Developing hard-to-recover reserves, and improving the viability of mature assets, demands cutting-edge enhanced oil recovery (EOR) techniques — foremost of which are high-technology wells and multi-stage fracking, as well as the application of new strategies in displacing remaining oil, recovery of which is not possible through traditional methods
The construction of high-technology wells allows geologically complex structures to be brought into development, enabling hard-to-recover reserves to be brought into production. Such complex reserves comprise 70 percent of Gazprom Neft’s resource base, with high-technology wells now comprising more than 50 percent of the company’s total well stock. One of the key enhanced recovery techniques is horizontal drilling, significantly increasing surface oil-flow and, consequently, productivity.
A further technology in enhanced oil recovery is the drilling of multilateral wells, increasing the coverage area within strata. The first operational dual-bore well on the Yamal Peninsual, with horizontal wells running to a length of 1,000 metres, was constructed at the Novoportovskoye field.
A further technology aimed at increasing strata coverage involves the construction of a so-called “Fishbone” well — a horizontal well with multiple offshoots or branches. This construction allows significantly greater coverage of oil-saturated sections of strata in comparison with traditional horizontal wells while, at the same time, involving less extensive drilling works than are required in creating a multistage well. The fishbone construction allows each of the branches (“laterals”) to be directed at separate reservoirs, without having to encroach on adjacent strata containing either water or gas. This method of well construction is currently being actively embedded at the Vostochno-Messoyakhskoye field.
Hydraulic fracking technology, widely used worldwide for several decades, involves the high-pressure injection of a liquid mixture, causing fissures to be formed in the strata through which oil is able to run to the bottom of the well. A proppant agent is then used to keep these fissures open.
With the development of horizontal drilling, multi-stage fracking technology, involving the direct creation of fissures throughout several sections of a well, has become widely used. Today this tends to be used in conjunction with other technologies in enhanced oil recovery, although it is being constantly improved.
In developing complex low-permeability reservoirs the inadequacy of standard multi-stage fracking has become obvious insofar as each newly-fracked zone has to be kept separate from the preceding one by a metal or composite ball. The diameter of these balls is reduced from zone to zone, with the result that the way these wells are constructed makes more than 10 fracking operations impossible. New spaced-perforation technology has no such limitations.
Multi-stage fracking through spaced perforation involves multi-use compacted “cushions”-packers which expand under pressure to isolate those areas in which fracking has been completed. Once complete, the cushion deflates to its normal size and the equipment is transported to the next port.
Spaced-perforation technology was used by Gazpromneft-Khantos in 2016 to undertake what was then a record-breaking
In repeated multi-stage fracking (re-fracking) a special chemical compound is used to isolate fissures created in previous fracking operations. Gazprom Neft’s first multi-stage re-fracking operations were undertaken by Gazpromneft-Noyabrskneftegaz at the Vyngapurovskoye field in the Yamalo-Nenets Autonomous Okrug. Records held by Schlumberger show this to be the first time such technology has been used at a traditional reservoir, not just in Russia but worldwide.
The drilling of horizontal wells with multi-stage fracking is the key technology in drilling for shale oil —including in production at the Bazhenov formation, which is very similar in terms of oil occurrence. The most recent insights into the geological structure of the Bazhenov formation suggest there are two key formations: an oil source bed, containing kerogenic shale (polymeric organic matter, which appears in such formations as shale oil) and interstratified beds containing light oil. The latter, moreover, comprises some 30 percent of the total depth of the formation. Such complex composition demands specific multi-stage fracking technologies, of which “рlug & perf” is one.
The strata is opened up using abrasive-jet perforation, with each perforation creating several fissures resulting in the development of a network rather than a single fissure, as is the case in standard fracking operations and each perforation subsequently “plugged” with a special composite.
Gazprom Neft is the first company in Russia to implement full-cycle technological solutions used throughout the global oil and gas industry in developing shale oil reserves at the Palyanovsky block, part of the Krasnoleninskoye field in the Khanty-Mansiysk Autonomous Okrug. This has involved, in particular, horizontal well sections being reinforced with flexible cement, meaning the fissures created can be relied upon to be kept apart, followed by multi-stage fracking involving the high-speed injection of process mud. The combination of good isolation and high-speed injection in fracking makes possible the formation of a concentrated network of fractures throughout the entire length of the horizontal section, thereby increasing the volume of hydrocarbons made available in development.
The identification and implementation of new enhanced oil recovery strategies, allowing field development to be optimised, is one of the key priorities of Gazprom Neft’s “Technology Strategy”. Gas and chemical injection EOR techniques are foremost here.
In the former, gas is injected into the strata, dissolving into the oil and reducing its viscosity as well as increasing its volume, thus forcing the oil out. Such technology not only increases the oil recovery factor (ORF), but also optimises the use of associated petroleum gas (APG).
The company has thus far focussed on alkaline surfactant polymer (ASP) flooding in its use of chemical EOR techniques. The principle behind this is the sequential injection of alkaline solutions, surfactants and polymers into strata. The alkali helps reduce absorption of the expensive components that are to follow; the surfactants act as soap, reducing the capillary tension of the oil and washing it off of the rock surface; and the polymers force the oil out.
A 1,000-cubic-metre-capacity ASP mixing facility was commissioned in March 2016 as part of pre-commissioning testing at the Salym Group of fields. Chemical (ASP) flooding can release up to 90 percent of oil left after traditional production techniques.
Several innovative software packages have been developed at Gazprom Neft as part of a programme of IT support in oil production. One of these —The Field Data and Well Control information system — allows the storage of well data and information in a single database; the design of time-limited operating processes and the monitoring of any deviation therefrom; the estimation of well potential; the identification of wells needing repair; and optimisation of the production process.
Various functions — including performance records for downhole equipment, breakdown notifications, and the compilation of reliability ratings are all handled through the “Mechfond” software system.
As part of the implementation of a comprehensive research programme on the Bazhenov formation, Gazprom Neft specialists, together with academics and scientists from the Moscow Institute of Physics and Technology (MIPT), have developed software enabling calculations to be made on the most efficient aspects of hydraulic fracking in deposits containing hard-to-recover reserves.
This is the only IT product in the world to be developed for use on the Bazhenov formation, allowing the modelling of fissure formation in strata including length, depth, width and other geometric data, and the estimation of oil reserves recoverable from such a well. Ultra-complex mathematical and physical models are used in this process, taking the impacts of dozens of factors into account.