CN102465693A - Underground coal gasification drilling well body structure and construction method thereof - Google Patents

Abstract

The invention discloses a construction method of a coal underground gasification drilling well body structure, which is characterized by comprising the following steps: drilling a borehole extending from the surface at least to the coal seam; lowering a combustible casing having a predetermined length in a wellbore, said lowering of said combustible casing being continued by means of a further casing connected to an upper end of said combustible casing when lowered to a predetermined position in the wellbore, such that a lower end of said combustible casing is located at a predetermined position in the coal seam; and securing the combustible casing and the additional casing in place in the wellbore. The invention also provides a corresponding well structure.

Description

An underground coal gasification drilling well body structure and its construction method

technical field

The invention relates to an underground coal gasification drilling well body structure and a construction method of the coal underground gasification drilling well body structure.

Background technique

Gasifier drilling in the underground coal gasification process includes two types of process wells: the inlet well and the gas outlet well. Whether the process drilling design is reasonable or not directly affects the selection and stable operation of the gasification process. It is the key to the stable production of underground coal gasification. and the key to low cost. In underground coal gasification production, the main function of the gas inlet and outlet wells is to send the gasification agent to the coal seam to be gasified through the inlet well, and the coal is burned and gasified in situ to produce coal gas and ash, and the coal gas is transported through the gas outlet well. Exported to the ground, the ash remains in the ground.

In the field of traditional oil and natural gas, the design of drilling wellbore structure is the basic design of drilling engineering. The selection of drilling wellbore material and its lowering position are important parts of wellbore structure design. The rationality of basic design directly affects the oil and gas well. Whether safe, high-quality, high-speed and economical drilling can reach the target layer and protect the reservoir to achieve stable production and prevent damage.

The drilling of underground coal gasification furnace construction refers to petroleum drilling. The well structure usually adopts petroleum series steel casing to be lowered from the ground through the well to the lower part of the coal seam, and then cemented and sealed in turn, and the hole is formed into the well. In the process of underground coal gasification with this kind of structure design, due to the special geological structure conditions of the coal seam, problems such as the following will appear: the supply of gasification agent is not in place, and the difficulty of penetration is increased, so that the local coal seam cannot be gasified and burned; The accumulation of ash at the bottom of the hole will block the air outlet or the surface pipeline; a local liquid seal will be formed at the bottom of the gas inlet and outlet, resulting in large fluctuations in system resistance. Therefore, a reasonable well structure will help to improve coal recovery, gas output stability, and reduce sharp changes in system resistance.

Contents of the invention

The purpose of the present invention is to provide an optimized wellbore structure design and corresponding construction method for inlet and outlet gas wells, which can realize the positioning supply of gasification agent and reduce the blockage and water seal of the inlet and outlet gas wells.

According to one aspect of the present invention, there is provided a method for constructing a borehole structure of an underground coal gasification borehole, which is characterized in that the method includes: drilling a borehole extending from the ground at least to the coal seam; length of combustible casing, when the combustible casing is lowered to a predetermined position in the wellbore, the combustible casing is continued to be lowered by means of another casing connected to the upper end of the combustible casing, so that the positioning the lower end of the combustible casing at a predetermined location in the coal seam; and securing the combustible casing and the further casing in place in the wellbore.

According to another aspect of the present invention, an underground gasification drilling well body structure is provided, the drilling well body structure includes: a wellbore extending from the surface to at least the coal seam and a working casing located in the wellbore, characterized in That is, the working casing includes an upper casing and a lower combustible casing, wherein the lower end of the combustible casing is located at a predetermined position in the coal seam.

According to the drilling well body structure and construction method thereof of the present invention, it has the following beneficial effects:

(1) Combustible casing and non-combustible hard casing such as petroleum steel casing are combined with low cost.

(2) The combustible casing is lowered to the gasification coal seam, which can realize the positioning supply of gasification agent and is conducive to penetration.

(3) The combustible casing is easy to ablate, without slagging or agglomeration, which effectively reduces the accumulation of ash and slag during production, reduces clogging of ash and slag and water seal, improves the operation stability of the gasifier, and prolongs the service life of the gas outlet drilling hole. Indirectly reduce production costs.

