Performance of a tapered vertical well in an infinite-acting reservoir – a novel approach

Abstract

This study adopts a new form of vertical well technology involving the use of a tapered well completion. It presents a mathematical model for evaluating the performance of a tapered vertical well masked by an infinite acting flow regime. Matthews and Russell’s solution to the radial flow diffusivity equation was utilized infiguring the strength of a vertical wellbore designed with a tapered configuration. To accomplish objective, pressure drawdown per unit rate was computed employing three distinct vertical tapered well completion combinations: Conventional, 2-Step tapered and 3-Step tapered completion. The derived model was demonstrated using a hypothetical well and reservoir case. Sensitivity of unit rate function to tapered height and wellbore radii was critically examined using several tapered ratios. Results obtained are compared against that from a conventional well configuration. It shows a better performance for a 2-step tapered vertical well and an even better performance when the well is tapered in 3-Steps. Furthermore, as the tapered ratio became farther apart, a better performance resulted. Radial flow persisted the larger the number of tapering. The number of taper possible was seen to be limited by the pay thickness. Reservoir, wellbore and fluid properties also largely affected well performance for all cases of completion considered. The completion efficiency of the tapered vertical well was seen to exceed largely that of the conventional vertical well completion on the basics of pressure drawdown per unit flowrate. This paper successfully shows that the capacity of the vertical well has not yet been fully exploited. It therefore follows that a tapered vertical well completion is more efficient that the conventional vertical well and is strongly recommended to Petroleum Engineers and the Oil and Gas industry in general especially for reservoirs with a large pay thickness where high rates are desired.

Keywords: Tapered Well, Performance evaluation, Infinite-acting, Pressure drawdown, completion, Reservoir, Pressure drawdown/unit flowrate.