A soluble and flushable bridge plug and an L-type horizontal well staged fracturing method using the same

Abstract

The present invention belongs to the field of coalbed methane exploitation, and specifically discloses a soluble and flushable bridge plug and an L-type horizontal well staged fracturing method using the same. The soluble and flushable bridge plug comprises a soluble bridge plug and a soluble flushing valve, and the soluble flushing valve is connected to the lower end of the soluble bridge plug through a connecting buckle. The L-type horizontal well staged fracturing method adopts a soluble and flushable bridge plug for staged fracturing, and after each stage of fracturing is completed and the pump is stopped, the wellhead valve is opened for rapid release. The soluble and flushable bridge plug provided by the present invention can not only force the soluble bridge plug to move forward when pumping liquid when pumping the bridge plug, but also enable sufficient fluid to flush the fracturing sand and coal powder that have been precipitated and accumulated in front of the bridge plug due to rapid release from the tail of the bridge plug, so that the soluble bridge plug can smoothly reach the predetermined position for perforation fracturing, and rapid release can eliminate the clogging of the seepage channel by coal powder in the coal seam, reduce the damage of chemical pollution to the coal seam, and improve the return rate of the fracturing fluid.

Description

Technical Field

[0001] The invention belongs to the field of coalbed methane mining, and in particular relates to a soluble and flushable bridge plug and an L-shaped horizontal well staged fracturing method using the bridge plug. Background Art

[0002] In the field of coalbed methane exploration and development, it is usually adopted to drill an "L"-shaped horizontal well in the coal seam, cement the well with casing, and then perform segmented perforation and segmented hydraulic fracturing. Then, the methane molecules (coalbed methane) adsorbed on the surface of coal particles are desorbed and produced by drainage and pressure reduction to achieve coalbed methane extraction. At present, the main segmented fracturing methods for L-shaped horizontal wells include ordinary tubing dragging bottom seal segmented sandblasting perforation fracturing and pumping soluble bridge plug segmented perforation fracturing.

[0003] The advantages of the tubing-drag bottom seal sandblasting perforation staged fracturing method are simple and reliable process, convenient perforation, low comprehensive cost and high cost-effectiveness. Its main disadvantages are slow layer conversion time and insufficient fracturing displacement (caused by sandblasting perforation tubing), which cannot meet the large-volume fracturing of medium-deep coalbed methane. The advantages of the pump-injected soluble bridge plug staged fracturing method are mainly short perforation layer conversion time, which can achieve large-scale volume fracturing with large-volume dense cutting of multiple clusters of perforations at one time, especially large-scale volume fracturing of medium-deep coalbed methane to obtain higher gas production. The disadvantage is that since the large-scale volume fracturing method is derived from shale gas fracturing, in order to improve the sand carrying capacity, a large amount of polymer compounds are added to the fracturing fluid. The coal seam has a strong adsorption to these polymer compounds, and it is difficult to desorb them, resulting in serious pollution of the coal seam, difficulty in desorption of coalbed methane, and difficulty in producing adsorbed gas. In addition, due to the fragility of coal seam structure, large-scale fracturing will produce a large amount of coal dust. As many as more than ten stages of fracturing are completed before the overall release (rather than release after a single stage of fracturing), the fracturing fluid stays in the coal seam for a long time, the fracturing fluid return rate is low, and the pollution is further aggravated. Moreover, unified control of release and release cannot eliminate the blockage of coal dust in the micro-cracks of the coal seam. If the fracturing fluid is quickly released and quickly returned after fracturing, the return rate of the fracturing fluid will be greatly improved, the pollution of the coal seam by polymer compounds will be reduced, the blockage of coal dust will be eliminated, and the phenomenon of sand spitting and burying in the formation wellbore will also be reduced. If a quick release and release are performed after each stage of fracturing, some fracturing sand will be deposited and accumulated in the wellbore. When clustered perforation and soluble bridge plugs are pumped in the transition stage, these aggregated fracturing sands will prevent the soluble bridge plugs from reaching the predetermined perforation and sealing position, resulting in failure to perforate and fractur at the predetermined position. Although pump-injected segmented cluster perforating tools and soluble bridge plugs have achieved large-scale volume fracturing transformation of medium-deep coal seams and achieved high gas production, they also have obvious disadvantages, such as the use of high-molecular compounds polluting coal seams, the retention of fracturing fluid in coal seams during production time, which aggravates coal seam pollution, the overall controlled release after gas pressure cannot eliminate the blockage of coal powder produced by fracturing to the cracks, and the hidden danger of horizontal wellbore blockage caused by the return of fracturing sand. These reasons lead to low fracturing fluid return rate, low coal seam desorption degree, low recovery rate, and low comprehensive economic benefits. Summary of the invention