(4) The combustible casing is lighter than the non-combustible hard casing such as petroleum steel casing, and it is easier to lower.

Specific embodiments of the present invention will be described below in conjunction with the accompanying drawings.

Description of drawings

Embodiments of the present invention are schematically shown in the accompanying drawings, wherein: Figures 1 to 4 show schematic views of the construction method of the drilling well structure according to the present invention, in particular, Figure 4 shows the basis for completion The drilling well body structure of the present invention.

Explanation of reference signs: 1-surface, 2-well hole, 3-upper casing, 4-cementing cement, 5-coal seam roof, 6-pressure-bearing sealing connection, 7-combustible casing, 8-coal seam, 9- Coal floor.

Detailed ways

Referring first to Figure 4, there is shown a drilling wellbore structure in accordance with the present invention. As shown in FIG. 4 , the drilling shaft structure according to the present invention includes: a wellbore 2 extending from the ground 1 at least to the coal seam 8 between the coal seam roof 5 and the coal seam floor 9, including an upper casing 3 and a lower combustible casing. 7 working casing, cementing cement 4, etc. The working casing is positioned in the wellbore 2, and the lower end of the combustible casing 7 is positioned at a predetermined position in the coal seam. In one embodiment, the combustible casing 7 can be designed such that its length is substantially equal to the thickness of the coal seam and is lowered until its lower end is substantially flush with the coal seam floor 9 . In another embodiment, the combustible casing 7 can be designed such that its length is substantially equal to 1/2 of the thickness of the coal seam, and is lowered to its lower end close to the coal seam floor 9 . The working casing may be held in place by cement 4, for example.

An important feature of the present invention is that the lowermost part of the working casing is a combustible casing 7 instead of a traditional steel casing. According to the present invention, the combustible sleeve 7 should have the characteristics of low melting point and flammability, so that while providing gasification agent passage, it can also burn at the high temperature of coal seam gasification combustion, and will not produce a large amount of ash or cause blockage The wellbore or the upper casing in turn affects the gas production.

According to a preferred embodiment of the present invention, the working sleeve has a multi-section structure, that is, the lowermost combustible sleeve 7 is connected to the upper sleeve 3 through the connection part 6 . The connection portion 6 is preferably a pressure-tight connection portion. Since high pressure may be generated at the initial stage of the passage of fluid such as gasification agent or gas, the pressure-bearing sealing connection part is preferably designed such that: at the initial stage of passage of fluid (such as gasification agent or gas), the There will be no water leakage or air leakage at the joint. The connecting portion 6 can be realized, for example, by connecting two adjacent sleeves with internal and external threads at their respective ends.

It should be particularly noted that, according to the present invention, the above-mentioned upper sleeve 3 connected to the lowermost combustible sleeve 7 can be one section or multiple sections, and can be a non-combustible hard sleeve such as a ceramic sleeve or The standard petroleum steel casing in the field of oil exploitation can also be a combustible casing that is the same as or similar to the lowermost combustible casing 7, or can be any combination of non-combustible hard casing and combustible casing.

According to an embodiment of the present invention, the lower combustible sleeve 7 and the upper sleeve 3 may be a continuous integral structure.

In addition, the combustible casing 7 should also have predetermined strength and pressure resistance, so that it will not be damaged before being lowered to the predetermined position in the coal seam.

According to the present invention, the combustible sleeve 7 can be, for example, glass steel pipe, PE pipe, PVC pipe and the like.

According to the present invention, the well hole may be an air intake well. At this time, correspondingly, the predetermined position is the position of the coal seam to be gasified, and the working sleeve sends the gasification agent to the coal seam to be gasified. In addition, the well hole may also be a gas outlet well. At this time, correspondingly, the predetermined position is a coal bed gasification position, and the coal gas obtained from the coal bed gasification is led to the ground through the working casing.

According to another aspect of the present invention, there is also provided a method for constructing the above-mentioned drilling wellbore structure. The method generally includes the following steps: (1) drilling a wellbore extending at least to the coal seam; (2) lowering the working casing including the lower combustible casing so that the lower combustible casing is lowered to a predetermined location in the coal seam. position; and (3) securing the working sleeve.

