The article discusses the source of water cut for wells of the Bazhenov formation with hydraulic fracturing in case of RN-Yuganskneftegas oil fields. The current assumptions about the sources of water supply for wells of the Bazhenov formation are considered, including the influence of fracture fluids, fracture invasion in upstream and downstream development facilities intervals, filtration of self reservoir water. Cases of leakage of the column are excluded due to the exclusively technical nature. Data of the testing Bazhenov formation wells before and after the active introduction of hydraulic fracturing are presented. Conclusions are drawn regarding the distribution of the water content of well tests; the intervals of the most common water cut values are highlighted. Examples of water cut in wells with a long production period, where the volume of extracted water exceeded the volume of injected fracture fluid, are shown. The nature of the distribution of bound water in the rocks of the Bazhenov formation is described. The estimation of the water saturation by core studies and nuclear magnetic logging (NMR) represented. The probability of fracturing of nearby productive objects with fractures is considered from the point of view of geology, geomechanical models and typical injection plans. The process of analyzing the NMR data in the process of creating a scale model, which led to the allocation of low-porous intervals in the Under-Achimov clays above the Bazhenov formation, is presented. A hypothesis has been formulated that combines the analysis of existing ideas about the source of water cut and the results of the allocation of low-porous intervals in the Podachimov clays. To confirm the results, a program of field tests of wells has been formed, including testing of intervals of Under-Achimov clays and laboratory studies of surface samples of liquids from various objects. Already implemented tests have shown the water saturation of the intervals of the Under-Achimov clays, as well as high values of reservoir pressures that allow wells to operate in the gushing mode, which currently confirms the formulated hypothesis.
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