A Novel Application of Lateral Resistivity in Carbonate Reservoir Evaluation: A Case Study on the Eastern Edge of Caspian Basin

Abstract

In carbonate reservoirs, it is difficult to characterize the reservoir properties, because of the strong heterogeneousness, the various types, and the complex mechanisms. And the pore, hole/vuggy, fracture are often associated with different genesis, mechanisms, and scales. In this paper, it provides a novel method to solve some practical problems of oil field based on lateral resistivity logs. In the petrophysical evaluation of the carbonate reservoirs of the study block, for lack of other special logging data, the very few imaging pictures were analyzed, core data were read, and a large number of conventional logging data were processed in a statistical method. The shapes, the values, and the arrangements of the deep, shallow and microspherically focused resistivity curves were illustrated, the quantitative and qualitative identification modes for identifying reservoir types were summarized, the reservoir evaluation index (REI) of was proposed. It takes the carbonate reservoirs in the eastern margin of the Caspian Sea Basin as an example in this paper. On the base of observation of lithologies, pore structures and petrophysical properties, analyzing and summarizing the inter relationships of rock structures, lithologies, the dominant pore types, and physical properties, the reservoirs can be divided into the following five categories: the pore type, the pore-fracture one, the fracture-pore one, the pore-dissolved hole/vuggy one, and the fracture one. By using lateral resistivities and parameters of REI, the types of carbonate reservoirs were identified, the quantitative calculation of fracture porosity was calculated, and the reservoir production capacity was analyzed and defined in qualitative way. The methodology here is convenient, simple, and practical, and it is well applied in the reservoir evaluation and production prediction of Carboniferous carbonate reservoirs in this block.