The Effect of Temperature and Confining Pressure on Single-Phase Flow in Consolidated Rocks (includes associated paper 9087 )

Abstract

Single-phase flow through consolidated rocks is conducted under conditionsof elevated temperature and overburden pressure. Unique permeabilityreduction with increasing temperature is observed with distilled water, while a slight increase is noted with white mineral oil and no change isfound with gas. With gas flow, slippage and turbulence at hightemperatures also are investigated; results agree closely with theory. Introduction In all reservoir engineering calculations, absolutepermeability is a basic parameter and traditionally has beenmeasured at room conditions, with the assumption thatabsolute permeability changes only with core loading pressure. As a result, most reservoir engineers use asingle value of absolute permeability throughout a rangeof temperatures. It was only in the late 1960s that changes in absolutepermeability were observed with temperature. In 1968, Greenberg et al. reported data on the permeability towater of nine artificially consolidated hydrological porous medium samples for a limited temperature span[80 to 140 deg. F(26.7 to 60 deg. C)]. The Greenberg et al.results showed either slight-to-moderate decreases inpermeability, no change at all with increasingtemperature, or increases in permeability in two cases.No confining pressure was applied to the cores. In 1969, Afinogenov reported a large reduction ofpermeability to oil with increased temperature, up to100-fold between 70 and 200 deg. F(21.1 and 93.3 deg. C).He also observed extreme permeability reductions withincreasing confining pressure for pressures ranging from300 to 15,000 psi (2.1 to 103 MPa). Qualitatively, these results agreed with those inpreviously published works, but quantitatively thedecrease observed was much greater than one mightexpect. No attempt-was made to study the combinedeffect of temperature and confining pressure on absolutepermeability. The effect of radial and/or axial stress on variousphysical properties of rocks has been studied by severalinvestigators. A review of earlier work was made in1967 by Wilhelmi and Somerton. They measured poreand elastic properties of rocks simultaneously under awide range of triaxial stress conditions. One of the firstcontributions in this area was made in 1952 by Fatt andDavis. They showed that permeability at 15,000-psi (103-MPa) confining pressure could be 25 to 60%smaller than the permeability at zero confining pressure, depending on the type of rocks studied. In 1963, work on the effect of overburden pressure onpermeability was extended by Gray et al. to sandstonepermeability anisotropy. Permeability reduction wasshown to be a function of the ratio of radial to axialstress, with maximum reduction evidenced underuniform stress - i.e., when the axial stress was equal to theradial stress. (The results reported here were obtained under conditions of uniform stress). We usually consider the effect of the net confiningpressure on absolute permeability. If k is defined as thefraction of pore pressure counteracting the confiningpressure, the net confining pressure is the confiningpressure less lambda x (pore pressure). Several investigaorsfound that the best correlating value is lambda = 0.85. Mosttemperature studies have considered a temperature rangefrom 75 to 350 deg. F (23.9 to 176.7 deg. C). JPT P. 1051^