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Yurubcheno-Takhomskaya oil and gas accumulation zone (YTZ) located in the western part of the Siberian platform is known as a really challenging exploration object. The main reservoirs are located in Riphean carbonates made up of single p.u. porosity dolomites. Prospective drilling of the territory demonstrated high heterogeneity of this formation. Prospective wells drilled to this formation tests results vary from 0 to more than 600 m3 oil per day. The article describes efforts made on a new exploration approach elaboration based on an integral analysis of the structural, seismic and borehole data. First of all, this is seismic profiling on the regular orthogonal grid with the employment of modern seismic techniques and technologies, and also the study of the distribution of fractures in-situ (directly in the location of the deposition) with the integrated use of equipment and technology of formation micro-scanners and dipole sonic tools. This new approach consists on high-potential zone localization controlled by the disintegrated levee-like stromatolithic constructions, which are more exposed to fractured formation due to high silification in the southern and northern slopes of the Madrinskiy and Irkineevo-Katangskiy rifts respectively. Besides, highly productive may turn out to be the highly fractured streaks and sections, controlled by the regional and zonal fault zones. Such localization of the highly productive sections within the huge oil-and-gas-bearing territory allows hoping for the realization of the opportunity of the recovery of reserves of the entire region by limited number of high flowrate wells with the natural recovery drive. Introduction Yurubcheno-Takhomskaya oil and gas accumulation zone (YTZ), located in the western part of the Siberian platform (Fig.1), was identified in 1973 while drilling the Kuyumbinskaya parametric well (K-1), which discovered the accumulation of gas with daily flowrate of 200 thousand cubic meters under the clastic Vendian sediments in the carbonate depositions of the Riphean. The following exploration effort identified the extensive oil and gas accumulation zone with the total square of 20 000 km2, main reserves of which are associated with the Riphean depositions (from 0,8 to 1,1 billion years of age) and partially with the Vendian depositions (approximately 0.6 billion years old). The discovery of oil and gas presence in the rocks of such age in this region of the Siberian platform was a big surprise, since there were no preconditions for the formation of the HC deposits both in ancient times at that moment of time based upon the concepts of 1970es. As a result of the exploration effort taken in 1980-es the structural model of the pre-Vendian units of the YTZ was developed. It was deemed that the basis of the YTZ is constituted of main massive deposit, associated with a gigantic natural reservoir in the Riphean multiple-aged mostly dolomitic vugular-fractured reservoirs, covered by Vendian-Lower Paleozoic cap, saliferous in the Cambrian interval. The discovery of the accumulations of HC in the deep Riphean horizons and nonanticlinal deposits in the terrigenous deposits of the Vendian in the southern boundary of the zone was predicted. Nonetheless, technical capabilities of exploration at that time did not give the opportunity to meet the challenge of prospecting and exploration of that extremely geologically complicated block of resources, called since then the YTZ. This referred both to the capabilities of seismics, which could not differentiate some fine features of the geological cross-section under several trappean and saliferous caps in high-velocity cross-section, and to the borehole surveys of the high-resistivity carbonate mass of mostly fractured reservoirs of the Riphean age.

TX 75083-3836 U.S.A., fax 01-972-952-9435. AbstractThe Maloichskoe field is located in the southeastern part of the West Siberian basin in Novosibirsk oblast (Fig. 1). It was the first field in the basin where commercial oil was produced from the Paleozoic basement. The reservoir consists mostly of limestones and dolomites that are intensively fractured and contain numerous vugs in some zones. The reservoir properties of the matrix are generally negligible, and the production potential of wells is mostly associated with natural fractures and vugs.The presented study was our first project in Russia where a complete integrated approach was implemented to properly characterize a fractured reservoir. The approach included the following tasks: 1) Identification of fractured intervals in wells using a special technique of BKZ logs processing, 2) Spectral imaging and high-resolution inversion of the seismic data, 3) structural analysis of the field, 4) construction of the reservoir properties model, 5) construction of the fracture distribution model using the Continuous Fracture Modeling approach (CFM).The final geologic model served as a basis to select the locations for the new wells. The new locations were proposed in the zones with the most intensive development of a network of natural fractures (according to the model). The drilling was associated with significant losses of drilling mud that was an indirect indication of presence of significantly fractured zones. The wellbore image FMS that was recorded in the well, showed a good level of correspondence between the model forecast and the actual result. The well contains interval of numerous fractures and large vugs. Eventually, the well showed a good production results and currently is one of the best producers in the field.As such, we recommend application of the described integrated approach for modeling complex fractured reservoirs in the other fields of Russian Federation.

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