Gazpromneft Noyabrskneftegaz has completed its first operations in multistage re-fracturing via a horizontal well at a traditional reservoir*, at its Vyngapurovskoye field, Yamalo-Nenets Autonomous Okrug. Re-fracturing is used to increase the oil recovery factor (RF) — an improved RF being an important indicator in field development. The uniqueness of this operation lies in the use of a special “chemical-mechanical” or “dynamic deflection” component to block fissures created as a result of previous fracking operations.
Specialists from Gazpromneft-Noyabrskneftegaz, together with experts from the Gazprom Neft Scientific and Technical Research Centre and the Novosibirsk branch of international service company Schlumberger, completed five rounds of re-fracturing at a horizontal well. Following the completion of initial test operations, re-fracturing was successfully undertaken at two further horizontal wells. This new technology is being implemented under the company’s “Technology Strategy”, directed at improving efficiency in field development.
The number of high-technology wells within Gazprom Neft well stock is increasing every year, including horizontal wells for multi-stage fracking: the number of new horizontal wells for multi-stage fracking at Gazprom Neft increased practically two-fold in 2015, to 347. Re-fracturing increases oil flow from the strata, increasing the RF while also extending the effective operational life of the well.
The key difficulty in undertaking re-fracturing operations lies in the necessity of isolating fissures created during initial fracking, in order to include those areas with the most likely sources of additional oil inflow. Gazprom Neft’s re-fracturing operations at the Vyngapurovskoye field involved re-fracturing at a well with irregular composition**, where the re-sealing of old fracking fissures was not structurally possible. Isolation of pre-existing fissures was achieved through the use of chemical-mechanical deflection technology: in this instance, fissures created under previous fracking operations were isolated through the use of a special chemical component. Such a strategy prevents any solution used in new fracking operations from reaching previously created fissures, avoiding any wastage in new fracking operations. According to Schlumberger specialists, this is the first time such technological operations have been used at traditional (terrigenous or terrestrial) reservoirs not just in Russia, but practically anywhere in the world.
Implementation of this new re-fracturing technology was supported by 4D geomechanical modelling of the licence block at which operations were to be undertaken. This allowed the impact of the current state of development on new fracking fissures to be assessed, and — on the basis of the model developed as a result — the optimum fracking strategy to be identified: the first time such a practice has been utilised in the Russian oil and gas industry.
Vadim Yakovlev, First Deputy CEO, Gazprom Neft, commented: “Gazprom Neft is continually improving efficiency in field development. The company is committed to using the most cutting-edge methodologies in improving oil recovery, fine-tuning the technologies used, and reducing costs in high-technology operations. The experience gained means we can start rolling out re-fracturing technology at other assets throughout the company.”
* Traditional reservoirs are the most common kind. In terms of their lithological composition (lithology being the science of modern (or “neoteric”) sedimentary rocks — their composition, structure, origin and distribution patterns) they can be categorised into two main reservoir types — terrigenous (composed of sand and silt) and carbonate. Terrigenous reservoirs are the most common, accounting for more than half of the world’s oil reserves and almost all reserves in the West Siberian Basin.
** Hydraulic fracturing (fracking) can be undertaken through the multiple opening and closing of frac-ports separating one area of the well (at which fracking is being undertaken) from another. This subsequently allows the opening and closing of separate frac-ports remaining from initial multi-stage fracking operations and, on that basis, allows the injection of a re-fracturing solution into as yet undeveloped areas. Since initial fracking at the Vyngapurovskoye field involved single-use casings, re-fracturing operations were undertaken with the use of a special deflecting agent.