Paper: Design of A Major CO2 Flood, North Ward Estes Field, Ward County, Texas

The reservoir engineering aspects of the design of a major West Texas co2 flood are presented. The design included (1) a detailed fieldwide geologic study to characterize the principal Yates reservoirs, (2) a CO2 injectivity test to identify any reduction in injectivity either during or following CO2 injection, (3) laboratory work including oil-CO2 phase behavior, slim tube tests with pure and contaminated CO2 corefloods to determine recovery of waterf lood residual oil by CO2 flooding, (4) reservoir simulation to predict flood performance. A comprehensive waterflood evaluation proceeded the selection of average pattern models ~/for reservoir simulation. These three-dimensional models, which have up to twelve layers each, were history matched over the 33 year waterflood period. Predictions were made for continuation of the waterflood and for CO2 flooding. Additional reservoir simulation was conducted to determine the optimum economic co2 slug size and to study the differences in recovery efficiency between line drives and five spots. Scale-up procedures were developed to predict from the average patterns the incremental oil production for the 3840 acre project area. It is predicted that CO2 flooding will recover an additional 8% of the original oil in place (OOIP). The optimum CO2 slug size lies between 38% to 60% hydrocarbon pore volume (HCPV). The optimum water-alternating-gas (WAG) ratio is 1: 1. Gross and net CO2 utilization ratios are 12 and 4 MSCF/STB (2136 and 712 m3/m3), respectively.