This will be described in detail below in conjunction with the above-mentioned situation where the working sleeve has a multi-segment structure.

As shown in Figures 1 to 4, for the case where the working casing is a multi-stage structure, the method may include the following steps:

Step 1: Complete the open hole or well hole 2 that extends at least to the coal seam and meets the design requirements, as shown in Figure 1;

Step 2: Lower the combustible casing 7 conforming to the design length (such as the thickness of the coal seam) from the hole of the wellbore, and when it is lowered to a predetermined position (such as when the upper end of the combustible casing 7 is close to the hole of the wellbore), use The pressure-bearing sealing connection part 6 connects the second casing 3 on the combustible casing 7, as shown in FIG. 2 , and then continues to lower the combustible casing 7 by means of the second casing 3;

Those skilled in the art should be able to understand that this step can also be carried out as follows: firstly, the second casing 3 is connected on the combustible casing 7 by using a pressure-bearing sealing connection part, and then the two casings are connected from the opening of the wellbore. The combination of decentralized;

Step 3: When lowering to a predetermined position, for example, when the upper end of the second casing 3 reaches the vicinity of the wellbore opening, connect the upper end of the second casing 3 with a pressure-bearing seal and lower the third casing pipe, so that the pressure-tight connection is repeated and the nth casing is lowered, n is an integer greater than or equal to 3, until the lower end of the combustible casing 7 is lowered to a predetermined position, as shown in Figure 3;

It should be understood by those skilled in the art that the above-mentioned third to nth sleeves may not be necessary. In other words, in special cases it may be sufficient to lower the combustible sleeve to the intended location with the aid of a single sleeve.

Step 4: Complete the post-drilling construction, cementing, through hole completion, logging, hydraulic test, etc., and complete the final well body structure, as shown in Figure 4.

In order to further understand the present invention, especially the method of the present invention, several specific examples are described below.

Example 1

The depth of the hole is 500 meters below, the pre-gasification coal seam position is 484～495 meters, and the net coal thickness is 8 meters as an example to illustrate the implementation steps of the present invention:

Complete the drilling and coring construction with a depth of 500 meters in the open hole;

According to the coring results, it is determined that the lower end of the petroleum steel casing is 486 meters, and the lower end of the glass steel pipe is 492.5 meters;

Connect the 6.5-meter-long glass steel pipe to the petroleum steel casing, and use the screw connection method to lower the glass steel pipe to 486 meters underground;

Lower the oil steel casing to about 0.5 meters above the ground (install the ground pipe network);

Carry out post-drilling construction, cementing, through-hole completion, well logging, hydraulic testing, etc.

Example 2

The depth of the hole is 480 meters below, the pre-gasification coal seam position is 470～478 meters, and the net coal thickness is 6 meters as an example to illustrate the implementation steps of the present invention:

Completed the drilling and coring construction with a depth of 480 meters in the open hole;

According to the coring results, it is determined that the lower end of the petroleum steel casing is 468 meters, and the lower end of the PE pipe is 475.5 meters;

Connect the 7.5-meter-long PE pipe to the petroleum steel casing, and use the screw connection method to lower the PE pipe to 475.5 meters underground;

Lower the oil steel casing to about 0.5 meters above the ground (install the ground pipe network);

Carry out post-drilling construction, cementing, through-hole completion, well logging, hydraulic testing, etc.

Example 3

The depth of the hole is 580 meters below, the pre-gasification coal seam position is 570～578 meters, and the net coal thickness is 6 meters as an example to illustrate the implementation steps of the present invention:

Completed the drilling and coring construction with a depth of 580 meters in the open hole;

According to the coring results, it is determined that the lower end of the petroleum steel casing is 568 meters, and the lower end of the PVC pipe is 575.5 meters;

Connect the 7.5-meter-long PVC pipe to the petroleum steel casing, and use the screw connection method to lower the PVC pipe to 575.5 meters underground;

Lower the oil steel casing to about 0.5 meters above the ground (install the ground pipe network);

Carry out post-drilling construction, cementing, through-hole completion, well logging, hydraulic testing, etc.

According to the drilling well body structure and method thereof of the present invention, the beneficial effects are as follows:

(1) Combustible casing and non-combustible hard casing such as petroleum steel casing are combined with low cost.

