scholarly journals Variation characteristics of coal-rock mechanical properties under varying temperature conditions for Shanxi Linfen coalbed methane well in China

2021 ◽  
Vol 11 (7) ◽  
pp. 2905-2915
Author(s):  
Xin Li ◽  
Jie Zhang ◽  
Cuinan Li ◽  
Ben Li ◽  
Haoyang Zhao ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Coalbed Methane ◽  
Surrounding Rock ◽  
Fracture Angle ◽  
Temperature Conditions ◽  
Change Characteristics ◽  
Variation Characteristics ◽  
Coal Rock ◽  
Rock Mechanical Properties ◽  
Primary Fracture

AbstractIn the actual exploitation process of coalbed methane (CBM), as the fluid in the wellbore continues to circulate, the surrounding rock of the CBM well will continuously exchange heat with the fluid in the wellbore, resulting in continuous changes in the temperature of the surrounding rock itself. Linfen, Shanxi is the main exploitation area for CBM in China. This paper aims further to improve the exploitation efficiency of CBM in this area and conducts experimental research on the change characteristics of coal-rock mechanical properties under varying temperature conditions. The experimental results show that under constant pressure conditions, the higher the temperature, the lower the stress value when the coal-rock breaks. In the process of reaching peak strength, the higher the temperature, the higher the proportion of coal-rock plastic deformation in its entire deformation stage. The compressive strength, elastic modulus, and main crack length of coal-rock will decrease with temperature. The Poisson's ratio and primary fracture angle will increase with the increase of experimental temperature.

Characteristic Law of Borehole Deformation Induced by the Temperature Change in the Surrounding Rock of Deep Coalbed Methane Well

2021 ◽  
pp. 1-18
Author(s):  
Xin Li ◽  
Jie Zhang ◽  
Cuinan Li ◽  
Weilin Chen ◽  
Jingbin He ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Coalbed Methane ◽  
Linear Equations ◽  
Surrounding Rock ◽  
Experimental Temperature ◽  
Borehole Stability ◽  
Fracture Angle ◽  
High Deformation ◽  
Rock Temperature ◽  
Primary Fracture

Abstract The borehole stability of the coalbed methane (CBM) well has always been vital in deep CBM exploration and development. The borehole instability of the deep CBM well is due to many complicated reasons. The change in the surrounding rock temperature is an important and easily overlooked factor among many reasons. In this research, we used methods that include experiment and numerical simulation to study the characteristic law of the borehole deformation induced by the changes in the surrounding rock temperature of deep CBM well. The experimental results of the stress–strain curves of five sets of experiments show that when the experimental temperature rises from 40 °C to 100 °C, the average stress when coal samples are broken gradually decreases from 81.09 MPa to 72.71 MPa. The proportion of plastic deformation in the entire deformation stage gradually increases from 7.8% to 25.7%. Moreover, the characteristics that some key mechanical parameters of coal samples change with the experimental temperature are fitted, and results show that as the experimental temperature rises from 40 °C to 100 °C, the compressive strength, elastic modulus, and main crack length of coal samples show a gradually decreasing trend. By contrast, the Pois-son's ratio and primary fracture angle show a gradually increasing trend. Moreover, the relativity of the linear equations obtained by fitting is all close to 1, which can accurately reflect the corresponding change trend. Numerical simulation results show that a high temperature of the surrounding rock of the deep CBM well results in a high range of stress concentration on the coal seam borehole and high deformation.

scholarly journals Experimental Analysis of the Mechanical Properties and Resistivity of Tectonic Coal Samples with Different Particle Sizes

Energies ◽  
2021 ◽  
Vol 14 (8) ◽  
pp. 2303
Author(s):  
Congyu Zhong ◽  
Liwen Cao ◽  
Jishi Geng ◽  
Zhihao Jiang ◽  
Shuai Zhang
Keyword(s):  
Mechanical Properties ◽  
Particle Size ◽  
Compressive Strength ◽  
Elastic Modulus ◽  
Uniaxial Compressive Strength ◽  
Coalbed Methane ◽  
Coal Sample ◽  
Fine Particles ◽  
Particle Sizes ◽  
Tectonic Coal

Because of its weak cementation and abundant pores and cracks, it is difficult to obtain suitable samples of tectonic coal to test its mechanical properties. Therefore, the research and development of coalbed methane drilling and mining technology are restricted. In this study, tectonic coal samples are remodeled with different particle sizes to test the mechanical parameters and loading resistivity. The research results show that the particle size and gradation of tectonic coal significantly impact its uniaxial compressive strength and elastic modulus and affect changes in resistivity. As the converted particle size increases, the uniaxial compressive strength and elastic modulus decrease first and then tend to remain unchanged. The strength of the single-particle gradation coal sample decreases from 0.867 to 0.433 MPa and the elastic modulus decreases from 59.28 to 41.63 MPa with increasing particle size. The change in resistivity of the coal sample increases with increasing particle size, and the degree of resistivity variation decreases during the coal sample failure stage. In composite-particle gradation, the proportion of fine particles in the tectonic coal sample increases from 33% to 80%. Its strength and elastic modulus increase from 0.996 to 1.31 MPa and 83.96 to 125.4 MPa, respectively, and the resistivity change degree decreases. The proportion of medium particles or coarse particles increases, and the sample strength, elastic modulus, and resistivity changes all decrease.

scholarly journals Study on Impact Damage and Energy Dissipation of Coal Rock Exposed to High Temperatures

2016 ◽  
Vol 2016 ◽  
pp. 1-10 ◽  
Author(s):  
Tu-bing Yin ◽  
Kang Peng ◽  
Liang Wang ◽  
Pin Wang ◽  
Xu-yan Yin ◽  
...  
Keyword(s):  
High Temperatures ◽  
Failure Modes ◽  
Split Hopkinson Pressure Bar ◽  
Impact Damage ◽  
Time History ◽  
Hopkinson Pressure Bar ◽  
Absorbed Energy ◽  
Failure Patterns ◽  
Temperature Conditions ◽  
Coal Rock

The dynamic failure characteristics of coal rock exposed to high temperatures were studied by using a split Hopkinson pressure bar (SHPB) system. The relationship between energy and time history under different temperature conditions was obtained. The energy evolution and the failure modes of specimens were analyzed. Results are as follows: during the test, more than 60% of the incident energy was not involved in the breaking of the sample, while it was reflected back. With the increase of temperature, the reflected energy increased continuously; transmitted and absorbed energy showed an opposite variation. At the temperature of 25 to 100°C, the absorbed energy was less than that transmitted, while this phenomenon was opposite after 100°C. The values of specific energy absorption (SEA) were distributed at 0.04 to 0.1 J·cm−3, and its evolution with temperature could be divided into four different stages. Under different temperature conditions, the failure modes and the broken blocks of the samples were obviously different, combining with the variation of microstructure characteristics of coal at high temperatures; the physical mechanism of damage and failure patterns of coal rock are explained from the viewpoint of energy.

Integration of Chemofacies and Rock Mechanical Properties Using Machine Learning Algorithms: Implications for Geomechanics and Hydraulic Fracture Stimulations in Paleozoic Formations, Saudi Arabia

2021 ◽  
Author(s):  
Maaruf Hussain ◽  
Abduljamiu Amao ◽  
Khalid Al-Ramadan ◽  
Sunday Olatunji ◽  
Ardiansyah Negara
Keyword(s):  
Machine Learning ◽  
Mechanical Properties ◽  
Saudi Arabia ◽  
Spatial Distribution ◽  
Chemical Composition ◽  
Rock Strength ◽  
Machine Learning Algorithms ◽  
Unconventional Reservoirs ◽  
Geochemical Properties ◽  
Rock Mechanical Properties

Abstract The knowledge of rock mechanical properties is critical to reducing drilling risk and maximizing well and reservoir productivity. Rock chemical composition, their spatial distribution, and porosity significantly influenced these properties. However, low porosity characterized unconventional reservoirs as such, geochemical properties considerably control their mechanical behavior. In this study, we used chemostratigraphy as a correlation tool to separate strata in highly homogenous formations where other traditional stratigraphic methods failed. In addition, we integrated the chemofacies output and reduced Young's modulus to outline predictable associations between facies and mechanical properties. Thus, providing better understanding of lithofacies-controlled changes in rock strength that are useful inputs for geomechanical models and completions stimulations.

scholarly journals Approximate Dynamic Programming Based Control of Proppant Concentration in Hydraulic Fracturing

Mathematics ◽  
2018 ◽  
Vol 6 (8) ◽  
pp. 132 ◽  
Author(s):  
Harwinder Singh Sidhu ◽  
Prashanth Siddhamshetty ◽  
Joseph Kwon
Keyword(s):  
Mechanical Properties ◽  
Dynamic Programming ◽  
Hydraulic Fracturing ◽  
Young’S Modulus ◽  
Large Scale ◽  
Approximate Dynamic Programming ◽  
Young's Modulus ◽  
Computational Cost ◽  
Control Technique ◽  
Rock Mechanical Properties

Hydraulic fracturing has played a crucial role in enhancing the extraction of oil and gas from deep underground sources. The two main objectives of hydraulic fracturing are to produce fractures with a desired fracture geometry and to achieve the target proppant concentration inside the fracture. Recently, some efforts have been made to accomplish these objectives by the model predictive control (MPC) theory based on the assumption that the rock mechanical properties such as the Young’s modulus are known and spatially homogenous. However, this approach may not be optimal if there is an uncertainty in the rock mechanical properties. Furthermore, the computational requirements associated with the MPC approach to calculate the control moves at each sampling time can be significantly high when the underlying process dynamics is described by a nonlinear large-scale system. To address these issues, the current work proposes an approximate dynamic programming (ADP) based approach for the closed-loop control of hydraulic fracturing to achieve the target proppant concentration at the end of pumping. ADP is a model-based control technique which combines a high-fidelity simulation and function approximator to alleviate the “curse-of-dimensionality” associated with the traditional dynamic programming (DP) approach. A series of simulations results is provided to demonstrate the performance of the ADP-based controller in achieving the target proppant concentration at the end of pumping at a fraction of the computational cost required by MPC while handling the uncertainty in the Young’s modulus of the rock formation.

scholarly journals Determination of Long Horizontal Borehole Height in Roofs and its Application to Gas Drainage

Energies ◽  
2018 ◽  
Vol 11 (10) ◽  
pp. 2647
Author(s):  
Gang Wang ◽  
Cheng Fan ◽  
Hao Xu ◽  
Xuelin Liu ◽  
Rui Wang
Keyword(s):  
Numerical Simulation ◽  
Theoretical Model ◽  
Fracture Zone ◽  
Coalbed Methane ◽  
High Efficiency ◽  
Gas Drainage ◽  
Methane Drainage ◽  
Working Face ◽  
Variation Characteristics

Accurately determining the height of the gas-guiding fracture zone in the overlying strata of the goaf is the key to find the height of the long horizontal borehole in the roof. In order to determine the height, in this study we chose the 6306 working face of Tangkou Coal Mine in China as a research example and used both the theoretical model and discrete element method (DEM) numerical simulation to find the height of the gas-guiding fracture zone and applied the height to drill a long horizontal borehole in the roof of the 6303 working face. Furthermore, the borehole was utilized to deep into the roof for coalbed methane drainage and the results were compared with conventional gas drainage measures from other aspects. The height of the gas-guiding fracture zone was found to be 48.57 m in theoretical model based on the bulk coefficient and the void ratio and to be 51.19 m in the DEM numerical simulation according to the temporal and spatial variation characteristics of porosity. Taking both the results of theoretical analysis and numerical simulation into consideration, we determined that gas-guiding fracture zone is 49.88 m high and applied it to drill a long horizontal borehole deep into the roof in the 6303 working face field. Compared with conventional gas drainage measures, we found that the long horizontal borehole has the high stability, high efficiency and strong adaptability for methane drainage.

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