The Tungolskoye Oil Field is located in the central part of Licence 61. This structure was initially delineated by seismic data in 1967-68. Additional seismic data was obtained in 1970-71. Further seismic surveys were run in 1993-1994.
The Tungolskoye No. 1 well discovered oil on the structure in 1973. The well tested oil from the Upper Jurassic (J1) reservoir with initial flow rates of 52.8 m3/day (332 bopd) through a 12 mm choke for 30 minutes then the well started pulsating. Stabilised flow was achieved on a 3mm choke at 10.5 m3/day (66 bopd) with 20 % water. Reservoir pressure is 262 atm. The specific gravity of the oil is 0.825 g/cm3 or an API gravity of 40 degrees.
All of the vintage seismic data over the Tungolskoye structure has been reprocessed and reinterpreted by PetroNeft, and new high resolution CDP seismic data was been acquired over the feature during the winter of 2005/2006 and additional infill lines were acquired during the winter of 2006/2007.
PetroNeft drilled one further delineation well, Tungolskoye No. 4, on the feature commencing the winter of 2006/2007. The well had 15 metres of net oil pay in the J1 interval based on the core data and independent log interpretations and the well initially tested an inflow of 40 bopd. However, due to mechanical problems the Company was unable to achieve a representative flow test from the interval. The well was subsequently sidetracked to re-access and fully test the relevant reservoir interval. The side-tracked well bore successfully penetrated the reservoir about 100 metres to the east and 5 metres structurally higher than the vertical hole. However, the Company still had mechanical problems with the testing. The well was subsequently suspended in order to move the exploration rig to the West Korchekskaya location while winter roads were in place.
Beginning in 2012, PetroNeft entered into an agreement with TomskGeophysicalCompany (TGK) to reprocess and reinterpret all of the existing seismic and well data at Tungolskoye and Traverskaya. This very comprehensive report that was finished in March 2013. The new structural map at Tungolskoye shows a large portion of the structure (>10 sq kms) up-dip from the existing T-1 and T-4 wells which encountered thick oil pays with good non stimulated test results. The field wide owc based on these wells was interpreted at -2,526 m tvdss.
The T-5 delineation well was drilled near the crest of the structure to confirm the latest TGK structural map and test the flow in the vertical section. The vertical pilot hole of the T-5 well was successfully completed in October 2014. The Upper Jurassic J1 oil reservoir horizon was intersected at -2,495.8 metres true vertical depth subsea (tvdss), which was approximately 11 metres high to the T-1 well to the south. This was consistent with expectations and confirmed the structural interpretation of Tungolskoye. The logs indicated that the J1 interval consisted of 8.2 metres of net pay. An open hole test was conducted over this interval and tested at a pro-rated inflow of 100 bopd unstimulated.
The horizontal segment of the Tungolskoye No. 5 well was then drilled and completed in the J1-1 and J1-2 Upper Jurassic intervals in early February 2016. The total horizontal segment was just over 350 metres of which over 80% was located in the productive J1-1 and J1-2 reservoirs. The well initially produced about 600 bopd using an Electric Submersible Pump (ESP). The oil was trucked 25 km to the Lineynoye central processing facility utilizing winter roads. The well subsequently started producing at a high water cut as a result of coning water from a lower zone. The well confirmed the technical viability of horizontal wells.
Development of the Tungolskoye oil field commenced in 2015. The development project included the construction of a 26 km pipeline and power line to connect the Tungolskoye oil field back to the Lineynoye central processing facility in Q1 2015. The programme initially included five horizontal (1,000 m horizontal segments) and up to six vertical wells. Drilling commenced in April 2015 and was completed in December 2015. The programme ultimately consisted of 4 horizontal and 4 vertical wells. The programme was revised after drilling the third well in the programme (T-508) which indicated a higher oil water contact than expected.
The T-508 and T-509 vertical wells have confirmed the oil water contact at about -2,516 m tvdss on the east and north side of the field. This compares to an oil water contact of -2,526 m tvdss as defined in the T-1 and T-4 wells in the south west part of the field. There will be a reserve decrease at Tungolskoye based on this result.
The planned drilling programme at Tungolskoye is now complete.Updated March 2016