ALGORITHM FOR DETERMINING SIGNS OF FRACTURE ACTIVATION IN INJECTION WELLS PRODUCING CARBONATE RESERVOIRS

Flooding in carbonate reservoir production is complicated by two most common issues related to natural fracturing activation and technogenic fracturing formation in these deposits: premature encroachment of the production well stock due to the breakthrough of injection water from injection wells and formation pressure drop due to a low injection efficiency factor. Depending on the geological structure of a section and related contrast in its geomechanical properties, these issues are manifested in different extents. For instance, calculations made by the authors demonstrated that the average injection efficiency factor is 50 % for Tournaisian deposits, and 65 % for Kashirskian-Podolskian deposits, which agrees with their geological characteristics.The most reliable existing method to identify the active fracturing signs in injection wells is the inflow performance relationship curve. Currently, only a few percent of the injection well stock in the deposits of the Republic of Bashkortostan have been covered by this method. The proposed algorithm for identifying active fracturing signs is universal and consists in complexing methods (Hall plot and pressure drawdown curve) which are less reliable as compared to the indicator diagram. But most importantly, studies using this method cover practically the entire injection well stock. A total of 93 % of the operating injection wells using carbonate reservoirs of Kashirskian-Podolskian and Tournaisian deposits of the Republic of Bashkortostan have been analyzed using this algorithm. The results of the analysis showed that active fracturing signs simultaneously identified using Hall plots and pressure drawdown curves are present in 9,5 % of the analyzed injection wells. At the same time, oil production increase in the adjacent production wells has been observed for 35 % wells since the occurrence of these signs. For 65 % wells, where oil production in the adjacent production wells has dropped since the occurrence of active fracturing signs, measures for injection well operation control have been suggested and implemented. The estimated additional oil production resulting from these measures is 62.2 thousand tons, and the average specific daily gain is 1,7 tons/day.