A C02 Foam Conformance Pilot in US Gulf Coast Region

Abstract The use of foams for gas floods conformance control attracts a renewed interest in recent years. Nowadays, despite the low oil price environment, some foam EOR projects remain active both at lab and pilot scale. Indeed, such applications have the potential to not only improve the oil rate, but may also reduce costs associated with gas injection and cycling. In other words, foam can increase gas injection efficiency both in terms of oil production and of gas consumption. In this paper, we describe the design of a dedicated foaming formulation and its application in a CO2 foam pilot in a CO2 flood in the US Gulf Coast. The main hurdle for formulation design was the use of a high salinity and hardness production water for chemicals injection. Our experimental approach to overcome this challenge was based on successive steps, comprising automated solubility evaluation of multi-component formulations, adsorption measurements, foam stability evaluation and finally corefloods in reservoir conditions. Following this lab work, we carried out the foam injection pilot on a 40 acre, 6-well flood pattern consisting of three injectors and six producers. Conformance rather than indepth mobility control was targeted, and a relatively low foam volume representing 1% pore volume of the pattern was thus injected. The treatment was applied as three alternating slugs of aqueous foaming solution and CO2 over a period of four months, with the aim of generating foam in-situ in the near- wellbore area. Strong foam formation in the near-wellbore was evidenced by a strong drop in CO2 injectivity after each surfactant slug. Injectivity then slowly recovered, with a slower recovery as a function of the slug number, indicative of foam propagation deeper in the reservoir. Injection logs showed an efficient diversion of CO2 from thief zones to previously poorly swept reservoir intervals. On the production side, although much less CO2 was injected, oil rate was relatively constant, exhibiting little decline. We interpret this as a consequence of the injected CO2 flooding new reservoir zones with higher residual oil saturation. Overall, the strong decrease in CO2 consumption at a relatively constant oil rate translates into a noticeable increase of the injected CO2 efficiency. This paper describes the formulation design and the foam pilot implementation in challenging conditions, in particular with regard to salinity and hardness of the available injection water. It qualifies foam as a straightforward, low risk conformance method. Indeed, besides potential increases in oil rate, the enhancement of CO2 injection efficiency demonstrates the success of this application.