Return to Achimov: A Comparison of the Achimov and Neocomian Beds in the Noyabrskiy Region
Kirill Nikolayev
Unclaimed Reserves
The Achimov suite is the lowermost level of the Lower Cretaceous deposits overlying the Jurassic play. Its geological structure is complex, and that is why it took some time to start developing the Achimov. In some fields exploration activities to estimate the Achimov deposits and the possibility of bringing it into commercial production has been going on for several decades.
Gazpromneft-Noyabrskneftegas’s first attempts to bring the Achimov deposits into production were made back in the eighties. Aleksandr Naumov, a prominent geologist, was seeking to prove his clinoform, Neocomian model during the exploration of the Yety-Pourovskiy Field (currently developed by Gazpromneft-Mouravlenko). One key bit of evidence was the discovery that the shelf bed changes into the Achimov suite along the line of six exploration wells. Production tests were subsequently performed on these wells. However, the flow rates turned out to be considerably lower than in the adjacent wells drilled in the Neocomian beds.
The main issues encountered by oilmen developing the Achimov beds were the reservoirs poor quality and connectivity. At 2750 -2950 m where the Achimov payzone occurs in the Noyabrskiy Region, the rocks are represented by alternating fine-grained sandstones, siltstones and claystones where the permeability does not exceed 3 mD and the frequently is below 1 mD. In comparison, the permeability of the Neocomian beds, formed by fine, medium and coarse sandstones is almost 7 times higher, reaching 20 mD. Apart from this, the beds are highly shaled-up and carbonised which makes interpretation of the well logging data more difficult. It is hardly surprising that production tests in the eighties resulted in low flow rates and cumulative production per well. Bearing in mind a complex structure and high degree of reservoir compartmentalization in the Achimov series, further development of these beds, using technologies available at the time, was found to be unfeasable.
Gazpromneft-Noyabrskneftegas intensify activities related to the pools where production was previously considered sub-economic. Currently, the subject of developing hard-to-recover reserves of Western Siberia becomes increasingly important. Most frequently, it refers to the development of the Bazhenov suite. However, while the Bazhenov development is at a pilot stage, the oilmen are starting to develop reserves in the other promising formation – the Achimov suite. The Achimov beds are less spread than the Bazhenov ones, however, these reserves allow the life of enterprises with falling production, including Gazpromneft key assets in the Yamal-Nenets Autonomous District, to be considerably extended.
By the start of the new century, methods of enhanced oil recovery were significantly improved with intense development of horizontal well drilling technology and multi-stage and high-volume fracking. New methods of well completion were being developed and side-tracking technology became widely used. These innovations resolved the majority of the issues encountered during the Achimov production tests and allowed commercially viable flow rates in the wells drilled. Noyabrskneftegas also reverted to this course – production tests in one of the reservoirs started in the Yaraynerskoye Field in 2000. However, this project was not developed any further as the enterprise had a large number of undeveloped Neocomian deposits on their books, which were considerably more profitable to develop.
Reserves for the Second Life
Fields in western Siberia are currently facing challenging times: most of them have long passed their peak, production is falling and, essentially, no large, new fields of easy-to-produce oil are being discovered. It is, therefore, quite logical that geologists turned their attention to the harder to recover Achimov deposits. In 2013 and 2014 Gazpromneft – Noyabrskneftegas drilled eight horizontal wells in Ач (Ach) formation in the Vyngapourovskoye Field, using multi-stage fracking. During the first month of production all the wells had sufficiently high average flow rates: some 110 cubic metres/day of liquids and 53 tonnes/day of oil. At the time, the average oil production rate in the Neocomian beds in those areas did not exceed 20 tonnes per day.
Side-tracking was performed in two other wells in the Achimov formation in the Vyngapourovskoye Field in 2014. After well intervention initial flow rates reached 31-35 tonnes per day. The experiment was considered a success and options for using this technology in other areas of the Vyngapourovskoye Field are being currently considered.
Bringing the net pay up to the Jurassic base brings new prospects to the old fields in Noyabrskiy Region, particularly taking into the account the fact that availability of oil production infrastructure in these fields will reduce the cost of produced oil. Such vast expansion of the enterprise’s resource portfolio will provide work for Noyabrskiy oilmen for years to come.
Roustem Gimaletdinov, Deputy General Director – Chief Geologist, Gazpromneft – Noyabrskneftegas
In general, developing fields which have historically been considered unprofitable has become a key part of Gazpromneft-Noyabrskneftegas expansion plans. After fracking, the well produced 20 tonnes per day of oil and 35 cubic metres/day of liquid. Currently, the average daily oil flowrate in this well is approximately 16 tonnes. Having achieved a positive result, the geologists estimated reserves in this well and entered the following into the books: Category С1 – over 6 million tonnes (of which over 1.5 million tonnes are recoverable), С2 – 24.5 million tonnes (6.5 million tonnes recoverable).
Gazpromneft – Noyabrskneftegas are continuing efforts to commence development of the Achimov beds. Currently our staff are working with geologists from Gazpromneft Research and Development Centre to develop programmes for further exploration , and to bring these reserves online by drilling new wells and side tracking.
The search for previously unstudied pools and confirmation of the existing pool boundaries are planned in the Karamov Field in the nearest future. Further exploration will enable reduction in geological risks associated with low exploration maturity of the secondary formations as well as considerable increase in the reserves. Currently the initial recoverable reserves in the Vyngapourovskoye Field are estimated at 3.5/5.7 million tonnes of oil (Categories С1/С2), in the Novogodneye Field – 5.8/0.8 million tonnes, in the Yaraynerskoye Field – 2.9/1.1 million tonnes and in the Karamovskoye Field – 1.6/6.4 million tonnes. Thus, initial recoverable oil reserves in the Achimov formation deposits of Gazpromneft – Noyabrskneftegas are 13.8/14 million tonnes. In 2015 the geologists plan to increase the Achimov Category C1 oil reserves by 1 million tonnes as
a minimum.
Published with thanks to Gazprom Neft & Sibirskaya Neft MAGAZINE
