Prediction of In-Situ Permeability: Significance of Rock Type Identification in Resevoir Characterization of Tight Gas Sandstones: ABSTRACT

Abstract

The accurate prediction of in-situ permeability is fundamentally important in reservoir characterization. Analyses of several thousand core samples from low permeability ([open quotes]tight[close quotes]) gas sandstones of the Travis Peak, Cotton Valley and Frontier Formations reveal that the rate of permeability decrease is a function of Rock Type (interval of rock characterized by unique pore geometry). These tight gas sandstones consist of alternations of several Rock Types, depending on changes in environment of deposition and diagenesis. In such complex sequences, in-situ permeability cannot be successfully predicted using only an initial value of permeability. A knowledge of both the initial permeability (at minimum net effective stress) and pore geometry are required to predict in-situ permeability at any given value of net effective stress. Pore geometry characteristics that control in-situ permeability include size and shape aspects of both the pore throats and the pore bodies. These can be, in part, a function of mineral composition. In some instances, they are independent of composition. SEM-based pore image analysis of pore bodies and pore throats allows for the identification of different Rock Types. This information, when coupled with an initial value of permeability, allows for the prediction of permeability at any given value ofmore » net effective stress in the Travis Peak, Cotton Valley and Frontier Formations of Texas and Wyoming.« less