Pseudo-skin Factors for Partially-Penetrating Directionally-Drilled Wells

Abstract

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. Abstract An analytical solution derived recently to study the unsteady-state flow of a slightly compressible fluid toward slanted wells was modified to compute the pseudo-skin effect created by partial penetration and slant of a well. It was partial penetration and slant of a well. It was found, as expected, that the pseudo-skin factor due to the slant of a well has a negative value and it appears to be affected by both the location of the producing interval in the formation and the producing interval length. producing interval length Introduction Many authors have studied steady-state and the unsteady-state flow toward a partially-penetrating well. They considered a well partially-penetrating well. They considered a well perpendicular to the producing formation and perpendicular to the producing formation and concluded that this type of well completion causes a decrease in well productivity. However, as pointed out by Cinco, et al., many wells do not penetrate the producing formation perpendicularly. Instead, there is an angle perpendicularly. Instead, there is an angle between the wellbore axis and a normal to the formation horizontal plane. These wells may be termed "directionally-drilled," or "slanted" wells. This situation creates an increase in well productivity with respect to a partially penetrating well which is perpendicular to the penetrating well which is perpendicular to the formation. Cinco, et al., studied the unsteady-state flow of a slightly compressible fluid toward slanted wells in an infinite slab reservoir, and presented a solution which can be applied to presented a solution which can be applied to fully and partially-penetrating wells. It was shown that the unsteady flow toward a slanted line source includes three flow periods:a radial flow period,a transitional flow period, anda pseudo-radial flow period. They also presented results for a fully-penetrating slanted presented results for a fully-penetrating slanted well of infinite conductivity, and concluded that the slant of a well causes an increase in well productivity which can be handled as a negative productivity which can be handled as a negative pseudo-skin effect that is constant for large pseudo-skin effect that is constant for large values of time. The purpose of this work is to evaluate the pseudo-skin effect for a partially-penetrating pseudo-skin effect for a partially-penetrating slanted well of infinite conductivity (uniform pressure at the wellbore) in an infinite slab pressure at the wellbore) in an infinite slab reservoir, and to show how to correct the skin factor calculated from well test analysis for the deviation from the vertical.