Silurian-Lower Devonian Carbonates of the Timan-Pechora Basin, Northeastern European Russia: Field-Based Studies of Reservoir Properties

Simon J. Tull, Robert A. Scott

Silurian-Lower Devonian Carbonates are an important play in the Timan-Pechora Basin, particularly in the Khoreyverskaya region in the north of the basin. Reservoirs consist mainly of vuggy dolomites which are developed beneath a basinwide pre-late Middle Devonian unconformity. Late Givetian-early Frasnian (Kynovskiy-Sargayevskiy) mudrocks overlying the unconformity form the regional top seal. Traps are associated with the updip termination of reservoir units beneath the unconformity.

An analogue for this play has been studied on the River Shar'yu, which drains the Chernyshev Ridge, a pop-up structure at the front of the Urals fold-and-thrust belt. This structure comprises the southern boundary of the Khoreyverskaya region. On the River Shar'yu, Upper Silurian (Pridoli Series, Grebenskoy regional stage) vuggy dolomites occur approximately 20 m below the unconformity surface. Intense leaching has resulted in the formation of a well connected system of vugs, which give the dolomites a distinctive rubbly appearance over a stratigraphic interval of 15-20 m. The vugs are typically 10-20 mm in diameter, and are lined with carbonate crystals and solid bitumen. in some cases the vugs are completely occluded by solid bitumen, or by authigenic clay minerals. Moldic and intra article porosity is also present within coral and other skeletal remains, but is less common.

It will be shown that the Shar'yu locality offers an excellent opportunity to study reservoir development and hydrocarbon habitat of the Silurian play, not least because of the very limited exposure of Silurian rocks elsewhere in the north of the Timan-Pechora Basin.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995