Horizontal wells have become major factors in reservoir development mainlybecause of productivity enhancement per well over vertical wells, as well ashaving fewer water coning and sand production problems. Well productionincrease becomes particularity impressive in reservoirs where the verticalpermeability is larger compared with horizontal one, or when the reservoir isvery thin. We have in this paper quantitatively analyzed those factors andexplored their effects on production front a general slant well, using a newlydeveloped steady-state single phase flow solution. The solution provides auseful comparative measure to study the various productivity-enhancementmechanisms of an inclined or horizontal well in an anisotropic reservoir, andat the same time enables us to define the conditions under which horizontalwells may become worse than vertical wells in productivity. The results canhelp engineers design the best productivity system in general levered reservoircases.


Horizontal wells are often used to achieve higher per well fluid productionfrom oil and gas reservoirs. Particularly in off-shore development, highlyinclined and horizontal wells are necessary for economical fielddevelopment.

Theoretical analysis of the productivity of horizontal wells has been anactive area and several solutions are reported. Borisov gave a closed-formapproximation to predict steady-state horizontal well production for isotropicreservoirs. An approximate augmentation solution for a horizontal well whichaddressed anisotropic permeability effects was derived by Joshi, where heconsidered a two-dimensional anisotropic permeability case. Transient solutionsare also frequently seen in the literature, but only for horizontal wells.Theoretical solutions for an inclined well, which are essential to compare withthe productivity of a vertical well in the same reservoir, are largely absentfrom the literature. Lee reported some results for fluid flow to a slant wellbased on a numerical simulation.

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