Formations with a bottomhole static temperature below 70 degC are very common for quite a number of Russian oil provences such as Komi, Samara Area, Orenburg, Tatarstan Bashkiria, and Eastern Siberia. Many of these formations are now being developed with proppant fracturing which incorporates a lot of flow back issues due to the various reasons including high viscosity oil, aggressive TSO designs and cycle loads on a proppant pack due to ESP change regime. There are a number of solutions to prevent proppant flow back and the most common one is usage of resin-coated proppants. At temperatures below 70degC RCP needs chemical activation in order to achieve a solid proppant pack consolidation. Depending on temperature range and coating structure various types of activators can be used. Traditionally commercial activators were used at very high concentrations that may compromise proppant pack conductivity and performance fracturing fluid. Alternative techniques are based on using fiber technologies and unconventionally shaped proppants.The majority of flowback control techniques have been tested in Volga-Urals region of Russia, Orenburg, Samara and Bashkiria areas. Novel additives that accelerate curing, RCP was successfully implemented and pumped during hydraulic fracturing on the most oil fields of Samara area. Flow back problems were observed only at extremely low temperature reservoir (Ͻ30 degrees Celcius) with highviscous (ϳ100ϩ cP) oil. Paper uncovers the details of activation process with detailed laboratory investigation for several RCPs and activators, proposes decision matrix for low temperature flow back control techniques, its applicability and design. Problem: Proppant Flow backProppant flow back is the term used to describe the problem of proppant being produced out of a hydraulically created fracture during well cleanup or reservoir production. This phenomenon can create several problems. Once removed from the fracture, proppant cannot contribute to fracture conductivity or reservoir production, moreover, productivity of the remaining fracture is severely affected. Proppant flowing back from the fracture may cause mechanical problems with downhole equipment, especially for the wells equipped with an electrical submersible pump (ESP).
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.
Hydraulic fracturing de-facto is the most common stimulation technique that is employed worldwide. Russia is following the same trend and most of the new and old wells are considered for hydraulic fracturing. However, eventually as more and more reservoirs become depleted operators are looking forward to formations with so called "hard-to-recover" deposits in order to sustain hydrocarbon production.These "hard-to-recover" deposits include:• Unconventional shale pays similar to US -Bazhenov and Domanik formations.• Caspian, Arctic, and Sakhalin offshore • Eastern Siberia green fields • Mature fields and formations where conventional stimulation is not as effective as expected due to variety of reasons.
The Volga-Urals basin is one of the largest oil-producing regions in Russia. Orenburg region, located in Volga-Urals, has more than 100 oil fields with great variety of formation properties. The majority of formation fluids are characterized by high gas/oil ratio (GOR) and high bubblepoint pressure. Today, most reservoirs are depleted and produce at bottomhole flowing pressure below bubblepoint pressure. These factors yield multiphase and non-Darcy flow in propped hydraulic fractures, which drastically decreases production. As a result, hydraulic fracturing treatments with conventional proppant are not effective.Proppant flowback is another critical problem after hydraulic fracturing. There are a few solutions widely accepted by industry, and one of the most popular is a resin-coated proppant (RCP). Usually the coating is activated by temperature; however, for formations with low bottomhole static temperature (BHST), RCP may not be efficient. Many formations in Volga-Urals have a low BHST, which requires a different technology from RCP to eliminate proppant flowback.A recently developed rod-shaped proppant was proposed as a solution to both problems specified above. In comparison with conventional proppant, it provides higher fracture conductivity with integrated flowback control due to random alignment of proppant grains while packing. This property results in improved fracture cleanup from treating fluids. The rod-shaped proppant also acts to prevent proppant flowback through specific shapes of grains. The significant benefit over conventional RCP is that rod-shaped proppant does not have any BHST limitations, does not require any chemical activation, and does not have special flowback requirements.Since the introduction of rod-shaped proppant in Russia, 10 fracturing treatments have been successfully carried out with this new proppant in Vakhitovskoe, Lebyzhinskoe, Vostochno-Kapitonovskoe, and Sorochinsko-Nikolskoe oil fields. Well production analysis proved that rod-shaped proppant was more effective than conventional proppant: productivity index is 26 to 67% higher. Further, no proppant flowback issues were detected on wells fractured with rod-shaped proppant. The first successful implementation of this product in Russia is described in detail with laboratory data, a thorough production analysis, and case histories. Pump rate (m3/min) / Расход (м3/мин) Pressure (bar), Proppant concentration (KgPA) / Давление (бар), концентрация проппанта, (кг/м3) Time (hh:mm) / Время (чч:мин) Lebyazhenskoe L26 D1 / Лебяженское L26 Д1 Main Job / Отчёт по Обработке ГРП Treating Pressure (bar) / Давление в линии (бар) Annulus Pressure (bar) / Давление в затрубье (бар) Prop Con POD Densitometer (KGPA) / Концентрация проппанта с плотномера блендера (кг/м3) BH Prop Con POD Densitometer (kg/m3) / Концентрация проппанта на забое с плотномера блендера (кг/м3) Bottomhole Pressure Measured (Bar) / Замеренное забойное давление (бар) Slurry Rate In-line Flowmeter (m3/min) / Расход жидкости с расходомера (м3/мин)
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