Experience in Geological Modeling of Complex Oil Deposits

The paper presents the results of detailed geological modeling (GM) of complexly constructed reservoirs based on the examples of three deposits of Western Siberia located in different oil and gas bearing areas (OBAs) and having specific geological features. The deposits of the field name by V. Vinogradov are located in the Krasnoleninskoye OBA, oil reserves concentrated in resevoirs of the Neocomian, middle and lower Jurassic, pre-Jurassic basement. The complexity of the structure of productive complexes is characterized by different facies conditions of genesis, thin-layered structure, low FCP, inconsistency of sections, multilevel system of disjunctive dislocations, lithological limitations of deposits. Geological modeling and assessment of oil reserves were carried out taking into account the revision of petrophysical studies and on the basis of the modern interpretation of the materials of the wide-azimuth seismic acquisition of CDP-3D (kinematic linkage with previous profile works; acoustic, synchronous and azimuth AVA inversions, attribute analysis with the aim of forecasting disjunctives and reservoir properties). The final representation of the GM of oil field is expressed by an interconnected structural framework at all levels of the productive section, lithological facies maps of reservoirs, distributions of effective thicknesses over the area of the field, geometrization of all identified deposits. At the Imilor field, located in the northern part of the Sredneobskoye OBA, most of the productive objects contain so-called hard-to-recover reserves, in particular, the layers of the Achimov formation. The complexity of geomodelling of deposits in these strata is associated with the determination of the boundaries of the spread of the anomalous structure of the Bazhenov suite, the mapping of tectonic disturbances, and textural irregularities. Layers can have a continuous and “spotted” oil saturation even at significant reservoir heights corresponding to the ultimate saturation zone. After the hydraulic fracturing, these layers give back water-cut products from the very beginning of development. For the purpose of constructing hydrodynamic models, detailed lithological models were fulfilled in which the distribution of three lithotypes over the reservoir volume was taken into account: “sandstone” (collector), “siltstone” (conditional noncollector), “clay” (non-selector). This version of the lithology cube proved to be the most acceptable from the standpoint of the current dynamics of the wells in comparison with the traditional representation of the GM (collector, non-collector). The petroleum potential of the Pyakyakhinskoye oil and gas field (located in the Pur-Tazovskoye OBA) is stratigraphically linked to reservoirs in the section from the Aptian to the Berrias-Valanzhin deposits. An example of the PK18 layer (the Pokur suite) demonstrates a significant change in the GM of the oil and gas reservoir as a result of processing and interpretation of 3D seismic (lithofacies, geometrization of reservoir parameters and deposit type).

В настоящее время практически все компании в Западной Сибири вовлекают в разработку залежи нефти и газа с весьма сложным геологическим строением, которые характеризуются наличием тектонических нарушений, литологической неоднородностью продуктивных резервуаров вплоть до отсутствия коллекторов, тонкослоистым разрезом, низкими фильтрационно-емкостными свойствами и т.п. В этой связи возрастает значимость детального геологического моделирования с использованием современных подходов обоснования всех геолого-геофизических параметров, внутренней структуры и геометризации залежей нефти и газа.