The article is devoted to studying the issues of segregation and relaxation of reserves and taking into account these effects when forming a program of development optimization of the production target BS10 of the Mamontovskoye field, which is at a late stage of development. The results of the analysis of actual drilling data from wells and sidetracks, sampling and testing of core material, studies of transit wells using carbon-oxygen logging with the subsequent implementation of measures to transfer them into production at the production target BS10 confirm the theoretical ideas about the effects under consideration occurring in the formation. The processes of relaxation of reserves in the reservoirs of the production target BS10 lead to the localization of oil pillars in the top part of the reservoir, which is additionally confirmed by the results of hydrodynamic modeling. Taking these effects into account is crucial when planning the most efficient drilling activities. For offshore objects in Western Siberia, which are at a late stage of development, where fresh water was injected to maintain reservoir pressure, one of the effective methods for determining the current saturation of the formation in conditions of low salinity of formation waters is carbon-oxygen logging. The results of research and commissioning of wells indicate a connection between the residual oil-saturated thicknesses and their starting parameters. Logging shows a high differentiation of the current oil saturation along the section with the accumulation of hydrocarbons near the top of the formation. Based on the results of core studies, a vertical differentiation of the fluid saturation value in the formation can be traced. Oil shows are contrastingly illuminated in the ultraviolet glow in the upper part of the section, while lower down the section the glow is less pronounced, which indicates the depletion of the initial recoverable reserves in the lower part of the formation. The glow data correlates well with the interpretation results of geophysical studies. The positive experience gained while drilling horizontal wells in a separate section of the production target BS10 served as a decisive factor for starting to scale up infill drilling to the production target as a whole. The results of the work are applicable to a number of production targets which are at a late stage of development and are characterized by similar filtration and capacitance properties in order to increase the efficiency of production of current reserves.
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