During the past two decades, fracturing stimulation has become a production driver for a much greater part of the oil industry worldwide. Because of the extensive reservoir formation types, fracturing scenarios widely vary from conventional to unconventional cases. Fracturing is one of the few options for commercial hydrocarbon production in some extremely tight reservoirs. Unfortunately, many of the tight formation scenarios achieve fracture inititation and/or extension only under extremely high pressure, thus frequently reaching mechanical forces close to the well completion limitations. Among the different techniques used, the controlled breakdown technique (CBT) helped significantly improve pump rates in some fracture initiation and injection conditions. This technique controls pressure, while considering the completion's mechanical limits. This paper discusses the process and appropriate conditions for CBT application and evaluates when it is convenient or even crucial to help enhance fracture initiation and development.
Up to three thousand barrels of stimulation fluids are pumped during a single vertical fracture treatment in carbonate reservoir of Saudi Arabia with the objective of creating sufficient conductive reservoir contact for commercial production. The post-stimulation production performance in deep, tight, and sour carbonate gas reservoirs often does not meet expectations due to complex reservoir characterization and poor transmissibility. The post-stimulation cleanup period often takes much longer due to resistance in unloading the pumped fluids. Carbon dioxide (CO2) with 30% foam quality (FQ) has been introduced for the first time during acid fracturing treatment in the tight, sour and high pressure, high temperature (HPHT) carbonate gas reservoir of Saudi Arabia to reduce consumption of fresh water, minimize reservoir damage, reduce the flowback period and eliminate the need for nitrogen lifting with coiled tubing (CT). The water and acid volume were reduced by one third through energizing the fluids system with CO2 during acid fracturing treatment in the candidate well. The Pad fluid was a zirconate crosslinked gel that was optimized for low pH to maintain stability in the presence of CO2. To minimize fluid leak-off and improve diversion effects, a chemical diverting system was included in the CO2 energized acid fracture treatment. A non-emulsifier foaming agent was used in the Pad and acid blends to create the desired emulsion with CO2. The post-fracture flowback period was reduced significantly and a 2.5 fold increase in the gas rate was realized. The addition of liquid CO2 to HCl in quantities sufficient to produce emulsion allows live acid to retard and penetrate much deeper than HCl itself. The CO2 strips hydrocarbon from the rock and allows acid to effectively react to the rock surface. CO2 remains in the liquid or supercritical phase during injection mode and flows back in the gas phase over a wide range of temperature and pressure allowing pumped fluids to recover in fast and safe manner. This paper is focused on laboratory tests of fluid systems, and the design, execution and evaluation of CO2 energized acid fracturing treatment, and a safe flowback strategy used for sour wells with high a concentration of CO2.
Up to three thousand barrels of stimulation fluids are pumped during a single vertical fracture treatment in carbonate reservoir of Saudi Arabia with the objective of creating sufficient conductive reservoir contact for commercial production. The post-stimulation production performance in deep, tight, and sour carbonate gas reservoirs often does not meet expectations due to complex reservoir characterization and poor transmissibility. The post-stimulation cleanup period often takes much longer due to resistance in unloading the pumped fluids. Carbon dioxide (CO2) with 30% foam quality (FQ) has been introduced for the first time during acid fracturing treatment in the tight, sour and high pressure, high temperature (HPHT) carbonate gas reservoir of Saudi Arabia to reduce consumption of fresh water, minimize reservoir damage, reduce the flowback period and eliminate the need for nitrogen lifting with coiled tubing (CT). The water and acid volume were reduced by one third through energizing the fluids system with CO2 during acid fracturing treatment in the candidate well. The Pad fluid was a zirconate crosslinked gel that was optimized for low pH to maintain stability in the presence of CO2. To minimize fluid leak-off and improve diversion effects, a chemical diverting system was included in the CO2 energized acid fracture treatment. A non-emulsifier foaming agent was used in the Pad and acid blends to create the desired emulsion with CO2. The post-fracture flowback period was reduced significantly and a 2.5 fold increase in the gas rate was realized. The addition of liquid CO2 to HCl in quantities sufficient to produce emulsion allows live acid to retard and penetrate much deeper than HCl itself. The CO2 strips hydrocarbon from the rock and allows acid to effectively react to the rock surface. CO2 remains in the liquid or supercritical phase during injection mode and flows back in the gas phase over a wide range of temperature and pressure allowing pumped fluids to recover in fast and safe manner. This paper is focused on laboratory tests of fluid systems, and the design, execution and evaluation of CO2 energized acid fracturing treatment, and a safe flowback strategy used for sour wells with high a concentration of CO2.
Saudi Aramco has long faced significant challenges to remove scales from the wells due to the high H2S contents and the sub hydrostatics reservoir pressure. Conventional techniques often fell short of expectations in the past, there had been cases of uncontrolled H2S releases at surface, which caused major HSE issues to the personnel; also coiled tubing (CT) got stuck due to sudden loss of circulation stemming from the inability to control the bottom-hole pressure and the instability of the fluid system during the scale removal treatment. As a result of those repeated issues, scale removal treatments were suspended for some time waiting for a safe technique to be devised. As a first step, the service company proposed to use a non-damaging chemical plug technique to temporarily plug the open perforations during the scale removal treatment, in an effort to avoid H2S release and to maintain circulation. The first results of this technique showed a marked improvement, which led the operator to resume the descaling operations, but in some operations the isolation process was extended several days and a large amount of fluid were injected into the formation, leading to induced damage, requiring high volume acid stimulation treatment and longtime flow back operation, to get the well back in production. To further optimize descaling operations via CT in Saudi Aramco, a novel scale removal technique was introduced that leverages the real-time downhole monitoring capabilities of CT equipped with fiber optics, to obtain a constant feedback on downhole conditions and allow swift adjustments to ensure safe operations. It also uses a redesigned foam system and implements a new pressure and fluid management system (PFMS), to eliminate the use of the temporary plug across the formation. With CT fiber-optic real-time telemetry, engineers can control the bottom-hole pressure throughout the intervention, to maintain the well slightly over-balanced and to prevent H2S from being released during fluid circulation. This system counts with a bottom-hole assembly (BHA) that gathers a full array of real-time sensors (pressure, temperature, casing collar locator, gamma ray, load measurements), and is compatible with downhole tools that require high flow rate to operate — in this case, a 2-7/8-in. turbine with a nominal flow rate of 2.8 bpm). This BHA can withstand a high level of shocks, vibrations and bottom-hole temperatures in excess of 300°F. As for the foam system, it ensures stable solid transport from downhole to surface conditions minimizing leak off into the formation, while the pressure flow management system (PFMS) is used to accurately control wellhead pressures, thanks to an array of auto chokes to control solid returns, and to remove entrained gasses (including H2S) from the returning fluid.
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