Low salinity water and CO2 miscible flooding in Berea and Bentheimer sandstones

Abstract

Low salinity water (LSW) was combined with CO2 in a miscible water alternating gas (WAG) hybrid scheme to elucidate our understanding on the interrelationships of these enhanced oil recovery (EOR) methodologies. This study focused on sandstones reservoirs using Berea and Bentheimer core samples. Synthetic formation brine simulating Saudi reservoirs’ brine and light Saudi Arabian crude were used as reservoir fluids. The high salinity water (HSW) used was sea water from the Arabian Gulf, while the LSW was the same sea water diluted ten times. Four runs where conducted with various schemes of LSW and HSW in secondary mode and CO2-WAG in tertiary modes at a WAG ratio of 1:1 and 0.2 pore volume slug size. In Berea cores, LSW miscible CO2-WAG in tertiary mode was the most effective scheme with ultimate original oil in place (OOIP) recovery of 82.40%, incremental tertiary recovery was 35.10%, which was 66.20% of the residual oil in place (ROIP) after secondary waterflood. The dual mechanisms of fines migration due to the clay minerals present in Berea and attendant miscible CO2 effect resulted in an improved recovery. This was much higher than what was observed in HSW miscible CO2-WAG in Berea, with an ultimate OOIP recovery of 65.20% and 16.44% incremental tertiary recovery, which is a meager 34.34% of the ROIP after secondary flood. In the Bentheimer cores however, there were no substantive differences in the incremental tertiary recoveries due to LSW miscible CO2-WAG over HSW miscible CO2-WAG in the tertiary mode. The incremental recoveries were 19.23% which is 41.29% ROIP after secondary flood for the LSW CO2-WAG and 20.98% which is 58.62% ROIP after secondary flood for the HSW CO2-WAG. These results reinforces the necessity of conducting experimental studies using representative reservoir core samples before implementing such EOR schemes. It can be inferred that LSW improved recovery should first be applicable in a candidate reservoir before augmenting LSW with miscible CO2-WAG.