Laboratory permeability measurements of low permeability (less than 1 md) reservoir rock is significantly affected by test confining pressure. Knowledge of the confining pressure is required to predict permeability at reservoir conditions. A permeability at reservoir conditions. A model is proposed which relates electrical conductivity, permeability, and pore dimensions to confining pressure. The model assumes that rock pores are interconnected by thin cracks and microfractures which can be modeled by rectangular slits. For this model, core permeability is related to confining pressure by a third order polynomial, and electrical conductivity Is polynomial, and electrical conductivity Is related to confining pressure by a first order polynomial, Electrical conductivity and permeability versus confining pressure measurements were made on test cores having laboratory Klinkenberg permeabilities from 20 to 200 microdarcys. The experimental measurements were found to be consistent with the slit model theory. Introduction Thomas and Ward have shown that the measured permeability of many western gas sandstone cores is significantly decreased by increased test confining pressure, whereas effective porosity is only slightly affected. Jones and Owens developed an empirical method for relating permeability to confining pressure which is valid for a variety of low-permeability western gas sandstone core. The results are consistent enough to suggest that a rock matrix model can be developed to relate pore geometry to laboratory permeability. Their studies suggest that low-permeability reservoir rock consists of a matrix material containing larger pores which contribute mostly to the rock porosity. The larger-pores are interconnected by smaller pore throats that restrict permeability and are easily deformed by changes in confining pressure. Wyllie and Gardner developed a capillary model in which pores and pore throats are assumed to be short sections of capillary tubes. Stacking sections of the capillary tubes together in a random manner forms a model which can relate porosity, electrical conductivity, and permeability. porosity, electrical conductivity, and permeability. Archie's equation is often inferred from the Wyllie-Gardner model. It is possible to extend the capillary model to include the effects of confining pressure. The extension is made by assuming that each capillary tube is a thick-walled cylinder to which the confining pressure is applied. As the confining pressure is increased, the inside diameter of the capillary is reduced which reduces the permeability and electrical conductivity. This model could be useful if the pore throats were nearly round capillary tubes. It is more likely that pore throats in low-permeability sands can be described better as slits, cracks or micro-fractures. For the same cross-section area, a slit will be a much weaker structure than a capillary tube and will undergo a larger change in area due to an applied external stress. Our paper proposes that a slit model can paper proposes that a slit model can describe the effect of confining pressure on permeability and electrical conductivity for permeability and electrical conductivity for low permeability reservoir rock. Slit Model Theory The following assumptions have been made for the model:Flow paths through the core are independent and consist of a series of pores connected by rectangular slits.The slits are uniform in size in each flow path.Permeability and electrical conductivity are limited primarily by slit dimensions and fluid properties.Viscous flow is assumed; slit entrance and surface roughness effects are neglected. p. 391

Eugene Island Block 77 field is a shallow pier cement salt dome with a low relief overhang that is productive from Upper Miocene sands at depths between 13,300 and 15,800 feet (3.260 - 3.690 seconds). These hydrocarbon accumulations are trapped in steeply dipping beds between the salt mass and the rim syncline. Varied gas-water contacts in field wells suggest that radial faults also control reservoir limits. Maps produced from 2D seismic data provided limited structural detail due to:The wide spacing between linesThe presence of migration artifacts and sideswipe problems that mask minor faults and make salt interface maps ambiguous. To resolve these problems, a three-dimensional seismic survey was performed using a bay-cable technique. The increased density of subsurface sampling, together with the advantages of 3D migration and the ability to view and interpret the data from the horizontal plane, enabled a highly detailed interpretation to be performed. Maps produced from the 3D volume far surpass the detail possible from the previous 2D data. The salt-mess boundary, together with a complex system of regional growth and radial faults associated with the dome, has been mapped. Introduction Eugene Island Block 77 Dome is 18 miles off the Louisiana coast approximately 90 miles southwest of New Orleans in the federal waters of the Gulf of Mexico. Figure 1 details the location of the area. The dome and surrounding field are in blocks 62, 63, 76, and 77 of the Eugene Island area, all of which are leased to Hunt Oil Company. The dome has apparently emerged from the deepest point of a localized syncline, as can be seen from the generalized regional structure map of Figure 2. Regional faulting is closely associated with the many surrounding salt features, which are both shallow pier cement and deep seated. The Block 77 dome is a shallow pier cement dome that comes to within 750 feet of the surface. Figure 3 is a well traverse through the southeast flank of the dome between depths of -8000 feet and -15,000 feet. The line of section illustrates the salt, wells 77 #1 and 77 #2, and the rim syncline beyond. The #1 well was drilled without encountering any salt; it penetrates the shallow (brown) horizon at approximately -12,700 feet and the deep (green) horizon at -14,600 feet. The #2 well is only 1400 feet to the northwest, yet it penetrates 6000 feet of salt before encountering climatic sediments beneath the salt overhang. This well also penetrated the shallow horizon but TD? end before reaching the deep horizon. Diameter ridings suggest dip close to the salt to be around 40. A complete interpretation of a salt dome prospect such an this requires not only the structural interpretation of horizons of interest but also a detailed interpretation of the salt interface. In this study, this knowledge of the salt face was required to aid in planning well deviations around the salt stock so that future wells may be positioned close to the up dip limit of any reserves to maximize potential recoveries.

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