Publications

Sandstones and carbonates have different properties as a reservoir. Sandstone contained silica tend to negatively charged, while carbonate contained calcium tends positively charged. Limy sandstone which is a combination of both these rocks would have different properties. In this paper, Laboratory experiment was conducted to determine the effect of carbonate to the oil recovery factor in carbonate-cemented-sandstone core. Three types of artificial were made with various composition of Sandstone-Cement-Carbonate: Core A (50:50:0), Core B (50:20:30) and Core C (50:15:35). The Contact angle between brine-air, oil-air and surfactant-air on thin section core of each core were measured to identify the wetting phase and the effect of surfactant for improving brine wettability. Spontaneous imbibition test using formation water and surfactant were employed to determine oil recovery factor. The contact angle of brine-air (θw=90.74o) is larger than oil-air angle (θo=10.56o). Consequently, oil is more wetting than formation water. After surfactant addition, the contact angle of surfactant-air (θs=24.62 o) is lower than brine-air (θw=90.74o) which show surfactant effect on improve brine wettability. Oil-air contact angle in carbonate-sandstone core (θo=7.98o) is smaller than sandstone core (θo=19.72 o) caused by the effect of carbonate which make oil is more wetting. In spontaneous imbibition test, the oil recovery using formation water on high permeability core (k=5.7 Darcy) only reach 22.09%. Moreover, the oil recovery using surfactant reach 100% although the core permeability is lower (k=0.356 Darcy). As the effect of carbonate contain, the oil recovery on core C (sandstone-carbonate) is lower than core A both using formation water (RF Core C=17.94% and RF Core A=22.09%) and surfactant (RF Core C=79.43% and RF Core A=100%). Based on contact angle measurement and imbibition test, the more carbonate contain result more oil wetting and lower oil recovery.