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 Breakdown Pressure Calculating Model for Open Hole Completion CBM Well Hydraulic Fracturing

2014 ◽  
Vol 7 (1) ◽  
pp. 12-19
Author(s):  
Li Yuwei ◽  
Ai Chi ◽  
Liu Yu ◽  
Gao Changlong
Keyword(s):  
Hydraulic Fracturing ◽  
Shear Failure ◽  
Spatial Relationship ◽  
Wall Rock ◽  
Calculation Model ◽  
Tensile Failure ◽  
Borehole Wall ◽  
Breakdown Pressure ◽  
Rock Body ◽  
Open Hole

The open hole completion CBM borehole wall intersects with the weak surface such as cleats and fractures. In the process of hydraulic fracturing, the fractures may origin from coal body or cleats, which makes the rupture mechanism and rupture models of the borehole wall being different from the conventional reservoirs. The previous model for calculating breakdown pressure of open hole completion borehole wall considering tension failure has poor applicability for calculating breakdown pressure. Considering the spatial relationship of the intersection of borehole wall and cleats, analyzing the stress state of borehole wall rock and cleats wall, and basing on elastic mechanics and fracture mechanics, the breakdown pressure calculation model for CBM open hole completion hydraulic fracturing was established. In the model, fractures initiate from coal rock body, tensile failure along with face cleats, shear failure along with face cleats, tensile failure along with butt cleats and shear failure along with butt cleats five kinds of damage modes were considered. According to example calculation, the breakdown pressure of HX-L1 well calculated using the model is 14.81 MPa. The actual pressure obtained by bottom hole pressure gage is 15.42 MPa, and the relative error is 3.96%. The calculated result agrees with the actual conditions. It can be concluded that the model can be used to calculate the breakdown pressure for open hole completion CBM well hydraulic fracture.

scholarly journals Investigation of Hydraulic Fracturing Crack Propagation Behavior in Multi-Layered Coal Seams

2020 ◽  
Vol 10 (3) ◽  
pp. 1153 ◽  
Author(s):  
Shirong Cao ◽  
Xiyuan Li ◽  
Zhe Zhou ◽  
Yingwei Wang ◽  
Hong Ding
Keyword(s):  
Coal Seam ◽  
Hydraulic Fracturing ◽  
Crack Propagation ◽  
Principal Stress ◽  
Fracture Propagation ◽  
Clean Energy ◽  
Burial Depth ◽  
Coal Seams ◽  
Initiation Pressure ◽  
Dip Angle

Coalbed methane is not only a clean energy source, but also a major problem affecting the efficient production of coal mines. Hydraulic fracturing is an effective technology for enhancing the coal seam permeability to achieve the efficient extraction of methane. This study investigated the effect of a coal seam reservoir’s geological factors on the initiation pressure and fracture propagation. Through theoretical analysis, a multi-layered coal seam initiation pressure calculation model was established based on the broken failure criterion of maximum tensile stress theory. Laboratory experiments were carried out to investigate the effects of the coal seam stress and coal seam dip angle on the crack initiation pressure and fracture propagation. The results reveal that the multi-layered coal seam hydraulic fracturing initiation pressure did not change with the coal seam inclination when the burial depth was the same. When the dip angle was the same, the initiation pressure linearly increased with the reservoir depth. A three-dimensional model was established to simulate the actual hydraulic fracturing crack propagation in multi-layered coal seams. The results reveal that the hydraulic crack propagated along the direction of the maximum principal stress and opened in the direction of the minimum principal stress. As the burial depth of the reservoir increased, the width of the hydraulic crack also increased. This study can provide the theoretical foundation for the effective implementation of hydraulic fracturing in multi-layered coal seams.

scholarly journals Analysis of Shunted Screen Gravel Pack Process and Calculation of Friction in Deepwater Horizontal Wells

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Fei Xu ◽  
Shengtian Zhou ◽  
Chong Zhang ◽  
Yi Yu ◽  
Zhao Dong
Keyword(s):  
Pressure Gauge ◽  
Calculation Model ◽  
Simulation Software ◽  
Gas Field ◽  
Carrier Fluid ◽  
Fracture Pressure ◽  
Open Hole ◽  
Packing Process ◽  
Gravel Packing ◽  
Gravel Pack

Shunted screen gravel packing is a kind of technology which is difficult to complete gravel packing with the conventional method in low fracture pressure formation and long wellbore length condition. According to the characteristics of LS 17-2 deepwater gas field, the shunted screen packing tool was designed and the gravel packing process and packing mechanism were analyzed. The variation law of the flow friction, flow rate distribution in multichannel, and other parameters of the shunted screen gravel packing were analyzed and calculated. The friction calculation model of different stages of gravel packing was established. A gravel packing simulation software was developed to simulate the friction in different stages of shunted screen gravel packing. The parameters such as sand-dune ratio, pumping sand amount, packing length, and packing time in the process of packing were also calculated. In deepwater horizontal well gravel packing, the results show that the friction ratio of the string is the largest in the stage of injection and α-wave packing. While the friction increases rapidly in the stage of β-wave packing because the carrier fluid needs to flow through the long and narrow washpipe/screen annulus. Particularly when the β-wave packing is near the beginning of the open hole, the packing pressure reaches the maximum. The calculated results are in good agreement with the measured results of the downhole pressure gauge. The model and software can provide technical support for the prediction and optimization of gravel packing parameters in the future.

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.

Experimental Investigation on Wellbore Strengthening Based on a Hydraulic Fracturing Apparatus

2017 ◽  
Vol 140 (5) ◽  
Author(s):  
Cheng Cao ◽  
Xiaolin Pu ◽  
Zhengguo Zhao ◽  
Gui Wang ◽  
Hui Du
Keyword(s):  
Plastic Deformation ◽  
Hydraulic Fracturing ◽  
Development Stage ◽  
Pressure Curve ◽  
Lost Circulation ◽  
Fracture Pressure ◽  
Instability Development ◽  
Fracturing Process ◽  
Crack Stability ◽  
Wellbore Strengthening

Lost circulation is a serious problem which always exists in the petroleum industry. Wellbore strengthening by lost circulation materials (LCMs) is a commonly applied method for mitigating lost circulation. This paper presents a hydraulic fracturing apparatus to investigate the effect of material type, concentration, and particle size distribution (PSD) of LCMs on wellbore strengthening behavior. In addition, the characteristics of pressure curves in the fracturing process are analyzed in detail. The results showed that the fracture pressure of the artificial core can be increased by LCMs, and there exists an optimum concentration of LCMs for the maximum wellbore strengthening effect. The LCMs with wide PSD can significantly increase the fracture pressure. However, some LCMs cannot increase or even decrease the fracture pressure; this is resulting from the LCMs with relatively single PSD that makes the quality of mud cake worse. The representative pressure curve in the fracturing process by drilling fluids with LCMs was divided into five parts: the initial cake formation stage, elastic plastic deformation stage, crack stability development stage, crack instability development stage, and unstable plugging stage. The actual fracturing curves were divided into four typical types due to missing of some stages compared with the representative pressure curve. In order to strengthen the wellbore in effective, good LCMs should be chosen to improve the maximum pressure in the elastic plastic deformation stage, extend the stable time of pressure bearing in the crack stability development stage, and control the crack instability development stage.

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