The article discusses the sedimentation conditions of terrigenous sediments of the Tyumen suite in the west of the Ob region. It is shown that the ЮС2 reservoir rocks layer was formed in the setting of a wave delta, which occupied the coastal part of the extensive coastal plain in the Bathonian. The geological section of sedimentary rocks is represented by two typical elements of the delta: 1) a front that includes mouth bars processed by waves into a beach and bar complex with distributary delta channels embedded in it, and 2) a delta plain with distributary channels and crevasse splay sands.
The main reservoir is represented by the bar facies of the proximal and distal zones with the cyclical sequences and a regressive particle size profiles. The most high-quality reservoir rocks are concentrated in the proximal zone with increased sandiness and coarser granulometric composition. Sandstones form well-connected continuous bodies with different-scale layering of wave ripples, along the direction of which the flow profiles of production wells are oriented. In the distal zone of the bar deposits, the grain size, sorting and thickness of the sandy layers decrease, and the length and thickness of the layers of clayey siltstones increase, which impairs the reservoir properties and violates the cohesion of sandy bodies.
The highest injectivity of injection wells is characteristic of sandstones of the proximal zone of mouth bars and sandy deposits of the flow facies of the distributary delta channels, which have a high permeability. In low-permeable and low-pore reservoirs of distal zone of the mouth bars, the average injectivity of wells decreases more than twice. Macrofacial heterogeneity, which determines the filtration structure of the reservoir and its hydrodynamics, should be taken into account when designing the system for the location of injection and production wells, estimating residual hydrocarbon reserves and choosing geological and technological measures for their extraction.
References
1. Rykus M.V., The influence of secondary transformations on terrigenous reservoirs quality (In Russ.), Geologiya, geofizika i razrabotka neftyanykh i gazovykh mestorozhdeniy, 2018, no. 12, pp. 40–45.
2. Rykus M.V., Rykus N.G., Sedimentologiya terrigennykh rezervuarov uglevodorodov (Sedimentology of terrigenous hydrocarbons reservoirs), Ufa: Mir pechati Publ., 2014, 324 p.
3. Kontorovich A.E., Kontorovich V.A., Ryzhkova S.V. et al., Jurassic paleogeography of the West Siberian sedimentary basin (In Russ.), Geologiya I geofizika = Russian Geology and Geophysics, 2013, V. 54, no. 8, pp. 972–1012.
4. Zakharov V.A., Shurygin B.N., Levchuk M.A. et al., Eustatic signals in the Jurassic and lower cretaceous (neocomian) deposits of the West-Siberian sedimentary basin (In Russ.), Geologiya I geofizika = Russian Geology and Geophysics, 1998, V. 39, no. 11, pp. 1492–1504.
5. Rykus M.V., Lithofacies peculiarities of oil and gas-containing complexes of the Pursk region of Western Siberia (In Russ.), Neftegazovoe delo, 2019, V. 17, no. 2, pp. 14–26.
6. Chzhan Ts., Rykus M.V., About the influence of geological heterogeneity of mouth bar on the hydrodynamics of the reservoir rock of Red Forest field (China) (In Russ.), Neftegazovoe delo, 2015, no. 1, pp. 33–46.
7. Belozerov V.B., Ivanov I.A., Rezyapov G.I., Upper Jurassic deltas of West Siberia (In Russ.), Geologiya I geofizika = Russian Geology and Geophysics, 2001, V. 42, no. 11–12, pp. 1888–1896.
