Sequence Stratifigraphic Analysis of Stratigraphic Oil Traps in the West Siberian Neocomian

Oleg M. Mkrtchyan and John M. Armentrout

Large depositional oil traps (Priob, Sugmut, etc.) have been discovered in the West Siberian Neocomian. Sequence stratigraphic analysis of well logs and seismic reflection profiles demonstrate that reservoirs of these fields represent sands deposited during lowstand, transgressive and highstand phases of relative sea level cycles. Transgressions and regressior advanced in regional longitudinal and local latitudinal directions. The regional longitudinal pattern is dominated by westward prograding clinoforms formed as the sediment supply exceeded the accommodation space. Lock northward and northwestward prograding complexes appear to be controlle by local basin-floor topography. In each systems tract, the coastal zones were landward from the shelf-breaks resulting in domina ce of marine facies each depositional shelf-edge.

Lowstand systems tracts are represented on the upper slope by prograding wedges with thin shelfal equivalents or correlative unconformities Sands deposited in these lowstand regressive facies comprise the main reservoir at Sugmut and a subordinate reservoir at Priob. Transgressive systems tracts are dominantly shale but in the Priob field one early transgressive parasequence sand contains an oil accumulation where immediately overlies a highstand shelf sand. Highstand systems tracts are represented by regional sheets over the shelf and by thick progradational complexes over the upper slope. Most of the sands occur within the late highstand parasequences and are difficult to correlate due to channel incision. Most Priob field reserves occur in the late highstand parasequences.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California