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 Study on gas drainage effect of hydraulic fracturing in soft coal seam

2020 ◽  
Vol 185 ◽  
pp. 01004
Author(s):  
Liangwei Li
Keyword(s):  
Coal Seam ◽  
Hydraulic Fracturing ◽  
Gas Flow ◽  
Water Injection ◽  
Fracture Initiation ◽  
Gas Content ◽  
Gas Drainage ◽  
Soft Coal ◽  
Drainage Effect ◽  
Soft Coal Seam

Aiming at the difficulty of gas drainage by drilling along the seam in soft coal seam, the permeability of coal seam was increased by hydraulic fracturing test in the field, and the permeability and gas drainage parameters of coal seam before and after fracturing were studied. The results show that: ① The fracture initiation pressure of 3# coal seam in Guojiahe coal mine is 15~20MPa. When the water injection is 30~40m3, the fracturing radius is 15m, when the water injection is 50 ~ 60m3, the fracturing radius can reach 20m, when the water injection reaches 70m3, the fracturing radius can reach 30m; ② Driven by high pressure water, the gas in the fractured area migrates to the unfractured area, and the gas content in the fractured area decreases; ③ The attenuation coefficient of natural gas flow after fracturing is reduced by 50% compared with that before fracturing, and the permeability coefficient of coal seam after fracturing is increased by 50 times compared with that of original area; ④ The recovery concentration after fracturing is much higher than that before fracturing.

Numerical Simulation on Propagation Mechanism of Hydraulic Fracture in Fractured Rockmass

2014 ◽  
Vol 488-489 ◽  
pp. 417-420 ◽  
Author(s):  
Xiao Xi Men ◽  
C.A. Tang ◽  
Zhi Hui Han
Keyword(s):  
Hydraulic Fracturing ◽  
Fracture Initiation ◽  
Coupling Model ◽  
Natural Fracture ◽  
Tensile Fracture ◽  
Propagation Mechanism ◽  
Initiation And Propagation ◽  
Fracturing Process ◽  
Two Factors ◽  
Seepage Characteristics

Hydraulic fracturing process in fractured rockmass which with an existing single natural fracture at its various conditions: its different angles and different lengths was simulated by using RFPA2D(2.0)-Flow version which adopts the finite element method and considers the heterogeneous characteristics of rock in meso-scale, creates seepage-stress-failure coupling model. The effect tendency of natural fractures angle and length on the seepage characteristics of fractured rockmass was given through the description of tensile fracture initiation and propagation in the rock specimens. The simulation results show that the effect of these two factors on fractures initiation, propagation and rockmass stability under the hydraulic fracturing could be remarkable.

scholarly journals Simplified Mathematical Model for the Description of Anomalous Migration of Soluble Substances in Vertical Filtration Flow

2020 ◽  
Vol 4 (2) ◽  
pp. 20
Author(s):  
Vsevolod Bohaienko ◽  
Volodymyr Bulavatsky
Keyword(s):  
Mathematical Model ◽  
Numerical Solutions ◽  
Initial Boundary ◽  
Initial Boundary Value Problem ◽  
Filtration Velocity ◽  
Engineering Practice ◽  
Filtration Flow ◽  
Complex Flow ◽  
Flow Potential ◽  
Simplified Mathematical Model

Since the use of the fractional-differential mathematical model of anomalous geomigration process based on the MIM (mobile–immoble media) approach in engineering practice significantly complicates simulations, a corresponding simplified mathematical model is constructed. For this model, we state a two-dimensional initial-boundary value problem of convective diffusion of soluble substances under the conditions of vertical steady-state filtration of groundwater with free surface from a reservoir to a coastal drain. To simplify the domain of simulation, we use the technique of transition into the domain of complex flow potential through a conformal mapping. In the case of averaging filtration velocity over the domain of complex flow potential, an analytical solution of the considered problem is obtained. In the general case of a variable filtration velocity, an algorithm has been developed to obtain numerical solutions. The results of process simulation using the presented algorithm shows that the constructed mathematical model can be efficiently used to simplify and accelerate modeling process.

Hydraulic Fracturing Process: Roles of In Situ Stress and Rock Strength

2012 ◽  
Vol 616-618 ◽  
pp. 435-440
Author(s):  
Yan Jun Feng ◽  
Xiu Wei Shi
Keyword(s):  
Hydraulic Fracturing ◽  
Analytical Model ◽  
Field Experiments ◽  
Rock Strength ◽  
Fracture Initiation ◽  
In Situ Stress ◽  
Experimental Investigations ◽  
Propagation Process ◽  
Fracturing Process

This paper presents results of a comprehensive study involving analytical and field experimental investigations into the factors controlling the hydraulic fracturing process. Analytical theories for fracture initiation of vertical and horizontal borehole are reviewed. The initiation and propagation process of hydraulic fracturing is performed in the field by means of hydraulic fracturing and stepwise hydraulic fracturing, the effect of factors such as in-situ stress and rock strength on fracture propagation process is studied and discussed. The fracture initiation pressures estimated from the analytical model and field experiments are compared as well as the fracturing process during case 1and case 2. Results from the analytical model and field experiments conducted in this study are interpreted with a particular effort to enlighten the factors controlling the hydraulic fracturing process.

