Gas injection into tight oil reservoirs, as a secondary recovery technique, can be favorable and promising in terms of high gas injectivity and good displacement/sweeping efficiency over water injection. Particularly, CO2 injection is the best option due to its superior miscibility effect with oil and in consideration of geological storage of the greenhouse gas. In this study, CO2 injection into a tight oil reservoir for IOR is assessed and a pilot project is underway. The reservoir is located in the G89 Block of Shengli Oilfield East China, which has very poor water injectivity due to very low permeability of less than 5 mD in average, and has been producing via natural depletion since 2005. The original reservoir pressure was over 40 MPa, and the reservoir temperature of 126 . A CO2 injection and storage program has been proposed, and CO2 will be from a coal-fired power plant 30 km away under a Sinopec’s CCS (Carbon Capture and Storage) scheme. Laboratory investigation includes PVT experiments, slim tube test and core flooding/displacement experiments, in order to study the miscibility effect and displacement efficiency via CO2 injection at various conditions. Reservoir simulations were performed to predict the IOR potentials of CO2 injection at different pressures, namely at immiscible, miscible and near-miscible modes. The MMP (Minimum Miscibility Pressure) of the reservoir oil is determined as over 29 MPa, while the reservoir pressure at the beginning of CO2 injection was around 23 MPa after several years’ depletion. Therefore, CO2 flooding at a near miscible mode will prevail. A field pilot of CO2 injection at current reservoir conditions (at near-miscible mode) is designed and its performance is presented in the paper.
展开▼
