New Results on the Displacement of a Fluid By Another in a Porous Medium

Abstract

Abstract Reservoir engineers have many problems in forecasting the oilfields exploitation if they use the laboratory data on the relative permeability curve vs saturation. permeability curve vs saturation. This leads one to wonder whether this concept is valid in transient flow, whether data have been made by suitable methods, whether the static relation between capillary pressure vs saturation is preserved in variable flow, whether lack of familiarity with combination laws concerning this function is not the reason for the dissatisfaction of the engineers. The present paper deals with the first three points. present paper deals with the first three points. Three series of oil displacement by gas have been made on a homogeneous sandstone core. Pressure in the two phases and saturation Pressure in the two phases and saturation (gammagraphy) have been measured all along the core. Pressure profiles have been found by the least-square method. Relative permeability has been calculated on each point and at each time by continuous equations. These studies have shown us that the relation relative permeability vs saturation is the same all along the transient fluid flow and that the relation capillary pressure vs saturation is the same as the one established by the restored states static method. Thus, the validity of this concept concerning transient fluid flow is proved. The Welge, Johnson, Bossler and Naumann method arrives at different results from those we have obtained. To explain this difference we show that the theoretical hypotheses of their method are far removed from reality. In conclusion, experimental results are simulated by numerical model taking into account capillary phenomena. The limit conditions established by experiments and used in numerical simulation are (1) inflow side (constant gas-injection pressure; pressure gradient is zero in oil) and (2) outflow side (out-gas pressure equal to the displacement pressure; pressure in oil is zero). The pressures are relative pressures. pressures Introduction When sweep efficiency of one fluid displacing another has to be predicted, the approach to the problem is nearly always identical. Laboratory displacement tests are performed on small samples that are supposed to performed on small samples that are supposed to be representative of the reservoir. After analyzing the data by the simplified method of Welge, Johnson, Bossler and Neumann, the relative permeability-saturation relationships are derived. In order to characterize more completely the porous medium, the capillary pressure-saturation relationship is also pressure-saturation relationship is also determined by the restored-state technique.