Experimental investigation on crack competitive extension during hydraulic fracturing in coal measures strata

Hu, Qianting; Liu, Le; Li, Quangui; Wu, Yueshen; Wang, Xiaoguang; Jiang, Zhizhong; Yan, Fazhi; Xu, Yangcheng; Wu, Xiaobin

doi:10.1016/j.fuel.2019.117003

Cited by 76 publications

(25 citation statements)

References 21 publications

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“…Coal reservoir types are classified based on the longitudinal thickness (from the vertical direction of coal seam), proportion, and spatial combination of different coal structures. The coal reservoirs can generate new fractures and are beneficial to reservoir reconstruction during fracturing because of the high strength and hardness of both the undeformed, and cataclastic, coal, while the reservoir is bad for reservoir reconstruction because of the crushing of granulated, and mylonite, coal [62]. For the analysis, the undeformed, and cataclastic coal are classified as hard coal and granulated, and mylonite coal are classified as soft coal [63].…”

Section: Classification Of Reservoir Type By Proportion and Combinatimentioning

confidence: 99%

Classification of Coal Structure Combinations and Their Influence on Hydraulic Fracturing: A Case Study from the Qinshui Basin, China

Liu

Wang

et al. 2020

Energies

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Coal structure directly correlates to permeability and hydraulic fracturing effects. Underground coal mining indicates that a single coal section generally contains multiple coal structures in superposition, making how to recognise the coal structure combination and predict its influence on coal permeability a challenging problem. Based on well-drilling sampled cores, the geological strength index (GSI), and well-logging data, the DEN, GR, CALX, and CALY were selected to establish a model to predict GSI by multiple regression to identify coal structure from 100 coalbed methane wells. Based on fitting GSI and corresponding permeability test values, injection fall-off (IFO) testing, and hydraulic fracturing results, permeability prediction models for pre- and post-fracturing behaviour were established, respectively. The fracturing effect was evaluated by the difference in permeability. The results show that a reservoir can be classified into one of nine types by different coal structure thickness proportion (and combinations thereof) and the fracturing curves can be classified into four categories (and eight sub-categories) by the pressure curve. Up-down type I and type II reservoirs (proportion of hard coal >60%) and intervening interval type I reservoir (proportion of hard coal >70%) are prone to form stable and descending fracturing curves and the fracturing effects are optimal. Intervening interval type II (hard coal:soft coal:hard coal or soft coal:hard coal:soft coal ≈1:1:1) and up-down type III (hard coal:soft coal =1:1) form descending type II, rising type I and fluctuating type I fracturing curves and fracturing effect ranks second; up-down type IV and V (proportion of hard coal <40%), interval type III (proportion of hard coal <30%), and multi-layer superposition-type reservoirs readily form fluctuating and rising fracturing curves and fracturing effects therein are poor. The research results provide guidance for the targeted stimulation measured under different coal structure combinations.

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Section: Classification Of Reservoir Type By Proportion and Combinatimentioning

confidence: 99%

Classification of Coal Structure Combinations and Their Influence on Hydraulic Fracturing: A Case Study from the Qinshui Basin, China

Liu

Wang

et al. 2020

Energies

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“…Warpinski and Teufel et al (1987) revealed from field results that the in-situ stress and fluid pressure could influence the hydraulic fracturing procedure. The effects of elastic modulus, Poisson's ratio, and in-situ stress on fracture geometry were studied by means of experiment and field investigation (Liang et al, 2017;Chen et al, 2019;Hu et al, 2020;Liu et al, 2020). For instance, Li et al (2014) comprehensively studied the effect of the formation mechanical property (in-situ stress, elastic modulus, and permeability) differences between adjacent layers over hydraulic fracture propagation, and it turned out that the mechanical properties of strata have a great influence on the fracture extension; Yinlong investigated the influence of the intermediate principal stress on the mechanical properties of cubic coal and soft sandstone under two different true triaxial loading conditions and discussed the influence interval of the intermediate principal stress on the strength of sandstone and coal in detail.…”

Section: Introductionmentioning

confidence: 99%

Numerical Simulation of Fracture Propagation Characteristics of Hydraulic Fracturing in Multiple Coal Seams, Eastern Yunnan, China

et al. 2022

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As a reservoir reconstruction technology, hydraulic fracturing is a key method to improve the production of coalbed methane (CBM) wells. The CBM reservoir in eastern Yunnan, an important CBM exploration and development zone in China, is characterized by multiple thin coal seams. Compared to the fracturing of the single-layer coal seam, the combined seam fracturing technology is more difficult and complex. To study the fracture propagation characteristics and influencing factors of hydraulic fracturing in multiple coal seams, taking No. 9 and No. 13 coal seams as the research objects, the fracturing process was numerically simulated by using the finite element method and ANSYS software in this work. Based on the mathematical model of low permeable coal-rock mass, a two-dimensional hydraulic fracture model was established. In addition, the fracture geometries of combined seam fracturing were studied quantitatively. The results indicate that although No. 9 coal and No. 13 coal seams have similar rock mechanical properties, the propagation process and final geometry of a fracture are different. The reliability of the simulation results is verified by the comparison of experimental parameters and field investigation. The results prove the feasibility of combined seam fracturing in eastern Yunnan. The high Young’s modulus and thickness of the coal seam make the fracture geometry longer, but the fracture height is smaller. The low Young’s modulus, high Poisson’s ratio, and thickness of the No. 13 coal seam result in an increase in the length and height of the No. 9 coal seam. The increase in Young’s modulus of interlayer inhibits the propagation of fractures, while the high thickness and low Poisson’s ratio of interlayers facilitate the extension of the length and inhibit the extension of the height. This work provides a case reference for combined seam fracturing of coal reservoirs and has practical significance for the development of CBM characterized by multiple coal seams in eastern Yunnan.

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“…Geometric shape, and in the case of multi-layer fracturing, the cracks of thinner or softer coal seams will develop and expand first. 25,26 Shuai Chen compared the coal sample fracturing method with liquid nitrogen injection with pure water, and liquid nitrogen can effectively promote the generation of macroscopic cracks in the coal and increase the degree of coal sample damage under constant confining pressure. As the injection pressure increases, the penetration rate is exponentially increasing.…”

Section: Introductionmentioning

confidence: 99%

Variation law of roof stress and permeability enhancement effect of repeated hydraulic fracturing in low‐permeability coal seam

Liangwei

2021

Energy Science & Engineering

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Experimental investigation on crack competitive extension during hydraulic fracturing in coal measures strata

Cited by 76 publications

References 21 publications

Classification of Coal Structure Combinations and Their Influence on Hydraulic Fracturing: A Case Study from the Qinshui Basin, China

Classification of Coal Structure Combinations and Their Influence on Hydraulic Fracturing: A Case Study from the Qinshui Basin, China

Numerical Simulation of Fracture Propagation Characteristics of Hydraulic Fracturing in Multiple Coal Seams, Eastern Yunnan, China

Variation law of roof stress and permeability enhancement effect of repeated hydraulic fracturing in low‐permeability coal seam

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