Principles of mapping lithofacial and petrophysical variability of post-sedimentary dolomites with a porous type of void space

UDK: 553.98, 552.543
DOI: 10.24887/0028-2448-2019-1-16-19
Key words: R. Trebs and A. Titov fields, carbonate sediment, Upper Silurian, facies types of deposits, petrophysical heterogeneity, well flow rates
Authors: A.S. Dushin (RN-BashNIPIneft LLC, RF, Ufa), G.F. Gaymaletdinova (RN-BashNIPIneft LLC, RF, Ufa), R.I. Risaev (RN-BashNIPIneft LLC, RF, Ufa), M.V. Rykus (Ufa State Petroleum Technological University, RF, Ufa), R.H. Masagutov (Academy of Sience of the Republic of Bashkortostan, RF, Ufa)

The article is about the influence of lithofacies heterogeneity on the reservoir properties of the Upper Silurian carbonate sediment of R. Trebs and A. Titov fields and mapping methods for this heterogeneity. The work identified the factors that have had the greatest influence on the structure of the void space. The carbonate rocks are dolomites of Silurian Age, originally formed under the conditions of mobile shoal water of the ancient carbonate epicontinental platform that during epigenesis partly lost their primary properties. The void space of such reservoirs is modified due to the influence of post sedimentation processes (mineralization, desalination, dolomitization, and others). However, some connections between reservoir properties and facies conditions can be traced because post sedimentation processes acting selectively as facies zonality has not disrupted the structure of the void space, only emphasized its heterogeneity. The predominance of porosity types is intergranular, intercrystalline, small-cavernous that relate to the porous type reservoir gives opportunity for confident extrapolating the heterogeneity data obtained from laboratory studies for all pay zones.

According to core data, the change of reservoir properties is defined. The change was reconstructed according to logging data with well stock information. All this made it possible to map the variability of the void space for the reservoir pay zone. The obtained results are confirmed by the field performance as comparison of initial and relative well flow rates, as well as by their time gradient taking into account the selected thickness of the most permeable rocks.

The considered tools of geological and petrophysical mapping can be used with low reservoir thickness, high variability and seismic data do not allow make quantitative forecast in such complex reservoirs either.


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