An Experimental Study of Techniques for Increasing Oil Recovery from Oil Reservoirs with Tar Barriers

Abstract

ABSTRACT A number of major oil reservoirs in the Middle East have a tar barrier between the oil zone and the underlying water zone, with a strong bottom water drive. This investigation is aimed at oil recovery from such reservoirs. Specifically, it is intended to explore several recovery methods that could be used for increasing oil recovery from such reservoirs. As far as one can ascertain, little or no work has been published on this subject of vital importance in Saudi Arabia, Kuwait, and Iraq. The present investigation was experimental in nature, utilizing several models, and a variety of recovery schemes. In all instances, three zones were initially set up in the models: a light oil zone on top, a water zone at the bottom, and a tar zone between the two. The thicknesses of the oil and tar zones were varied to cover a range of conditions. The bottom water zone was equipped with a water drive. The different recovery techniques tested were: (i) injection of water into the oil zone (internal waterflood), without a bottom water drive, (ii) internal waterflood, with a bottom water drive, (iii) bottom water drive, (iv) injection of solvent into the tar zone, (v) injection of steam into (a) oil zone, (b) tar zone, and (c) water zone. The results show that when waterflooding the oil zone, an important factor is the extent of communication between the water zone and the tar zone. Such communication can be established by use of solvents or steam, though such processes are admittedly inapplicable in some of the deeper formations. Once communication is attained, an internal waterflood can be very effective. With bottom drive alone, recovery was found to be low in view of water channelling and coning. Solvent injection runs showed that large volumes of a suitable solvent will have to be injected in order to obtain the necessary communication. Steam injection into the oil zone mitigated the benefits of a water drive. However, injection into the tar zone was effective both in promoting the bottom water drive, and also in recovering some of the tar, although this was not a primary objective. Injection into the bottom water zone was largely ineffective, since the heating of the overlying tar layer required very large volumes of steam.