scholarly journals A Calculation Model of the Net Pressure for Forming Map Cracking in Coalbed with Cleats During Hydraulic Fracturing Process

2015 ◽  
Vol 8 (1) ◽  
pp. 193-197
Author(s):  
Li Yuwei ◽  
Ai Chi ◽  
Liu Yazhen
Keyword(s):  
Hydraulic Fracturing ◽  
Principal Stress ◽  
Coalbed Methane ◽  
Maximum Principal Stress ◽  
Calculation Model ◽  
Coal Bed ◽  
Minimum Principal Stress ◽  
Fracturing Process ◽  
The Face ◽  
Net Pressure

An important prerequisite for achieving efficient exploitation of coalbed methane wells is through forming map cracking by hydraulic fracturing. In order to analyze the mechanical mechanism for forming map cracking of the coal bed with cleats, the mechanical conditions for forming map cracking during hydraulic fracturing process of coal bed was proposed using extensional faulting in elastic mechanics and the shear damage criterion, and the minimum net pressure calculation model for forming map cracking was established when the butt cleat and face cleat in coal opened at the same time. It can be concluded through using the calculation model that the net pressure value that needed for forming map cracking first decreased and then increased with the increasing of the angle between the face cleat and the direction of horizontal minimum principal stress. The cleats and fissures developed along the horizontal maximum principal stress were easy to open and extend under the effect of hydraulic fracturing. The variation of the internal friction coefficient variation of the face cleat had little effect on the minimum net pressure that was needed for forming map fracturing after the angle between the direction of face cleat and horizontal minimum principal stress is determined.

A Fast Calculation Method for Natural Fractures Activation Considering Stress Shadow and Study on the Law of Natural Fractures Activation State Changes

2021 ◽  
Author(s):  
Yan Qiao ◽  
Yang Zhang ◽  
Tianhong Jiang ◽  
Guobin Zhang ◽  
Qing Chen ◽  
...  
Keyword(s):  
Hydraulic Fracturing ◽  
Principal Stress ◽  
Calculation Method ◽  
Maximum Principal Stress ◽  
Natural Fractures ◽  
Fast Calculation ◽  
Fracture Spacing ◽  
Stress Shadow ◽  
Minimum Principal Stress ◽  
Net Pressure

Abstract During hydraulic fracturing process of the Permian Basin in North America, the cluster spacing has been shortened to 3m, and stress shadow can no longer be ignored. Many scholars have studied the influence of stress shadows to optimize cluster spacing. For reservoirs with natural fractures, how to activate more natural fractures through hydraulic fracturing has become the purpose. However, few scholars have studied changes in the activation law of natural fractures under stress shadow conditions. This paper establishes stress change value around single fracture according to Sneddon formula, and calculates the maximum and minimum principal stress according to plane principal stress calculation formula. Considering attenuation of net pressure, stress field of multiple fractures is established, and influence of various factors on stress re-orientation is studied. Finally, considering attenuation of net pressure with distance, according to discriminant formulas of tension & shear activation, the proportion of natural fractures that are easily activated is calculated. By designing orthogonal experiments, the influence of different factors on the proportion of activated natural fractures was studied. The stress increase in the direction of the minimum principal stress is much greater than the increase in the direction of the maximum principal stress. The stress increases in the direction of the maximum principal stress at the tip of the hydraulic fracture. The tip position between hydraulic fractures is "neutralized" due to the superposition of shear stress. Stress-fracture angle and the in-situ stress difference are the common main influencing factors for both tensile and shear activation, but the net pressure has little effect on the tensile activation of natural fracture. The fracture spacing has little effect on the activation of natural fractures. When formulating the fracturing scheme, we should pay more attention to the net pressure rather than the fracture spacing. This article provides a fast calculation method for the activation state of natural fractures considering the stress shadow, which provides a reference index for activating more natural fractures and increasing the production of a single well.

scholarly journals Numerical simulation on the simultaneous stress interference of parallel multiple hydraulic fractures

2021 ◽  
pp. 014459872110019
Author(s):  
Weiyong Lu ◽  
Changchun He
Keyword(s):  
Principal Stress ◽  
Hydraulic Fracture ◽  
Stress Ratio ◽  
Fracture Network ◽  
Hydraulic Fractures ◽  
Fracture Spacing ◽  
Induced Stress ◽  
Minimum Principal Stress ◽  
Fracturing Process ◽  
Stress Ratios

During horizontal well staged fracturing, there is stress interference between multiple transverse fractures in the same perforation cluster. Theoretical analysis and numerical calculation methods are applied in this study. We analysed the mechanism of induced stress interference in a single fracture under different fracture spacings and principal stress ratios. We also investigated the hydraulic fracture morphology and synchronous expansion process under different fracture spacings and principal stress ratios. The results show that the essence of induced stress is the stress increment in the area around the hydraulic fracture. Induced stress had a dual role in the fracturing process. It created favourable ground stress conditions for the diversion of hydraulic fractures and the formation of complex fracture network systems, inhibited fracture expansion in local areas, stopped hydraulic fractures, and prevented the formation of effective fractures. The curves of the maximum principal stress, minimum principal stress, and induced principal stress difference with distance under different fracture lengths, different fracture spacings, and different principal stress ratios were consistent overall. With a small fracture spacing and a small principal stress ratio, intermediate hydraulic fractures were difficult to initiate or arrest soon after initiation, fractures did not expand easily, and the expansion speed of lateral hydraulic fractures was fast. Moreover, with a smaller fracture spacing and a smaller principal stress ratio, hydraulic fractures were more prone to steering, and even new fractures were produced in the minimum principal stress direction, which was beneficial to the fracture network communication in the reservoir. When the local stress and fracture spacing were appropriate, the intermediate fracture could expand normally, which could effectively increase the reservoir permeability.

