Well drilling process method for thin seam directional well overlarge mining height deep ponding goaf

Abstract

The invention discloses a drilling process method for a thin seam directional well overlarge mining height deep ponding goaf, which comprises the following steps of: (1) when a wellbore is detected to be abnormal in a drilling process, immediately stopping drilling, starting drilling operation, and synchronously implementing combustible gas monitoring; grouting operation is carried out according to well conditions in the pulling-out process, and a wellhead blowout preventer is closed after grouting operation is completed; (2) coal gangue and a well cementation material are injected into the wellbore in a segmented mode after drilling is conducted, and a composite barrier layer covering the goaf is formed; and (3) detecting the quality of the barrier layer after the well cementation material is solidified, recovering drilling after the quality is qualified, and retreating the barrier layer until the standard is reached if the quality is unqualified. The coal gangue can be obtained from local materials, a formed solidified structure is very beneficial to directional return of rock debris in well drilling, and well drilling can be effectively and conveniently completed without well deviation falling.

Description

Technical Field

[0001] The present invention belongs to the technical field of coalbed methane extraction, and particularly relates to a drilling process method for a directional well in a thin coal seam passing through a highly water-filled goaf with a large mining depth. Background Art

[0002] In the Sihe block, there are many developed thin coal seams with a considerable total coal thickness. With the excavation of the No. 3 coal seam and the exploitation of coalbed methane resources in the No. 3, No. 9, and No. 15 coal seams in the Sihe block, the development of thin coal seam wells (directional + passing through goafs) has become an important resource to ensure the stable gas production in the block. The thin coal seam development work carried out by CUCBM in the Panhe block has also achieved remarkable results, and 50% of the production comes from the development of thin coal seams.

[0003] The main problem encountered in the development of thin coal seam wells is that they need to pass through goafs and maintain directional well deviation during the process of passing through goafs. At present, this technology is mainly explored and summarized in practice. Currently, it is mainly nitrogen circulation, and the disadvantage is that the void is obvious and it is simply impossible to maintain directional well deviation, especially when drilling through a highly water-filled goaf with a large mining depth, the effect is not ideal. Summary of the Invention

[0004] In order to ensure the normal return of cuttings when a thin coal seam well, especially a directional well, passes through a highly water-filled goaf with a large mining depth, the present invention provides a drilling process method for a directional well in a thin coal seam passing through a highly water-filled goaf with a large mining depth.

[0005] The present invention adopts the following technical solutions. A drilling process method for a directional well in a thin coal seam passing through a highly water-filled goaf with a large mining depth includes the following steps: (1) When abnormal conditions in the wellbore are detected during drilling, immediately stop drilling and start the hoisting operation, and simultaneously implement combustible gas monitoring; during the hoisting process, perform grouting operations according to the well conditions, and after completion, close the blowout preventer at the wellhead; (2) After hoisting, inject filling materials and cementing materials into the wellbore in sections to form a composite barrier layer covering the goaf; (3) After the cementing materials solidify, detect the quality of the barrier layer. If it is qualified, resume drilling; if it is unqualified, reprocess the barrier layer until it meets the standard.

[0006] Further, in step (2), the filling material is coal gangue, and the filling amount is calculated according to the void volume of the wellbore and injected to a position 1 - 2 m above the roof of the goaf; the cementing material uses cement slurry added with a quick-setting agent, and a cement column at least 20 m higher than the roof of the goaf is poured.

[0007] Further, in step (1), the combustible gas monitoring is implemented using a four-in-one gas detector, the grouting operation includes two mode selections: continuous grouting and intermittent grouting, and the blowout preventer is a full-closed gate valve.

[0008] Further, in step (3), a waiting setting time of 1 - 2 days is set. When the quality is qualified, the operation is resumed using the nitrogen drilling process. When the quality is unqualified, the barrier layer is penetrated by the drill string and the filling treatment in step (2) is repeated.

[0009] Further, air screw drilling is used for directional wells.

[0010] The present invention has the following beneficial effects: For thin coal seam wells, especially directional wells, when passing through large mining depth and water - filled goaf areas, the methods of reaming the well, filling with coal gangue, and grouting cement slurry (with accelerator) are adopted. After the waiting setting time is sufficient, normal nitrogen drilling is carried out; coal gangue can be obtained locally, and the solidified structure after grouting cement slurry (with accelerator) is very beneficial for the directional return of cuttings in drilling, and can effectively and inexpensively ensure that the well deviation does not drop and the drilling is completed. Description of the Drawings

[0011] Figure 1 is a schematic diagram of the completion of a thin coal seam directional well passing through a large mining depth and water - filled goaf area of the present invention. Detailed Embodiments

[0012] In order to better understand the purpose, structure, and function of the present invention, the following further describes in detail a drilling process method for a thin coal seam directional well passing through a large mining depth and water - filled goaf area of the present invention with reference to the drawings.

