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Acid Fracturing

The Experts below are selected from a list of 1533 Experts worldwide ranked by ideXlab platform

Ruxin Zhang – 1st expert on this subject based on the ideXlab platform

  • effect of Acid Fracturing on carbonate formation in southwest china based on experimental investigations
    Journal of Natural Gas Science and Engineering, 2020
    Co-Authors: Bocheng Zhou, Ruxin Zhang, Yue Xiao, Kunpeng Zhang

    Abstract:

    Abstract Acid Fracturing is the most effective stimulation method to obtain a high production of carbonate formation which is an important oil and gas resource for China to meet the increase in demand for energy. However, the tough reservoir characteristics of carbonate formation, deeply buried, high pressure and temperature and complex reservoir space, cause the mechanism of Acid Fracturing ambiguous. Therefore, a series of experiments are conducted on outcrop cores and downhole cores to study the effect of clean Acid and gelled Acid on carbonate formation. Moreover, the 3D scanner is used to depict the uneven surface of Acid etched fracture. The results of rock mechanics experiments indicate that Acidizing decreases rock mechanics properties: gelled Acid reduces compression strength and Poisson’s ratio, whereas, clean Acid lowers tensile strength and Young’s modulus. Furthermore, 3D scanning digital images reveal that the reaction between Acid and rock matrix results in two main surface etching patterns: rough etching pattern is generated by clean Acid, but channel etching pattern is created by gelled Acid. Based on the results of fracture conductivity experiments, Acid etched fracture conductivity depends on surface etching pattern and mineral content. Channel etching and high calcite content are conducive to a high fracture conductivity. In addition, Acid etched fracture propagation behavior is affected by Acid type and natural fractures. Clean Acid causes a small and narrow Acid affected area, but gelled Acid results in a larger and broader one. Therefore, fracture conductivity and fracture propagation behavior are two important factors to evaluate the effectiveness of Acid Fracturing.

  • investigation on Acid Fracturing treatment in limestone formation based on true tri axial experiment
    Fuel, 2019
    Co-Authors: Ruxin Zhang, Mian Chen

    Abstract:

    Abstract Acid Fracturing treatment is the most effective method for stimulating limestone formations, which are abundant in the northeast Sichuan basin of China. The effective Acid etching improves the fracture width, resulting in high fracture conductivity, while fracture propagation behavior is always affected by discontinuities and the fractured vuggy structure. Hence, the fracture geometry differs from that in homogeneous formations. However, the fracture propagation mechanism remains unclear. In order to understand the process more clearly, a series of large-scale, true tri-axial simulation experiments were conducted for the first time to investigate the fracture initiation and propagation in limestone formations under Acid Fracturing treatment. Moreover, the effects of multiple factors on fracture propagation were discussed, and a 3D scanner was used to depict and describe the fracture surface etching feature. The experimental results demonstrated that natural fractures had a serious impact on the fracture initiation and propagation. The induced fracture initiated from the open-hole section to form a transverse fracture, or from the natural fractures to form a longitudinal or an inclined fracture. The fracture surface was rougher in the Acid Fracturing than in hydraulic Fracturing, owing to the non-uniform Acid fluid dissolution. The black-brown remains on the fracture surface were the result of Acid etching, which could be used to judge the fracture propagation direction and area. However, the roughness degree of the fracture surface near the wellbore was larger than that far from the wellbore. Furthermore, HCL fluid was likely to etch the fracture surface within a short propagation distance, while clean-Acid fluid promoted induced fractures to propagate at a long distance. Furthermore, a slow decrease in the extension pressure in the fracture curve indirectly indicated that the Acid fluid reacted with the matrix and propagated slowly, which was a sign of successful Acid Fracturing treatment. According to the experimental results, the Acid etched width and fracture propagation distance are assumed to be two important factors for estimating the Acid Fracturing treatment performance.