(2) The combustible casing is lowered to the gasification coal seam, which can realize the positioning supply of gasification agent and is conducive to penetration.

(3) The combustible casing is easy to ablate, without slagging or agglomeration, which effectively reduces the accumulation of ash and slag during production, reduces clogging of ash and slag and water seal, improves the operation stability of the gasifier, and prolongs the service life of the gas outlet drilling hole. Indirectly reduce production costs.

(4) The combustible casing is lighter than the non-combustible hard casing such as petroleum steel casing, and it is easier to lower.

Claims (11)

1. A method for constructing an underground coal gasification borehole body structure, characterized in that the method comprises: Boreholes are drilled from the ground extending at least as far as the coal seam; running a combustible casing of predetermined length in the wellbore, When the combustible casing is lowered to a predetermined position in the wellbore, continue to lower the combustible casing by means of another casing connected to the upper end of the combustible casing, so that the lower end of the combustible casing is at the at a predetermined location in the coal seam; and The combustible casing and the further casing are secured in place in the wellbore. 2. The method according to claim 1, wherein the step of lowering comprises: first lowering the combustible casing from the opening of the wellbore, and then when the upper end of the combustible casing is close to the opening of the wellbore, When using a pressure-sealed connection, connect a second sleeve to the upper end of the combustible sleeve, and use the second sleeve to continue lowering the combustible sleeve; A second piece of casing is attached to the casing, and the combination of the two is lowered from the orifice of the wellbore. 3. The method according to claim 2, characterized in that, the step of lowering further comprises: when the upper end of the second casing pipe reaches the vicinity of the hole opening of the wellbore, connecting the second casing with a pressure seal The upper end of the second casing is connected and the third casing is lowered, so that the pressure-tight connection is repeated and the nth casing is lowered, n is an integer greater than or equal to 3, until the lower end of the combustible casing is lowered to a predetermined position. 4. The method according to claim 1, characterized in that, the connection is a pressure-sealed connection, and the pressure-sealed connection is designed so that: in the initial stage of the fluid flow path penetration, the connection will not leak or leak. gas phenomenon, and said connection can be realized by an internal and external threaded connection of the combustible sleeve and the ends of said further sleeve. 5. The method according to claim 1, characterized in that, the combustible casing is configured to be combustible at the temperature of coal seam gasification combustion, and has predetermined strength and pressure resistance, so that when lowered into the well The predetermined position in the hole is not damaged before. 6. The method according to claim 1, wherein the combustible sleeve is a glass steel pipe, a PE pipe or a PVC pipe, and the other sleeve is a combustible sleeve or a non-combustible hard sleeve, and the The non-combustible hard casing includes ceramic casing and standard petroleum steel casing. 7. An underground gasification drilling well body structure, the drilling well body structure comprises: a wellbore extending from the ground to a coal seam at least and a working casing positioned in the wellbore, characterized in that the working casing comprises The upper casing and the lower combustible casing, wherein the lower end of the combustible casing is located at a predetermined position in the coal seam. 8. The structure according to claim 7, characterized in that, the upper casing and the combustible casing are connected through a pressure-bearing sealing connection part, and the pressure-bearing sealing connection part is designed such that: in the fluid flow path At the initial stage of penetration, there will be no water leakage or air leakage at the connection part, and the connection part can be realized through the internal and external screw connection of the combustible sleeve and the end of the upper sleeve. 9. The structure according to claim 7, characterized in that, the combustible casing is configured to be combustible at the temperature of coal seam gasification combustion, and has predetermined strength and pressure resistance, so that when it is lowered into the well The predetermined position in the hole is not damaged before. 10. The structure according to claim 7, wherein the combustible sleeve is a glass steel pipe, PE pipe or PVC pipe, the upper sleeve is a combustible sleeve or a non-combustible hard sleeve, and the Non-combustible rigid casings include ceramic casings as well as standard petroleum steel casings. 11. The structure according to claim 7, characterized in that, the wellbore is an inlet well or a gas outlet well, the predetermined position is the position of the coal seam to be gasified or the coal seam gasification position, and the working casing The chemical agent is sent to the coal seam to be gasified or the gas is exported to the ground.

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