Development of new testing procedures to measure propped fracture conductivity considering water damage in clay-rich shale reservoirs: An example of the Barnett Shale

Zhang, Junjing; Kamenov, Anton; Zhu, Ding; Hill, A.D.

doi:10.1016/j.petrol.2015.09.025

Cited by 30 publications

(16 citation statements)

References 19 publications

(17 reference statements)

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“…In this study, transient tests were conducted to measure the permeability to CO 2 at different pressures. The permeability values were calculated using Equations (5) and (6) [35], where a pressure difference between upstream and downstream less than 0.2 MPa is adopted to reduce the influence of pore pressure on permeability:…”

Section: Permeability Testing Under Transient Conditionsmentioning

confidence: 99%

“…Water-based fracturing fluids are currently used, but the combination of water and shale matrix with strong water imbibition results in severe formation damage. The softening effect caused by the imbibition of water can lead to strength reduction of fracture surfaces, and large deformation of fracture surfaces greatly reduces its self-propping potential and increases the embedment depth of proppants, which greatly compress the fracture width and may even close the fracture completely [4,5]. The imbibition of water into the shale matrix easily causes a blocking effect in tiny pore throats, which closes the channels for gas transport from the shale matrix to the created fractures [6].…”

Section: Introductionmentioning

confidence: 99%

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Experimental Study of Matrix Permeability of Gas Shale: An Application to CO2-Based Shale Fracturing

Zhang

Ranjith

2018

Energies

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Because the limitations of water-based fracturing fluids restrict their fracturing efficiency and scope of application, liquid CO 2 is regarded as a promising substitute, owing to its unique characteristics, including its greater environmental friendliness, shorter clean-up time, greater adsorption capacity than CH 4 and less formation damage. Conversely, the disadvantage of high leak-off rate of CO 2 fracturing due to its very low viscosity determines its applicability in gas shales with ultra-low permeability, accurate measurement of shale permeability to CO 2 is therefore crucial to evaluate the appropriate injection rate and total consumption of CO 2. The main purpose of this study is to accurately measure shale permeability to CO 2 flow during hydraulic fracturing, and to compare the leak-off of CO 2 and water fracturing. A series of permeability tests was conducted on cylindrical shale samples 38 mm in diameter and 19 mm long using water, CO 2 in different phases and N 2 considering multiple influencing factors. According to the experimental results, the apparent permeability of shale matrix to gaseous CO 2 or N 2 is greatly overestimated compared with intrinsic permeability or that of liquid CO 2 due to the Klinkenberg effect. This phenomenon explains that the permeability values measured under steady-state conditions are much higher than those under transient conditions. Supercritical CO 2 with higher molecular kinetic energy has slightly higher permeability than liquid CO 2. The leak-off rate of CO 2 is an order of magnitude higher than that of water under the same injection conditions due to its lower viscosity. The significant decrease of shale permeability to gas after water flooding is due to the water block effect, and much longer clean-up time and deep water imbibition depth greatly impede the gas transport from the shale matrix to the created fractures. Therefore, it is necessary to substitute water-based fracturing fluids with liquid or super-critical CO 2 in clay-abundant shale formations.

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Section: Permeability Testing Under Transient Conditionsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Experimental Study of Matrix Permeability of Gas Shale: An Application to CO2-Based Shale Fracturing

Zhang

Ranjith

2018

Energies

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“…Shale and proppant properties combined control the propped fracture conductivity along with the closure stress. , When the proppant load is low, the conductivity is mainly controlled by the shale properties. Contrary to the high proppant load, the proppant characteristics become more important in determining the fracture conductivity. , …”

Section: Introductionmentioning

confidence: 99%

Machine Learning-Based Propped Fracture Conductivity Correlations of Several Shale Formations

et al. 2021

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In hydraulic fracturing operations, small rounded particles called proppants are mixed and injected with fracture fluids into the targeted formation. The proppant particles hold the fracture open against formation closure stresses, providing a conduit for the reservoir fluid flow. The fracture’s capacity to transport fluids is called fracture conductivity and is the product of proppant permeability and fracture width. Prediction of the propped fracture conductivity is essential for fracture design optimization. Several theoretical and few empirical models have been developed in the literature to estimate fracture conductivity, but these models either suffer from complexity, making them impractical, or accuracy due to data limitations. In this research, and for the first time, a machine learning approach was used to generate simple and accurate propped fracture conductivity correlations in unconventional gas shale formations. Around 350 consistent data points were collected from experiments on several important shale formations, namely, Marcellus, Barnett, Fayetteville, and Eagle Ford. Several machine learning models were utilized in this research, such as artificial neural network (ANN), fuzzy logic, and functional network. The ANN model provided the highest accuracy in fracture conductivity estimation with R 2 of 0.89 and 0.93 for training and testing data sets, respectively. We observed that a higher accuracy could be achieved by creating a correlation specific for each shale formation individually. Easily obtained input parameters were used to predict the fracture conductivity, namely, fracture orientation, closure stress, proppant mesh size, proppant load, static Young’s modulus, static Poisson’s ratio, and brittleness index. Exploratory data analysis showed that the features above are important where the closure stress is the most significant.

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“…The slick‐water damage directly influences the exploitation of shale reservoirs. Therefore, the overall operation tendency of shale fracturing is to reduce the slick‐water damage to the reservoirs …”

Section: Introductionmentioning

confidence: 99%

“…Therefore, the overall operation tendency of shale fracturing is to reduce the slick-water damage to the reservoirs. [23][24][25] The current practice is to reduce the molecular weight of PAM before flowing back. It is believed that a low molecular weight chain is fit to recover the permeability of shale reservoirs.…”

Section: Introductionmentioning

confidence: 99%

Reduced adsorption of polyacrylamide‐based fracturing fluid on shale rock using urea

Yang

Wang

Guo

et al. 2018

Energy Science & Engineering

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Hydraulic fracturing is generally necessary to achieve economically viable production rates during exploitation of shale reservoirs. Polyacrylamide‐based fracturing fluid is commonly used in shale fracturing. Polyacrylamide (PAM) becomes adsorbed in the shale micro‐fractures, decreasing the permeability of the reservoir. For improving the production of shale after being stimulated, the adsorption behavior and adsorption mechanism between the PAM and shale are studied. An ultraviolet spectrophotometer is used to obtain the amount of adsorption. To observe the adsorption morphology, a scanning electron microscope is employed. The action force between the PAM and shale rock is analyzed through Fourier transform infrared spectroscopy, zeta potential instrument, and X‐ray photoelectron spectroscopy. The results indicate that hydrogen bonding is the key force between the PAM and shale. A kind of shale micro‐fractures model is designed to determine the recovery of permeability. Urea breaks the hydrogen bonding and keeps the molecular of HPG stretch which can decrease the amount of adsorption on the shale surface and effectively recover the permeability of shale micro‐fractures up to 72.46% after being damaged. In conclusion, it is believed that the competitive adsorption is a new approach for remediation of the permeability damage by PAM‐based fracturing fluid and has great potential in oil field application.

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Development of new testing procedures to measure propped fracture conductivity considering water damage in clay-rich shale reservoirs: An example of the Barnett Shale

Cited by 30 publications

References 19 publications

Experimental Study of Matrix Permeability of Gas Shale: An Application to CO2-Based Shale Fracturing

Experimental Study of Matrix Permeability of Gas Shale: An Application to CO2-Based Shale Fracturing

Machine Learning-Based Propped Fracture Conductivity Correlations of Several Shale Formations

Reduced adsorption of polyacrylamide‐based fracturing fluid on shale rock using urea

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