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Kiselev, Nikita (Schlumberge) | Vernigora, Denis (Schlumberge) | Borisenko, Alexey (Expert) | Rapeyko, Vitaly (Schlumberger) | Zotov, Kirill (Schlumberger) | Miklin, Yuriy (RN-Uvatneftegaz) | Prokhorov, Alexey (RN-Peer Review and Technical Development Center) | Denis, Zolnikov (RN-Peer Review and Technical Development Center)
Abstract Massive implementation of multi-stage fracturing treatments increased demands in water. Huge number of oil fields haven't got access to the fresh water sources. This fact forces service companies to utilize high TDS water sources for hydraulic fracturing. Currently available solutions for preparation of crosslinked fluid based on high TDS water involve implementation of organometallic systems which are too expensive and operationally complicated. This paper describes approach for preparation of borate- based fluid utilising high TDS water. Thorough laboratory optimization of the fracturing fluid has been performed and novel approach for fracturing fluid composition has been involved to develop next generation of robust borate fracturing fluids being able to withstand high TDS of the water. Fluid was evaluated in terms of both stability and viscosity recovery after application of high shear stress. Optimized fluid formulation has been used during multi-stage fracturing treatment with 7 stages. High TDS water of Cenomanian formations was utilized as a water source. During treatments as high as 700 kgPA proppant concentration has been reached. During optimization novel approach involving implementation of low boron containing fluid with massive content of alkali was introduced. Low boron content is required for preventing syneresis in high ionic strength media caused by Debye-Huckel effect. High alkali concentration meantime required to keep fluid at high pH and avoid weakening of bonds between borates and polymer. Too high alkali concentration worsens viscosity recovery after high shear stress application and this fact dictates implementation of both immediate and delayed alkali compounds. Pre-job water treatment is also important. Addition of reagents being able to convert natural radical oxidizing aids in less damaging forms is imperative. During the treatment fluid was additionally tuned to reduce frictional losses in tubing by compensating effect of proppant on the rate of crosslinking components diffusion. And treatment design was modified to address increased efficiency of the fluid caused by filter-cake enhancement by delayed alkali. The study showed availability of approaches which allow to implement high TDS water sources for preparation of borate crosslinked fluids confirmed by successful field implementation. These practices can be widely used in industry for performing multi-stage fracturing treatments in areas with lack of fresh water sources and to shorten water preparation cycle time.
Abstract Currently, Russia experienced a rapid growth in horizontal wells drilling. The most popular method of completion is hydraulic fracturing. About 99% of hydraulic fracturing fluids are prepared using water. This fact undoubtedly increases the importance of technology and practices of collecting and utilizing water from underground and surface sources. The current direction of development of multi-stage hydraulic fracturing is increasing the number of stages and the volume of the proppant. So the main task of fracturing companies in Russia is to optimize the process of collecting and preparing water without increasing the cost of hydraulic fracturing. The use of organometallic fluids fracturing is the most common solution for use of unconventional water sources. However, due to the high cost of organometallic liquids, borate fluids will be considered in this work. Existing quality control requirements applied to hydraulic fracturing fluids cannot be directly used to study the rheological properties of fluids based on alternative sources of water — produced water from artesian wells and low temperature water. In connection with the foregoing, in the framework of this work, a new approach to testing and quality control of hydraulic fracturing fluids is presented. In case of using water with low temperature (15 degC in summer, 25 degC in winter), it is crucial to maintain the required recovery rate of fluid viscosity after application of high shear rates when passing through perforations in the near wellbore zone. In the case of the use of artesian water, it will be crucial to maintain the necessary stability of the liquid in a highly mineralized medium. During the hydraulic fracturing campaign in 2017-2019, pilot works were carried out using low temperature water and water from artesian wells. Implementation of water with a lower temperature leads to a reduction in the time of preparation for hydraulic fracturing by 33-50% reduction in heating time for the fluid. As a result, this practice leads to an increase in the monthly amount of work and the production of hydraulic