SU1765465A1 - Method of pulsed action on gas-bearing coal bed - Google Patents

Abstract

Use: gas degassing of coal seams. SUMMARY OF THE INVENTION: A well is drilled on the formation, it is cased, perforated and the coal seam is opened. X The natural pickup of the coal seam is then determined. In the first cycle of exposure, the working pressure in the well is created equal to 1.1-1.3 lateral rock pressure. After the first cycle of exposure, the formation capacity is determined, and the working pressure created in the well in the second cycle is set equal to the product of the lateral pressure on the injectivity ratio after the first cycle of exposure to the natural pickup of the coal seam. The injection capacity of the coal seam is determined after each exposure cycle, and in each subsequent cycle the working pressure is increased to a value equal to Pe Kp-1 / Kp-2, where K is the formation pick-up; n is the cycle number. The working pressure in the last cycle is set equal to (1.5-2.01 SRg + Rpl), where Pr is the total rock pressure; RPL gas pressure in the reservoir. In the well, pressure is created by powder pressure generators. Their number is determined by the formula. 1 hp f-ly. WITH S

Description

The invention relates to the mining industry and can be used in the development of gas bearing and outburst coal seams for their preliminary degassing and, thus, the creation of safe working conditions.

There is a method of hydraulic segmentation of a coal seam, which consists in drilling a well in a coal seam, its casing and perforation, cyclically injecting the working fluid into the formation with a gradual increase in its viscosity in each cycle. In the process of carrying out the process, it is necessary to use substances whose viscosity increases from cycle to cycle. The process of extracting them is very complicated, so a part remains in the reservoir, reducing its permeability, and therefore, the degree of degassing is not achieved.

The known method of hydraulic dissection of a coal seam, including the drilling of a well on a coal seam, its

x |

ON SL J O SL

casing and perforation, cyclic injection of working fluid into the reservoir. In the first injection cycle, the pressure of the fluid is adjusted to the ultimate strength of the coal in compression, and in each subsequent cycle to open the next fracture system, the fluid pressure is increased by the ratio of the phase permeability of the main and open fracture systems.

The described method does not allow the occurrence of tangential cracks, which significantly reduces the effectiveness of the degassing of the formation.

The aim of the invention is to increase the effectiveness of the effect by creating cracks in the formation located along concentric circles and connecting the radial cracks.

The goal is achieved by the fact that in the method of pulsed impact on a gas-bearing coal seam, including drilling a well from the surface, its casing and cyclic injection of fluid in a pulsed mode into the reservoir, its natural pickup and lateral rock pressure are determined before the fluid is injected into the reservoir, in the first injection cycle, a working pressure in the well is created, equal to 1.1-1.3 times the lateral rock pressure; in the first injection pressure cycle, a pressure equal to the product of the lateral rock pressure and relative pressure Acceptability of the reservoir after the first cycle of exposure to the natural injectivity of the reservoir, and in each subsequent injection cycle creates pressure, determined from the ratio

 KP-1 / KP-2,

where Rp is the pressure in the well, MPa;

RB - lateral rock pressure, MPa;

K - coal injectivity, m3 / s MPa;

n is the cycle number

moreover, in the last injection cycle, a pressure is created equal to 1.5-2.0 sums of the total rock pressure and gas pressure in the formation. In addition, pressure in the well is created by powder pressure generators.

The method is carried out as follows.

A well is drilled on the formation, it is cased, perforated and the coal seam is opened. The natural pickup of the coal seam is then determined. To do this, water is poured into the well with a measuring tank to the wellhead, and as it absorbs, water is periodically added to the well, measuring

until the termination of water absorption. A change in the injectivity of the formation gives a quantitative characteristic of the effect on the coal seam. Using the formula

, 1-n,

where y is the bulk density of overlying rocks, t / m3;

H is the depth of the coal seam, m, the lateral rock pressure is determined.

In the first cycle of exposure, the working pressure in the well is set to (1.1-1.3) RB. This pressure creates an initial network of cracks (radial), oriented along the natural fracturing systems of the coal seam.

Working pressure can be created by hydraulic or pneumatic pressure. The most effective use of powder pressure generators, the number of which determines their ratio

Pp.z.

1 Sc

RR WG

Go to Sn.3. C Vn.3. Pn.3, f

where Sc, Sn.3. - cross-sectional area of the well and charge, respectively, cm2;

Рр, Рg - working and total rock pressure, respectively, kgf / cm2; f - powder power, kgf cm / kg; K - coefficient taking into account the reduction of pressure in the well due to the cooling of the powder gases, 4;

Cf is the speed of sound in a liquid, cm / s; RJ v ° n.3. liquid density and charge, respectively, kg / cm3;

Vn.s. - rate of burning powder, cm / s.

Using the logging elevator and its equipment, powder generators are lowered into the well. To reduce energy losses, powder generators are placed against the perforated portion of the column.

The working pressure in the well is measured by a special (kresherny) instrument mounted on a geophysical cable. After the charges are lowered, rock salt (or sand) is poured into the well to create a safety

bridge, reducing the loss of energy for the removal of water from the well. The salt (or sand) is then destroyed by water.

After the first cycle of exposure, the pickup of the coal seam is again determined. The working pressure in the second cycle exceeds the lateral rock pressure by a number of times equal to the ratio of the injectivity of the formation after the first cycle of exposure (Kch) to the natural injectivity of the formation (K0).

Thus, the pressure in the well in the second exposure cycle is set to

K1

IS

Having determined the amount of powder generators required to create working pressure P2, the charge is lowered into the well and burned. After exposure, the injectivity of the formation is measured again, and the working pressure in the third cycle is set to

 m

-

where K.2 is the injectivity of the formation after the second cycle of exposure.

The working pressure in the well from cycle to cycle is increased to a value equal to the limiting one determined from the ratio

, 5-2.0 (Pr + Rpl),

where Rpl - gas pressure in the reservoir, MPa;

Pr is the total pressure, MPa.

The gas pressure in the reservoir (Ppl) is determined from the ratio

, 01 (Hi-H0),

where HI is the depth of the reservoir, m;

But - the depth of the gas weathering zone, m.

The advantage of the proposed method in comparison with the prototype is to increase the efficiency of advance degassing by increasing the area

ten

15

20

25

thirty

35

40

free surfaces of cracks in the coal seam, which increases the phase permeability of the reservoir to methane.

Claims (2)

1. A method of pulsed impact on a gas-bearing coal seam, including drilling a well from the surface, its casing and cyclic injection of fluid in a pulsed mode into the reservoir, characterized in that, in order to increase the effectiveness of the effect, by creating cracks along the concentric circle m and connecting radial cracks, prior to the injection of fluid into the formation, its natural pickup and lateral rock pressure are determined, and in the first injection cycle, the working pressure in the well is created, e 1.1-1.3 values of the lateral rock pressure, in the second injection cycle, pressure is created equal to the product of lateral pressure on the ratio of the reservoir injectivity after the first cycle of action to the natural injectivity of the reservoir, and in each subsequent injection cycle the pressure determined from mathematical expression  KP-1 / KP-2, where Rp is the pressure in the well, MPa; RB - lateral rock pressure, MPa; K - pickup coal seam; n is the cycle number moreover, in the last injection cycle, a pressure is created equal to 1.5-2.0 sums of the total rock pressure and gas pressure in the formation. 2. A method according to claim 1, characterized in that the pressure in the well is created by powder pressure generators.