Yudin, A. (Schlumberger) | Tarakanov, I. (Schlumberger) | Klyubin, A. (Schlumberger) | Ablaev, A. (Schlumberger) | Zharikov, M. (Gazprom Dobycha Urengoy) | Vashkevich, A. (Gazprom Dobycha Urengoy) | Yaskin, I. (Gazprom Dobycha Urengoy) | Sabirov, L. (Gazprom Dobycha Urengoy)
This paper was prepared for presentation at the Young Professional Session of the SPE Russian Oil and Gas Exploration and Production Technical Conference and Exhibition held in Moscow, Russia, 14–16 October 2014.
In the Urengoyskoe field, Russia, the Achimov deposits are found at depths of nearly 4000 m and feature a more complex geological structure when compared to the Cenomanian and the Valanginian deposits. Furthermore, the Achimov deposits feature abnormally high formation pressure (over 600 bar) and are characterized by a multiphase state of hydrocarbons. To achieve economic well production, performing stimulation treatments in the Achimov formation of Urengoyskoe gas condensate field is required.
Hydraulic fracturing proved to be a reliable method for increasing well productivity from the Achimov formation by a factor of 2.5; however, well completion restrictions allow for placing only small-size proppant mesh. Proppant fracturing treatments are conducted with high-polymer loading to ensure fluid stability at high formation temperatures, which leads to further reduction of fracture cleanup efficiency. These effects reduce the effective half-length and compromise the full production potential.
New channel fracturing technology that creates open-flow channels inside the proppant pack was selected to improve production. Channels are created by pulsating proppant at surface. Pulses with proppant are separated by pulses of clean fluid, which creates proppant clusters inside the fracture, holding the walls of the fracture open. Fracture cleanup is conducted through channels without restrictions to fluid and polymer flowback. Thus, the channels improve effective fracture half-length and, consequently, gas condensate rates. The increased drainage area also improves hydrocarbon recovery.
Previously in Russia, channel fracturing was used primarily in oil fields. The largest gas operator in Russia has initiated an extensive pilot campaign for channel fracturing in new areas of the Urengoyskoe field. To date, seven wells have been successfully completed with channel fracturing, leading to a significantly higher productivity of 30% versus offset conventionally stimulated wells and lower drawdown.
Like any mature industry that has been around for decades; each with their tried and true technologies; the ESP industry also has its standard technologies which have been applied in varying degrees over the years. The level of success to which these technologies have reached has clearly been seen in the immense growth seen in the ESP industry. This is not to say that there have not been improvements to stage design (e.g. radial vs. mixed flow vs. axial, vane geometries), motor and motor seal design (E.g. induction motor technology and SAGD designs) and deployment methods, but these improvements have been slight deviations from what had been accepted as “standard”.
Historically, ESP stages have been Type 1 or Type 4 Ni-resist and despite the changes in designs as mentioned, the stage materials have essentially remained the same. A change in the stage material and processing paradigm has drastically widened the historic application window.
This paper will elaborate on how a new stage technology combined with Permanent Magnet Motor technology deliver a unique solution providing a wider range of efficient operations (ROR), greater gas and sand handling capability without specific gas handling equipment and a shorter overall package.
The technology will be described, specifically how it is radically different than the case stages typically used today and the results of field trials demonstrating this wider range and its ability to handle produced sand.
Traditional Stage Material, Processes and Limitations
As mentioned above, ESP stages have historically been manufactured from Type 1 or Type 4 Ni-resist although Type 1 Ni-resist is exponentially more prevalent in downhole ESPs (upwards of around 95%+ of the pump stages in use). Without wanting to complicate this paper with metallurgical jargon, Type 1 Ni-resist is essentially “Cast Iron” with the addition of approximately 15% Nickel (plus other trace metals). The addition of Nickel to stage recipe is mainly to increase its hardness slightly and to improve the stages corrosion and abrasion resistance. The addition of the Nickel although highly beneficial in many ways does affect its processability.
Type 4 Ni-resist takes the Type 1 Ni-resist a step further by increasing the percentage of Nickel from 15% to approximately 25%. This increase in the percentage of Nickel does increase the benefits gained from the addition of it as with the lower 15% with an added benefit of increased Oxygen corrosion resistance. This additional 10% increase in Nickel however the increase in cost has made its wide use cost prohibitive. Additionally, the presence of Oxygen in a downhole environment is extremely rare. This is why Type 4 Ni-resist is used mainly in horizontal ESP applications where the presence of Oxygen is much more common.
Yudin, Alexey (Schlumberger) | Enkababian, Philippe (Schlumberger) | Lyapunov, Konstantin (Schlumberger) | Nikitin, Alexey (Rosneft) | Sitdikov, Suleyman (Rosneft) | Serdyuk, Svetlana (Rosneft) | Serdyuk, Alexander (Rosneft)
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 four-year 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.