Reduction in Permeability With Overburden Pressure

Abstract

Oil bearing rocks, usually found at depths of 2,000 to 10,000'Ft, areelastically deformed by overburden pressure. Although the change in porositywith pressure in a number of example rocks has been shown to be small, it wasthought that overburden pressure might have a significant effect onpermeability. This note presents results of an investigation to determine themagnitude of the change in permeability with pressure. In routine core analysis, permeabilities are measured on rock samples whichare not under overburden pressure. If permeability measured in this way differsfrom permeabilities measured under overburden pressure, a systematic error isintroduced into well productivity calculations. The experiments described inthis report were made to determine the magnitude of the change and thus to givean estimate of the error introduced into the calculations. The error introducedby the neglect of the change in permeability when overburden pressure isremoved may account for part of the difference between well productivitycalculated from core analysis and the actual well productivity. The results obtained in this investigation have only qualitativesignificance because of the difficulty in reproducing in the laboratory thestress conditions on the rock buried in the earth. The assumption which isusually made is that the rocks in the earth are under a uniform pressure equalto the weight per unit area of the vertical overburden column from the rock inquestion to the surface of the earth less the pressure of the liquid in thepores of the rock. For an overburden consisting of sandstones and shales (ofassumed average specific gravity of 2.3) and for a liquid pressure equal to thepressure in a salt water column (of specific gravity 1.0) reaching from therock to the surface, the resulting net pressure on the rock is approximately0.56 psi per ft of depth. Experimental Method Clean, dry sandstone core plugs one in. in diameter and about three in. longwere mounted in a copper foil jacket as shown in Fig. 3 or molded in a Lucitejacket as shown in Fig. 4. All cores except those labeled "2" in Fig. 1and "8" in Fig. 2 were measured in the copper foil jacket. Cores"2" and "8" were measured' in the Lucite jacket. T.N. 147

Investigation of Efficiency Improvements During Co2 Injection in Hydraulically and Naturally Fractured Reservoirs

“…Wyble (1958) performed similar experiments on three different sandstone samples to determine the changes in conductivity, porosity and permeability at pressure range 0 to 5,000 psig. His results were consistent with the observation by Fatt and Davis (1952). During the experiments, different overburden pressures (radial force) were applied only to the cylinder core while the axial direction was kept at constant atmospheric pressure.…”

“…The reduction in permeability with overburden pressure has been well known. Fatt and Davis (1952) presented the changes in permeability with pressure at range 0 to 15,000 psig and found that overburden pressure caused a reduction in permeability of the consolidated oil-bearing sandstone samples by as much as 50 per cent at 10,000 psig. Wyble (1958) performed similar experiments on three different sandstone samples to determine the changes in conductivity, porosity and permeability at pressure range 0 to 5,000 psig.…”

Research on Stress Sensitivity of Fractured Carbonate Reservoirs Based on CT Technology

“…Stress sensitivity phenomena occur in the process of oil and gas field development of fractured reservoirs [13][14][15]39]. Natural fractures are the main fluid flow channels in tight sandstone and fractured carbonate reservoirs [40], which are the main factors in the development of oil and gas wells.…”

“…Permeability is well known to negatively correlate with the effective stress [13], and the stress-dependent permeability becomes the norm of petrophyiscal characterization for, but not limited to, fractured reservoirs [14,15]. Experimental studies on the stress-sensitivity reveal that fracture aperture is the reciprocal of the effective stress, and is one of…”

In situ mining through leaching: Experimental methodology for evaluating its implementation and economic considerations

“…The natural compression of the material by the overburden weight results in an increase in density and decreasing porosity with increasing depth (Fatt, 1952;Bass, 1980). The increase in pressure due to taller leach columns also leads to a reduction in the porosity and, therefore, a decrease in leaching efficiency (Dixon, 2007).…”