RU1795115C - Method for directional fracturing of rock - Google Patents

Abstract

The invention is intended to create directional cracks around wells. The method includes drilling wells, placing liners with cavities in them, and fracturing. What is new is that the liner cavities are formed in the form of an embryonic gap with edges converging at an acute angle, and the space between the borehole walls and liners is filled with a hardening composition with a strength equal to or greater than the strength of the enclosing rocks. 1 s.p. f-ly, 2 ill.

Description

The invention relates to the mining industry and can be used to destroy rock blocks and soften rocks while controlling the roof or bearing capacity of pillars.

A known method of creating cracks is that a charge of explosives is placed in the borehole, made in the form of two cones connected by bases, and the charge is counter-initiated. According to this method, a crack can be formed only in a plane located at an angle of 90 ° to the axis of the well. In addition, the explosive fracture technology is unsafe when processing rock masses containing gas-bearing coal seams.

There is also a known method of creating cracks based on hydraulic fracturing of a rock mass through stress concentrators in the form of nucleating cracks formed in the borehole walls. The main

A disadvantage of the known method is the high complexity of the operation of cutting an embryonic gap in the borehole walls.

As a prototype, a method of creating a network of cracks in a rock mass has been adopted, which consists in placing a tube with through-cuts in the walls in the well, sealing the well and supplying liquid to the tube under pressure.

. A disadvantage of the known method is the low efficiency of directed cracking. The parallel banks of the slits and the presence of a gap between the tube and the walls of the borehole do not allow a sufficient concentration of stresses to be created and hydraulic fracture development in strong rocks can be initiated.

The aim of the invention is to increase the efficiency of directed cracking in rocks by forming stress concentrators along the crack front.

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The goal is achieved. that in the method of creating directional cracks in rocks, including placing liners with cavities in the wells and performing hydraulic fracturing, the liner cavities are formed in the form of embryonic slots with edges that converge at an acute angle, and the space between the walls of the well and liners is filled with a hardening composition with strength equal or greater strength of the host rocks. An epoxy-sand mixture with a volume ratio of 1: 1 is used as a hardening composition.

Figure 1 shows a diagram of the hydraulic fracturing of roof rocks; figure 2 - the position of the liner in the well during hydraulic fracturing.

The method is carried out as follows. To unload the mine working 1, passed through the coal seam 2, it is necessary to create a directed crack 4 in the roof 3, the plane of which is inclined at an angle a to the contact surface of the coal seam with the roof rocks and meet the specified contact at a distance a from the upper corner of the excavation. A well 5 is drilled from the mine at an angle {$ to the contact surface, the bottom of which is at a distance h from the coal seam.

The value of individual parameters is determined from the following expressions

/ arcta tl. | . h p arctan c + a + h. ctg a, i

Y a-0

where c is the distance from the wellhead to the upper production angle;

I is the length of the well section to the location of the fracture.

In order to create a crack, an insert 6 is used, which is made integral (ceramic, plastic) or detachable (metal). Inside the liner has an embryonic gap 7 in the form of a cavity with edges converging at an acute angle in a plane that is inclined at an angle to the axis of the housing. The cavity channel 8 is connected to the pressure head slrTTj

Rally 9. To ensure the transition of the process of cracking from the cavity of the liner into the rocks surrounding the borehole, the space 10 between the liner and the walls of the borehole is filled with hardening material, which is able to provide them with a dense and durable sieplenmr. and having strength indicators not lower than the corresponding rock indicators in the place of the planned gap. For example, a hardening epoxy sand mixture with a volume ratio of 1: 1 is satisfactory for these conditions. In a series of experiments, the following indicator values were obtained; Sezh from 70 to 86 MPa and E from 5.1 10 to 5.4 -104 MPa. This mixture can be used in hydraulic fracturing of almost all rocks found in coal deposits. A change in the volume ratio towards an increase in the sand content leads to an undesirable change in the consistency of the mixture, and with an increase in the proportion of epoxy glue,

the curing time of the mixture is reduced, which creates inconvenience in working with the composition.

After the mixture has hardened, a working fluid is supplied under pressure through a pressure line 9, under the influence of which an increase in the stress concentration occurs at the point of the slit 7. When the stresses reach critical values determined by the strength of the material, it develops near the slit boundaries from the insert through the fastening composition into the walls of the well and

further inland. Due to the detachable connection or rupture of the liner along the slit plane, joint deformations of the liner and surrounding rocks are provided, which stimulate the formation of an artificial hydraulic fracture in them during the initial phase of the process.

After the completion of the fracturing process, the next well is installed, but

vy liner, seal, connect to the pressure line and repeat the cycle.

Claims (2)

SUMMARY OF THE INVENTION 1. A method of creating directional cracks in rocks, including drilling wells, placing liners with cavities in them and performing hydraulic fracturing, characterized in that, in order to increase the efficiency of the formation of directed cracks in rocks by forming stress concentrators along the front crack formation, the cavity of the liners is formed in the form of a germinal gap with banks converging at an acute angle, and the space between the walls of the well and the liners is filled with a hardening composition with ochnostyu equal or greater strength surrounding rocks. 2. The method according to claim 1, characterized in that an epoxy-sand mixture with a volume ratio of 1: 1 is used as a hardening composition.