Coalbed methane flow characteristics based on fractal geometry and stochastic rough fracture network

2021 ◽  
pp. 1-19
Author(s):  
Binwei Xia ◽  
Yafei Luo ◽  
Chao Pan ◽  
Tao Gong ◽  
Huarui Hu ◽  
...  
Keyword(s):  
Fractal Geometry ◽  
Coalbed Methane ◽  
Flow Characteristics ◽  
Fracture Network ◽  
Rough Fracture ◽  
Methane Flow

scholarly journals Experimental Investigation of Water-Sand Mixed Fluid Initiation and Migration in Filling Fracture Network during Water Inrush

2021 ◽  
Vol 2021 ◽  
pp. 1-20
Author(s):  
Bin Yang ◽  
Tianhong Yang
Keyword(s):  
Particle Size ◽  
Critical Velocity ◽  
Network Flow ◽  
Water Inrush ◽  
Functional Relation ◽  
Flow Characteristics ◽  
Fracture Network ◽  
Nonlinear Flow ◽  
Two Phase ◽  
And Migration

For water inrush induced by fracture network flow, the critical velocity of the incipient motion of sand particles was obtained, and the functional relation between critical velocity and particle size was established through a series of tests on the nonlinear flow characteristics of a filling fracture network. The influence of the particle size distribution, hydrodynamic force, and geometric features of the fracture network on the characteristics of particle loss; distribution laws; and water-sand, two-phase migration was also explored. Moreover, the interactions amongst water, movable particles, the surface of the skeleton, and fracture walls, and the formation mechanism of the flow channel were qualitatively analyzed. In addition, the change rules of the mass loss characteristics and porosity of the samples with time were tested successfully. The calculation methods of the permeability and non-Darcy factor of the filling fracture network were also determined.

scholarly journals Flow characteristics of fractal fracture with different fractal dimension and different fracture width

2021 ◽  
Vol 25 (6 Part B) ◽  
pp. 4477-4484
Author(s):  
Jun-Jun Liu ◽  
Jing Xie ◽  
Yi-Ting Liu ◽  
Gui-Kang Liu ◽  
Rui-Feng Tang ◽  
...  
Keyword(s):  
Fractal Dimension ◽  
Rock Mass ◽  
Flow Characteristics ◽  
Fracture Network ◽  
Basic Element ◽  
Single Fracture ◽  
Flow State ◽  
Complex Flow ◽  
Fracture Width ◽  
Fracture Models

Single fracture is the most basic element in complex fracture network of rock mass. Therefore, the study of flow characteristics of single fracture is an important way to reasonably predict the complex flow state in engineering rock mass. In order to study the flow characteristics of fractal single fracture, fracture models with dif?ferent fractal dimension and different fracture width are established in this paper. The results show that: the blocking effect of rough structure on fluid is obviously enhanced under high pressure. In addition, it is weakened and reaches a steady-state with the increase of fracture fractal dimension. The larger the fracture width is, the more obvious the phenomenon is. The hydraulic gradient index tends to 0.5 with the increase of fracture width when fractal dimension is greater than 1.3. It also could tend to 0.5 with the increase of fractal dimension when fracture width is greater than 1 mm.

Modelling Methane Extraction from Stimulated Coalbed Influenced by Multidomain and Thermal Effects

2021 ◽  
Author(s):  
Wai Li ◽  
Jishan Liu ◽  
Jie Zeng ◽  
Yee-Kwong Leong ◽  
Derek Elsworth ◽  
...  
Keyword(s):  
Thermal Effects ◽  
Coalbed Methane ◽  
Thermal Strain ◽  
Fracture Network ◽  
Extraction Process ◽  
Mine Safety ◽  
Shanxi Province ◽  
Well Production ◽  
Proposed Model ◽  
Coal Deformation

