Finding the Most Profitable Slug Size

Several current sophisticated oil recovery projects involve injection of a slug consisting of a micellar solution, and carbon dioxide or a hydrocarbon solvent. Slug costs combined with low oil saturation may result in marginal economics; thus, the economic success or failure of a miscible project may hinge on choosing the proper slug size. Oil recovery, hence profit, is a function of, among other things, slug size. An illustration shows 4 recovery curves. One shows laboratory data for micellar solution floods in which various slug sizes were used. The other 3 curves were computed from these data by assuming that for each of them there were 2 equal-volume, equal-porosity layers, identical in all respects except for absolute permeability. Oil recovery is reduced with increasing permeability contrast, partly because slug is not equally accepted by the 2 layers, and partly because the tighter layer is not completely swept before the economic limit is reached. Other recovery curves could be generated, simulating more layers, pattern geometries other than linear, or other desired degrees of complication. These examples suggested smaller slug should be used with increasingly stratified reservoirs, quite the opposite conclusion from a classical paper on the subject. Although this technique has limitationsmore » and is not intended to be a complete economic analysis, it is a quick, convenient method for evaluating the feasibility of a project.« less