CN102278089A - Method for improving stability of casing pipe of ground gas pump drainage well - Google Patents

Abstract

The invention relates to a method for improving the casing stability of a surface gas drainage well, which comprises the following steps: fixing the casing to the gas drainage well; Construct several pressure relief boreholes in the coal seam near the wall of the gas drainage well hole, and release the gas pressure of the coal seam through the several gas pressure relief boreholes; when the gas pressure of the coal seam is reduced to the initial level Afterwards, the well fluid in the gas pumping well is emptied. The method for improving the casing stability of surface gas drainage wells involves firstly constructing a pressure-relief drilling hole through an underground roadway to reduce the gas pressure of the coal seam near the hole wall, and then drain the drilling fluid after the gas pressure in the coal seam is reduced to the original value. Therefore, the requirements on the anti-extrusion strength of the casing are reduced, which is beneficial to ensure that the anti-extrusion strength of the casing is higher than the extrusion force of the coal seam gas outside the pipe, thereby ensuring the safety of the casing.

Description

A Method for Improving the Stability of Casing in Ground Gas Drainage Well

technical field

The invention relates to the security technical field of the mining industry, in particular to a method for improving the stability of the casing of a surface gas drainage well. the

Background technique

The large-caliber gas drainage shaft on the ground is a channel for coal mines to discharge gas to the ground after pre-pumping underground. It is one of the effective methods for preventing gas accidents in coal mines and comprehensively utilizing energy in my country. the

Large-diameter gas drainage wells generally require lowering of the working casing in the hole. The casing plays the role of protecting the wellbore, strengthening the well wall and sealing water, gas and various complex formations. The stability of the working casing is the key to the success of the large-diameter gas drainage well project. the

The instability of the casing can be divided into two forms: rupture and deformation. Once the casing ruptures, the groundwater in the upper formation may flow into the working face through the borehole, affecting downhole safety; if the casing is deformed (collapsed), the cross-sectional area of the gas flow will be reduced and the pumping capacity will be reduced. The cost of a deep-hole and large-diameter gas drainage well is usually more than several million yuan. Once the casing becomes unstable, it will bring huge economic losses to both the owner and the construction unit. the

The traditional construction method is: after the casing is lowered into the hole and the pipe fixing is completed, the drilling fluid in the drilling hole is immediately discharged. After the well fluid in the hole is discharged, the pressure difference between the inside and outside of the casing wall increases. When the pressure of the formation pore fluid on the wall of the borehole is high, the casing will fail due to the pressure difference between the inside and outside of the casing exceeding the casing’s anti-extrusion strength. stable, causing casing failure. the

Contents of the invention

In view of the deficiencies in the above background technologies, the present invention provides a method for improving the casing stability of surface gas drainage wells, which aims to be easy to operate and can effectively prevent casing instability. the

The present invention is achieved in this way, a method for improving the stability of the ground gas drainage well casing, which comprises the following steps:

Casing and pipe fixing for gas drainage wells;

After the casing is fixed, construct several pressure relief boreholes from the underground roadway into the coal seam near the wall of the gas drainage well hole, and discharge the coal seam through the several gas pressure relief boreholes gas pressure;

After the gas pressure of the coal seam drops to the initial level, the well fluid in the gas drainage well is evacuated.

Further, the following contents are included in the step of fixing the casing pipe:

When the gas drainage well is formed at the end hole of the gas drainage well, the casing is lowered into the gas drainage well;

After the casing is lowered to the bottom of the gas drainage well, pipe-solid cement is injected into the annular gap between the wall of the gas drainage well and the casing through the grouting hole at the bottom of the casing pulp;

After the pipe-fixed cement slurry is solidified, a pipe-fixed cement circle is formed in the annular gap between the wall of the gas drainage wellbore and the casing, and the casing is fixed.

Further, before the gas drainage well pierces the coal seam, the gas pressure of the coal seam is at the initial level, and when the casing is solidified, the gas pressure of the coal seam is at the liquid level of the drilling fluid. Column pressure, at the end of the casing, the gas pressure of the coal seam is the liquid column pressure of the cement slurry of the solid pipe. the

Compared with the prior art, the present invention has the beneficial effect that: the present invention does not directly drain the drilling fluid in the borehole after the solid pipe cement is solidified, but first constructs the pressure-relieving borehole through the underground roadway to reduce the coal seam near the hole wall. After the gas pressure in the coal seam is reduced to the original value, the drilling fluid is emptied, which reduces the requirement for the casing's anti-extrusion strength, which is conducive to ensuring that the anti-extrusion strength of the casing is higher than that of the coal seam gas outside the pipe. The extrusion force ensures the safety of the casing. the

Description of drawings

Fig. 1 is a schematic view of the usage state of the method for improving the casing stability of a surface gas drainage well provided by an embodiment of the present invention. the

the

Symbol Description

Casing 1

Drilling Fluid 2

Solid pipe cement circle 3

coal seam 4

Pressure relief drilling 5

Alleyway 6

Borehole wall 7

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention. the

Please refer to FIG. 1 , which is a method for improving the casing stability of a surface gas drainage well provided by an embodiment of the present invention. The method for improving the casing stability of a surface gas drainage well is applied to the casing 1 of a gas drainage well. the

