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 single trace analogue seismic data acquired in 1967 and 1968.
The first prospect well (S-370) in this area was drilled in 1971 at 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 tvdss). They consist of phyllitized silty sandstone and phyllite. No hydrocarbons were identified in the well.
The second well (S-371) was drilled on the north-eastern flank of the Sibkrayevskaya structure and encountered no hydrocarbons.
The Sibkrayevskaya structure was further delineated by modern CDP 2D seismic data 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 the S-370 well. 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 the S-372 well parallel to the S-370 well to test the potential «missed pay» interval. Based on the log and core data S-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 was of good quality with an API gravity of 37 degrees, which is consistent with other fields in the Licence area. The S-372 well was drilled in a flank position on the structure and the structural map showed an area of over 50 square kilometres up dip from the oil-down-to level defined in the well. Sibkrayevskaya was a very large structure which required additional seismic and well delineation. The discovery also extended the area of known oil to the northeast corner of the licence area and significantly improved the prospectivity of other structures in the area.
As of April 2013 Ryder Scott attribute 53.03 million barrels of 2P reserves to Sibkrayevskoye and it was likely that the ultimate recoverable reserves in the field could be significantly larger than this. The next steps were to drill an additional delineation well (S-373) and to acquire additional modern high resolution CDP 2D seismic data over the field.
The S-373 appraisal well was successfully drilled and tested from February to May 2015. Log and core data over the primary J1 sandstone reservoir interval confirmed 11.5 m of net oil pay. A cased-hole drill stem test of the interval -2,329 to -2,346 m tvdss flowed at a stabilised rate of 100 bopd on a 4 mm choke (unstimulated natural flow). Well tests on the S-373 well in winter 2015/16 confirmed good oil flow rates of over 200 bopd using an Electrical Submersible Pump as predicted. The reservoir interval is completely saturated with oil to its base and is located about 19 m structurally higher than the equivalent oil saturated interval in the S-372 well, which is also oil saturated throughout. Horizontal wells in the planned development scheme will have significantly higher production rates.
Prior to the S-373 well Ryder Scott estimated the 2P reserves at over 50 million bbls, making this the largest oil field discovered on License Block 61 to-date. Additional seismic data was also acquired over the structure in the 2014/2015 winter season as part of a 1,000 km CDP 2D seismic acquisition programme in the northern part of Licence 61. At the end of 2015 LLC “Sibneftegeofizika” completed their seismic and well data processing and interpretation studies at the Sibkrayevskoye oil field and prepared the “Resource Passport” for the field. This comprehensive document will serve as the basis for the Russian State (GKZ) Reserve Registration as well as the Company’s 2P reserves. Their estimation for C3 Resources Original Oil-in-Place (OOIP) is 361.84 million bbls. Assuming a 30% recovery factor this equates to about 109 million bbls recoverable.
The next step in field development will be to convert the C3 Resources into C1+C2 Reserves and have them approved and registered by GKZ. The 2P and 3P reserves will also be recalculated.
Based on the new seismic data the Sibkrayevskoye structure extends to the southeast and is much larger than previously mapped. However much of this area is located over 10 km from existing well control and PetroNeft plans to drill the S-374 delineation well in this portion of the field in 2016. The drilling pad has already been constructed and we are in the process of moving the drilling rig to location. The S-374 location is shown in the attachments. As currently mapped the top of the main reservoir interval is at -2,315 m tvdss. This is about 8 metres high to the S-373 well and 50 m above the oil water contact (owc) as defined by the S-370 and S-372 wells.
Assuming a positive result from the S-374 well, the Sibkrayevskoye Oil Field could be in the 100 million bbl range which would qualify as one of the largest oil fields discovered in the Tomsk Region in the last 25 years.
It will be the key development asset for Licence 61 for many years to come.
Updated March 2016