Optimization of Tertiary Water-Alternate-CO2 Flood in Jilin Oil Field of China:Laboratory and Simulation Studies

摘要

Most of the low permeability oil reservoirs in Jilin oil field ofChina have reached their economic limit of production bywaterflooding and even many wells have been abandoned dueto low productivity. Interest in recovery enhanced technologyof tertiary miscible or immiscible CO2 flooding is increasingin these low permeable reservoirs. In this paper, a laboratorystudy using a high-pressure PVT cell and a simulation studyusing full-field fully equation-of-state (EOS) compositionalreservoir modeling were undertaken to optimize the design ofa miscible or immiscible CO2 flood pilot project for the XinliUnit in Jilin oil field. The laboratory study includes phasebehavior analysis, asphaltene deposition assessment, andminimum miscibility pressure (MMP) determination in theCO2 corefloods. Based on building a full-field 3D geologicmodel and history matching waterflood performance, apreliminary CO2 flood reservoir modeling has been used todistinguish displacement mechanisms and reservoirperformance of natural depletion, continued waterflooding,continuous CO2 and water-alternate-CO2. The simulationstudy and the pilot test showed water-alternate-CO2 afterwaterflooding is an effective method of improved oil recoveryfor the low permeability reservoir and it can appreciablyreduce water production and enhance oil recovery. Simulationstudies has also been completed to determine an optimalwater-CO2 ratio, optimal CO2 slugs and optimal CO2 injectionrate. The pilot operation is now well implementing accordingto above-mentioned study achievements. Future plans forwater-alternate-CO2 optimization include continuation ofperformance monitoring to help optimize tapering strategy inorder to enhance further oil recovery in the low permeabilityoil reservoir.