Petroleum industry is the major contributor to the economy of the Republic of Tatarstan ensuring natural resources and energy security of the region and the whole of Russia. While planning oil and gas geological prospecting activities, just like any other financial and business operation, decisions are made based on their technical and economic efficiency. Efficient planning of geological prospecting activities should also take into account such important figure as total investment per unit increment of hydrocarbon reserves. While planning the evolution of this parameter for quantitative representation of the strategic targets of an enterprise, historical data are also considered. In other words, a look-back analysis of geological and economic efficiency of previous activities is necessary. Of particular importance is exploration drilling success rates expressed as percentage and total costs per unit of reserves increment. From 2013 to 2017, 30 wildcat wells and 15 exploratory wells have been drilled at license blocks operated by Tatneft with total drilling meterage of approximately 77 km. Average success rate of prospecting and exploratory drilling for the same period exceeded 70 %. Incremental recoverable oil reserves of В1+С1+В2+С2 categories from drilling of wildcat wells made, considering the write-off, approximately 4 million tons, from drilling of exploratory wells – 2 million tons. Specific recoverable oil reserves per exploration well slightly exceeded 137 thousand tons, while incremental oil reserves per 1 meter drilled were estimated at about 83 tons. Over the past five years, average total cost per one incremental ton of recoverable oil made 1167 rubbles. Results of drilling success rate estimates imply strong dependence of this parameter on the degree of exploration maturity of the territory and linear dimensions (area and vertical closure) of drilling prospects. Thus, higher drilling success rates in coal formations can be attributed to distinct and better-defined traps associated with such rocks compared to Devonian sediments. Obviously, more information is available to geologists for location of exploratory wells than in the case of wildcat drilling; namely, well logging data from offset wells, refined structural plan based on drilling data, structural correlations and profiles, production rates from offset wells in C1 region of the discovered accumulation and other. All of the above also yield higher drilling success rates.
