Abstract

Formation evaluation provides the input data for reserves’ estimation and oil recovery strategy. Usually core analysis and log-interpretation calibrated with core data are the primarily sources of information. If there are some unsolved problems during core analysis stage, both log-interpretation and following estimations and conclusions could be wrong.

We faced with such situation while evaluating properties of weakly consolidated sandstones and un-consolidated sands in Permian formations of Tatarstan Republic in Russia a few years ago. The problems were primarily associated with destruction of the rocks structure during the core recovery. Weight hydrocarbon saturation and grain size distribution were the only properties determined for these formations by conventional core analysis. It was impossible to determine porosity, permeability and volume hydrocarbon saturation which are critical for modeling and reservoir engineering purposes.

Improved non-conventional method of core analysis described in this paper has been applied to solve this problem. The method suggests different approach depending on rocks’ consolidation. Since year 2005 more than 900 meters of core from twenty-three parametric wells were studied using the method proposed in this paper. As a result, necessary correlations for log interpretation have been adjusted. Application of the method allowed reasonable evaluation of the heavy-oil Ashalchinskoye field. The estimation for porosity has been increased from 30% to 34%, and permeability estimates were increased from 300 mD to 1-3 D. The new estimates of the reservoir properties allowed to suggest SAGD method for oil recovery, which otherwise would be uneconomical. The SAGD method is currently being implemented in this oilfield. Thus, the described unconventional core analysis method has proved its efficiency and can be recommended for further usage.

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