In reservoir engineering practice, decline curve analysis (DCA) techniques have been commonly used for recoverable reserves estimates. The benefits of the DCA-based production forecasting method include minimum requirements to reservoir characterization input data; processing of actual historical reservoir performance data; comprehensive accounting for reservoir characteristics and specific technological reservoir engineering aspects; and the simplicity of the method. Various decline curves are based on the statistical evaluation of reservoir performance curves for concrete reservoirs, so, they cannot be used universally. The study focused on the Carboniferous and the Devonian sandstone and carbonate reservoirs of all oil fields developed by Tatneft PJCS. Calculations showed that considering reservoir types and producing conditions, the most reliable are forecasting methods after A.M. Pirverdyan, I.G. Permyakov, A.V. Kopytov, S.N. Nazarov, G.S. Kambarov, and the method developed by TatNIPIneft. In the framework of the in-depth study of carbonate reservoirs, which involved ninety-nine accumulations in Tatarstan, additional forecasting techniques that account for waterflood performance, stage of reservoir development, and the extent of reserves’ depletion were analyzed. Eight forecasting techniques were used for each carbonate reservoir to estimate reserves. Reliability limits for the calculated data have been determined. Based on the specified criteria, the accuracy of the calculation results was checked, and the appropriate forecasting methods were selected. It was found that certain methods can only give reliable results on condition of steady watercut increase in the pre-forecast period. Furthermore, the accuracy of certain forecasting methods depends on the stage of development and the extent of reserves’ depletion. It was concluded that applicability of certain analytical methods is limited by reservoir geology, current development status, and waterflood performance. The most appropriate methods for Tatarstan carbonate reservoirs performance analysis have been identified, as well as the screening and applicability criteria. These methods provide an accurate and prompt analysis of the field development process and reservoir management decisions, so the operator makes no delay in taking necessary steps to improve reservoir performance.
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