Abstract
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.
Highlights
Many oil reservoirs are characterized by the presence of a highly viscous hydrocarbon layer at the oil/water contact
Tar is believed to have originated from the same source that generated the oil during the migration time, the present characteristics of the tarmat are clearly different from the characteristics of the reservoir oil
The mixture was allowed to react for one minute, addition of solvent was continued until tar was dissolved completely in solvent (Figure 10)
Summary
Many oil reservoirs are characterized by the presence of a highly viscous hydrocarbon layer (tarmat) at the oil/water contact. Such tarmats are found in many major oil reservoirs in the world and, in the Middle East. The thickness of tar-mat columns in traditional petroleum reservoirs varies from a few feet to several hundred feet These tar-mat zones have additional bitumen or heavy oil, with in-situ viscosity above 10,000 cp and gravity below 10°API. They generally are located at the bottom of the oil column [3]. According to several geochemical studies presented by various researchers, tar mats form due to water washing, natural deasphalting, biodegradation, and gravity segregation, which results in grade variations in the composition with changes in depth [2,6]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callMore From: Journal of Petroleum & Environmental Biotechnology
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
