Carbonate reservoirs are well known for their heterogeneity with the properties such as flow capacity and storage varying in a very wide range both laterally and vertically. This intrinsic complexity impedes the evaluation of such reservoirs and limits any reliable predictions of their petrophysical characteristics from well log interpretation. Hence it becomes essential for any rock physics model to establish and validate any relevant justifiable correlations between the petrophysical and lithological parameters given the degree of geological heterogeneity related to the depositional environments and diagenetic processes and changes. This problem required careful and thorough examination and review of all the knowledge accumulated on the Upper Devonian carbonates developed on the East European Platform within the territory of the Republic of Bashkortostan. The findings were used as a framework for a reference petrophysical database and corresponding rock physics model consistent with the established depositional environments.
The paper presents the correlation of identified lithologic and facies heterogeneity and petrophysical properties of the Upper Devonian carbonate plays within the Republic of Bashkortostan. Each structural and facies zone (SFZ) is characterized by a prevailing association of lithotypes with specific inherent lithologic, structural and textural features. The main criterion for differentiating petrophysical classes in the Upper Devonian carbonate sequence is proved to be the type of the void space in lithologically homogeneous rocks subject to secondary diagenetic changes. The petrophysical classes are characterized by their own rock physics parameters and correlation functions, invariables and regular cut-off values.
The developed petrophysical model will be used for reliable assessment of volumetric parameters in reserve calculations for the producing Upper Devonian platform carbonate plays in Bashkortostan.
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