scholarly journals Analytical Solution and Simulation of Oil Deliverability Analysis for Reorientation Hydraulic Fracture in Low-Permeability Reservoirs

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Xinyu Qiu ◽  
Botao Kang ◽  
Pengcheng Liu ◽  
Shengye Hao ◽  
Yanglei Zhou ◽  
...  
Keyword(s):  
Analytical Solution ◽  
Principal Stress ◽  
High Water ◽  
Maximum Principal Stress ◽  
Low Permeability ◽  
Minimum Principal Stress ◽  
High Water Cut Stage ◽  
High Water Cut ◽  
Water Cut ◽  
Low Permeability Reservoirs

The hydraulic refracturing operations are often used to improve oil deliverability in the low-permeability reservoir. When the development of oilfields has entered a high water cut stage, oil deliverability can be promoted by refracturing reservoirs. The orientation of the new fracture formed by refracturing will be changed. The new formed fracture is called reorientation fracture. To calculate the oil deliverability of the refracture wells, a three-section fracture which includes reorientation fracture was established. The multiwell pressure drop superposition theory is used to derive the analytical solution of the refracture wells which includes the reorientation fracture. The numerical simulation was conducted to validate the results of the analytical solution. Comparing the refracture well deliverability of reorientation and nonreorientation, permeability, deflection angle, and the length of reorientation fracture will jointly control the productivity of refracture well. When the permeability in the direction of maximum principal stress is greater than the permeability in the direction of minimum principal stress, the capacity of reorientation fractures is relatively large. The deflection angles and the length of the reorientation fracture will directly affect the drainage area of the fracture, thus affecting productivity. The reorientation fractures generated by repeated fracturing have great potential for improving oil deliverability in the anisotropic low-permeability reservoirs.

scholarly journals The Calculation Model of Initiation Pressure During Hydraulic Fracturing Process of Perforated Coal Seams

2013 ◽  
Vol 6 (1) ◽  
pp. 30-35 ◽  
Author(s):  
Li Yuwei ◽  
Ai Chi
Keyword(s):  
Hydraulic Fracturing ◽  
Pressure Gauge ◽  
Calculation Model ◽  
Tensile Failure ◽  
Coal Seams ◽  
Rock Body ◽  
Fracture Pressure ◽  
Fracturing Process ◽  
Pressure Calculation ◽  
Initiation Pressure

There are lots of cleats, fractures and many other structure weak planes in coal seams, which make the bullet holes and cleats intersecting. During the hydraulic fracturing process in coal seams, fractures will initiate at coal rock body of borehole wall, and cleats or fractures are different from conventional reservoirs. Thus a new model for initiation pressure calculation during coal seams fracturing should be established. Based on the rock mechanics and elasticity mechanics, and also on network distribution characteristics of coal seam cleats and the space position relationships between the intersected bullet holes and cleats, stress distribution around the bullet holes and at the cleats wall were deducted. The model was established in tensile failure condition. The calculated initiation fracture pressure of Well HX-3 was 10.71MPa. The pressure obtained from bottom hole pressure gauge was 11.24MPa. The relative error was 4.72%. The model could be applied for initiation pressure calculation during hydraulic fracturing process in coal seams. The fractures would initiate at the cleats during fracturing.

scholarly journals The Influence of the Injected Water on the Underground Coalbed Methane Extraction

Energies ◽  
2020 ◽  
Vol 13 (5) ◽  
pp. 1151
Author(s):  
Yanbao Liu ◽  
Zhigang Zhang ◽  
Wei Xiong ◽  
Kai Shen ◽  
Quanbin Ba
Keyword(s):  
Hydraulic Fracturing ◽  
Coalbed Methane ◽  
Gas Flow ◽  
Critical Time ◽  
Shanxi Province ◽  
Coal Bed ◽  
Hydraulic Pressure ◽  
Intrinsic Permeability ◽  
Permeability Evolution ◽  
Two Phase

The increasing demand on coal production has led to the gradually increase of mining depth and more high methane mines, which bring difficulties in terms of coalbed methane (CBM) extraction. Hydraulic fracturing is widely applied to improve the production of CBM, control mine gas, and prevent gas outbursts. It improves coal bed permeability and accelerate desorption and migration of CBM. Even though the impacts of hydraulic fracturing treatment on the coal reservoirs are rare, negative effects could not be totally ignored. To defend this defect, the presented work aims to study the influence of water filtration on coal body deformation and permeability evolution. For this purpose, a simulation based finite element method was developed to build a solid-fluid coupled two-phase flow model using commercial software (COMSOL Multiphysics 5.4). The model was verified using production data from a long strike borehole from Wangpo coal mine in Shanxi Province, China. Several simulation scenarios were designed to investigate the adverse impacts of hydraulic fracturing on gas flow behaviors. The mechanisms of both relative and intrinsic permeability evolutions were analyzed, and simulation results were presented. Results show that the intrinsic permeability of the fracture system increases in the water injection process. The impacts of water imitation were addressed that a critical time was observed beyond which water cannot go further and also a critical pressure exists above which the hydraulic pressure would impair the gas flow. Sensitivity analysis also showed that a suitable time and pressure combination could be observed to maximize gas extraction. This work provides an efficient approach to guide the coal bed methane exploitation and other unconventional gas reservoirs.

Sign in / Sign up

Export Citation Format

Share Document