Developing hard-to-recover reserves, and improving the viability of mature assets, demands cutting-edge enhanced oil recovery (EOR) techniques — foremost of which are building high-tech wells and multi-stage fracking, together with the application of new strategies in displacing remaining oil, which cannot be recovered through traditional methods
Drilling high-tech wells
The construction of high-technology wells allows geologically complex deposits to be brought into development, meaning hard-to-recover reserves can be brought into production. Hard-to-recover reserves make up 70 percent of Gazprom Neft’s resource base, which is why high-tech facilities account for more than 60% of the company’s total drilling— the highest level in Russia.
One of the key techniques in enhancing oil recovery is drilling horizontal wells, significantly increasing the inflow surface and, consequently, production volumes.
A further technology in enhanced oil recovery involves drilling multilateral wells, which increases strata coverage. One of the company’s most complex wells is being built at the Tazovskoye oil and gas condensate field, where Gazprom Neft, in 2018, achieved a record length for a horizontal shaft, at 2,263 metres — a record for the company — while drilling multilateral cased-borehole wells. The wells at the Tazovskoye oil and gas condensate fields are comparable to offshore wells in their uniqueness and complexity.
A further technology aimed at increasing strata coverage involves the construction of so-called “Fishbone” wells — horizontal wells with multiple offshoots or branches. This construction allows significantly greater coverage of oil-saturated sections compared to traditional horizontal wells while, at the same time, requiring less extensive drilling works than would be involved in building a multistage well. Each of the branches (“laterals”) is directed at a separate reservoir, without encroaching on adjacent strata containing either water or gas. This method of well construction is now being actively deployed at the Vostochno-Messoyakhskoye field.
Hydraulic fracking technology has already been in use worldwide for several decades. Helped by powerful pumping stations, fluid is injected into a well: this causes fissures to be formed in the strata, through which oil flows 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, which involves fissures being directly created throughout several sections of a well, has become widely used. Nowadays this tends to be used in conjunction with other enhanced oil recovery (EOR) techniques, although it is constantly being improved.
A key feature of the Orenburg field is the high viscosity of its oil, which is held in low-permeability carbonate reservoirs, with low reservoir temperature. One way of increasing oil recovery, which is quite widely used here, is acid fracturing (acid fracking), which involves using acid as a fracking fluid to “dissolve” the carbonate reservoir. Gazprom Neft is now developing a more effective multi-stage acid-proppant fracking at the Orenburg oil and gas condensate field, deployment of which is increasing well productivity by more than 50%.
Another cutting-edge multi-stage fracking technology — “non-ball and socket fracking” (Mongoose fracking) makes it possible not only to increase oil recovery, but also to undertake downhole investigations and — something of considerable importance — undertake repeated fracking operations (re-fracking). Under re-fracking, fissures created through earlier fracking are isolated using a special chemical solution. The company’s first ever multi-stage re-fracking operation was undertaken at the Gazpromneft-Noyabrskneftegaz Vyngapurovskoye field in the Yamalo-Nenets Autonomous Okrug.
A re-fracking operation using special chemical formulations and next-generation polymers was undertaken at the Archinskoye field (Tomsk Oblast) in 2018. Rolling out this technology could increase oil production at fields with carbonate reservoirs (which comprise more than 40% of the company’s recoverable reserves) by up to 50%
Using modern digital technologies makes it possible to increase efficiency in multi-stage fracking. In 2018 the Gazprom Neft Science and Technology Centre developed the first domestic digital product for simulating the formation of hydraulic fractures to increase oil recovery , as part of a Russian consortium.
Initial estimates suggest this technology can reproduce fissure characteristics
Developing the Bazhenov Formation
Drilling horizontal wells with multi-stage fracking is the main technology used in shale-oil production — including 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 separated with special composite plugs.
Gazprom Neft was the first company in Russia to implement full-cycle technological solutions (used throughout the global oil and gas industry) in developing 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 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 that can be brought into production.
Integrated and effective technologies, that would make it possible to produce Bazhenov oil profitably on a commercial scale, do not yet exist, however. Gazprom Neft has been involved in developing such technologies, creating the Bazhenov Technology Centre in the Khanti-Mansi Autonomous Okrug. But addressing such a massive task single-handedly is beyond even the biggest and best-resourced company: to which end the Centre has become a unique forum, bringing together oil companies, equipment producers and innovators. The Centre has been awarded the status of a National Project.
Gas and chemical injection in enhanced oil recovery
Identifying and deploying new EOR strategies, meaning field development can be optimised, is one of the key priorities in 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 associated petroleum gas (APG) utilisation.
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 the 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 m3/day-capacity ASP mixing facility has been commissioned at the Salym group of fields as part of pre-commissioning testing, with the oil recovery factor (ORF) at the pilot block here reaching 69% — almost double the Russian industry average.
The effectiveness of this method is seriously impacted by the high cost of surfactant-polymer substances, not yet in production in Russia, however. Gazprom Neft’s “RosPAV” project, directed at developing an effective polymer-surfactant mixture for domestic production, and being implemented together with Salym Petroleum Development, Norchem and Tyumen State University, has been launched to address precisely those problems. As part of that project, 11 new surfactants, capable of replacing foreign alternatives, have, for the first time, been synthesized in Russia. Successful completion of these tests will mean the company can move over to deploying this technology commercially, in Western Siberia. Initial estimates suggest that its deployment across the company’s 10 largest assets could result in additional production in the order of 172 million tonnes.
Using software to improve efficiency in field development
Several innovative software packages have been developed at Gazprom Neft as part of an IT support programme for oil production. One of these —the Field Data and Well Control information system — allows well data to be stored in a single, integrated database, meaning operating regimes can be determined, over a specific period of time, and any deviation therefrom monitored, as well as allowing well potential to be estimated, and any wells needing repair (or any necessary fine-tuning of the production process) to be identified.
Various functions — including performance records for downhole equipment, breakdown notifications, and the compilation of reliability ratings are all handled through the “Mechfond” software system.