Currently underway is commercial production of extra-viscous oil in the fields of the Republic of Tatarstan using steam-assisted gravity drainage (SAGD) technique. A large amount of updated field data obtained during appraisal drilling as a preparatory stage for extra-viscous oil production operations, systematization of geophysical and geological data with rock typing, paleogeographic reconstructions and modeling enabled identification of the zones exhibiting oil saturation heterogeneity and complex geological structure. A significant factor interfering with the production of extra viscous oil is the presence of shaled-out interlayers associated with lack of reservoir continuity, when a sharp change of facies types from predominantly sandstone to interbedding clays, siltstones and sands is observed in shallow marine shelf conditions on bar slopes and barrier islands. Prior to operation of horizontal wells drilled in such zones a number of issues shall be tackled. Firstly, it is necessary to select optimal compositions depending on rock mineralogy, calculate the required injection volume and concentration of chemical agents, which will also depend on rock characteristics (the clay and carbonate component), such that the injection volume be large enough to provide the desired benefits, on the one hand, and not too large to favor the formation of direct flow channels between parallel horizonal (injection and production) wells which will further lead to steam breakthrough. Negative effects on tubing string and perforation interval shall be minimized through selection of optimal composition and treatment strategy. To date, combined efforts of specialists from research and production departments of Tatneft Company resulted in development of the technology that mitigates detrimental effects of the above-mentioned factors during the development of extra-viscous oil reservoirs using SAGD technique.
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