scholarly journals A Modeling Study of the Productivity of Horizontal Wells in Hydrocarbon-Bearing Reservoirs: Effects of Fracturing Interference

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Lei Huang ◽  
Peijia Jiang ◽  
Xuyang Zhao ◽  
Liang Yang ◽  
Jiaying Lin ◽  
...  
Keyword(s):  
Hydraulic Fracturing ◽  
Horizontal Well ◽  
Finite Difference Methods ◽  
Horizontal Wells ◽  
Fracture Initiation ◽  
Design Parameters ◽  
Porous Media Flow ◽  
Propagation Mechanism ◽  
Well Productivity ◽  
Fracturing Process

Commercial production from hydrocarbon-bearing reservoirs with low permeability usually requires the use of horizontal well and hydraulic fracturing for the improvement of the fluid diffusivity in the matrix. The hydraulic fracturing process involves the injection of viscous fluid for fracture initiation and propagation, which alters the poroelastic behaviors in the formation and causes fracturing interference. Previous modeling studies usually focused on the effect of fracturing interference on the multicluster fracture geometry, while the related productivity of horizontal wells is not well studied. This study presents a modeling workflow that utilizes abundant field data including petrophysical, geomechanical, and hydraulic fracturing data. It is used for the quantification of fracturing interference and its correlation with horizontal well productivity. It involves finite element and finite difference methods in the numeralization of the fracture propagation mechanism and porous media flow problems. Planar multistage fractures and their resultant horizontal productivity are quantified through the modeling workflow. Results show that the smaller numbers of clusters per stage, closer stage spacings, and lower fracturing fluid injection rates facilitate even growth of fractures in clusters and stages and reduce fracturing interference. Fracturing modeling results are generally correlated with productivity modeling results, while scenarios with stronger fracturing interference and greater stimulation volume/area can still yield better productivity. This study establishes the quantitative correlation between fracturing interference and horizontal well productivity. It provides insights into the prediction of horizontal well productivity based on fracturing design parameters.

ON THE EXPRESS ESTIMATION OF GEOMETRICAL PARAMETERS OF A HYDRAULIC FRACTURING CRACK FIXED ON A PROPPANT USING THE METHODS OF MATHEMATICAL MODELING

2020 ◽  
Vol 6 (3) ◽  
pp. 79-92
Author(s):  
Alexey S. Shlyapkin ◽  
Alexey V. Tatosov
Keyword(s):  
Mathematical Model ◽  
Hydraulic Fracturing ◽  
Rapid Assessment ◽  
Geometric Parameters ◽  
Engineering Practice ◽  
Geometrical Parameters ◽  
Technological Parameters ◽  
Additional Information ◽  
Software Products

Improving technologies and increasing the number of activities related to hydraulic fracturing increase the requirements for the speed and quality of engineering support. For hydraulic fracturing design, there are specialized software products-hydraulic fracturing simulators, which are based on mathematical models of various dimensions. Taking into account the influence of filtration leaks into the reservoir and the behavior of proppant particles in the crack largely determine the shape of the fracture crack. In the model representation, these factors are taken into account, but they need to be clarified in order to increase the quality of the forecast and estimate the productivity of the crack, which determines the relevance of this area of study. In this paper, we propose an analysis that allows us to quickly evaluate the geometric parameters of the crack when changing the technological parameters and properties of the fracture fluid. The presented mathematical model is based on a one-dimensional mathematical model in PKN representation (Perkins — Kern — Nordgren model). All calculations presented in this paper were performed using the certified TSH Frac software package designed for modeling the geometric parameters of hydraulic fracturing cracks. The results of the study can be used in engineering practice for rapid assessment of the geometric parameters of a hydraulic fracturing crack. Subsequent adjustment and adjustment of the model can be carried out when additional information is obtained during small-volume test uploads in the well under study.

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.

scholarly journals Solid-Gas Coupling Model for Coal-Rock Mass Deformation and Pressure Relief Gas Flow in Protection Layer Mining

2018 ◽  
Vol 2018 ◽  
pp. 1-6 ◽  
Author(s):  
Zhuohui Zhu ◽  
Tao Feng ◽  
Zhigang Yuan ◽  
Donghai Xie ◽  
Wei Chen
Keyword(s):  
Rock Mass ◽  
Gas Flow ◽  
Coupling Model ◽  
Pressure Relief ◽  
Coal Rock ◽  
Rock Mass Deformation ◽  
Protection Layer ◽  
Mining Coal ◽  
Migration Law ◽  
Mass Deformation

The solid-gas coupling model for mining coal-rock mass deformation and pressure relief gas flow in protection layer mining is the key to determine deformation of coal-rock mass and migration law of pressure relief gas of protection layer mining in outburst coal seams. Based on the physical coupling process between coal-rock mass deformation and pressure-relief gas migration, the coupling variable of mining coal-rock mass, a part of governing equations of gas seepage field and deformation field in mining coal-rock mass, is introduced. Then, a new solid-gas coupling mathematical model reflecting the coupling effects of gas adsorption/desorption, gas pressure, and coal-rock mass deformation on the mining coal-rock mass deformation and pressure relief gas flow is established combined with the corresponding definite conditions. It lays a theoretical foundation for the numerical calculation of the deformation of mining coal-rock mass and the migration law of gas under pressure relief in the outburst coal seam group.

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.

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