Abstract

Due to the complexity of unconventional gas reservoirs (shale, tight, and coalbed methane), various analytical models have been developed to estimate formation parameters. This paper presents the results of the modification and application of some analytical production data models. These analytical models were developed by Arévalo and Bello. Additionally, dynamic characterization results are presented using a new model that considers the effects of gas adsorbed in the formation and ultimately improve well production analysis and the evaluation of some formation parameters. For this study, production data were taken from wells located in the Eagle Ford formation in northeastern Mexico. The data were softened in order to utilize the Arévalo models for homogenous-isotropic and low permeability heterogeneous-anisotropic formations. To identify the flow models and formation parameters, the flow diagnostic plot [m(pi) – m(pwf)] /qgvs. t and the specialized plot [(m(pi) – m(pwf)] /qgvs. √t were used. Afterwards, the Bello model was applied to analyze double porosity formations and horizontal wells with multiple fracturing stages. Using the flow diagnostic and specialized plots, four flow regimes were identified (early linear in the fracture system, bilinear in the matrix-fracture system, linear in the matrix, and boundary-dominated) and the reservoir parameters were calculated for constant flowing bottomhole pressure. Finally, from these models, an analytical model was developed that takes into account the effects of gas adsorbed in the formation. This analytical model derives from the Bump model to consider changes in gas compressibility (cg) and the King model to consider changes in the gas compressibility factor (z). It also considers Langmuir isotherms, which characterize gas desorption in the reservoir due to pressure drops. With these models, the dynamic characterization of the unconventional gas reservoirs was improved, allowing for a more accurate estimation of the reservoir parameters and subsequently the optimal development and exploitation of these fields.

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