fracturing fleets. Extended laboratory studies revealed that, developed for low temperature conditions, the hydraulic fracturing fluid not only satisfies the parameters for transferring and holding the proppant in the NWB zone, but even surpasses the liquid prepared by the traditional method (25 degC in summer, 35 degC in winter). The main goal of optimization of hydraulic fracturing fluid prepared using artesian water was to reduce the negative impact of some ions, primarily iron ions and hydrocarbonate ions. The presence of these ions in the hydraulic fracturing fluid leads to deterioration of the thermal stability of the hydraulic fracturing fluid. However, following the recommendations developed for the preparation of a fracturing fluid based on artesian water, it is possible to significantly reduce the influence of both one and other ions. The use of artesian water in the area of pads located near artesian wells, has reduced the time of water transportation by 50%. Pilot treatments were successfully carried out, showing a satisfactory level of production after hydraulic fracturing, comparable to similar work using conventional surface water preparation techniques using the standard procedure. Reduction of preparation time, optimization of resources required for water treatment, and reduction of negative environmental impact confirm the significant economic benefits of the methodology described in this paper. This approach, using the environmentally safe "green" chemistry as part of a hydraulic fracturing fluid, allows operators to minimize the negative impact of production factors on the environment and confirm the effectiveness and environmental friendliness of hydraulic fracturing technology as a well workover.
Fedorov, Andrey Vladimirovich (Schlumberger) | Fedorov, A.. (Schlumberger) | Fu, D-K.. (Schlumberger) | Mullen, K.. (Schlumberger) | Kochmar, L.. (Schlumberger) | Lungwitz, B.. (Schlumberger) | Dessinges, M.. (Schlumberger)
Abstract An appropriate fracturing fluid is one of the key elements for success of hydraulic fracturing treatments. In western Siberia, borate crosslinked polymer fluid has been widely used because of the high viscosity required for placement of large-size proppants. The first step to obtain the viscosity is to hydrate or dissolve a dry form of polymer and prepare a linear gel. This operation requires a minimum temperature of 25°C. Because the average temperature is below 20°C all year and as low as – 40°C in the winter (Fig. 1), this temperature requirement, coupled with the lack of freshwater sources in some locations, presents both logistical and operational challenges.Figure 1: Average temperature in Tyumen Region, W. Siberia Water produced from the Cenoman formation is readily available in many locations in western Siberia (Blackbourn Report 2010). With temperatures ranging from 35 to 50°C, Cenoman water could be an ideal source for preparing fracturing fluids. However, the water contains boron and a high level of magnesium and calcium that cause undesirable instant crosslinking of linear gel and shear and thermal instability. To eliminate the impacts of those elements, we introduced a chelating additive to the water to sequester the cations species and optimized the initial fluid pH to improve thermal stability. The concentration of chelating agent is further adjustable to ensure consistency in crosslinking delay time and to provide shear insensitivity. Using Cenoman water and equipment for continuous mixing of fracturing fluid has greatly improved the operational efficiency and service quality of fracturing treatments in western Siberia. The time to complete a single fracturing treatment was reduced from 2 days to less than 1 day. In some cases, two treatments were performed in 1 day. As of December 2008, more than 500 fracturing treatments had been performed using Cenoman water with an average of over 94% proppant-placement rate.
Ely, John W. (Ely and Associates Corp) | Fowler, Steven L. (Ely and Associates Corp) | Tiner, Robert L. (Ely and Associates Corp) | Aro, Dustin J. (Ely and Associates Corp) | Sicard, Jr., George R. (Ely and Associates Corp) | Sigman, Tanner Austin (Marietta College)
Over the past 10 years Ely Corp has supervised more than 100,000 “Slick Water Fracture treatments”. After more than 30 years of dominance by extremely viscous crosslinked gels, viscous oils, emulsions and foams, the industry has in selection of fracturing fluids, moved to the point that the vast majority of fracturing fluids are either water and friction reducer or combinations of linear gel and or crosslinked gel that is very rapidly degraded to water once in the formation. In a similar time frame our industry has moved rapidly away from specific selection criteria of proppant based on strength under closure and conductivity profiles which were enhanced by both size, particle distribution, and inherent strength. The dominate proppants now used in the industry are smaller proppant such as 40/70 and 70/140 (100 mesh).