Mian Chen – 2nd expert on this subject based on the ideXlab platform

  • Study of alternating Acid Fracturing treatment in carbonate formation based on true tri-axial experiment
    Journal of Petroleum Science and Engineering, 2020
    Co-Authors: Kunpeng Zhang, Mian Chen, Changlin Zhou, Li Jiaxin

    Abstract:

    Abstract Acid Fracturing is a useful technique to stimulate carbonate reservoirs. Nowadays, Acid leak-off becomes a vital problem during the operation of Acid Fracturing. In order to encounter this issue, alternating Acid Fracturing has been developed. However, the fracture propagation and the interaction between hydraulic fractures and natural fractures/caves during alternating Acid Fracturing are ambiguous. Hence, a series of alternating Acid Fracturing experiments covering coupling mechanics and chemical interaction were conducted for the first time. In this study, slick water, self-generating Acid, cross-linked gel, and gelled Acid were used as a Fracturing fluid whereas the specimens for this experiment are carbonate outcrop which excavated from Dengsi Formation. The results show that: (1) Acid Fracturing can reduce Fracturing pressure effectively as the Acid will etch and weaken the natural fractures to let them easily connecting each other; (2) different pad fluid properties will have different impacts on the Acid Fracturing performance; (3) the interaction of hydraulic fractures and natural filled caves can be divided into five categories, and two of them had been observed in the experiments. Moreover, a new curvature-calculation algorithm has been developed based on the 3-D scanning technology. The results have a great significance for Acid Fracturing design and physical simulation experiments.

  • investigation on Acid Fracturing treatment in limestone formation based on true tri axial experiment
    Fuel, 2019
    Co-Authors: Ruxin Zhang, Mian Chen

    Abstract:

    Abstract Acid Fracturing treatment is the most effective method for stimulating limestone formations, which are abundant in the northeast Sichuan basin of China. The effective Acid etching improves the fracture width, resulting in high fracture conductivity, while fracture propagation behavior is always affected by discontinuities and the fractured vuggy structure. Hence, the fracture geometry differs from that in homogeneous formations. However, the fracture propagation mechanism remains unclear. In order to understand the process more clearly, a series of large-scale, true tri-axial simulation experiments were conducted for the first time to investigate the fracture initiation and propagation in limestone formations under Acid Fracturing treatment. Moreover, the effects of multiple factors on fracture propagation were discussed, and a 3D scanner was used to depict and describe the fracture surface etching feature. The experimental results demonstrated that natural fractures had a serious impact on the fracture initiation and propagation. The induced fracture initiated from the open-hole section to form a transverse fracture, or from the natural fractures to form a longitudinal or an inclined fracture. The fracture surface was rougher in the Acid Fracturing than in hydraulic Fracturing, owing to the non-uniform Acid fluid dissolution. The black-brown remains on the fracture surface were the result of Acid etching, which could be used to judge the fracture propagation direction and area. However, the roughness degree of the fracture surface near the wellbore was larger than that far from the wellbore. Furthermore, HCL fluid was likely to etch the fracture surface within a short propagation distance, while clean-Acid fluid promoted induced fractures to propagate at a long distance. Furthermore, a slow decrease in the extension pressure in the fracture curve indirectly indicated that the Acid fluid reacted with the matrix and propagated slowly, which was a sign of successful Acid Fracturing treatment. According to the experimental results, the Acid etched width and fracture propagation distance are assumed to be two important factors for estimating the Acid Fracturing treatment performance.

Shicheng Zhang – 3rd expert on this subject based on the ideXlab platform

  • a new method to improve long term fracture conductivity in Acid Fracturing under high closure stress
    Journal of Petroleum Science and Engineering, 2018
    Co-Authors: Lufeng Zhang, Guoqing Xu, Shicheng Zhang, Fujian Zhou, Zhun Li

    Abstract:

