Compressibility of porous rocks: Part II. New relationships

Pore volume compressibility is one of the physical properties of a reservoir that must be specified in many reservoir-engineering calculations. The main objective of this work is to provide new general formulas for pore volume compressibility versus porosity on the basis of measured compressibilities of some limestone and sandstone rocks in a wide range of porosity values and of varied type; the measurements were performed on Hungarian reservoir rock samples. The obtained laboratory results were compared with the published correlations of consolidated limestone samples as well with values for friable and strongly consolidated sandstones. The validity of using compressibility data from the literature was investigated. The measured data showed poor agreement with the published correlations. The first approach to find better and more accurate rock compressibility correlations consisted of combing all the data available from the literature, using the same formula of Horne’s type. However, this attempt did not give satisfying fitting results. In the next step, by using twelve different fitting formulas, and other comprehensive nonlinear fitting regression programs, new rock compressibility correlations for limestone and sandstone rocks, with better goodness of fit, were developed. These new correlations can be generalized and used for most of oil and gas reservoirs.