The switch to thin fluids was mainly because of intense efforts from individuals such as George Mitchell and other innovative companies who steadfastly believed in the potential of producing from virtually impermeable matrix source rock and were open to try any available technology. The switch to small proppant was driven in most cases by the lack of transport capability of the thin fluids, and in many cases due to lack of available higher strength proppant.
The success of these slick water frac fluids has, in our opinion, been due to creating a drastically different geometry combined with much larger volumes. The type of frac fluids described have been present in the history certainly since the 50’s but not with comparable rate and volume and typically not with the dominate proppant being 40/70 or smaller.
The paper will, utilizing our data base and public production data, illustrate what has truly changed the dynamic of fracturing in our industry. We will also illustrate techniques to optimize slick water fracs based on a combination of new generation technology and experience in not only source rock shale but many so called conventional reservoirs which have only now become economical with use of high volume slick water treatments where more conventional viscous fluids failed.
Based on the broad success of these fluids, we will propose a hypothesis for why these fluids and proppants, which defy conventional frac theory, have made the industry more closely evaluate even the most basic frac theories that we have followed for multiple decades.
Bhagavatula, Ramkamal (Kuwait Oil Company) | Rajagopalan, Vijay Shankar (Kuwait Oil Company) | Chellappan, Suresh (Kuwait Oil Company) | Al-Ashwak, Amna (Kuwait Oil Company) | ElMofti, Mohamed (Halliburton) | Boueshi, Alaeldin (Halliburton) | Eid, Waleed (Halliburton) | Allam, Ahmed (Halliburton) | Abdelbaky, Amr (Halliburton) | Davis, John (Halliburton)
Abstract This paper discusses the successful application of a pillar fracturing technique in a water injection well wherein a major operator previously experienced poor injectivity within the target zone. The aim of the pillar fracturing technique was to achieve the highest possible fracture conductivity to enhance water injectivity for reservoir pressure maintenance. This technique creates infinite conductivity channels with proppant distributed within the fracture as aggregates or groups separated by clean fluid. These proppant groups function as pillars to hold the fracture open and help enable fluid flow in the open channels between proppant pillars. The conductivity of a partially open fracture with proppant pillars can be several orders of magnitude greater than that of a conventional fracture filled with proppant after closure. After a pillar style hydraulic treatment, the propping agent remains in the fracture grouped to form pillars because of the sticky resin that was applied to the proppant just before being blended (intermittently) into the fluid system that was pumped during the treatment. This helps the grains in the resulting pillars to adhere together and help prevent the fracture from entirely closing, forming open conduits for fluid flow. The overall success of this fracturing stimulation treatment depends on the sequenced pumping technique, allowing the propping agent to form proppant aggregates during their placement into the formation. This paper presents the enhanced pillar fracturing technique, pre-job well analysis and design, Minifrac data calibration, and actual pumping operation execution. The well intersects a reservoir with sandstone lithology that had not been fractured previously. The sandstone formation is subdivided into three intervals of 60, 40, and 60-ft thickness, with distinct shale layers separating them. Based on the log interpretations and formation geomechanical analysis, two pillar fracturing stages were determined necessary to treat the entire targeted formation and maintain balanced injectivity in all three intervals. An optimum hydraulic fracturing design was developed and executed to deliver optimal well performance. Actual operational execution involved use of specially designed surface equipment and adhesive enhancement proppant coating to install highly conductive flow paths while maintaining reservoir and proppant pack stability. This resulted in a successful treatment that sustained 16,000 barrels of water injection per day (BWIPD). The successful application of the pillar fracturing technique in this well motivated the operator to extend the pillar fracturing technique to other injector and producer wells.