Air Foam Injection for IOR: from Laboratory to Field Implementation in Zhongyuan Oilfield China

Abstract

Abstract The Hu-12 Block, located in ZhongYuan Oilfield, Henan Province China, contains many small but highly heterogeneous oil reservoirs, with low permeability oil bearing formations and high permeability mixed (oil/water) layers. The reservoir temperature is 90 °C, and the original reservoir pressure of nearly 25 MPa, and with high salinity of formation water (around 200,000 mg/l). After 20 years of water injection, the recovery factor achieved was only 20–25%, and average water cut has reached to over 95%. N2 gas injection has been tried with less success due to early gas breakthrough from high permeability zones. Since 2006, high pressure air foam and air injection (Air Foam Alternative Air Injection, AFAAI) has been proposed and implemented in one of the reservoirs, in order to block high permeability water zones and increase the sweeping efficiency of air and water injection. A series of laboratory experiments have been conducted to study the oxidation kinetics of air/air foam with oil and the blocking and displacement efficiency of air foams in different oil sands. Reservoir simulation has also been carried out for predicting the reservoir response to air foam injection and optimizing the injection process. Air foam and air injection was started in the field since May 2007 in a well group with 1 injector and 4 producers, using a small high pressure air compressor (40 MPa, 7 m3/min air rate). Up to now, 460,000 Nm3 air and 2920 m3 foam surfactant solution have been injected into the reservoir. The field results show that no oxygen/N2 breakthrough was observed and a significant increase in oil production with water cut reduced by 4%. The detailed laboratory study and field experience are presented in this paper. Introduction There are many successful air injection projects for light oil reservoirs reported in the literature,1–3 and low temperature oxidation (LTO) process of air and air foam injection for IOR have attracted some attentions in recent years probably due to high oil price and the improvement of air injection facilities. 4–6Air foam technique has the advantages of both air and foam injection processes, with its lower cost in gas supply, thermal effect of air injection, and mobility control function of foams. It can decrease the relative permeability of injected fluids, block high permeability zones, improve sweep efficiency, and increase oil recovery. Air foam alternative air injection (AFAA) is an innovative IOR technology for light oil reservoirs with high water cuts, and highly heterogeneous oil bearing formations. For light oil reservoirs, the mechanisms of IOR via air injection is much like a conventional gas injection, with some other effects resulted from LTO reactions, which generate heat and flue gases containing CO2 and N2. The thermal effect may reduce oil viscosity and promote evaporation of light oil components, but it is not essential for light oil reservoirs.7–9 In this study, the feasibility of using the air and air foam injection techniques in a light oil reservoir with medium to high permeability has been assessed, and a field pilot has been implemented.