scholarly journals Numerical investigation on rules of fracture propagation during hydraulic fracturing in heterogeneous coal-rock mass

2019 ◽  
Vol 21 (4) ◽  
pp. 1147-1162 ◽  
Author(s):  
Zhigang Yuan ◽  
Yaohua Shao ◽  
Donghai Xie ◽  
Fei Huang
Keyword(s):  
Rock Mass ◽  
Hydraulic Fracturing ◽  
Numerical Investigation ◽  
Fracture Propagation ◽  
Coal Rock

Numerical Simulation of Hydraulic Fracture Propagation Characteristics of Low Permeable Coal-Rock Mass

2012 ◽  
Vol 482-484 ◽  
pp. 1668-1671 ◽  
Author(s):  
Zhi Gang Yuan ◽  
Hong Tu Wang ◽  
Nian Ping Liu
Keyword(s):  
Rock Mass ◽  
Hydraulic Fracturing ◽  
Hydraulic Fracture ◽  
Fracture Propagation ◽  
Injection Pressure ◽  
Horizontal Stress ◽  
Propagation Model ◽  
Fracture Length ◽  
Coal Rock ◽  
Hydraulic Fracture Propagation

Based on the coal-rock mass deformation model, hydraulic pressure descent model in fracture, fracture propagation model and its growth criterion, the mathematical model of hydraulic fracturing of low permeable coal-rock mass is established, and the influencing factors such as injection pressure, elastic modulus of coal-rock mass and in-situ stress, which affect the characteristics of hydraulic fracture propagation, are studied using the ANSYS software. The results show that fracture length presents a linear increase and widest width increases as an exponent function with the increase of injection pressure, and the ability of making fracture width is greater than fracture length during late fracturing; besides, with the increase of Young’s modulus of coal-rock mass and least horizontal stress, fracture length and widest width decrease, which are independent of maximum horizontal stress. The obtained conclusions provide a guiding role for the optimization of operation parameters of field hydraulic fracturing of low permeable coal-rock.

scholarly journals Numerical Modeling on Hydraulic Fracturing in Coal-Rock Mass for Enhancing Gas Drainage

2018 ◽  
Vol 2018 ◽  
pp. 1-16 ◽  
Author(s):  
Zhigang Yuan ◽  
Yaohua Shao
Keyword(s):  
Mathematical Model ◽  
Rock Mass ◽  
Hydraulic Fracturing ◽  
Gas Flow ◽  
Numerical Solutions ◽  
Fracture Initiation ◽  
Engineering Practice ◽  
Gas Drainage ◽  
Fracturing Process ◽  
Coal Rock

The mechanism of how hydraulic fracturing influences gas drainage in coal-rock mass is still not clear due to its complex mechanism. In this work, statistical distributions are firstly introduced to describe heterogeneity of coal-rock mass; a novel simultaneously coupled mathematical model, which can describe the fully coupled process including seepage-damage coupling during hydraulic fracturing process and subsequent gas flow during gas drainage process, is established; its numerical implementation procedure is coded into a Matlab program to calculate the damage variables, and it partly uses COMSOL solver to obtain numerical solutions of governing equations with damage-flow coupling; the mathematical model and its implementation are validated for initial damage pressure and mode of a single solid model without considering flow-damage coupling, as well as fracture initiation pressure and influence of heterogeneity on damage evolution of hydraulic fracturing considering flow-damage coupling; and finally, based on an engineering practice of hydraulic fracturing with two boreholes, the mechanism of how hydraulic fracturing influences gas drainage is investigated, numerical simulation results indicate that coal-rock mass pore-fissure structure has been improved, and there would exist a gas migration channel with characteristics of higher porosity and lower stresses, which demonstrates significant effects and mechanism of hydraulic fracturing on improving coal-rock permeability and enhancing gas drainage. The research results provide a guide for operation of hydraulic fracturing and optimal layout of gas drainage boreholes.

scholarly journals Mechanisms of Crack Initiation and Propagation in Dense Linear Multihole Directional Hydraulic Fracturing

2019 ◽  
Vol 2019 ◽  
pp. 1-15
Author(s):  
Jiangwei Liu ◽  
Changyou Liu ◽  
Qiangling Yao
Keyword(s):  
Rock Mass ◽  
Crack Initiation ◽  
Hydraulic Fracturing ◽  
Principal Stress ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Crack Initiation And Propagation ◽  
Initiation And Propagation ◽  
Coal Rock

Artificially fracturing coal-rock mass serves to form break lines therein, which is related to the distribution of cracked boreholes. For this reason, we use physical experiments and numerical simulations to study the crack initiation and propagation characteristics of dense linear multihole drilling of fractured coal-rock mass. The results indicate that only in the area between the first and last boreholes can hydraulic fracturing be controlled by dense linear multihole expansion along the direction of the borehole line; in addition, no directional fracturing occurs outside the drilling section. Upon increasing parameters such as the included angle θ between the drilling arrangement line and the maximum principal stress σ1 direction, the drilling spacing D, the difference Δσ in principal stress, etc., the effect of directional fracture is gradually weakened, and the hydraulic fractures reveal three typical cracking modes: cracking along the borehole line, bidirectional cracking (along the borehole line and perpendicular to the minimum principal stress σ3), and cracking perpendicular to σ3. Five propagation modes also appear in sequence: propagating along borehole line, step-like propagation, S-shaped propagation, bidirectional propagation (along the borehole line and perpendicular to σ3), and propagation perpendicular to σ3. Based on these results, we report the typical characteristics of three-dimensional crack propagation and discuss the influence of the gradient of pore water pressure. The results show clearly that crack initiation and propagation are affected by both the geostress field and the pore water pressure. The pore water pressure will exhibit a circular-local contact-to-integral process during crack initiation and expansion. When multiple cracks approach, the superposition of pore water pressure at the tip of the two cracks increases the damage to the coal rock, which causes crack reorientation and intersection.

