The time has come for a large-scale study and development of hydrocarbon pools in geologically complex formations in the Northern part of the West-Siberian oil and gas basin. These include continental formations of the Aptian age, Achimov fondothem deposits of the Neocomian clinoform sequences, and subaerial sedimentary bodies of the Middle Jurassic sequence.
The considered group of pay features and prospects involves channel sedimentation forms: paleochannels, avandelta channels, incisions, canyons, paleoravines. Even with the sparse network of prospecting and exploration wells on the Yamal Peninsula, in the Nadym-Pur and Pur-Taz petroleum-bearing regions, some of them open various channel forms. Contrary to general belief, they turned out to be filled with impenetrable predominantly clay rocks.
There are many indirect signs of their development on top of the direct evidence of opened clay (impenetrable) channels. There are instances of the irregular distribution of formation fluid in the structural geometry of formations, while neither faults nor subregional zones of clay formation are predicted by geological or geophysical data. Besides, the seismic data reveals paleochannels, underwater channels, or quite wide avandelta valleys crossing the formation development zone or cutting off its sectors.
The depth of the stratigraphic incisions of ancient riverbeds reaches 10–20 m, and for the canyons of the avandelta channels, it is 150 m: sufficient to interrupt average-thickness formations. The deep erosion of formations with imposed wide impenetrable barriers forms solid lithological and stratigraphic screens, which for some reason are missing in geological and evaluation models of pools. Instead, research often uses unjustified tectonic faults absent in the seismic data.
Meanwhile, many paleochannels and other channel forms are confidently mapped by modern 3D seismic surveys using the common depth point method, especially in the Aptian-Albian-Cenomanian sequence. In deep sequences (Neocom, Middle Jurassic), the proportion of confidently delineated channels is smaller, though almost all such features can be mapped with some accuracy using advanced attribute analysis. More widespread use of lithological and stratigraphic screens is needed to increase the geological accuracy of pay feature and prospect models.
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