CO2-EOR Pilot Study on Deep Buried Low Permeability Hill Fracture Reservoir in Liaohe Oilfield

This is the first paper tells you how to design the well pattern and well spacing, how to optimize the injection and production parameters in buried hill fracture reservoir with great depth and low permeability. In addition, we also present the matched injection and production instruments developed for carbon dioxide flooding. All of these can provide reference and experience for this kind of reservoir. We get exact parameters for simulation through different tests such as PVT tests, miscible experiments and displacement experiments. Then critical parameters such as well pattern, well spacing as also as injection-production rate are determined after analysis of field injection pilot date and numerical simulation with the test results. At the same time, wellhead injection pressure, injection tube diameter are got through calculation with software and dynamic corrosion tests in lab. Anti-gas lift technology through combination of gas anchor and unusual pump and corrosion protection facility by chemical agent are also developed to ensure success of pilot. Laboratory experiment results show that oil volume expansion can reach 53.3% while viscosity reduces from 0.423 mPa·s to 0.221 mPa·s. Preliminary injection tests show that the maximum daily injection rate is 60 t/d and absorption strength is 5.14 m3/(d.m) which is 6 times of water absorption strength. So we get the conclusion that effective displacement can be achieved and CO2-EOR is feasible. Reversed nine-spot well pattern is adopted and the distance between injector and producer is 210 to 235 m which is reasonable for this kind of buried hill fracture reservoir and the predicted ultimate recovery is 40.05%. In the pilot, tube with Ф73 mm diameter is used and designed injection rate is 30 t/d while wellhead pressure is 46.6 MPa which is basically the same to the calculation value. The pump setting depth is 2250 to 2440 m and combination anti-gas facility is adopted to meet the gas-oil ratio smaller up to 800, a critical factor to be considered. In the past one year, the number of effective wells accounts to 48% with daily production increased from 2 t/d to 8 t/d and the natural decline rate decreased from 26.1% to 6.9%. A satisfied pilot result has been got. The paper introduces the parameters optimization, matched technology of field pilot and the pilot result that can provide a reference. CO2-EOR way is an effective way for this kind of reservoir and can benefit to reduce carbon dioxide discharge.