Abstract
This paper presents the results of oil recovery from short fractured and unfractured carbonate cores using a high speed centrifuge. Also, we will provide results of oil recovery in long cores. The short cores are 1.5-inch long while the long cores are 12-inch long. The experiments are designed to decipher contributions from rock matrix in presence and absence of fractures, and for imbibition and gravity drainage oil recovery with and without surfactant. The laboratory results are scaled to field using scaling rules as well as numerical simulation.
The purpose of this research is to demonstrate that surfactant oil recovery can be a viable enhanced oil recovery process in fractured carbonate reservoirs when fracture distribution and connectivity are favorable. Furthermore, these carefully designed experiments improve our understanding of how oil mobilization can be enhanced in fractured carbonate rocks and how the process can be modeled and solved numerically.
The cores were selected from a carbonate outcrop, saturated with brine, displaced with a 22-centipoise crude oil from a specific field, and were aged to promote oil-wetness. A typical unfractured long core had a spontaneous imbibition oil recovery of zero, but produced 2% oil in a 5000 ppm anionic surfactant solution. The long fractured cores had a spontaneous imbibition oil recovery of 21% and a surfactant oil recovery of 38%. The short cores in the centrifuge produced substantially more oil because of enhanced gravity effects. The implication of these results to field applications, and much more, will be discussed in the paper.
We were able to match experimental results using an in-house numerical model, where, we believe, the model's theoretical basis is consistent with the physical principles of fluid flow in porous media. The results of these experiments, and our experience in a major fractured carbonate reservoir, have given us a better understanding of the mechanism of enhanced oil production in fractured carbonate reservoirs by dilute surfactant solution and micellar solutions. We are hoping that the results of this research will promote field applications.
