CO2 flooding of a strong waterdrive reservoir has begun along the Texas Gulf Coast. Ninety (90) million SCF of CO2 will be injected daily during 2011 to re-pressure the reservoir and rates as high as 1 billion SCF per day (including recycle) will ultimately be used to develop this giant oil field. Design of this CO2 flood at a depth of 6,000 feet has focused upon pattern design, operating pressure, and the impact of aquifer influence. Success of CO2 floods, hinges upon the ability to increase reservoir pressure to, or near, miscibility pressure and to effectively sweep the reservoir. Laboratory and field performance data have been utilized to improve the design of this continuous CO2 injection project.

Some of the largest oil reservoirs in the world are composed of high permeability sandstones with large aquifers. These reservoirs are attractive candidates for CO2 flooding due to the size of the initial oil deposits; however recoveries due to the strong waterdrive and good quality sands often result in low residual and/or remaining oil saturations. With oil zone thickness often exceeding 100 feet, significant challenges exist in developing optimum completion strategy and pattern selection. For the Hastings CO2 flood, five-spot injection patterns will be staggered so that the upper and lower portions of the reservoir have dedicated injectors and producers, thus improving vertical sweep. Water injection profiles have also shown that perforation shot density is key to insuring uniform vertical sweep given the minimal pressure drop across each perforation when low viscosity CO2 is injected. Reservoir pressure within the floodable area must also be maintained (preventing leakoff) in order to maximize displacement efficiency. This is accomplished by use of water injection wells placed downdip to act as a water curtain, thus reducing leakoff of pressure into the infinite acting aquifer. As expansion of the EOR project develops additional patterns downdip, water injectors will be placed further downdip, while the updip injectors will be placed on CO2.

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