Jiang Youwei

Displacement mechanisms of air injection in low permeability reservoirs

Abstract By means of physical modeling and numerical simulation, this paper makes a systematic study on oil displacement mechanism by air injection in low permeability reservoirs. Based on the findings, production performance by air drive is studied through the application of a real low permeability reservoir model. Studies show that air intake capacity is far greater than water intake capacity in low permeability reservoirs. Therefore, air injection, which can effectively supplement and maintain reservoir pressure, can build effective pressure displacement system much easier than water injection. Low-temperature oxidization reaction will occur between oil and the oxygen in air, which consumes oxygen and forms nitrogen drive. At the same time, CO2 and large amounts of heat are generated, and the temperature in some parts of the reservoir can reach about 200°C. Nitrogen drive contributes 69%; temperature increasing and CO2 generation contribute 26.7% and 4.3% respectively for the total recovery of air drive. Recovery factors by air drive, nitrogen drive and water drive are also studied respectively by using the real low permeability reservoir model. Recovery factor by air drive for 30 years reaches 21.5%, and it is twice as large as that of water drive, which is 10.6% for the same period. Production performance is significantly improved. Air drive is an effective way for improving production performance and increasing recovery factor.

Foam Assisted Air Injection (FAAI) for IOR at Hailaer Oilfield: Prospects and Challenges

The Xi11-72 Block, located in Hailaer Oilfield, Inner Mongolia Autonomous Region, China, contains many ultra-low permeability ( 0.7). Primary production and limited water flooding experience at adjacent Blocks have shown that the recovery factor in these reservoirs is very low due to lack of reservoir energy and poor water injectivity. Since 2009, Foam Assisted Air Injection (FAAI) has been proposed, in order to block natural fractures, maintain reservoir pressure and/or increase sweeping and displacement efficiency. 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 foam assisted air injection and optimizing the injection process. Air injection pilot test started in the field since 23 April 2011 in a well group with 1 injector and 6 producers, using a Skid-mounted high pressure air compressor (40 MPa, 7 m3/min air rate). Oxygen breakthrough was observed (oxygen contents 3.7%) on 13 May 2011, and then assisted foam was injected to inhibit air breakthrough. Up to 30 June 2011, five foam slugs had been injected into the reservoir. The field results show that air injection can enhance injection capacity; assisted foam injection can inhibit air breakthrough effectively; and oil production can be significantly increased with water cut reduced by 4%. The detailed laboratory study, field experience and prospects and challenges analysis are presented in this paper.