Simplified Wellbore Flow Modeling of Gas/Condensate Systems

Abstract

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 89754, "Simplified Wellbore Flow Modeling in Gas-Condensate Systems," by C.S. Kabir, SPE, ChevronTexaco, and A.R. Hasan, SPE, U. of Minnesota-Duluth, prepared for the 2004 SPE Annual Technical Conference and Exhibition, Houston, 26-29 September. Predicting long-term reservoir performance with realistic wellbore models is fraught with uncertainty because of the complexity of two-phase flow. Even a calibrated two-phase-flow model departs from its expected performance trend when changes in flow conditions occur. The full-length paper explores the possibility of using simplified approaches to computing bottomhole pressure (BHP) from wellhead pressure (WHP), measured rates, gravity of producing fluids, and tubular dimensions. Statistical results from BHP computations on three independent data sets comprising 167 gas/condensate-well tests show that the homogeneous model compares quite favorably with mechanistic two-phase-flow models. Introduction Two-phase-flow modeling of gas/condensate wells has not received as much attention as that of oil wells. The popular Gray correlation appears to do a good job in most gas/condensate wells. However, applicability of this correlation outside the bounds of its specified parameters remains unclear. A user must specify one computational approach for flow in pipes when long-term integrated reservoir/wellbore/flowline performance is sought over a field’s producing life. Declining condensate/gas ratio (CGR) and increasing water production with time have the potential for complicating any modeling effort. Besides the two-component gas/liquid Gray correlation, other approaches have emerged for modeling gas/condensate flow. The semimechanistic model of Govier and Fogarasi represents the multi-component approach with flash calculations. In contrast, the wet-gas concept offered by Peffer et al. suggests extreme pseudoization with single-component gas. Computational Approach and Results Data from the literature and those from a few west African fields with medium- to high-CGR production were used. In all, 167 tests were examined. The methods used were the homogeneous model; the steady-state OLGA; those of Gray, Aziz et al., and Ansari et al.; and the wet-gas approach, advanced by Peffer, in which the gas gravity is weighted to include the density of the produced liquid.