Analytical Investigation of Unconventional Reservoir Performance During Early-transient Multi-phase Flow Conditions
Author | : Miao Zhang |
Publisher | : |
Total Pages | : |
Release | : 2016 |
Genre | : |
ISBN | : |
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Unconventional gas resources accounted for more than 50% of total U.S. gas production in 2012 and its contribution is expected to increase to 75% by 2040 (EIA, 2015). In these unconventional gas reservoirs, reservoir and fluid characteristics can be significantly different from those in conventional resources, rendering traditional production data analysis methods inadequate. Those effects include long-time transient periods due to ultra-low permeability, pressure-dependent permeability and exemplified large capillary pressure. Development of reliable analysis methods to successfully capture these complex effects demands the formulation of new solutions to the governing flow equations which consider these complex nonlinearities. It is the interest of this study to develop more rigorous performance models for these types of systems derived from fundamental governing flow equations. This study presents a series of novel and rigorous semi-analytical solutions to the governing partial differential equations applicable to single-phase gas and multiphase flow in unconventional reservoirs. Focusing on early-transient periods, the proposed semi-analytical method utilizes similarity theory to transform the system of nonlinear PDEs to ordinary differential form, which is later solved via shooting method coupled Runge-Kutta numerical integration. The work starts with early-transient single-phase gas flow in linear and radial flow regimes under constant pressure and rate production conditions, followed by its direct extension to multiphase flow system using the black-oil fluid formulation. The application of the proposed multiphase flow solution to actual productionhighlighting producing gas-oil-ratio predictionis also discussed. Additionally, the proposed semi-analytical solution is proven capable of solving the multiphase flow equations under fully compositional fluid formulation. In the last chapter, capillary pressure effectsa multiphase flow effect widely recognized to be significant in unconventional system due to nano-scale pore sizeis studied using the proposed semi-analytical method. Besides studying capillary pressure as an additional pressure drop on fluid flow, the effect of capillary pressure on phase behavior and properties is also analyzed. All the results in this work are validated by matching with finely-gridded commercial numerical simulator.