Before drilling, there is a certain initial level of gas pressure P0 in the coal seam 4. When the coal seam 4 is uncovered by drilling, the gas in the coal seam 4 near the borehole wall 7 will The pressure increases to the well fluid column pressure P1. During the pipe fixing period after the casing 1 is lowered, the gas pressure of the well wall coal seam 4 is equal to the liquid column pressure P2 of the pipe cement slurry. Since the bulk density of the injected cement slurry is generally greater than the well fluid bulk density, there is generally P2>P1>P0. The process of drilling and fixing the pipe 1 increases the gas pressure in the coal seam 4 . When the drilling depth is large and the permeability of the coal seam 4 is low, the high gas pressure formed in the coal seam 4 is not easy to dissipate after the pipe fixing is completed, and a gas pressure higher than P0 is still maintained. After the drilling fluid 2 in the casing 1 is emptied, if the wall thickness of the casing 1 is difficult to provide sufficient anti-extrusion strength, the casing 1 will be unstable due to the excessive pressure difference between the inside and outside of the casing 1. the

Therefore, during the construction of the gas drainage well, the borehole wall 7 is filled with drilling fluid 2, and before the drill hole exposes the coal seam 4, the gas pressure in the coal seam is equal to P0. When the drill hole exposes the coal seam 4, the gas pressure in the coal seam is equal to the liquid column pressure P1 of the drilling fluid 2. After the gas drainage well is formed after the final hole of the gas drainage well, the casing 1 is lowered in the borehole. When the casing 1 is lowered to the design depth, the solid-pipe cement slurry is injected into the annular gap between the hole wall 7 and the casing 1 through the grouting hole at the bottom of the casing 1. After the grouting is completed, the gas pressure in the coal seam 4 is equal to The liquid column pressure P2 of the cement slurry. After the cement is solidified, a fixed pipe cement circle 3 is formed in the annular gap between the hole wall 7 and the casing 1 . the

The present invention constructs one or several pressure relief boreholes 5 in the coal seam 4 in the underground roadway 6 to reduce the gas pressure in the coal seam, so that the gas pressure in the coal seam is reduced from P2 to P0. the

The construction sequence of the present invention in practical application is as follows:

1) Carry out casing 1 solidification for the gas drainage well.

2) After the gas pumping well pipe is solidified and the cement is solidified, one or several pressure relief boreholes 5 are constructed in the coal seam 4 in the underground roadway 6, and the gas pressure in the coal seam is reduced through the pressure relief boreholes 5. The gas pressure in the coal seam 4 is reduced from P2 to P0. the

3) After the gas pressure in the coal seam is reduced from P2 to P0, the drilling fluid 2 in the casing 1 is drained. the

The invention analyzes the principle of drilling casing instability, and believes that the drilling fluid column pressure P1 and the cement column pressure P2 generated during the pipe fixing process will lead to an increase in the gas pressure of the coal seam 4 near the drilling hole. The present invention can effectively reduce the gas pressure in the coal seam 4 through the pressure relief drilling 5 implemented in the underground roadway 6, so that the gas pressure in the coal seam 4 can be restored to the original pressure of the coal seam 4 (that is, the initial level), reducing the pressure on the casing. 1 The requirement of anti-extrusion strength is conducive to ensuring the safety of casing 1. To further illustrate, the gas removed from the lowered coal seam 4 is discharged from the roadway 6 through a pipeline (not shown). the

Compared with the traditional construction method, the main difference of the present invention is that the present invention does not directly empty the drilling fluid 2 in the borehole after the solid pipe cement is solidified, but first constructs the pressure-relieving borehole through the underground roadway to reduce the borehole wall. 7 The gas pressure of the coal seam 4 nearby, after the gas pressure in the coal seam 4 is reduced to the original value, the drilling fluid 2 is drained, thereby reducing the requirement for the anti-extrusion strength of the casing 1, which is beneficial to ensure the anti-extrusion of the casing 1 The strength is higher than the gas extrusion force of the coal seam 4 outside the pipe 1, which ensures the safety of the casing 1. the

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the protection of the present invention. within range. the

Claims (3)

1. method that improves ground gas exhaust casing stability, it may further comprise the steps:

The gas exhaust well is carried out sleeve pipe manages admittedly;

Behind the solid duct ligation bundle of described sleeve pipe, several destressing boreholes of construction near the coal seam from underworkings described gas exhaust borehole wall are by the gas pressure in described several unrestrained described coal seams of gas destressing borehole;

After the gas pressure for the treatment of described coal seam is dredged and to be dropped to initial level, the well liquid in the described gas exhaust well of emptying again.

2. the method for raising as claimed in claim 1 ground gas exhaust casing stability is characterized in that, comprises following content in the step of the solid pipe of described sleeve pipe:

After the whole hole of gas exhaust well forms described gas exhaust well, transfer described sleeve pipe in the described gas exhaust well;

After described sleeve pipe is transferred to described gas exhaust bottom, manage cement paste admittedly by the annular gap injection of injected hole between described gas exhaust borehole wall and described sleeve pipe of described sleeve bottom;

The described pipe admittedly after cement paste solidifies forms in the annular gap between described gas exhaust borehole wall and described sleeve pipe and manages the cement circle admittedly, the solid duct ligation bundle of described sleeve pipe.

3. the method for raising as claimed in claim 2 ground gas exhaust casing stability, it is characterized in that, before described gas exhaust well is exposed described coal seam, the gas pressure in described coal seam is described initial level, before the solid pipe of described sleeve pipe, the gas pressure in described coal seam is the head of liquid of described drilling fluid, and when described sleeve pipe was consolidated the duct ligation bundle, the gas pressure in described coal seam was described head of liquid of managing cement paste admittedly.

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