The Oil-Water Relative Permeability Behaviour of A Low Permeable Reservoir

Abstract

Figures are missing from the paper. Abstract Much attention is now paid to the development of low permeable reservoirs. However, there is almost a dearth of literature on the study of relative permeabilities in rock samples with low permeability. Group J2S of QL Reservoir is characteristics of low porosity, low permeability and low crude oil viscosity. Oil-water relative permeabilities of QL Reservoir have been measured at two different oil/water viscosity ratios by using unsteady-state method. The experimental results showed that the oil-water relative permeabilities change with the changing of oil/water viscosity' ratio. It is explained that the oil-water relative permeabilities measured at oil/water viscosity ratio close to the oil/water viscosity ratio under reservoir condition coincide with the practical situation of QL Reservoir by comparing the injection-production ratio calculated from laboratory water flooding data with the practical one. The irreducible water saturations in QL Reservoir rocks range from 27.7% to 35.8% and its average value is 31.5%. The water flooding residual oil saturations range from 11.6% to 21.7% and its average value is 14.8%. Most of the water relative permeabilities at residual oil saturations range from 0.23to 0.50 and its average value is about 0.388. Oil-water 2-phase flowing limit ranges from 47.8% to 59.0% and its average value is about 53.7%. Moreover, the end water relative permeabilities are correlated with the air permeabilities of rock samples. That is, the bigger the air permeabilities of the rock samples, the higher the end water relative permeabilities. Introduction The development of a reservoir by water injection usually includes an oil-water 2-phase or an oil-gas-water 3-phase flowing in porous media(reservoir rock). The efficiency of development by water injection is closely related to the multi-phase flow in porous media which is dependent on rock permeability, pore structure, wettability, capillary pressure, interfacial tension, viscosity of fluid and relative permeability of each phase. The basic idea of relative permeability is simple. However, the factors to affect relative permeability are very complex. Many literatures about relative permeability published now explain that it is very difficult to obtain really representative and true relative permeability data. P. 497

Experimental study of the effect of CO2 on rock seepage characteristics

“…The correlation coefficients R2 of fitting curves are greater than 0.99, indicating that the fitting results are good [16]. The fitted seepage curve is a gradually rising curve, indicating that the gas seepage of sandstone and shale before and after CO 2 soaking has non Darcy seepage characteristics [22,23]. Compared with liquid CO 2 , the seepage curves of sandstone and shale before and after supercritical CO reaction change more obviously.…”

“…Under the condition of simulating the actual reservoir water saturation, the high-pressure displacement method is used to measure the gas seepage curve of the core before and after CO 2 soaking, that is, the relationship between flow and pressure gradient is obtained [21]. According to the research of Ren Xiaojuan's team [22,23], through fitting a large number of seepage experimental data, the empirical formula of low velocity seepage for single-phase fluid is obtained, as shown in Formula (1).…”

The Characteristics of Relative Permeability Curves in Naturally Fractured Carbonate Reservoirs

“…In recent years, many studies have been carried out on the characteristics of relative permeability curves. Lin et al (Lin and Shi 2000;Zhang and Yin 1999) studied the characteristics of relative permeability curves in low-or ultralow-permeability reservoirs. They pointed out that as the water saturation increased and water relative permeability increased gradually, oil relative permeability declined dramatically and became smooth at the last stage of waterflooding-as the two-phase-flow area narrowed-leading to lower oil recovery.…”