Abstract The process of extracting coalbed methane (CBM) is not only of significance for unconventional energy supply but also important in mine safety. The recent advance in fracking techniques, such as carbon dioxide (CO2) fracking, intensifies the complexity of stimulated coalbeds. This work focuses on developing a fully coupled multidomain model to describe and get insight into the process of CBM extraction, particularly from those compound-fractured coalbeds. A group of partial differential equations (PDEs) are derived to characterize gas transport from matrix to fractures and borehole. A stimulated coalbed is defined as an assembly of three interacting porous media: matrix, continuous fractures (CF) and radial primary hydraulic fracture (RF). Matrix and CF constitute a dual-porosity-dual-permeability system, while RF is simplified as an 1-D cracked medium. These media further form three distinct domains: non-stimulated reservoir domain (NSRD), stimulated reservoir domain (SRD) and RF. The effects of coal deformation, heat transfer, and non-thermal sorption are coupled into the model to reflect the multiple processes in CBM extraction. The finite element method is employed to numerically solve the PDEs. The proposed model is verified by comparing its simulation results to a set of well production data from Southern Qinshui Basin in Shanxi Province, China. Great consistency is observed, showing the satisfactory accuracy of the model for CBM extraction. After that, the difference between various stimulation patterns is presented by simulating the CBM extraction process with different stimulation patterns including (1) unstimulated coalbed; (2) double-wing fracture + NSRD; (3) multiple RFs + NSRD; (4) SRD + NSRD and (5) multiple RFs + SRD + NSRD. The results suggest that Pattern (5) (often formed by CO2 fracking) boosts the efficiency of CBM extraction because it generates a complex fracture network at various scales by both increasing the number of radial fractures and activating the micro-fractures in coal blocks. Sensitivity analysis is also performed to understand the influences of key factors on gas extraction from a stimulated coalbed with multiple domains. It is found that the distinct properties of different domains originate various evolutions, which in turn influences the CBM production. Ignoring thermal effects in CBM extraction will either overestimate or underestimate the production, which is the net effect of thermal strain and non-isothermal sorption. The proposed model provides a useful approach to accurately evaluate CBM extraction by taking the complex evolutions of coalbed properties and the interactions between different components and domains into account. The importance of multidomain and thermal effects for CBM reservoir simulation is also highlighted.

scholarly journals Analysis of hydraulic fracture behavior and well pattern optimization in anisotropic coal reservoirs

2020 ◽  
pp. 014459872096083
Author(s):  
Yulong Liu ◽  
Dazhen Tang ◽  
Hao Xu ◽  
Wei Hou ◽  
Xia Yan
Keyword(s):  
Hydraulic Fracture ◽  
Coalbed Methane ◽  
Fracture Network ◽  
Simulation Software ◽  
Natural Fracture ◽  
Hydraulic Fractures ◽  
Natural Fractures ◽  
Well Pattern ◽  
Well Pattern Optimization ◽  
The Impact

Macrolithotypes control the pore-fracture distribution heterogeneity in coal, which impacts stimulation via hydrofracturing and coalbed methane (CBM) production in the reservoir. Here, the hydraulic fracture was evaluated using the microseismic signal behavior for each macrolithotype with microfracture imaging technology, and the impact of the macrolithotype on hydraulic fracture initiation and propagation was investigated systematically. The result showed that the propagation types of hydraulic fractures are controlled by the macrolithotype. Due to the well-developed natural fracture network, the fracture in the bright coal is more likely to form the “complex fracture network”, and the “simple” case often happens in the dull coal. The hydraulic fracture differences are likely to impact the permeability pathways and the well productivity appears to vary when developing different coal macrolithtypes. Thus, considering the difference of hydraulic fracture and permeability, the CBM productivity characteristics controlled by coal petrology were simulated by numerical simulation software, and the rationality of well pattern optimization factors for each coal macrolithotype was demonstrated. The results showed the square well pattern is more suitable for dull coal and semi-dull coal with undeveloped natural fractures, while diamond and rectangular well pattern is more suitable for semi-bright coal and bright coal with more developed natural fractures and more complex fracturing fracture network; the optimum wells spacing of bright coal and semi-bright coal is 300 m and 250 m, while that of semi-dull coal and dull coal is just 200 m.

