Sibkrayevskoye Oil Field
The Sibkrayevskoye oil field is located in the north-eastern part of Lease No. 61. It is tectonically confined to the western slope of the Pyl-Karaminskiy megaswell. The structure was identified by seismic data acquired in 1967 and 1968.
The first prospect well (Well No. 370) in this area was drilled in 1971 in the crest of the structure. This well reached a depth of 2,904 m. It was cored at a number of horizons in the deposits of Kulomzinskaya, Maryanovskaya, Bazhenovskaya, Vasyuganskaya, and Tyumenskaya series, and in Paleozoic deposits. Basement deposits were encountered at a depth of 2,865 m (-2760 m TVD SS). They consist of phyllitized silty sandstone and phyllite. No hydrocarbons were identified in the well.
The second well (Well No. 371) was drilled on the north-eastern flank of the Sibkrayevskaya structure and encountered no hydrocarbons.
The Sibkrayevskaya structure was further delineated by seismic survey acquired in the 1990’s. PetroNeft reprocessed and reinterpreted all of the vintage seismic data in the area in 2005 and acquired some new high resolution CDP 2D data over the feature during the winter of 2005/2006.
In 2008, PetroNeft contracted Tomsk Geophysical Company to do a comprehensive reinterpretation of all of the well log and drilling data associated with well 370. As a result of this study an 8.4 m zone of potential «missed pay» was identified in the Upper Jurassic J1 reservoir interval.
In July and August 2011, PetroNeft drilled well 372 parallel to well 370 to test the potential «missed pay» interval. Based on initial log and core data well 372 encountered a 12.6 m zone of net oil pay in the J1 interval. An open hole test of this interval tested at a pro-rated inflow of 170 bopd unstimulated. The oil is of good quality with an API gravity of 37 degrees, which is consistent with other fields in the Licence area.
Sibkrayevskaya is a very large structure which will require additional seismic and well delineation. The 372 well was drilled in a flank position on the structure and current mapping shows an area of over 50 square kilometres up dip from the oil-down-to level defined in the well. Current indications are that the ultimate recoverable reserves in the field could be significantly larger than the 44 million barrel pre-drill target defined by Ryder Scott for the prospect. The discovery also extends the area of known oil to the northeast corner of the licence area and improves the prospectivity of other structures in this area.
