Исследование характера проявления микропроцессов на усовершенствованной капиллярной модели неоднородной пористой среды

Abstract

Background Due to the increasing relevance of the development of heterogeneous reservoirs, represented by alternating low and high permeable rocks or even clay, there are a lot of concerns of the effect of porous medium heterogeneity on the characteristics of the miscible oil displacement. High heterogeneity greatly reduces development time up to breakthrough and cumulative production, moreover it prolongs the development in comparison with a homogeneous formation. The scientific paper presents the results of laboratory studies of microscopic processes nature and physico-chemical phenomena occurring in a porous medium when gas displaces oil. The studies were provided on an improved two-layer model of capillary porous medium with different ratios of the capillaries radii, simulating an average pore radii of inhomogeneous layers. The quartz capillaries used for studies were canned in 1978, saturated with real oil in order to establish adsorption processes with dimensions comparable with the average pore diameter of the real oil reservoir. Aims and Objectives To study the microscopic processes nature in lithological variety of heterogeneous reservoirs when hydrocarbon gas displaces the stranded oil from the reservoir. Methods The laboratory studies were provided using the advanced two-layer model of capillary porous medium with different ratios of the radii of the capillaries, simulating an average pore radii of inhomogeneous layers. There were used the accepted instruments and devices up-to-date with the latest achievements of science and technology. Results The laboratory studies on the improved two-layer model of capillary porous medium with different ratios of the radii of the capillaries, simulating an average pore radii of inhomogeneous layers revealed the following patterns of microscopic nature and physical and chemical phenomena occurring in a porous medium during the oil displacement by hydrocarbon gas: • movement of the displacing gas in capillary channels of low-permeable layer causes the menisci formation and arises the capillary pressure, which is an obvious reason for decrease of displacement front velocity; • increase of hydrocarbon gas injection pressure leads to increase of interphase boundary velocity. Due to further increase of pressure the interphase boundary velocity reaches the maximum and then decreases and finally stabilizes, due to the formation of micro embryos in heterogeneous porous media if the pressure in the system is close to the saturation pressure; • the characteristic pattern of all experiments is the reduction of interphase boundary velocity, which could be explained by sedimentation of asphalt-resin-paraffin deposits on the pore walls; • asphalt-resin-paraffin deposition and adsorption on the rock surface is one of the reasons for the velocity reduction due to the electroosmosis phenomena, «negative» velocity which being added to the filtration velocity reduces it magnitude. Conclusion The studies show that displacement of stranded oil by hydrocarbon gas equalizes the displacement front velocity and prevents the gas breakthrough if the process is regulated in the light of the revealed characteristics.