Sugmut Field: A Forced Regression Deposit within the Neocomia Prograding Ciinoform Complex, West Siberian Basin, Russia
John M. Armentrout and Oleg. M. Mkrtchyan
The Volgian-Neocomian interval of the Middle Ob Region of the intracratonic West Siberian Basin consists of between 35 and 45 regional transgressive/regressive cycles infilling a basin which had an average water depth of approximately 200 meters. Within local clinoforms, wells have encountered elongate shelf-edge sandstone bodies ranging from 15 to 100 kilometers in strike-oriented length. in most areas the seismic interval correlative to the reservoir sandstone pinches-out against the foreset of the preceding clinoform. This geometric relationship, and the sharp-based log pattern of sandstones along the more landward margin of the sandstone body, suggests that the sandstone may have been deposited as a consequence marked downward shift in baselevei as part of a Iowstand rograding complex, or possibly as a late highstand forced regression deposit.
The Sugmut field, located in the northeast part of the study area, is 12 km wide east-west and 75 km long north-south, and grades laterally into shale to the west, south and east. Relative to the regressive phase isopach, the transgressive phase isopach thick shifts slightly northward and eastward indicating the direction of littorai drift and marginward transgression. ln the northern part of the field the shelf-edge sandstone interval may correlate with a thin depositional-dip oriented shelf sandstone mapped within the transgressive interval. This mapped pattern may be interpreted as lowstand incision of a fluvial system supplying sand to a shelf-edge delta followed by infilIing of the fluvial valley during transgression. Subsequent down-to-the- north regional tilt resulted in struct ral closure forming the Sugmut field trap.
AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California