Channel Fracturing Enhanced by Unconventional Proppant Increases Effectiveness of Hydraulic Fracturing in Devonian Formations of Russia's Oilfields

The Volga-Urals basin is one of the largest oil-producing regions in western Russia. The most prolific wells are producing from Devonian formations characterized by light crude oil with high bubblepoint pressure. Today, most of the Devonian reservoirs are depleted and produce at bottomhole flowing pressure below bubblepoint pressure, which yields multiphase and non-Darcy flow in hydraulic fractures, drastically decreasing production. As a result, conventional hydraulic fracturing treatments are less effective. To regain fracturing treatment efficiency, the restrictions to hydrocarbon flow inside the fracture must be minimized. To account for this, a new method of fracture conductivity generation was introduced. Channel fracturing creates open pathways inside the fracture, enabling infinite fracture conductivity. Channels are created by discontinuous proppant feeding at surface into viscous fracturing fluid. Dissolvable fibers are added to the slurry to separate proppant structures and prevent them from settling during treatment. Proppant structures act as bridges inside fractures; voids between them are essentially stable channels connected along the entire length of the fracture. While channel fracturing has already been implemented successfully in many places around the world, the fracturing conditions of Volga-Urals Devonian formations were still new for this technology. The Volga-Urals region is well known for high tectonic stresses and low fracturing-fluid efficiency. While channel fracturing treatments are being designed and pumped in a regime without tip-screenout (TSO) in other locations, channel fracturing treatments in Devonian formations often showed significant TSO. Production analyses showed consistent productivity increases, and in most cases, 2 folds higher compared with offset wells where conventional fracturing technology was used. After the success of the pilot campaign, proppant flowback was resolved by incorporating a rod-shaped proppant as a tail-in stage of channel fracturing schedules. The nonspherical shape of the proppant increases internal friction between the particles and mechanically holds them in place. In addition to improving proppant flowback control, the combination of technologies maximized conductivity of the near-wellbore area which connects channels and the wellbore. The success of more than 30 of such fracturing treatments expanded the pool of candidates for channel fracturing with rod-shaped proppant to meet the challenges of similar complex geological conditions. Introduction The Volga-Urals basin is one of the oldest and largest oil-producing regions in Russia. The first oil on the western edge of Ural Mountains was discovered in 1929. By 1977, decades of climbing production from the Volga-Urals basin were over, and production started to decline fairly sharply. The sharp decline mainly occurred because most of the resources are concentrated in a few extremely large fields and the rest are divided among a very large number of small fields. All giant fields were discovered before 1960 and had become mature by late 1970, while newly explored oil fields were too small to reverse the basin’s production decline. Today, the Volga-Urals basin is no longer Russia’s premier producer, but the basin is still responsible for nearly a quarter of Russian oil supply (Grace 2005). It is presently a stable, if declining, region that is favorably situated in the middle of the Russian refining and energy transportation infrastructure. The Orenburg region, an important component of the Volga-Urals basin, is located near other oil and gas producing provinces: Bashkortostan, Tatarstan, Samara region, and north Kazakhstan. There are more than 100 oil fields scattered in the western part of the Orenburg region. Most of the oil fields in the region currently belong to the Rosneft oil company, and this paper focuses on these fields. The geological structure of the Volga-Urals basin is very complex; the wells are producing