LITHOFACIES PECULIARITIES OF OIL AND GAS-CONTAINING COMPLEXES OF THE PURSK REGION OF WESTERN SIBERIA

Abstract

In the article, regional and local conditions of sediment accumulation in the Pursky region of Western Siberia are considered. It is shown that during the Jurassic-Cretaceous time, the sedimentation facies conditions were repeatedly changed due to the multiscale transgressive-regressive cycles of the basin development. The Jurassic transgressive macrocycle of sedimentation led to the platform cover formation on most of the ter- ritory and a gradual change of the continental sedimentation regime (tyumen suite), shallow-marine and marine (vasyugan / abalak suites) and further deep-sea (bazhenov suite) regimes. At the beginning of the neocom there is regression and reorganization of the basin, the formation of a prograde wedge-shaped complex of sediments with lateral build-up bodies and synchronous gravitational-landslide cones of removal. During the sea basin regression, a typical facial profile was formed, which was represented in the east near the drift sources by continental, further to the west by coastal-marine, shallow-marine and relatively deep-water facies. Oil and gas bearing sand deposits are characterized by a polyfacial structure and refer to natural reservoirs of non-structural type, formed in alluvial, deltaic, coastal-marine and relatively deep-water environments. To identify such reservoirs and assess their quality, the use of lithofacies studies aimed at restoring sedimentary environments is recommended. This is necessary primarily for the effective search of hydrocarbons, forecasting of oil and gas complexes, assessment of spatial changes in their quality, which largely determines the direction and strategy of exploration and production operations. Facial studies are important not only for the search of non-structural deposits, but also for the creation of realistic three-dimensional geological models. Such models with facies properties allow more reasonably assess the lithological complexity of the field, more reliably predict the petrophysical properties distribution, provide a selection of influence technological tools on the reservoir.