This paper presents the development of a new analysis technique that can be used to determine the gas-in-place for abnormally pressured gas reservoirs. This new approach requires only production data (p and Gp) and does not require a prior knowledge of formation and fluid compressibility data. Using a pressure-dependent compressibility function based on the generalized gas material balance equation, this approach can be used to model both the rock collapse and shale water influx theories presented in the literature. In this work we introduce two new plotting functions, c_e(p_i-p) versus (p/z)/(p_i/z_i) and (p/z)/(p_i/z_i) versus G_p/G, where these plotting functions are developed using the generalized gas material balance equation for a gas reservoir under the influence of a pressure-dependent formation compressibility function developed by Fetkovich (1998) in conjunction with the two straight-line trends observed on the p/z versus G_p plot for abnormally pressured gas reservoirs. Using these new plotting functions we develop a dynamic type curve matching technique that determines the gas-in-place (G). In addition to gas-in-place, this new technique can be used to calculate pore volume compressibility as a function of reservoir pressure.
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