A large number of producing fields in Kansas are entering the mature stage for primary and/or secondary depletion with declining oil rates and increasing water cut and GOR trend, The Ogallah field is considered as it is one of the oldest fields with bottom water drive in central Kansas; producing from the Arbuckle and other formations. The Arbuckle formation accounts for approximately 36% of Kansas Oil production. And there is still more that this formation can produce. There is a need to consider the improved oil recovery techniques.

CO2 injection is an effective technique for improved oil recovery in light oil reservoirs. This study investigates the feasibility of various CO2 injection modes in the Ogallah field. It also deals with the economic optimization studies for selecting the best mode of CO2 injection. Lease-4 in the field is selected as the target lease; with two wells in that lease for injecting CO2.

A PVT fluid model, in which the Peng-Robinson Equation of State is tuned to match the experimental results of swelling test, saturation pressure, density, and viscosity is used to represent the reservoir fluid properties. Using a compositional simulator, four injection techniques: 1) continuous CO 2 flooding, 2) water alternating gas (WAG), 3) hybrid WAG, and 4) CO 2 Huff and Puff were simulated to evaluate potential CO2 injection modes. The Optimum injection modes for this case study reservoir were established. Huff and Puff injection with a CO2 injection rate of 400 MSCF/day and an injection period of one month, soaking period of two months, and production period of three months was the most efficient recovery method. It yields the highest recovery factor of 56% OOIP including primary recovery with an average injection pressure not exceeding the 2000 psi, and a maximum NPV of 13 million dollars.