Alexey Yudin

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

First Steps of Channel Fracturing in Russia Set New Directions for Production Increase of the Oil Fields

Channel fracturing technique changes the concept of proppant fracture conductivity generation by enabling hydrocarbons to flow through open channels instead of the proppant pack. The new technique is based on four main components: proppant pulsing at surface with fracturing equipment and software, a special perforation strategy, fibrous material to deliver stable channels, and a set of models to optimize channels geometry. Channel fracturing in Russia’s oil fields began in 2008 as field testing operations in tight collaboration with the development team. Full-suite logs provided geomechanical models and ensured fracture channels optimization. An important result of those first treatments was long-term channels stability. The treated wells continue to show stable productivity over a fouryear period. As of today, more than 90 channel fracturing treatments have been pumped in Russia with no screen-outs. A very low screenout risk has become one of the most important advantages of the technology; the fibers make fluid more stable while the presence of clean pulses around proppant structures ensure bridging-free flow. As the channel’s conductivity does not depend on proppant size to hold channels open, treatments can be performed with smaller proppants (20/40 or 16/20 mesh) instead of larger proppants (12/18 mesh) that have an increased risk of screenout. In combination with abrasive jetting perforations, channel fracturing has proven to be an efficient stimulation solution for Russia’s multi-layered reservoirs. This completion technique ensures proper flow distribution into perforation clusters according to the channel’s specific requirements. It also allows reliable proppant admittance through jetted caverns. Channel fracturing increases the effective half-length with increased treatment size. A considerable number of channel fracturing jobs with proppant mass equal to standard fracturing designs have been performed—significantly increasing channeled length and providing better production in low permeability (1 to 3 mD) oil reservoirs. Based on production analysis of stimulated wells in five different areas, a correlation between incremental channel fracturing productivity over the conventional stimulation technique and kH value of the formation can be made: the higher the kH the more significant the advantage of the channel fracturing is in oil wells. Introduction Hydraulic fracturing in western Siberia is by far most effective method of oil production enhancement. Majority of the Neocomian formations have low permeability (1-3 mD) and high lamination in the fields around Nefteyugansk City. Priobskoe Field, one of the world’s largest conventional oil fields is a representative sample for the area. This giant field produces from three formations – AS12, AS11 and AS10, whose properties are shown in the Table 1. Many wells have simultaneous production from several intervals in which massive hydraulic fracturing treatments were placed since 2002 to maximize production. A history of the propped fracturing designs evolution was written by Timonov et al. 2006 and Nikitin et al. 2007. Priobskoe was always a primary target for new stimulation technologies, since it is relatively well-studied; fullsuite logs, core analysis, geomechanics studies and fracture geometry measurements are available for dozens of wells. Another feature of the formations is low water contents. Since this significantly lowers the risk of the fracture growing into a water zone, the optimum fracture design can be modeled without restrictions on the treatment size and proppant concentration. Several iterations in the optimization process were made with various new technologies that deliver longer