Some Aspects of the Potential Application of Surfactants or CO2 as EOR Processes in North Sea Reservoirs

Abstract

Summary This paper reviews some aspects of the quantitative assessment of two types of enhanced oil recovery (EOR) processes and their potential application to North Sea reservoirs. Calculations are described that were undertaken for a simplified conceptual reservoir model with properties akin to those of the Forties field. Possible initial conditions for EOR operation resulting from various stages of waterflooding are evaluated. The results of EOR assessment calculations using advanced three-dimensional chemical flood and compositional simulators are presented, for both a low-tension aqueous surfactant presented, for both a low-tension aqueous surfactant process and for CO2 displacement in association process and for CO2 displacement in association with a chase water drive. Introduction Development of oil reservoirs in the North Sea is now approaching the stage when the production rate is equal to the annual consumption of about 80 MMtons within the U.K. There are 26 fields where production is already occurring or development is in production is already occurring or development is in progress. The locations of the principal fields are progress. The locations of the principal fields are illustrated in Fig. 1. From the outset it was recognized that secondary recovery should be initiated in the early stages of primary production. This is exemplified by the introduction of water injection in most fields and gas reinjection in some fields as part of the current development plans. Using these methods, the overall oil recovery is expected to be at least 1,400 MMtons, equivalent to 18 years' consumption. The U.K. Dept. of Energy estimates, that the possible recoverable reserves from these fields may be as high as 2,600 MMtons. The remaining unrecovered oil in place after conventional depletion is expected to be about 60 % of the original (i.e., between 2,100 and 3,900 MMtons), which represents a very substantial target for EOR. If the development of s successful EOR process allowed recovery of 10 % or more of the residual oil after waterflooding, the U.K.'s period of self-sufficiency would be extended by several years, with substantial benefit to the probable shortfall in the U.K. energy position in the late 1990's. position in the late 1990's.The U.K. Dept. of Energy has funded an initial study program to determine the research and development in EOR that would be needed for the particular conditions of North Sea reservoirs. This particular conditions of North Sea reservoirs. This program was intended to (1) investigate the program was intended to (1) investigate the applicability of those EOR processes seen as having the best potential and (2) undertake calculations aimed at evaluating the process technology. The ability to predict EOR performance under real reservoir predict EOR performance under real reservoir conditions was considered a key issue. The studies have been undertaken at AEE Winfrith with three teams respectively concerned with the design of high- pressure displacement experiments in long cores, evaluation of mathematical modeling techniques, and quantitative assessment of EOR displacement under various conceptual reservoir conditions. In addition to this conceptual study, a number of more basic research projects have begun at several universities, and the petroleum companies in the U.K. have been encouraged to increase their EOR programs in a collaborative manner. programs in a collaborative manner.This paper highlights some aspects of the assessment studies undertaken at Winfrith and draws attention to some of the features of the supply of EOR materials. JPT P. 1617