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.
In the case of many workover operations associated with fluid loss inside the well or multistage refracturing, one of the most significant uncertainties is the fluid entry point. Starting from uneven depletion of the horizontal part of the well, not knowing the fluid entry point may lead to ineffective well restimulation and absence of any positive effect. In this paper new technique will be reviewed for several locations across Russia. Implementation of high-frequency pressure monitoring (HFPM) method and based on it, Well Watcher Stim technology, allows locating downhole events caused during well workover and refracturing without interruption of the well stimulation operations. The high frequency pressure monitoring technology is based on automatic processing of wellbore pressure oscillations recorded at the wellhead. The wellbore completion elements such as hydraulic fractures, casing diameter changes or wellbore restrictions serve as effective reflectors for the tube waves. In this paper, we will demonstrate an integrated approach to the utilization of high-frequency pressure monitoring technique, which has served as an engineering tool for fluid entry point validation in the projects all across Russia. The project validated the intrinsic benefits of the new approach in solving uncertainties about the fluid entry point. The Well Wacther Stim technology requires minimum changes in operational procedures, is easy and safe to install and provides real-time answers that allow the frac engineer to take decisions on location and optimize the re-fracturing process Selected stimulation approach enables the horizontal well refracturing operation to be concluded within 2-3 days, minimizing well intervention operations and reducing the overall costs and risks of the restimulation. The selected workover approach demonstrates reliable technique for fluid loss extensional control in well workover. One of the opportunities which is became available with high-frequency monitoring is analyze of conditions of well construction and downhole equipment. That was practically confirmed at a well with completion for multi-stage fracturing. Suspicion about damage of casing or sliding sleeves and corrosion of isolation packers was verified and localized. Further application of Well Watcher Stim made possible to decrease leakages by conventional reservoir dynamic fracture diversion technology and provide multi-stage fracturing with constant control of identified zones. This paper presents case studies of the technology that was used widely in Russia in the recent years proving reliability of high-frequency pressure monitoring technique. It will provide meaningful insight for the petroleum engineer who will look after solving uncertainties during well workover operations and refracturing.
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