scholarly journals A Fractal and Numerical Simulation Coupled Study of Fracture Network during Coal Mining Excavation

2014 ◽  
Vol 2014 ◽  
pp. 1-6
Author(s):  
Yanan Gao ◽  
Feng Gao ◽  
Man-chu Ronald Yeung
Keyword(s):  
Fractal Dimension ◽  
Fractal Geometry ◽  
Numerical Study ◽  
Fracture Network ◽  
Mining Engineering ◽  
Deformation Method ◽  
Discontinuous Deformation ◽  
Relationship Of ◽  
The Relationship ◽  
Rock Strata

This paper features a numerical study that is carried out by using discontinuous deformation method (DDA) and fractal geometry. The configurations of rock strata calculated by DDA were imported into a code that is written by using VC++ called “Fractal” to calculate the fractal dimension of the rock strata. As illustrated, a long wall mining case in China was presented. The relationship of the fractal dimension, excavation length, stress, and movement of strata were discussed. The evolution of fractal dimension can be considered as an index of instability or failure. The method proposed in this paper can be employed to predict the period weighting in long wall mining engineering.

scholarly journals APPLICATION OF FRACTAL GEOMETRY IN EVALUATION OF EFFECTIVE STIMULATED RESERVOIR VOLUME IN SHALE GAS RESERVOIRS

Fractals ◽  
2017 ◽  
Vol 25 (04) ◽  
pp. 1740007 ◽  
Author(s):  
GUANGLONG SHENG ◽  
YULIANG SU ◽  
WENDONG WANG ◽  
FARZAM JAVADPOUR ◽  
MEIRONG TANG
Keyword(s):  
Hydraulic Fracturing ◽  
Shale Gas ◽  
Fractal Geometry ◽  
Fracture Network ◽  
Gas Reservoirs ◽  
Stimulated Reservoir Volume ◽  
Reservoir Volume ◽  
Adsorbed Gas ◽  
Shale Gas Reservoirs ◽  
Shale Reservoirs

According to hydraulic-fracturing practices conducted in shale reservoirs, effective stimulated reservoir volume (ESRV) significantly affects the production of hydraulic fractured well. Therefore, estimating ESRV is an important prerequisite for confirming the success of hydraulic fracturing and predicting the production of hydraulic fracturing wells in shale reservoirs. However, ESRV calculation remains a longstanding challenge in hydraulic-fracturing operation. In considering fractal characteristics of the fracture network in stimulated reservoir volume (SRV), this paper introduces a fractal random-fracture-network algorithm for converting the microseismic data into fractal geometry. Five key parameters, including bifurcation direction, generating length ([Formula: see text]), deviation angle ([Formula: see text]), iteration times ([Formula: see text]) and generating rules, are proposed to quantitatively characterize fracture geometry. Furthermore, we introduce an orthogonal-fractures coupled dual-porosity-media representation elementary volume (REV) flow model to predict the volumetric flux of gas in shale reservoirs. On the basis of the migration of adsorbed gas in porous kerogen of REV with different fracture spaces, an ESRV criterion for shale reservoirs with SRV is proposed. Eventually, combining the ESRV criterion and fractal characteristic of a fracture network, we propose a new approach for evaluating ESRV in shale reservoirs. The approach has been used in the Eagle Ford shale gas reservoir, and results show that the fracture space has a measurable influence on migration of adsorbed gas. The fracture network can contribute to enhancement of the absorbed gas recovery ratio when the fracture space is less than 0.2 m. ESRV is evaluated in this paper, and results indicate that the ESRV accounts for 27.87% of the total SRV in shale gas reservoirs. This work is important and timely for evaluating fracturing effect and predicting production of hydraulic fracturing wells in shale reservoirs.

