Production data analysis for dual-porosity gas/liquid systems: A density-based approach

Production data analysis impacts assets value and financial decisions significantly. Naturally fractured reservoirs exist widely around the world. A common method to represent naturally fractured reservoirs is dual-porosity model. Intrinsic characteristics of dual-porosity systems and their unique rate-transient profile require models able to capture well behavior and to achieve production data analysis, which is a proven difficulty for dual-porosity gas system and not completely solved. Moreover, past studies on dual-porosity systems assume constant bottom-hole pressure (BHP) or constant rate production, which impose significant constraint to production data analysis. Recently a density-based approach for analyzing production data was proposed for single-porosity system, which has been proven to successfully describe gas well behavior under boundary-dominated flow (BDF). Using depletion-driven parameters, λ and β this state-of-the-art approach circumvents pseudo time. It was then extended to variable-pressure-drawdown/variable-rate gas systems and proven successful. In this study, we adopt a rigorously derived interporosity flow equation for gas, which captures viscosity-compressibility change of matrix outflow. Based on that, a density-based, rescaled exponential model for variable pressure drawdown/variable rate production was developed for dual-porosity gas system. Also, we explore straight-line analysis for convenient prediction of OGIP and production rate. The density-based model is tested in a variety of scenarios to showcase its validity. Moreover, based on Warren and Root model, a density-based exponential model for variable pressure drawdown/variable rate in dual-porosity liquid system is proposed and fully verified. A straight-line analysis is proposed to enable explicit OOIP prediction and convenient future production calculation. Moreover, a convenient double-exponential decline model under constant BHP is developed for liquid. To summarize our work, we developed rate-transient analysis method for two types of reservoirs-naturally fractured gas reservoir and naturally fractured oil reservoirs-producing at arbitrary type of production scenario in boundary-dominated-flow stage. The proposed method can evaluate reserve in a convenient and accurate manner. Moreover, the method to predict production using the theory is also provided. An explicit equation correlating dimensionless production rate and dimensionless time is also developed for dual-porosity liquid system producing at constant bottomhole pressure in both early transient stage and boundary-dominated-flow stage.