[0004] In view of this, in order to overcome the pollution of coal seams by polymer compounds used in large-scale staged fracturing by pumping bridge plugs, in order to overcome the disadvantages of generally low return rate of fracturing fluid caused by overall controlled release after fracturing, and the hazards of coal seam crack blockage caused by a large amount of coal powder retained in the coal seam. The present invention provides a soluble and flushable bridge plug, which can not only force the soluble bridge plug to move forward when pumping liquid, but also allow sufficient fluid to flush the fracturing sand and coal powder accumulated in front of the bridge plug due to rapid release from the tail of the bridge plug, so that the soluble bridge can smoothly reach the predetermined position for perforation fracturing, and after implementing large-volume volume fracturing to transform the coal seam, rapid release eliminates the return fracturing fluid, eliminates the clogging of the seepage channel by coal powder in the coal seam, reduces the damage of chemical pollution to the coal seam, and improves the return rate of the fracturing fluid.

[0005] In order to achieve the above object, the present invention adopts the following technical solution:

[0006] A soluble flushable bridge plug comprises a soluble bridge plug and a soluble flushing valve. The soluble flushing valve is connected to the lower end of the soluble bridge plug through a connecting buckle.

[0007] Preferably, the soluble flushing valve body is a ball valve, the valve core is connected to the valve seat through a spring, and the soluble flushing valve is automatically opened by the liquid flowing from the inside of the soluble bridge plug exerting pressure on the spring. The elastic coefficient of the spring can be set according to actual needs.

[0008] An L-type horizontal well staged fracturing method adopts the above-mentioned soluble and flushable bridge plug to perform staged fracturing.

[0009] Preferably, after each stage of fracturing is completed and the pump is stopped, the wellhead valve is opened for rapid release.

[0010] Preferably, the L-type horizontal well staged fracturing method specifically comprises the following steps:

[0011] (1) The first layer is perforated by tubing transmission, and fracturing operations are carried out after the tubing string is pulled out;

[0012] (2) After fracturing, open the wellhead valve for rapid release;

[0013] (3) Use a pressure pump to send the soluble and flushable bridge plug and the perforating tool string to the vicinity of the second perforation position;

[0014] (4) After the depth is calibrated, the perforating tool string is lifted to raise the soluble flushable bridge plug to the setting position, and the soluble flushable bridge plug is ignited to set the plug;

[0015] (5) Propose a perforating tool string;

[0016] (6) The ball pump is sent to the soluble and flushable bridge plug to start the second stage of fracturing;

[0017] (7) After fracturing is completed, open the wellhead valve for rapid blowdown;

[0018] (8) Repeat the above steps (3) to (7) until the remaining fracturing operation sections are completed.

[0019] It can be seen from the above technical solutions that compared with the prior art, the present invention has the following excellent effects:

[0020] The invention adopts fast spraying, which can not only greatly improve the return rate of fracturing fluid, but also bring the coal powder produced by fracturing to the ground, eliminate the risk of coal powder blocking the cracks of coal seams, and reduce the shutdown and well repair caused by sand accumulation in the wellbore. When the amount of fracturing return fluid reaches a certain proportion of the total amount of fluid entering the ground, the well is closed and spraying is stopped. When the fracturing fluid containing coalbed methane nano-desorption promoter is selected, the fracturing fluid has time to fully infiltrate the coal seam.

