Injection of Nitrogen Foam for Improved Oil Recovery in Viscous Oil Reservoirs Offshore Bohai Bay China

Abstract

Abstract Foam injection is a proven technique for improved oil recovery in both light and heavy oil reservoirs, especially for those with high heterogeneity, in which foam can improve the displacement and sweeping efficiency effectively. In this study, the feasibility of nitrogen foam injection for IOR from viscous oil reservoirs are investigated via laboratory experiments and field pilot analysis. The targeted oilfield is located offshore Bohai Bay (China), featured with high oil viscosity (up to 924 mPa.s) and severe heterogeneity of pay-zones. Water flooding has been applied in the oilfield, but the recovery factor is less than 20% and high water cut (over 85%) has been observed. Nitrogen foam injection was proposed in order to solve the problems and improve oil recovery. In this study, laboratory evaluation of nitrogen foam was conducted via foam testing and sandpack flooding. The results indicate that polymer enhanced foaming agents can greatly increase foam's performance. High blocking capability and displacement efficiency were observed in enhanced foam flooding experiments, indicating that nitrogen foam injection can mitigate the problems of heterogeneity and increase oil recovery in low permeability zones. A field pilot with 2 injectors and 13 producers involved has been conducted to verify the feasibility of the foam technique. The wellhead injection pressure was effectively increased after foam injection, and nearly all producers exhibited good response with incremental oil recovery and the average water cut dropped by 6.3% over 8 months of the field operation. The field pilot demonstrates the effectiveness of the nitrogen foam injection technique as an effective IOR method for the targeted oilfield and other similar oil reservoirs.