Transient pressure test analysis of horizontal wells in gas condensate reservoirs: Evaluation of conventional multi-phase pseudo-pressure solutions

Abstract

Transient pressure test analysis, as a tool to well and reservoir characterization, is not well developed in two-phase horizontal wells. As our best knowledge, potential of conventional multiphase pseudo-pressure solutions in horizontal well test analysis of gas condensate reservoirs below dew-point pressure has not been demonstrated yet. The most challenge is that flow regime around horizontal wells is not constant. Also, high velocity effects near wellbore are the other main conflict which need more investigation.The objective of this paper is to express encountered challenges in transient pressure test analysis of horizontal wells in gas condensate reservoirs below saturation pressure. For this purpose, based on simulated models, potential of the conventional multiphase pseudo-pressure solutions to interpret pressure behavior of these wells is examined. Also, their potential to estimate well and reservoir properties is investigated. After that, the reason for inability of these solutions in well test analysis of horizontal wells is explored. Furthermore, the effects of near wellbore phenomena on two-phase horizontal gas wells are studied.The results show that, during early radial flow, once bottom-hole pressure falls below dew-point, pressure data shows a composite behavior; however, two phase pseudo-pressure responses calculated by both steady-state and 3-zone solutions, can accurately correct the effect of liquid saturation. In the result, reservoir permeability is estimated with a good accuracy. The study also expressed that, during other flow regimes, deviation from single phase flow due to condensate accumulation cannot be corrected using conventional solutions of two-phase pseudo-pressure function. The reason is that fluid composition is not constant during any of the flow regimes except radial flow. Though, constant fluid composition is the basic assumption for the conventional solutions. Moreover, the result shows that non-Darcy effect in two-phase flow is less than single-phase. Also, positive coupling effect around horizontal wells is not as much significant as vertical wells.