Carbonate reservoirs which contains significant amount of the remaining oil reserves in the Tatarstan Republic and in Russia are normally always naturally fractured. The presence of natural fractures creates additional heterogeneity of the reservoirs structure and makes an essential impact on the development strategy for such reservoirs. An integration of modern logging methods and special studies of oriented cores can give better characterization of such complex reservoirs.
To estimate naturally fractured reservoirs' characteristics in carbonate deposits of the Tatarstan Republic the network of key wells were drilled with oriented cores recovered. To date ten such wells have been drilled. Core studies for qualitative and quantitative fracture system analysis have been made. Based on these studies main types, morphology and orientation of occurred fractures were identified. The depth, dipping angle, azimuth and distribution function has been determined for each fracture type from oriented core studies. Analysis of full-size core allowed estimating secondary porosity in intervals with caverns present. In the same intervals in addition to standard logging set special open hole logging was done including micro-resistivity and acoustic imagers, ultrasonic logging.
Core measurements and logging data was analyzed in specialized software FracaFlow. Based on this analysis it was shown that core data and log data are in good agreement to each other and can be used in combination for better reservoir description in carbonates. The core orientation technique works best for wells with high inclination while micro-imagers can only be used in low angle wells (less than 40°). Low aperture fractures can be successfully identified on core in thick formations however the core orientation method fails in thin interbedded formations. The enhancement for core orientation technique was suggested which uses formation dipping angle data.
Data received will help to evaluate carbonate reservoirs in more details. It will be taken in account while drilling new wells and for design of oilfields' development.