Investigation of the influence of natural fractures and in situ stress on hydraulic fracture propagation using a distinct-element approach

2015 ◽  
Vol 52 (7) ◽  
pp. 926-946 ◽  
Author(s):  
N. Zangeneh ◽  
E. Eberhardt ◽  
R.M. Bustin
Keyword(s):  
Rock Mass ◽  
Hydraulic Fracturing ◽  
Hydraulic Fracture ◽  
Distinct Element ◽  
Fracture Propagation ◽  
In Situ Stress ◽  
Natural Fractures ◽  
Geological Conditions ◽  
Hydraulic Fracture Propagation

Hydraulic fracturing is the primary means for enhancing rock mass permeability and improving well productivity in tight reservoir rocks. Significant advances have been made in hydraulic fracturing theory and the development of design simulators; however, these generally rely on continuum treatments of the rock mass. In situ, the geological conditions are much more complex, complicated by the presence of natural fractures and planes of weakness such as bedding planes, joints, and faults. Further complexity arises from the influence of the in situ stress field, which has its own heterogeneity. Together, these factors may either enhance or diminish the effectiveness of the hydraulic fracturing treatment and subsequent hydrocarbon production. Results are presented here from a series of two-dimensional (2-D) numerical experiments investigating the influence of natural fractures on the modeling of hydraulic fracture propagation. Distinct-element techniques applying a transient, coupled hydromechanical solution are evaluated with respect to their ability to account for both tensile rupture of intact rock in response to fluid injection and shear and dilation along existing joints. A Voronoi tessellation scheme is used to add the necessary degrees of freedom to model the propagation path of a hydraulically driven fracture. The analysis is carried out for several geometrical variants related to hypothetical geological scenarios simulating a naturally fractured shale gas reservoir. The results show that key interactions develop with the natural fractures that influence the size, orientation, and path of the hydraulic fracture as well as the stimulated volume. These interactions may also decrease the size and effectiveness of the stimulation by diverting the injected fluid and proppant and by limiting the extent of the hydraulic fracture.

scholarly journals Analysis of seismic tomography data for definition of hydraulic fracturing parameters in underground coal mines

2021 ◽  
Vol 315 ◽  
pp. 01021
Author(s):  
Gennadii Rout ◽  
Sergey Sokolov ◽  
Evgeniy Utkaev ◽  
Kolmakova Anastasiya
Keyword(s):  
Rock Mass ◽  
Hydraulic Fracturing ◽  
Seismic Exploration ◽  
Reliable Estimate ◽  
Underground Coal Mines ◽  
Before And After ◽  
Coal Rock ◽  
Definition Of ◽  
Rock Mass Fracturing ◽  
Excavation Site

The article analyzes the issue of reliable estimate of the unloading extent and the variation order of coal-rock massif geomechanical characteristics as a result of hydraulic fracturing undertaken from mine workings. For this purpose it is proposed to use the fracturing value of the studied rock mass. In case the possibility of comparison with geological and actual data doesn’t exist, the option of using the rock mass classification based on the estimated value of geophysical index that specifies rock mass fracturing is considered. To address the issue, a geophysical survey of the active roof at the excavation site in the operating coal mine was implemented with a method of a seismic radioscopy before and after hydraulic fracturing. According to the results of seismic exploration, a massif unloading degree and an extent of roof fracturing has been determined.

scholarly journals Combination of Pre-Pulse and Constant Pumping Rate Hydraulic Fracturing for Weakening Hard Coal and Rock Mass

Energies ◽  
2020 ◽  
Vol 13 (21) ◽  
pp. 5534
Author(s):  
Qingying Cheng ◽  
Bingxiang Huang ◽  
Luying Shao ◽  
Xinglong Zhao ◽  
Shuliang Chen ◽  
...  
Keyword(s):  
Rock Mass ◽  
Hydraulic Fracturing ◽  
Coal Mine ◽  
Longwall Mining ◽  
Block Size ◽  
Hard Coal ◽  
Pumping Rate ◽  
Thick Coal Seam ◽  
Coal Rock ◽  
Mining Face

The weakening of hard coal–rock mass is the core common problem that is involved in the top coal weakening in hard and thick coal seams, the hard roof control during the initial mining stage in the longwall mining face, and the hanging roof control in the gob of non-coal mine. Based on the characteristics of pulse hydraulic fracturing and constant pumping rate hydraulic fracturing, a weakening method for hard coal–rock mass by combining pre-pulse and constant pumping rate hydraulic fracturing is proposed. A complete set of equipment for the combined pulse and constant pumping rate hydraulic fracturing construction in the underground coal mine is developed. The pulse and constant pumping rate hydraulic fracturing technology and equipment were applied in the top coal weakening of the shallow buried thick coal seam. Compared with no weakening measures for top coal, the average block size of the top coal caving was reduced by 42% after top coal hydraulic fracturing. The recovery rate of the top coal caving mining face reached 85%, and it increased by 18% after hydraulic fracturing.

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