[0013] Please refer to Figure 1 , this well is a thin coal seam directional well with a three - opening wellbore structure, belonging to the situation of passing through a large mining depth and water - filled goaf area. The specific drilling process method includes the following steps: (1) During drilling, when phenomena such as loss of mud return at the wellhead, significant voiding, obvious underground water or water inrush are found, immediately organize the drill - pulling operation, cooperate with a four - in - one gas detector to detect the concentration of combustible gas. After pulling out the drill, close the full - closed gate valve. In case of necessity, grout while pulling out the drill to prevent out - of - control blowout.

[0014] (2) After pulling out the drill, contact the cementing truck to arrive at the site for preparation. At the same time, according to the calculated void volume in the well, pull enough coal gangue and fill it into the well from the wellhead to a position 1 - 2 m above the roof of the goaf area, and then carry out cement pouring: G - grade oil well cement needs to be injected, the density of the cement slurry is 1.6 - 1.8 g / cm3, and a certain amount of accelerator is required; the cement level in the well should be 20 m above the roof of the goaf area.

[0015] (3) Wait for setting for 1 - 2 days. First, measure the cement level. If successful, carry out normal nitrogen drilling; it is recommended to use air screw drilling for directional wells to ensure that the well deviation does not drop. If unsuccessful, penetrate with the drill string, continue to fill with coal gangue until qualified, and then carry out normal nitrogen drilling.

[0016] For directional wells, air screw drilling can ensure that the well deviation does not decrease.

[0017] In this drilling process method, the crossing of large mining-depth waterlogged goafs is achieved by filling with coal gangue and grouting cement slurry (accelerator). Its advantage lies in that the coal gangue (there are coal gangue mountains around the coal mine, and local materials can be used) is filled into the goaf to form a framework. After grouting cement slurry (accelerator), the structure will quickly solidify, which is very beneficial for the directional return of drill cuttings. By using this method, the goaf can be successfully crossed, and the well deviation can be ensured not to decrease, and the wellbore trajectory meets the standards.

[0018] It can be understood that the present invention is described through some embodiments. Those skilled in the art know that without departing from the spirit and scope of the present invention, various changes or equivalent substitutions can be made to these features and embodiments. In addition, under the teaching of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application belong to the scope protected by the present invention.

Claims

1. A drilling process for a thin coal seam directional well in a deep and waterlogged goaf with excessive mining height, characterized in that: The following steps are involved: (1) When an abnormality is detected in the wellbore during drilling, drilling is stopped immediately and the pull-out operation is started, and combustible gas monitoring is carried out simultaneously; during the pull-out operation, grouting operations are carried out according to the well conditions, and the wellhead blowout preventer is closed after completion; (2) After drilling, filler materials and cementing materials are injected into the wellbore in sections to form a composite barrier layer covering the goaf; (3) After the cementing material solidifies, the quality of the barrier layer is tested. If it passes the test, drilling is resumed. If it fails the test, the barrier layer is reprocessed until it meets the standards.

2. The drilling process of a directional well in a thin coal seam for drilling in a deep and waterlogged goaf with excessive mining height according to claim 1, characterized in that: The filling material in step (2) is coal gangue, and the filling amount is calculated according to the hollow volume of the wellbore and injected to a position 1-2 m above the roof of the goaf; the cementing material is cement slurry with an accelerated setting agent added, which is poured to form a cement column at least 20 m above the roof of the goaf.

3. The drilling process of a directional well in a thin coal seam for drilling in a deep and waterlogged goaf with a large mining height according to claim 1, characterized in that: The combustible gas monitoring in step (1) is implemented by using a four-in-one gas detector, the grouting operation includes two mode options: continuous grouting and intermittent grouting, and the blowout prevention device is a fully enclosed gate valve.

4. The drilling process of a directional well in a thin coal seam for drilling in a deep and waterlogged goaf with excessive mining height according to claim 1, characterized in that: In step (3), a waiting period of 1-2 days is set. When the quality is qualified, the nitrogen drilling process is used to resume the operation. When the quality is unqualified, the barrier layer is penetrated by the drill bit and the filling process of step (2) is repeated.

5. The drilling process of a directional well in a thin coal seam for drilling in a deep and waterlogged goaf with excessive mining height according to any one of claims 1 to 4, characterized in that: Directional wells are drilled using air screws.

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