scholarly journals Experimental Investigation on the Hydraulic Characteristics of the Two-Phase Flow in the Intersecting Rock Fractures

Geofluids ◽  
2022 ◽  
Vol 2022 ◽  
pp. 1-14
Author(s):  
Chen Wang ◽  
Lujie Zhou ◽  
Yujing Jiang ◽  
Xuepeng Zhang ◽  
Jiankang Liu
Keyword(s):  
3D Model ◽  
Two Phase Flow ◽  
Rock Fracture ◽  
Flow Characteristics ◽  
Inertial Force ◽  
Fracture Network ◽  
Phase Flow ◽  
Hydraulic Characteristics ◽  
Two Phase ◽  
Flow Experiment

An appropriate understanding of the hydraulic characteristics of the two-phase flow in the rock fracture network is important in many engineering applications. To investigate the two-phase flow in the fracture network, a study on the two-phase flow characteristics in the intersecting fractures is necessary. In order to describe the two-phase flow in the intersecting fractures quantitatively, in this study, a gas-water two-phase flow experiment was conducted in a smooth 3D model with intersecting fractures. The results in this specific 3D model show that the flow structures in the intersecting fractures were similar to those of the stratified wavy flow in pipes. The nonlinearity induced by inertial force and turbulence in the intersecting fractures cannot be neglected in the two-phase flow, and the Martinelli-Lockhart model is effective for the two-phase flow in intersecting fractures. Delhaye’s model can be adapted for the cases in this experiment. The turbulence of the flow can be indicated by the values of C in Delhaye’s model, but resetting the appropriate range of the values of C is necessary.

scholarly journals Similar constructive method for solving the model of coalbed methane flow through coalbed methane reservoirs

2018 ◽  
Vol 15 (4) ◽  
pp. 1783-1798 ◽  
Author(s):  
Bao Xi-Tao ◽  
Yan Yi-Fei ◽  
Yang Jiang ◽  
Yan Xiang-Zhen ◽  
Li Shun-Chu
Keyword(s):  
Coalbed Methane ◽  
Constructive Method ◽  
Flow Through ◽  
Methane Flow

Flow Characteristics of Foam in Fractures and Prediction of Preferred Paths

2021 ◽  
Author(s):  
Zhengxiao Xu ◽  
Zhaomin Li ◽  
Binfei Li ◽  
Danqi Chen ◽  
Xianghui Zeng ◽  
...  
Keyword(s):  
Network Model ◽  
Fractured Reservoirs ◽  
Flow Characteristics ◽  
Weighted Graph ◽  
Fracture Network ◽  
Dijkstra’S Algorithm ◽  
Sweep Efficiency ◽  
Foam Flow ◽  
Complex Fracture ◽  
Dijkstra's Algorithm

Abstract Foam is widely used in fractured reservoirs. The flow characteristics in complex fracture networks are still unclear, and there are few numerical simulations of foam fluid flow in fractures. In this study, a variety of combined visual fracture models were used to observe the flow characteristics of foam in the fracture. Firstly, based on the parallel fracture model, the foam flow characteristics under different fracture depths were explored, and then based on the complex fracture network model, the foam flow path and sweep efficiency are evaluated. Finally, the Dijkstra’s algorithm was used to determine the weighted graph of the fracture network nodes, and the preferred flow paths of the foam were predicted. The results show that when foam flows in parallel fractures with different depths, it preferentially flows in high permeability (100 μm) fractures, and there is gas trapping in low permeability (50 μm) fractures. In the irregular fracture network model, the sweep efficiency of the foam fluid is greatly affected by the foam quality, and the sweep volume is the widest when the foam quality is about 90%. The simulation results based on the Dijkstra’s algorithm can be fitted to the experimental results to a certain extent. By controlling the number of preferred paths and the weight of nodes, the plugging and regulating performance of the foam are characterized. These findings reflect the necessity of considering fractures when foam flows in reservoirs, and provide a certain experimental basis and theoretical guidance for the development of fractured reservoirs.

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