The Anticipated Effect of Diurnal Injection on Steamdrive Efficiency

Abstract

Introduction In recent years as much steam as water has been injected in California oil fields, and the oil production is somewhat greater from steam injection operations than from waterfloods. Steam drive in California has become a mature and standard production practice. As more and more information is reported, it is becoming apparent that steam drive is perhaps the most efficient of all recovery techniques in terms of volumetric recovery efficiency. It appears that only in some natural water-driven reservoirs in east Texas and south Louisiana will the recovery efficiency reach the 50 to 60% range that many steam drives are reported to be attaining. The steam drive is characterized. after steam breaks through to the producing well, by a slow but steady decrease in the ratio of oil produced to steam injected until the ratio falls below an economical value. The major cost for steam generation is the fuel used for steam generation. The cost of the fuel is directly related and comparable to the value of the crude; frequently the produced crude itself is used to fuel the steam generator. produced crude itself is used to fuel the steam generator. The use of any fuel that is cheaper to use than the produced crude would permit a higher ultimate recovery produced crude would permit a higher ultimate recovery before the economically limiting oil/steam ratio is reached. Moreover, with cheaper steam, the steam drive might be extended to the recovery of high-gravity crudes after waterflooding and of low-gravity tar sands. The anticipated oil/steam ratios for both these targets appear to be only marginally economical at this time as long as the produced petroleum is to be used as the source of fuel for steam generation. For example, at an oil/steam ratio of 0.1, only 23% of the recovered petroleum is available for product sales. Even before refinery losses are taken into account, it is apparent that the profitability of such a venture would be remote. The only justification for such a recovery operation would be as a means for producing liquid fuels and not as a means for making available new energy supplies per se. In keeping with these conclusions, coal and lumbermill wastes have been considered for use in steam generation; but feasibility studies indicate that transportation, handling, and other costs. particularly in California, are so great that these intrinsically cheaper fuels are more expensive to use than crude oil. The suggestion has been made to use solar energy to develop steam for such projects. Certainly, the economic advantage of solar energy for other than hot-water heating still has to be proved in the marketplace. Although solar energy is an inexhaustible resource, and it is not necessary to pay for the privilege of capturing it, the capital, operating, and maintenance costs, still to be quantified, are very high. However, providing a significant fraction of U.S. needs for liquid fuels in the future is of primary concern. Although the relationship between supply and demand currently has become ameliorated because of the interplay of numerous political and economic factors, an ultimate deficiency in U.S. supplies of liquid fuels still is to be anticipated. Therefore, it is reasonable to believe that massive solar power systems may be indicated for the future recovery of crude oil in the U.S. Solar power is, of course, cyclic in nature. Table 1 indicates the relative availability of sunlight for power generation in the San Joaquin Valley. Useable power is available for only one-third of the day, and there is a 25% variation between the peak of summer and the dead of winter. It was the purpose of this study to investigate the performance of steam drives when a diurnal, cyclic supply of steam is used. JPT P. 1814