Experimental Investigation on the Basic Law of Directional Hydraulic Fracturing Controlled by Dense Linear Multi-Hole Drilling

Using the dense linear multihole to control the directional hydraulic fracturing is a significant technical method to realize roof control in mining engineering. By combining the large-scale true triaxial directional hydraulic fracturing experiment with the discrete element numerical simulation experiment, the basic law of dense linear holes controlling directional hydraulic fracturing was studied. The results show the following: (1) Using the dense linear holes to control directional hydraulic fracturing can effectively form directional hydraulic fractures extending along the borehole line. (2) The hydraulic fracturing simulation program is very suitable for studying the basic law of directional hydraulic fracturing. (3) The reason why the hydraulic fracture can be controlled and oriented is that firstly, due to the mutual compression between the dense holes, the maximum effective tangential tensile stress appears on the connecting line of the drilling hole, where the hydraulic fracture is easy to be initiated. Secondly, due to the effect of pore water pressure, the disturbed stress zone appears at the tip of the hydraulic fracture, and the stress concentration zone overlaps with each other to form the stress guiding strip, which controls the propagation and formation of directional hydraulic fractures. (4) The angle between the drilling line and the direction of the maximum principal stress, the in situ stress, and the hole spacing has significant effects on the directional hydraulic fracturing effect. The smaller the angle, the difference of the in situ stress, and the hole spacing, the better the directional hydraulic fracturing effect. (5) The directional effect of synchronous hydraulic fracturing is better than that of sequential hydraulic fracturing. (6) According to the multihole linear codirectional hydraulic fracturing experiments, five typical directional hydraulic fracture propagation modes are summarized.

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EXPERIMENTAL INVESTIGATION ON THE IMPACT OF INITIAL PORE PRESSURE ON BREAKDOWN PRESSURE OF BOREHOLE RADIAL FRACTURE FOR UNSATURATED MORTAR HYDRAULIC FRACTURING UNDER TRUE TRIAXIAL STRESS

Journal of Porous Media ◽

10.1615/jpormedia.2018021402 ◽

2018 ◽

Vol 21 (11) ◽

pp. 1041-1057 ◽

Cited By ~ 1

Author(s):

Bingxiang Huang ◽

Xinglong Zhao ◽

Weichao Xue ◽

Tianyuan Sun

Keyword(s):

Experimental Investigation ◽

Hydraulic Fracturing ◽

Pore Pressure ◽

Triaxial Stress ◽

Radial Fracture ◽

Breakdown Pressure ◽

True Triaxial ◽

True Triaxial Stress ◽

The Impact

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Directional Hydraulic Fracturing (DHF) of the Roof, as an Element of Rock Burst Prevention in the Light of Underground Observations and Numerical Modelling

Energies ◽

10.3390/en14030562 ◽

2021 ◽

Vol 14 (3) ◽

pp. 562

Author(s):

Marek Jendryś ◽

Andrzej Hadam ◽

Mateusz Ćwiękała

Keyword(s):

Rock Mass ◽

Hydraulic Fracturing ◽

Coal Mining ◽

Rock Burst ◽

Coal Mine ◽

Seismic Activity ◽

Black Coal ◽

Directional Hydraulic Fracturing ◽

Before And After ◽

The Face

The following article analyzes the effectiveness of directional hydraulic fracturing (DHF) as a method of rock burst prevention, used in black coal mining with a longwall system. In order to define changes in seismic activity due to DHF at the “Rydułtowy” Black Coal Mine (Upper Silesia, Poland), observations were made regarding the seismic activity of the rock mass during coal mining with a longwall system using roof layers collapse. The seismic activity was recorded in the area of the longwall itself, where, on a part of the runway, the rock mass was expanded before the face of the wall by interrupting the continuity of the rock layers using DHF. The following article presents measurements in the form of the number and the shock energy in the area of the observed longwall, which took place before and after the use of DHF. The second part of the article unveils the results of numerical modeling using the discrete element method, allowing to track the formation of goafs for the variant that does not take DHF into consideration, as well as with modeled fractures tracing DHF carried out in accordance with the technology used at “Rydułtowy” coal mine.

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Numerical simulation of the laws of fracture propagation of multi-hole linear co-directional hydraulic fracturing

Energy Exploration & Exploitation ◽

10.1177/0144598721988993 ◽

2021 ◽

pp. 014459872198899

Author(s):

Weiyong Lu ◽

Changchun He

Keyword(s):

Hydraulic Fracturing ◽

Hydraulic Fracture ◽

Minimum Principle ◽

Fracture Propagation ◽

Axial Direction ◽

Rock Breaking ◽

Hydraulic Fractures ◽

Directional Hydraulic Fracturing ◽

Fracture Intersection ◽

Expansion Stage

Directional rupture is one of the most important and most common problems related to rock breaking. The goal of directional rock breaking can be effectively achieved via multi-hole linear co-directional hydraulic fracturing. In this paper, the XSite software was utilized to verify the experimental results of multi-hole linear co-directional hydraulic fracturing., and its basic law is studied. The results indicate that the process of multi-hole linear co-directional hydraulic fracturing can be divided into four stages: water injection boost, hydraulic fracture initiation, and the unstable and stable propagation of hydraulic fracture. The stable expansion stage lasts longer and produces more microcracks than the unstable expansion stage. Due to the existence of the borehole-sealing device, the three-dimensional hydraulic fracture first initiates and expands along the axial direction in the bare borehole section, then extends along the axial direction in the non-bare hole section and finally expands along the axial direction in the rock mass without the borehole. The network formed by hydraulic fracture in rock is not a pure plane, but rather a curved spatial surface. The curved spatial surface passes through both the centre of the borehole and the axial direction relative to the borehole. Due to the boundary effect, the curved spatial surface goes toward the plane in which the maximum principal stress occurs. The local ground stress field is changed due to the initiation and propagation of hydraulic fractures. The propagation direction of the fractures between the fracturing boreholes will be deflected. A fracture propagation pressure that is greater than the minimum principle stress and a tension field that is induced in the leading edge of the fracture end, will aid to fracture intersection; as a result, the possibility of connecting the boreholes will increase.

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