[0021] Although rapid blowout causes most of the returned fracturing sand to be discharged to the ground by high-speed fluid, a small amount of fracturing sand or coal particles are still retained in the horizontal wellbore. When fracturing the second-level coal seam, use the cable soluble flushable bridge plug to approach the landing point, start the pump truck to start pumping the soluble flushable bridge plug, and control the pumping displacement, so that the soluble flushable bridge plug can move forward at a certain speed, and a certain flow of liquid can pass through the soluble flushing valve in front of the soluble bridge plug to flush the fracturing sand and coal powder gathered in front of the bridge plug when the bridge plug moves forward, so that the bridge plug can reach the set position smoothly. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0023] Figure 1 This is a schematic diagram of the installation of the soluble and flushable bridge plug according to Example 1 of the present invention.

[0024] Figure 2 This is a schematic diagram of the structure of the soluble flushing valve in Example 1 of the present invention. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] Example 1

[0027] A soluble flushable bridge plug, comprising a soluble bridge plug and a soluble flushing valve, wherein the soluble flushing valve is connected to an end of the soluble bridge plug away from a perforating gun through a connecting buckle. The soluble flushing valve body is a ball valve, the valve core is connected to the valve seat through a spring, and the soluble flushing valve is automatically opened by the liquid flowing into the soluble bridge plug to press the spring.

[0028] Example 2

[0029] A method for staged fracturing of an L-shaped horizontal well, using the soluble and flushable bridge plug of Example 1 for staged fracturing, specifically comprising the following steps:

[0030] (1) The first layer is perforated by tubing transmission, and fracturing operations are carried out after the tubing string is pulled out;

[0031] (2) After fracturing, open the wellhead valve for rapid release;

[0032] (3) Use a pressure pump to send the soluble and flushable bridge plug and the perforating tool string to the vicinity of the second perforation position;

[0033] (4) After the depth is calibrated, the perforating tool string is lifted to raise the soluble flushable bridge plug to the setting position, and the soluble flushable bridge plug is ignited to set the plug;

[0034] (5) Propose a perforating tool string;

[0035] (6) The ball pump is sent to the soluble and flushable bridge plug to start the second stage of fracturing;

[0036] (7) After fracturing is completed, open the wellhead valve for rapid blowdown;

[0037] (8) Repeat the above steps (3) to (7) until the remaining fracturing operation sections are completed.

[0038] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A soluble and flushable bridge plug, characterized in that: The soluble and flushable bridge plug comprises a soluble bridge plug and a soluble flushing valve, and the soluble flushing valve is connected to the lower end of the soluble bridge plug through a connecting buckle.

2. A soluble and flushable bridge plug according to claim 1, characterized in that: The soluble flushing valve body is a ball valve, the valve core is connected to the valve seat through a spring, and the soluble flushing valve is automatically opened by the liquid flowing from the inside of the soluble bridge plug exerting pressure on the spring.

3. An L-type horizontal well staged fracturing method, characterized in that: The soluble and flushable bridge plug according to claim 1 or 2 is used for staged fracturing.

4. The L-type horizontal well staged fracturing method according to claim 3, characterized in that: After each stage of fracturing, the pump is stopped and the wellhead valve is opened for rapid release.

5. The L-type horizontal well staged fracturing method according to claim 4, characterized in that: The specific steps include: (1) The first layer is perforated by tubing transmission, and fracturing operations are carried out after the tubing string is pulled out; (2) After fracturing, open the wellhead valve for rapid release; (3) Use a pressure pump to send the soluble and flushable bridge plug and the perforating tool string to the vicinity of the second perforation position; (4) After the depth is calibrated, the perforating tool string is lifted to raise the soluble flushable bridge plug to the setting position, and the soluble flushable bridge plug is ignited to set the plug; (5) Propose a perforating tool string; (6) The ball pump is sent to the soluble and flushable bridge plug to start the second stage of fracturing; (7) After fracturing is completed, open the wellhead valve for rapid release; (8) Repeat the above steps (3) to (7) until the remaining fracturing operation sections are completed.

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