Abstract
Abstract
Enhanced oil recovery in unconventional reservoirs has established a track record in the past few years. It is an important technology to investigate and implement to pursue longevity in the thousands of horizontal laterals that are reaching their terminal decline towards abandonment. EOR techniques have been proven to be technically feasible and to a certain degree, economically attractive. The techniques described in this paper are 1) gas injection in the huff n' puff mode 2) surfactant injection in the huff n' puff mode and 3) co- injection of both miscible gas and surfactant. The objectives of this paper are to present laboratory evidence and field resu lts for the three techniques described.
This paper will present laboratory justification behind each of the three methods. Results from core data are presented for each of the three methods that include gas penetration, imbibition, and the use of both mechanisms for co-injection of gas and surfactant. Experiments using time-lapse CT scanning demonstrate the saturation changes as oil is displaced when core samples are exposed to gas, surfactant, or a combination of both.
Miscible gas experiments conducted using time-lapse CT scanning indicate gas penetration induces saturation changes on reasonable time scales. Wettability alteration by surfactants as determined by contact angle measurements will be presented. Ample contact angle and imbibition data demonstrate that wettability alteration is the key to application of surfactants in unconventional reservoirs. Both techniques have been applied in successful field projects.
A novel co-injection method with both miscible gas and surfactant is described. Application of co-injection using both gas and surfactant capitalizing on the synergy between the mechanisms is especially intriguing, both from a laboratory and field perspective. The technique utilizes both the diffusion/swelling mechanism of miscible gas along with the ability of surfactant to alter wettability resulting in gas sweeping the larger pore spaces and aqueous phase surfactants to displace oil in smaller pores via capillary pressure. Experiments are presented that show miscible gas displaces oil from larger pores and surfactant imbibition displaces oil from smaller pores during co- injection. Review of a co-injection project demonstrates key advantages over gas injection alone such as 1) prevention of rapid gas migration via fractures away from injection well 2) reduction of the necessity for high pressure compression to attain the Minimum Miscibility Pressure (MMP) by utilizing co-injection of surfactant and gas and 3) a superior gas utilization factor (GUF) as compared to gas-only projects showing the importance of surfactant during co-injection.