An Economic Appraisal of Steam Flooding In a Pennsylvania Field

Abstract

Abstract Various factors contributing to successful oil recovery by steam injection are discussed and the procedure is outlined for appraising application of this process to a particular field. An economic analysis is made for both a pilot test and a field-scale steam injection process by considering realistic development, equipment and operating expenses, coupled with an assumed recovery factor. In all caves, it is assumed that the producing formation is relatively shallow and that market value of the crude oil is that of a Pennsylvania crude. It is shown that the specified pilot test will be relatively expensive, but that, if injectivity and formation thickness are great enough, a field-scale steam injection process can be profitable. Introduction Numerous steam injection projects, many of which are currently active, have been initiated in oil-producing areas of the eastern United States. However, all these projects are experimental since, to the author's knowledge, none has been extended to a field-wide basis. Because success of steam recovery depends on economics, greatest success appears likely in the eastern U.S. where the highest price is paid for crude oil. A feasibility study must first be performed and, if success is indicated, it should be followed by a pilot test. If the pilot test is well engineered and sufficient data are collected, an appraisal should follow of the optimum field-scale development. Presented in this article (using currently available information) are cost analyses of a field trial and of a full-scale development for a general reservoir with characteristics similar to those found in the East. Uncertainties in a study of this type are emphasized. Feasibility Study Sufficient data have been published to adequately outline general requirements of a candidate reservoir for steam injection. Properties of the displacement mechanism must be coupled with oil recovery cost. Crude Properties Displacement of oil to producing wells is reportedly caused by these factor's:the cold waterflood ahead of the advancing steam and hot water,thermal expansion in both the hot water and steam regions,favorable modification of the oil-water viscosity ratio as a result of the temperature increase of each,thermal distillation of volatile components of the crude in the steam region and their subsequent condensation in the cooler regions andthe gas-drive effect of the vapor phase, which appears to enhance recovery. The importance of each factor depends on the nature of the crude oil to be displaced and the initial reservoir saturation. Thus, viscosity ratio change should be particularly important in recovering viscous crudes that occur in Kentucky, it should be moderately effective in displacing oil in the Franklin heavy oil field (Pennsylvania); and it should have virtually no effect (perhaps even a negative effect) on the lighter, conventional crude oils. On the other hand, thermal distillation should be particularly effective in increasing recovery of the light crude in the Bradford field. Residual oil should be reduced to low value; the lighter ends should be displaced forward faster than the steam plateau and then condense, reducing viscosity and swelling the oil at the point of condensation. Thermal expansion of both in situ oil and water should cause a redistribution in fluid saturations with a resultant shift in the relative permeability ratio curve. A laboratory analysis of crude in the candidate reservoir should determine relative importance of the foregoing factors and also the type of steam displacement process to be used. Reservoir Properties In the second phase of the feasibility study, reservoir properties are considered; i.e., the fraction of injected energy that will effectively displace the oil as injection proceeds is determined. Heat losses occur in surface equipment, in the injection wellbore and particularly in the reservoir underburden and overburden. The amount of heat loss in the last is proportional to the area exposed to high temperature and the length of time of the exposure. As injection continues, the area of overburden and underburden exposed to heat losses increases as the steam front moves away from the wellbore. JPT P. 1437ˆ