Factors Affecting Gas Slippage in Tight Sandstones of Cretaceous Age in the Uinta Basin

Abstract

Summary The gas permeability of some sandstones from Uinta County, UT was measured in the laboratory. The effect of confining pressure and partial water saturation on gas permeability was investigated. Measurements were conducted at pressures of up to 34.5 MPa and partial liquid saturations of up to 60%. We noted that the slope of the straight lime relating apparent gas permeability to reciprocal mean pore pressure decreased with increasing net confining pressure and with increasing partial water saturation. Gas permeabilities extrapolated to infinite pore pressure were often higher than liquid permeabilities under the same confining pressure conditions; scanning electron microscopic (SEM) observations indicated rock/fluid interactions. Geologic studies of end pieces cut off from core plugs revealed that porosity is reduced by quartz overgrowths. authigenic clays (kaolinite. illite. and minor quantities of chlorite), carbonate cements (calcite and dolomite), and physical compaction of labile rock fragments. In some samples, organic-rich laminae were found to lie parallel to bedding surfaces. Apparently, micro porosity had been formed by partial leaching of feldspars and rock fragments. Most of the pores were lined with authigenic clays that form highly irregular pore walls. Thin film intergranular pores, which were observed in samples impregnated with blue epoxy at ambient pressure, were not found in samples in which the epoxy was cured under a confining pressure of 34.5 MPa. Introduction The concept of slip during gas flow through capillaries with diameters small enough to be comparable to the mean free path of the gas was used by Klinkenberg to explain the discrepancies between gas and liquid permeabilities of porous media. He presented the following equation, which relates the apparent gas permeability, kg, of a gas flowing at a mean pore pressure, to the true permeability of the porous medium, k g. ..........................(1) In this equation, b is a constant and is a function of the capillary radius, rb, and of the mean free path of the gas, at pressure . ...................................(2) In Eq. 2, c is a constant approximately equal to one. Loeb showed that Poiseuille's law for viscous flow can be modified to account for slip and defined a coefficient of slip that can be shown equal to the term c in Eq. 2. As is evident from Eq. 2, the contribution resulting from slip is inversely proportional to the capillary radius. At mean pore pressures usually employed in the laboratory measurements of permeability. the slip effect is significant in the case of tight sands because of the small pore sizes. The dependence of tight sandstone permeability on confining pressure and partial water saturation has been documented by numerous investigators. It appears reasonable, therefore, that the slip effect also would be affected by confining pressure and water saturation. A series of experiments was conducted in conjunction with petrographic observations in an attempt to understand the possible alterations in pore dimensions that result from confining stress and partial water saturation. Samples investigated were from Well MAPCO RBU 11-17 F (Section 17, T10S, R20E) in the Uinta Basin, UT. They are petrographically similar to other low-permeability sandstones of late Cretaceous age from the region.

Determination of Klinkenberg Permeability Conditioned to Pore-Throat Structures in Tight Formations

“…In addition, the difference between the measured water permeability and the Klinkenberg permeability also exists, which is caused by a slip effect induced by a strongly hydrophobic wall of nanopores [7]. Substantial efforts have been made to depict such differences by using empirical correlations that would be practical tools for the efficient estimation of the absolute permeability [2,8,9]. Recently, different correlations with different overburden pressures have been established in the form of power functions between water permeability and Klinkenberg corrected gas permeability for the Upper and Lower Shuaiba Formation [10].…”

A New Model for Determining the Effective Permeability of Tight Formation

“…The comparison between gas permeability and liquid permeability is a good case for the impact of boundary layer on permeability measurement of the same reservoir. There exists gas slippage effect (Sampath and Keighin 1982;Daixun 2002;Carman 1956) when gas transports in the pore throats so that the boundary-layer effect is negligible. Gas permeability is normally larger than liquid permeability (Klinkenberg 1941;Dabbous et al 1974;Horne 2001, 2004).…”

Hydraulic versus pneumatic measurements of fractured sandstone permeability

“…Scatter between liquid -gas permeabilities are also reported in the literature (Lovelock, 1977;Sampath and Keighin, 1982;Rasmussen et al, 1993;Bloomfield and Williams, 1995;Jaritz, 1998) with a tendency for liquid permeability to be lower than gas permeability. The ratio of gas permeability to liquid permeability for sandstone cores ranges from 1 to 30 (Table 3).…”

“…Strongly hydrophilic minerals, particularly swelling clays can be important in controlling the liquid permeability (Mungan, 1965;Sampath and Keighin, 1982;Khilar et al, 1983;Khilar and Fogler, 1984;Bitton and Gerba, 1984;Appelo and Postma, 1993;Mohan et al, 1993;Rahman et al, 1995;Bloomfield and Williams, 1995;De Lima and Niwas, 2000;Civan, 2000). Smectites can swell with changing ionic conditions and eventually disperse and migrate with the Table 3 Scatter of liquid -gas permeability data from the literature…”

“…Much work has been carried out to study the correlation between liquid and gas permeabilities in sandstone (Lovelock, 1977;Sampath and Keighin, 1982;Rasmussen et al, 1993;Bloomfield and Williams, 1995;Jaritz, 1998), but the comparison between liquid and gas permeability has not yet been determined for a fractured sandstone. In this study, the intrinsic permeability is determined using air and brine as the fluid medium.…”