Journal of Petroleum & Environmental Biotechnology

Abstract

An Experimental Study for Enhancing the Recovery Factor of Tar Barrier Heterogeneous Reservoirs

Abdullah Alfayfi, Osama Elmahdy and Abiodun Matthew Amao

A number of major oil fields in the Arabian Gulf Region include tar barriers between oil and water zones. Such tar barriers partially or severely impede production as they resist fluid flow in the reservoir. Understanding tar distribution is therefore, essential for the prediction of reservoir performance under various developmental scenarios as in water flooding for secondary recovery. The objective of this study is to find out through experimental work the appropriate techniques for improving the recovery factor of different simulated tar quality that exists in the region. This investigation was carried out using different laboratory models with a view of selecting the appropriate one for the region. Consequently, improving tar mobility is one of our major objectives in this study. However, reservoir heterogeneity together with capillary pressure and dip angle would certainly affect such a process significantly. Core samples taken from Sarah sandstone formation outcrops in Al-Qassim area of Saudi Arabia were selected for laboratory experiments which represent heterogeneous sandstone reservoir rocks. The petrophysical properties of these sandstone rocks were thoroughly investigated by studying properties such as permeability, porosity, relative permeability, recovery factor, grain size distribution and pore size distribution. Displacement runs were conducted in 4 in. and 1.5 in. diameter Al-Qassim sandstone outcrops composite cores, simulating tar and crude oil zones in series, at a constant injection rate of 2 ml/min. These experimental runs were conducted at simulated reservoir conditions of 60°C, 3500 psi confining pressure and 1500 psi back pressure. Experimental results show that, the recovery factor was reduced by 26% approximately with tar present in the system. It increased by 9.2% approximately when the water flooding temperature was increased from 60°C to 90°C with tar. The recovery factor further increased to around 19% when a combination of hot water and solvent were used with tar.