EFFECT OF DISCRETIZATION ON CALCULATION OF SLANT WELL PRODUCTIVITY INDEX IN NUMERICAL RESERVOIR SIMULATION

Abstract

Slant well is a non-vertical form of wells used typically for extracting oil and gas resources that cannot be accessed through traditional vertical well drilling. Deviation in these wells results in the geometric skin factor, which has a negative value and increases the productivity index. Various analytical/semi-analytical equations estimate the geometric skin factor for the slant well for slightly compressible fluids. This study attempts to show that the productivity calculated by numerical simulation for the slant well in a single-phase (oil/gas) reservoir is sensitive to grid resolution. For this purpose, first, a slant well is defined within a local grid refinement (“LGR”) system. Afterwards, the slant skin factor is calculated for cases having different LGR resolution for a constant degree of inclination to find a reasonable LGR system. Then, the applicability of this optimum LGR for all deviation angles with comparison with analytical model is evaluated. This evaluation shows that optimum LGR is particular for each well deviation angle. Although some of the analytical/semi analytical models are developed for slightly compressible fluids, these models also are applicable for compressible fluids (i.e. dry gas). Furthermore, the calculated skin for the slant well in numerical simulation for optimum LGR is not sensitive to production rate or oil viscosity.