    Abstract Acid propped Fracturing is one of the most effective methods to enhance the stimulation effect, especially in the high-temperature deep carbonate formation. However, the short-term conductivity experimental data used in existing Acid Fracturing optimal designs may not be directly applicable to the real case. Aiming at this problem, this paper conducted a research on long-term Acid conductivity behavior and proposed a new method to raise Acid fracture conductivity under high closure stress. Frist, a series of experiments with carbonate core samples were conducted to investigate long-term Acid conductivity behavior of carbonate reservoirs with closure stress up to 100 MPa. Gelled and cross-linked Acids with different Acid-rock contact times were tested to analyze the effects of Acid type and Acid-rock contact time on the conductivity. Next, Acid fracture conductivity by adding proppant was tested to investigate the feasibility of increasing Acid fracture conductivity under high closure stress. Long-term conductivity was measured up to 168 h to analyze the impact of deformation and embedment of proppant on conductivity. Finally, proppant size and concentration on conductivity were optimized for maximizing conductivity. The study shows that the conductivity with gelled Acid is higher than the case with cross-linked Acid for the same contact time. When the contact time is 60 min, gelled Acid fracture conductivity has already reached its upper limit. The ideal combination of proppant size and concentration are optimized at different stress level. When the closure pressure is below 50 MPa, the conductivity is the highest at the proppant concentration of 0.75 kg/m2 using 20/40 mesh proppant. While the closure pressure exceeds 50 MPa, the conductivity is the highest at the proppant concentration of 3 kg/m2 using 40/70 mesh proppant. The Acid propped fracture conductivity decreases rapidly in 48 h and undergoes the gradual drop, remaining steady after 120 h. An analytical model of Acid propped fracture conductivity was also developed. This study provided an insight into optimizing Acid propped Fracturing design and predicting well performance.

  • wormhole propagation behavior and its effect on Acid leakoff under in situ conditions in Acid Fracturing
    Transport in Porous Media, 2014
    Co-Authors: Shenglai Yang, Ye Zhang, Shicheng Zhang

    Abstract:

    In Acid Fracturing, excessive Acid leakoff is thought to be the main reason that limits fracture propagation and live Acid penetration distance. Although Acid leakoff has been studied under experimental conditions, the Acid leakoff theory developed under experimental conditions cannot be extended to in situ conditions because the injection rate or pressure drop across a core plug is fixed in the experiments. In this paper, we used a model that couples a two-scale continuum model simulating wormholing in the invaded zone and a reservoir flow model for the compressed zone to simulate Acid leakoff process under in situ conditions. Based on this model, we investigated wormhole propagation behavior and its effect on Acid leakoff under in situ conditions. The study shows different wormhole propagation behavior under in situ conditions from that under experimental conditions. Wormholes grow fast at the beginning and slow down at later time due to the rise of reservoir pressure caused by the leakoff and the growth of the invaded zone. In oil reservoirs, wormholing has minor effect on Acid leakoff because of small compressibility and relatively high reservoir fluid viscosity, but in gas reservoirs, the influence of wormholing on Acid leakoff becomes significant due to large compressibility and low reservoir fluid viscosity. Acid viscosity has more notable influence on Acid leakoff in gas reservoirs than in oil reservoirs.

  • Acid leakoff mechanism in Acid Fracturing of naturally fractured carbonate gas reservoirs
    Advanced Materials Research, 2013
    Co-Authors: Lin Jing Xu, Shicheng Zhang

    Abstract:

    In Acid Fracturing, excessive Acid leakoff is thought to be the main reason that limits fracture propagation and live Acid penetration distance, so its very important to do research about Acid leak-off on naturally fractured carbonates. we developed a new model in this paper to simulate Acid leakoff into a naturally fractured carbonates gas reservoir during Acid Fracturing. Our model incorporates the Acid-rock reaction on the fractured surfaces. Given the information of the Puguang gas reservoir, the model predicts Acid filtration and leakoff rate over time. In this study, we found that Acid leak-off mechanism in naturally fractured carbonates is much different from that in reservoirs without natural fractures. The leakoff volume is several times of nonreactive Acid. Since the Acid widened natural fractures, leakoff velocity increase with time firstly , then decrease. While the leakoff velocity of the nonreactive fluid decrease sustained. We also analyze other sensitivity parameters of the Acid leakoff. In this model, we explain the Acid leakoff mechanism in naturally fractured carbonates, and provide a more accurate calculating of fluid loss.