Summary Linear flow is a fundamental reservoir-flow geometry typically associated with production from unconventional resources stimulated by means of hydraulic fracturing. Recently, linear flow has been intensively studied following the fast pace of development of unconventional resources. Previous studies have mainly focused on early transient behavior and behavior of composite linear-flow systems. In this work, a density-based analysis method is extended to study decline behavior of the linear-flow system in boundary-dominated flow (BDF). In this study, we first discuss traditional approaches used to model linear flow in gas reservoirs. Second, we show the applicability of the density-based method for gas linear flow both analytically and numerically. Next, late-time solutions are discussed, and the analytical forecasting solution that best describes the BDF behavior is selected for long-term decline-behavior studies. Previously reported results on radial flow as well as early transient-flow effect are also incorporated to provide a more complete understanding of decline behavior and the impact of flow geometry. We show that boundary-dominated responses in linear-flow scenarios fully develop at much later stages of reservoir depletion compared with radial-flow scenarios. As a result, and in marked contrast with radial flow, purely hyperbolic decline behavior may be completely lost in linear-flow scenarios during boundary-dominated conditions. It is demonstrated that most of the recoverable hydrocarbons are produced during the early transient period for linear-flow conditions, whereas most of them are recovered during the BDF period for radial flow. These results suggest that the availability of accurate early transient models is much more critical for the formulation of linear-flow-decline models than had been traditionally necessary for radial-flow-decline models.

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Accounting for gas-slippage and desorption effects is a critical step towards the reliable analysis of production performance in unconventional gas systems. This study demonstrates how to account for gas slippage and gas desorption effects in gas reservoirs using a density-based approach of analysis-an approach recently proposed for analyzing unsteady state flow of natural gas reservoirs. Gas-slippage and gas desorption models are incorporated into the original density-based approach by modifying the definitions of depletion-driven variables which are the basis of the density-based type of analysis. The proposed modification of the original approach successfully enables associated analysis techniques to be applicable to natural gas reservoirs with gas slippage and absorbed gas. Results indicate that by modifying the definitions of the depletion-driven variables, the density approach can effectively and successfully capture the effects from gas slippage and desorption. It is shown that gas flow rate can be successfully predicted by rescaling liquid solution with the modified density-based variables. This work illustrates the methodology required to do so and its application to production data prediction analysis for unconventional assets. 12 SPE 166377 pseudo pressure, M/L-t 3 , psi 2 /cp Subscript dimensionless variable initial conditions standard conditions (14.7 psia and 60 F) bottomhole flowing conditions Superscript * modified from original definition

Summary Accounting for depletion-dependent permeability and sorbed-phase effects is an important step toward achieving reliable analysis of production performance in unconventional gas systems. This study demonstrates how to account for pressure-dependent apparent-permeability (e.g., gas-slippage) and desorption effects in gas-production analysis of boundary-dominated data with a density-based approach. In this work, apparent-permeability and desorption models are incorporated into the original density-based approach by modifying the definitions of depletion-driven variables that are the basis of the density-based type of analysis. The proposed modification of the original approach successfully enables associated analysis techniques to be applicable to natural-gas reservoirs with gas slippage and adsorbed gas. Results indicate that by modifying the definitions of the depletion-driven variables, the density approach can effectively and successfully capture the effects from gas slippage and desorption. Through a number of case studies, we show that gas-flow rate can be successfully predicted by rescaling liquid solution with the modified density-based variables. As an illustration, we show that resource calculations able to fully take into account these effects are possible when long-term production data are available. This work details the methodology required to do so, and illustrates its application to production-data prediction analysis for unconventional assets.