Late Tula delta geology and hydrocarbons occurrences in the Upper Kama depression and adjacent area

UDK: 551.263
DOI: 10.24887/0028-2448-2019-12-86-90
Key words: facies, delta, channel, well, hydrocarbons accumulation, wireline logs, siliciclastic sediments of Tula formation
Authors: J.U. Komilov (RN-BashNIPIneft LLC, RF, Ufa), R.I. Maleev (RN-BashNIPIneft LLC, RF, Ufa), R.Kh. Masagutov (Academy of Sciences of the Republic of Bashkortostan, RF, Ufa), V.E. Tomilin (RN-BashNIPIneft LLC, RF, Ufa)

Since the late 70-ies of the last century, after the first oil discoveries in the shoestring sandstones of the Lower Carboniferous in the north-west of Bashkortostan (Upper Kama Depression and adjacent tectonic zones) additional G&G data have been acquired including 3,0 thousand new wells and extensive areas of 2D and 3D seismic. New findings were used to identify two separate units within the Tula formation. It is also provided significant insight into the lithology, facies and depositional environment of the paleochannels, delta sand bars, prodelta and siliciclastic sediments of the Late Tula. Their tectonic evolution, revealed finer details of the morphology and size of the known sand bodies, their reservoir properties and helped to track the sand play fairway used to locate new exploration targets. The deposition of sands was interpreted as controlled by two capes varying in size within a vast delta plain separated by a shallow-water sea bay with near N-S trend. Size analysis for the shoestring sands and well log data showed that the grains are well-sorted, the coarse fraction is absent and the medium and small-grained fraction is present in small quantities. The average values of porosity and permeability in the delta bar and paleochannel reservoirs are quite high and in the same range however they are much higher than in the flood-plain deposits. Hydrocarbons in delta bars and shoestring sands occur in the domes and anticline flanks, whereas the area of the pool largely depends on the length of the anticline bend at the intersection of the paleochannel and the uplifted structure plan. The research results were used to predict new exploration opportunities in the study area with high hydrocarbons potential and chances of new big discoveries.


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