achieved by a foam flood. A 3D compositional simulation model around the injection pattern of Yates Field Unit (YFU) 4045 was developed to evaluate the field implementation of the foam flood at Yates. The simulation model used the foam parameters derived from the laboratory experiments. The simulation results indicated that a field pilot can be implemented to achieve improved recovery in pattern YFU 4045. A continuous foam injection pilot was implemented for a period of 6 months by simultaneously injecting PG and surfactant solution with average concentration of 1,200 ppm that resulted in an average foam quality of 50%. Several surveillance techniques were implemented to confirm foam formation, such as setting a downhole pressure gauge and running injection profiles with and without the foam. A gas tracer was also injected to verify if gas diversion was achieved because of the foam injection. An analysis of the pattern producer performance shows a significantly higher incremental oil recovery after the foam flood compared with the initial estimates. A dimensionless scaling technique was developed using the foam flood pilot results to expand the foam flood to other areas of the field.