Gazpromneft-Sakhalin, a subsidiary of Gazprom Neft, has completed drilling of a prospecting and appraisal well at its Ayashsky licence block, located on the continental shelf of the Okhotsk Sea. As a result, a new hydrocarbon field has been discovered, with initial in-place reserves estimated at 255 million tonnes of oil equivalent (mtoe). Gazprom Neft says a detailed assessment of these reserves will be prepared by mid-2018.
The decision to drill at the Ayashsky prospective formation was taken on the basis of 3D seismic data. Exploration data received during offshore works at the Okhotsk Sea was carefully analysed prior to the development of the drilling programme. Gazprom Neft’s experience in the exploration and development of offshore fields, gained through the Company’s current offshore assets, helped complete the drilling as standard, and on schedule.
Cutting-edge technological solutions applied for the construction of the well enabled Gazpromneft-Sakhalin to build the prospecting and appraisal well during a narrow window of ice-free period at the Okhotsk Sea, on time and without incident. Specifically, the riser-free sludge-removal technology made it possible to control the stability of strata surrounding the borehole, as well as eliminating any possibility of geological material entering the marine environment. Drilling was carried out using a rotary steerable system, which allowed the maintenance of vertical control with automatic corrections. This enabled the use of the most “aggressive” penetration mode, shortening the construction time and minimising the number of run-in-hole/run-out-of-hole (RIH/ROOH or “tripping”) operations.
Core samples running to 162 metres were taken from anticipated productive strata (horizons) for the construction of the 2,700-metre-deep well, with extensive open- and closed- geophysical and hydrodynamic borehole exploration works undertaken.
Alexander Dyukov, CEO of Gazprom Neft, commented: “The development of Gazprom Neft’s offshore assets remains a strategic priority for the company. We continue the development and exploration of all offshore licence blocks in our portfolio. The discovery of a major field in the Okhotsk Sea proves the relevance of our experience and allows us to reassess prospects for developing offshore projects.”
The Ayashsky block in the Okhotsk Sea forms part of the Sakhalin-3 project. The block is located in the north—eastern part of Sakhalin Island’s continental shelf, 55 kilometres away from the coast. The sea at the first drilling site runs to a depth of 62 metres. 3D seismic works covering a total area of 2,150 square metres have already been completed at the Ayashsky block.
Gazpromneft-Sakhalin is a subsidiary of Gazprom Neft. The company is primarily engaged in the exploration and development of offshore oil and gas fields. It is the operator of the Dolginskoye oil field, at which geological prospecting works are currently ongoing, as well as the North-West block of the Pechora Sea, the Kheisovsky block in the Barents Sea, the Severo-Vrangelevsky block, covering the East-Siberian and Chukhchi Seas, and the Ayashsky block in the Okhotsk Sea.