Abstract
Members SPE-AIME
Abstract
Heavy oils are an important resource worldwide, and yet two-thirds of the heavy oil deposits cannot be exploited by means of thermal recovery methods, because the effective energy production approaches energy input for reasons of formation thickness, depth oil saturation and/or porosity. In such instances, especially if the heavy oil is not too viscous (below about 1000 centipoises), it may be economical to employ non-thermal recovery methods. These include polymer flooding, alkaline flooding, carbon dioxide polymer flooding, alkaline flooding, carbon dioxide (gaseous) floods, solvent floods, and other more specialized recovery methods, such as emulsion flooding, and combination techniques.
This paper discusses non-thermal heavy oil recovery methods, based upon their application in the field. The processes and their mechanistic features are briefly discussed in the light of laboratory observations, which tend to be more optimistic than field results.
The field tests, using non-thermal recovery are tabulated. This tabulation gives not only the reservoir rock and fluid characteristics, but also the reported test results, and any information on the economics of the respective tests. The salient injection-production data of each test are also considered. The data presented is designed to aid engineers in evaluating prospective field tests of the recovery methods considered.
It is shown that at the present time carbon dioxide (gaseous) seems to hold considerable promise for the recovery of moderately viscous heavy oils. While laboratory results are encouraging, field experience using this technique is still limited. Several field tests in progress would provide more information in the next few years. The remaining methods have met with mixed success. One of the more widely favored methods - caustic flooding - has performed rather poorly in the field. It is performed rather poorly in the field. It is concluded that given somewhat special conditions, non-thermal heavy oil recovery methods may be applicable to reservoirs considered to be marginal from the thermal recovery standpoint.
Introduction
As the more prolific heavy oil reservoirs approach depletion, attention is increasingly being directed to less attractive reservoirs, e.g. heavy oil reservoirs with thin pays, bottom water, gas cap, etc. This paper deals with the recovery of moderately viscous paper deals with the recovery of moderately viscous oils, having viscosities below 1000 cp in most cases, and API gravities in the vicinity of 20 degrees. Only non-thermal recovery methods are considered, primarily in the context of field tests, 65 of which are tabulated with all known details. The principal recovery methods considered are: waterflooding, polymer flood, caustic flood, and carbon dioxide flood. Other methods are also noted. A previous paper (44) listed 18 such field projects, compared to 65 in the present work. The four-fold increase reflects more the rise in oil prices and economic incentives, and less the prices and economic incentives, and less the technological advances of the last 8 years. About two-thirds of the heavy oil in the U.S. and Canada (Saskatchewan) occurs in reservoirs many of which are not suitable for the application of thermal methods. Some of these were listed in Ref. (44). The present tabulation of field tests shows 5 waterfloods, 30 polymer floods, 7 caustic floods, and 5 carbon dioxide (immiscible) floods. The balance of 18 field tests employs various other methods, viz. micellar flooding, hydrocarbon floods, solvent stimulation, gas or air injection, and in one case, injection of ammonium hydroxide. Many laboratory and a few mathematical simulation studies have been reported. Selected results from these sources will be discussed.
INCREASING OIL MOBILITY
The principal impediment in the recovery of viscous oils is oil viscosity, as a result of which oil mobility is low and any injected fluid is likely to "finger" through the oil, unless it is more viscous (or better, less mobile) than the oil. However, in such a case the injection pressure needed for an acceptable rate may be too high, and may exceed frac pressures. Some flexibility is provided by pattern pressures. Some flexibility is provided by pattern size reduction, within economic limits.
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