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 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.
Based on the new seismic data the Sibkrayevskoye structure extended to the southeast and is much larger than previously mapped. However much of this area was located over 10 km from existing well control. In order to capture the upside reserve case of 100 million bbls of oil the Joint Venture decided to to drill the S-374 delineation well in this portion of the field in 2016. The S-374 well was drilled to a total depth of 2,640 m MD. Two tight sandstone reservoirs with total net pay of 3.6 m were identified in the J1-2 interval based on the wireline logging. A cased-hole DST was conducted over the two intervals and the fluid inflow was minimal with about 6.3 bbls per day of mineralised water with no indications of hydrocarbons. Therefore the well was plugged and abandoned.
Following the result of the S-374 well, even though reserves in the Pad 1 area are defined by 4 prior wells, it was decided to further de-risk the Sibkrayevskoye development before comitting to substantial CAPEX on the pipeline to the Lineynoye CPF and field infrastructure and to drill an additional delineation well (S-375) in the Pad 2 area before sanctioning the project. In addition to the new data from the S-375 delineation well it gives us time to produce the S-373 well for another year on test production. This test production will stop in April when we lose the winter roads and ability to truck oil to the Lineynoye CPF.
While S-374 removed some of the upside from the Sibkrayevskoye oil field, the current 2P reserves are still over 50 million bbls which are defined by 4 wells in the northern part of the field. Sibkrayevskoye is one of the largest oil fields discovered in the Tomsk Region in the last 25 years. It is a very significant field with robust economics even in today’s lower oil price environment. It will be the key development asset for Licence 61 for many years to come.
Updated March 2017
