Vladimir V. Shimansky¹, Michail D. Belonin¹, Valentin K. Shimansky²
(1) VNIGRI, St. Petersburg, Russia
(2) VNIGRI, St. Petersburg

Abstract: Models of Stratigraphically Trapped Reservoir Formation (Western Siberia and Timan Pechora Basins, Russia)

Models for forming secondary porosity due to syngenetic and epigenetic destruction of organic matter are constrained by paleoreconstructions of depositional setting and epigenetic changes in non-anticline and deep-seated objectives. Examples include Cretaceous deep-water sand reservoirs within the regressive clinoforms of Wester Siberia basin, and Lower Paleozoic carbonate deposits of Timan-Pechora basin.

The Neocomian sandstone reservoirs in the western Siberia basins occur mainly in turbidity fan related to progradational clinoforms. The most prospective reservoirs were deposited by grain flows during regression and subsequently reworked by along-slope bottom currents. These reservoirs form stratigraphic traps due to updip pinchout within the clinoforms. Based on this model, 26 most favorable areas were mapped out by geophysical data for detailed exploration. First-pass ranking for exploration potential is based on those factors controlling a reservoir capacity greater than 8 % porosity, similar to that found in the very deep (? 5000 m) Kolvinskay and Tyumenskaya wells. Epigenesis of underlying and interbedded organic-rich facies provides fluids that may locally enhance reservoir capacity.

The reservoir potential for the Paleozoic carbonates is strongly related to syngenetic and epigenetic destruction of organic matter. The generation of secondary porosity (up to 15 %) can be attributed to dissolution of carbonate minerals as a result of progressive maturation of organic matter. Reservoirs of such origin, with secondary porosity about 10%, were identified in the Silurian carbonate deposits of the Varandei-Adzvinskaya, Kolvinskaya, and Khoreiverskay zones, in the Timan-Pechora basin. Based on this model, zones with the most potential for development of secondary porosity have been forecasted and the maps of these secondary reservoirs for Lower Paleozoic deposits have been constructed for Timan-Pechora basin.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana