scholarly journals Experimental Investigation on the Propagation of Hydraulic Fractures through Coal-Rock Interfaces

2021 ◽  
Vol 2021 ◽  
pp. 1-14
Author(s):  
Pengfei Wu ◽  
Jianlong Wang ◽  
Xiaofei Luo ◽  
Rujun Mo ◽  
Yaoqing Hu ◽  
...  
Keyword(s):  
Hydraulic Fracturing ◽  
Strain Energy Release ◽  
Fracture Morphology ◽  
Fracture Pattern ◽  
Coal Bed ◽  
Hydraulic Fractures ◽  
Coal Seams ◽  
Crack Network ◽  
True Triaxial ◽  
Coal Rock

Although hydraulic fracturing has been one of the primary stimulation methods for coal-bed methane (CBM) exploration, it is difficult to be applied in soft and low-permeability coal seams due to the instability of wells in such geological structures. In order to solve the problem, an idea of indirect fracturing is proposed, that is, fractures are initiated in stable and hard rocks and then propagated to coal seams in which crack networks can be formed. To verify the feasibility of such an approach, the true triaxial hydraulic fracturing experiments were conducted using two-dimensional and three-dimensional coal-rock combination samples, respectively. This study investigates the fracture patterns, pressure variation, and fracture morphology. The results show that in the process of fracture propagation from sandy mudstones to coals, the strain energy release rate in the sandy mudstones is 10.69∼25.53 times greater than that in the coal. When the fracture has a tendency to deflect toward the lower strength coal strata, under the condition of large K2/K1, the deflection criterion will be met first and the fracture will deflect and grow into the coal strata. In addition, the complex crack network can be generated when the hydrofracture intersects the coal-rock interface and the fracture pattern is analyzed.

scholarly journals Analysis of Hydraulic Fracture Morphology and Propagation under Different Perforation Azimuth Angles

2022 ◽  
Vol 2152 (1) ◽  
pp. 012048
Author(s):  
Zhongshan Shen ◽  
Hui Xue ◽  
Zhiqiang Bai
Keyword(s):  
Hydraulic Fracturing ◽  
Hydraulic Fracture ◽  
Fracture Propagation ◽  
Experimental System ◽  
Fracture Morphology ◽  
Azimuth Angle ◽  
Important Influence ◽  
Propagation Path ◽  
Hydraulic Fractures ◽  
True Triaxial

Abstract Perforation azimuth has an important influence on the nucleation, propagation path and morphology of hydraulic fractures. In this paper, the true triaxial hydraulic fracturing simulation experimental system is used to analyze the hydraulic fracture morphology and propagation path under different perforation azimuth angles. With the increase of the azimuth angle of perforation, the stable fracture propagation pressure of the fracturing sample also increases. When the azimuth angle of perforation is 0°, the propagation pressure is about 18 MPa, and when the azimuth angle of perforation is 90°, the propagation pressure is about 26.5 MPa, increasing by nearly 47.22%.

Digital Fracture Characterization at Hydraulic Fracturing Test Site HFTS-Midland: Fracture Clustering, Stress Effects and Lithologic Controls

2021 ◽  
Author(s):  
Debotyam Maity ◽  
Jordan Ciezobka
Keyword(s):  
Hydraulic Fracturing ◽  
Hydraulic Fracture ◽  
Test Site ◽  
Fracture Morphology ◽  
Rock Properties ◽  
Hydraulic Fractures ◽  
Strong Positive Correlation ◽  
Fracture Roughness ◽  
Fracture Characterization ◽  
Stress Effects

Abstract In this case study, we apply a novel fracture imaging and interpretation workflow to take a systematic look at hydraulic fractures captured during thorugh fracture coring at the Hydraulic Fracturing Test Site (HFTS) in Midland Basin. Digital fracture maps rendered using high resolution 3D laser scans are analyzed for fracture morphology and roughness. Analysis of hydraulic fracture faces show that the roughness varies systematically in clusters with average cluster separation of approximately 20' along the core. While isolated smooth hydraulic fractures are observed in the dataset, very rough fractures are found to be accompanied by proximal smoother fractures. Roughness distribution also helps understand the effect of stresses on fracture distribution. Locally, fracture roughness seems to vary with fracture orientations indicating possible inter-fracture stress effects. At the scale of stage lengths however, we see evidence of inter-stage stress effects. We also observe fracture morphology being strongly driven by rock properties and changes in lithology. Identified proppant distribution along the cored interval is also correlated with roughness variations and we observe strong positive correlation between proppant concentrations and fracture roughness at the local scale. Finally, based on the observed distribution of hydraulic fracture properties, we propose a conceptual spatio-temporal model of fracture propagation which can help explain the hydraulic fracture roughness distribution and ties in other observations as well.

scholarly journals The pilot appraisal of acid fracturing of coalbed methane reservoir in southeast Qinshui Basin, China

2016 ◽  
Vol 20 (4) ◽  
pp. 1 ◽  
Author(s):  
Yu Yang ◽  
Chengwei Zhang ◽  
Huijun Tian ◽  
Wangang Chen ◽  
Xiadong Peng ◽  
...  
Keyword(s):  
Hydraulic Fracturing ◽  
Coalbed Methane ◽  
Mining Area ◽  
Coal Bed ◽  
Coal Seams ◽  
Acid Sensitivity ◽  
Qinshui Basin ◽  
Acid Fracturing ◽  
Well Production ◽  
Macro Scale

The reserves of Coalbed Methane (CBM) in Qinshui Basin are quite promising, but the outputs from CBM wells are quite small even after massive hydraulic fracturing. Herein the fracture system with #3 and #15 coal seams in Qinshui basin was analyzed, and it was found that both of the macro-scale fractures and micro-scale fractures are filled with clay and carbonate minerals, which explains the low productivity of CBM wells after conventional hydraulic fracturing. Acid fracturing has long been an effective method for carbonate gas reservoir to improve the gas well production. However, there were few reports about the application of acid fracturing in coal bed methane field. Based on the mineral identification and acid sensitivity test, the feasibility of acid fracturing demonstrated that the acid does more help than damage to increase the permeability of coal seams in Qinshui basin. Onsite operations have shown that acid fracturing is applicable for the CBM wells in Jincheng Mining Area. It was also observed from the microseismic survey that when applying the acid fracturing treatment, the stimulated reservoir area depends on the acid volume pumped in the first stage, which is crucial to the success of the stimulation. Evaluación piloto de fractura ácida en depósitos de gas metano de carbón en el suroeste de la cuenca Qinshui, China  ResumenLas reservas de gas metano de carbón (CBM, del inglés Coalbed Methane) en la cuenca Qinshui son más que prometedoras, pero la producción en los pozos es muy pequeña, incluso después de fracturas hidráulicas masivas. En este trabajo se analizaron los sistemas de fractura de las vetas de carbón #3 y #15 de la cuenca Qinshui y se encontró que tanto las fracturas a macroescala como aquellas a microescala están cubiertas con arcillas y minerales carbonatos, lo que explica la baja productividad de los pozos de gas metano de carbón después de la fractura hidráulica convencional. La fractura ácida ha sido un método efectivo en los depósitos de gas carbonato para mejorar la producción en el pozo de gas. Sin embargo, existen pocos informes sobre la aplicación de la fractura ácida en el campo del gas metano de carbón. De acuerdo con la identificación mineral y las pruebas de sensibilidad ácida, la factibilidad de la fractura ácida demostró que el ácido es reparador en el incremento de la permeabilidad en las vetas de carbón de la cuenca Qinshui. Las operaciones in situ han demostrado que la fractura ácida es aplicable para los pozos de gas metano de carbón en el área minera de Jincheng. También se observó en el sondeo microsísmico que cuando se aplica un tratamiento de fractura ácida, el área del depósito estimulada depende del volumen de ácido bombeado en primera instancia, lo que es determinante en el éxito de la estimulación.

scholarly journals Study of Cyclic Fracturing in Vertical CBM Wells

2017 ◽  
Vol 10 (1) ◽  
pp. 108-117 ◽  
Author(s):  
Ting Li ◽  
Ji-fang Wan
Keyword(s):  
Hydraulic Fracturing ◽  
Economic Benefits ◽  
Natural Fracture ◽  
Coal Bed ◽  
Coal Bed Methane ◽  
Plastic Behavior ◽  
Natural Fractures ◽  
Stimulated Reservoir Volume ◽  
Reservoir Volume ◽  
Coal Rock

Background:Coal-bed methane productivity of single well is very low, and has been the bottleneck of the coal-bed methane industry in China.Objective:Although hydraulic fracturing is the only stimulation measure to develop CBM, it cannot increase production effectively, conventional fracturing method to create opening fractures should be improved. How to make good use of natural fractures, which are plentiful in CBM reservoirs, is also an important subject for hydraulic fracturing.Method:In this paper, the plastic deformation of coal rock is analyzed by harnessing a pseudo-Maxwell creep phenomenon, which is normally present in rock. The Kelvin-Voigt model is utilized to describe pseudo-plastic behavior of coal rock to determine pressurization and decay cyclic time for cyclic fracturing design. The mechanical requirement for shearing natural fractures is also analyzed, and shearing distance between the faces of natural fracture can be calculated by Westergaard stress function. Ultimately, the cyclic fracturing method is proposed according to theories about stress alteration and shearing of natural fractures. This method includes such periods as fracturing, pumping shut-down and so on.Conclusion:A complex fracture system can be created, which consists of opened and sheared fractures, then, large SRV(stimulated reservoir volume)and flowing drainage area can be acquired. In comparison with conventional fracturing method, this new way can make full use of the characteristics of CBM reservoirs and is more suitable to CBM. This method will lead to a significant increase of CBM production, and will achieve huge economic benefits.

scholarly journals A New Method to Improve the Fracturing Effect of Coal Seams by Using Preset Slots and Induced Stress Shadows

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-17
Author(s):  
Li Li ◽  
Lei Zhou ◽  
Honglian Li ◽  
Binwei Xia ◽  
Junping Zhou
Keyword(s):  
Coal Seam ◽  
Hydraulic Fracturing ◽  
Fracture Network ◽  
Coal Bed ◽  
Hydraulic Fractures ◽  
Large Area ◽  
Multiple Fractures ◽  
Complex Fracture ◽  
Induced Stress ◽  
Complex Fracture Network

Efficient extraction of coal bed methane before coal mining is essential to eliminate the risk of coal-gas outbursts. However, stimulation technologies should be implemented to enhance the conductivity of the coal seam. In this study, we propose a novel method to create a complex fracture network in underground coal mines with the integration of multiple hydraulic slotting and hydraulic fracturing. In this method, hydraulic slots are used to direct hydraulic fractures and initialize branch fractures, while hydraulic fracturing is used to extend the fractures. Given the mutually exclusive and attractive propagation of multiple fractures, a relatively evenly distributed fracture network can be generated. The results show that (1) the dynamically induced stress shadows of hydraulic fractures can cause exclusive and attractive propagation of multiple hydraulic fractures; (2) a preset slot that deviates from the principal stress can direct hydraulic fractures to a certain extent and generate branch fractures; and (3) with a staggered distribution of preset slots, a relatively large volume of the coal seam in both the minimum and maximum horizontal stress directions can be stimulated, creating a complex fracture network including many vertical branch fractures and a large area of horizontally layered directional fractures.

scholarly journals LABORATORY STUDIES OF VIBRATION INFLUENCE ON THE PERMEABILITYOF A COAL CORE CONTAINING A THROUGH CRACK

2020 ◽  
Vol 2 ◽  
pp. 180-186
Author(s):  
Leonid A. Rybalkin ◽  
Sergey V. Serdyukov
Keyword(s):  
Hydraulic Fracturing ◽  
Rock Pressure ◽  
Gas Permeability ◽  
Hydraulic Fractures ◽  
Laboratory Studies ◽  
Coal Seams ◽  
Permeability Changes ◽  
Coal Core ◽  
Seismic Vibrations ◽  
Fractured Coal

The degassing of coal seams unloaded from rock pressure is associated with the requirement to intensify the flow of gas to degassing wells. For this purpose, a hydraulic fracturing operation is performed. The paper considers the features of the integrated intensification of coal seams’ degassing performed by hydraulic fractures in the field of seismic vibrations. The work presents the results of laboratory studies of gas permeability changes in fractured coal containing a through crack under the influence of various geomechanical compression and amplitude frequency of seismic vibrations. The obtained results provide the opportunity to evaluate the possibility of seismic vibration’s implication to intensify the degassing of non-wedged hydraulic fractures in coal mines.

scholarly journals Fully three-dimensional propagation model of horizontal borehole hydraulic fractures in strata under the effect of bedding planes

2018 ◽  
Vol 36 (5) ◽  
pp. 1189-1209 ◽  
Author(s):  
Bingxiang Huang ◽  
Jiangwei Liu
Keyword(s):  
Hydraulic Fracturing ◽  
Hydraulic Fracture ◽  
Three Dimensional ◽  
Fracture Morphology ◽  
Bedding Plane ◽  
Propagation Model ◽  
Tensile Failure ◽  
Propagation Mechanism ◽  
Hydraulic Fractures ◽  
Bedding Planes

The bedding plane effect will occur when hydraulic fractures propagate to the bedding plane in sedimentary strata, resulting in the “≠,” “工,” or “/” shaped fracture morphology. Based on previous physical experiments results, this article analyzed the mecroscopic propagation mechanism of tensile failure and the mechanical conditions for main hydraulic fracture and the bedding plane fracture propagating, proposing the criteria for hydraulic fracture to penetrate through the bedding plane. A fully three-dimensional model of hydraulic fracture morphology in horizontal borehole hydraulic fracturing is established with the vertical water flow, water leak-off, and bedding plane effect taken into consideration. Basic equations of continuity, pressure decline, hydraulic fracture morphology, and others are solved. After that, true triaxial hydraulic fracturing experiments with samples containing bedding planes are conducted to verify the aperture, length, width, and height of hydraulic fractures in this model. The model is proved to be accurate and reliable.

scholarly journals Experimental Study on Crack Extension Rules of Hydraulic Fracturing Based on Simulated Coal Seam Roof and Floor

Geofluids ◽  
2022 ◽  
Vol 2022 ◽  
pp. 1-12
Author(s):  
Lu Gao ◽  
Xiangtao Kang ◽  
Gun Huang ◽  
Ziyi Wang ◽  
Meng Tang ◽  
...  
Keyword(s):  
Coal Seam ◽  
Hydraulic Fracturing ◽  
Principal Stress ◽  
Hydraulic Fracture ◽  
Large Scale ◽  
Confining Pressure ◽  
Maximum Principal Stress ◽  
Hydraulic Fractures ◽  
True Triaxial ◽  
Extension Direction

Hydraulic fracturing can increase the fracture of coal seams, improve the permeability in the coal seam, and reduce the risk of coal and gas outburst. Most of the existing experimental specimens are homogeneous, and the influence of the roof and floor on hydraulic fracture expansion is not considered. Therefore, the hydraulic fracturing test of the simulated combination of the coal seam and the roof and floor under different stress conditions was carried out using the self-developed true triaxial coal mine dynamic disaster large-scale simulation test rig. The results show that (1) under the condition of triaxial unequal pressure, the hydraulic fractures are vertical in the coal seam, and the extension direction of hydraulic fractures in the coal seam will be deflected, with the increase of the ratio of the horizontal maximum principal stress to the horizontal minimum principal stress. The angle between the extension direction of the hydraulic fracture and the horizontal maximum principal stress decreases. (2) Under the condition of triaxial equal confining pressure, the extension of hydraulic fractures in the coal seam are random, and the hydraulic fracture will expand along the dominant fracture surface and form a unilateral expansion fracture when a crack is formed. (3) When the pressure in one direction is unloaded under the condition of the triaxial unequal pressure, the hydraulic fractures in the coal seam will reorientate, and the cracks will expand in the direction of the decreased confining pressure, forming almost mutually perpendicular turning cracks.

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