One-section well cementation plugging method for passing through sandstone aquifer of goaf

Abstract

The method comprises the following steps that firstly, drilling is conducted to a certain depth below a goaf bottom plate, reaming is conducted below the goaf bottom plate, a borehole is formed, a water stop ring is welded to a preset position of the outer wall of a sleeve, a water swelling filling layer is arranged below the water stop ring, and the water swelling filling layer is arranged below the water stop ring; a cement bolt is poured at the preset position of the inner wall of the sleeve, a grouting hole is formed in the section, corresponding to the sleeve, of the sandstone aquifer, the sleeve is put into a borehole, the water stop ring is located at the bottom of the sandstone aquifer, the grouting hole is located in the section of the sandstone aquifer, cement paste is injected through the sleeve, and the cement paste enters the annulus through the grouting hole and returns to the ground; in conclusion, the method has the advantages that the construction procedure is simplified, the construction efficiency is improved, grout leakage is avoided, the plugging effect is enhanced, the engineering cost is reduced, and the long-term stability is improved.

Description

Technical Field

[0001] This invention belongs to the field of mine geological disaster control technology, specifically relating to a method for segmented cementing and sealing of sandstone aquifers in goaf areas. Background Technology

[0002] In oil and gas and unconventional energy drilling projects, especially in drilling operations that cross goaf areas, it is often necessary to simultaneously consider cementing and plugging shallow and medium-depth high-permeability sandstone aquifers and goaf areas. This type of operation is extremely common in the construction of coalbed methane, shale gas, geothermal wells, and mine gas extraction wells. In coal-bearing strata in North China and East China, shallow and medium-depth (300-500m) sandstone aquifers are generally characterized by high permeability, high water pressure, and easy leakage. Traditional cementing techniques are often difficult to achieve precise sealing of these sandstone aquifers, which can easily lead to drilling fluid loss, groundwater pollution, and wellbore abandonment. According to the "Statistical Report on Accidents in China's Coalbed Methane Drilling Projects (2023)," cementing failures caused by sandstone aquifer leakage account for 37% of all accidents, increasing the treatment cost by an average of 200,000 to 500,000 yuan per well. This indicates that existing cementing technologies have significant shortcomings under complex formation conditions, making research on them essential.

[0003] Currently, to address these situations, a cementing process route represented by the "two-stage" structure has gradually emerged in practical engineering. This process typically involves drilling to the bottom of the sandstone layer in the first stage and cementing it to seal the sandstone aquifer. Then, in the second stage, drilling continues to the bottom of the goaf for secondary cementing, thus completing the final cementing. While this method can achieve segmented sealing to some extent, it also brings problems such as cumbersome procedures, long construction cycles, and high costs. The second stage construction requires multiple drilling and cementing operations, increasing construction steps, extending the construction period, and resulting in low construction efficiency. The repetitive drilling and cementing work significantly increases drilling costs and is not suitable for the cementing process requirements under current complex formation conditions. At the same time, in sandstone aquifer sections, due to the frequent leakage or uneven coverage of cement slurry, water channeling or sealing failure is likely to occur, posing a significant risk and adversely affecting subsequent operations.

[0004] The methods for addressing the above problems include staged cementing and chemical plugging. However, staged cementing requires the installation of staged collars on the casing and the injection of cement slurry in stages. If the grouting pressure is too high during construction, it can easily lead to damage or blockage of the staged collar sleeves. If the pressure is insufficient, the cement slurry cannot effectively cover the target layer, resulting in a high failure rate of plugging. Chemical plugging methods require the injection of polymer colloids or resin-based materials to seal permeable fractures. While this can reduce leakage in the short term, it is prone to degradation or strength decay under high temperature, high pressure, and long-term downhole environments, eventually leading to secondary leakage, which still cannot meet the requirements.

[0005] To address this, we propose a segmented cementing method for sandstone aquifers in goaf areas, which solves the problems of complex construction procedures, long construction period, high construction cost, poor sealing effect, easy secondary leakage and insufficient stability in current applications. Summary of the Invention

[0006] In view of this, the present invention proposes a segmented cementing and plugging method for sandstone aquifers in goaf areas, which solves the existing technical problems of complex construction procedures, long construction period, high construction cost, poor plugging effect, easy secondary leakage and insufficient stability.

[0007] To achieve the above-mentioned technical objectives, the specific technical solution adopted by the present invention is as follows: A method for cementing and plugging a single section of sandstone aquifers in a goaf, comprising the following steps: S1. Drill to the target formation. First, drill to a certain depth below the bottom plate of the goaf, and then enlarge the hole below the sandstone bottom plate to form a wellbore. S2. Prepare the casing, weld a water-stop ring at a preset position on the outer wall of the casing, set a water-swellable filling layer below the water-stop ring, pour cement plugs at a preset position on the inner wall of the casing, and open grouting holes in the corresponding casing section of the sandstone aquifer. S3. Lower the casing into the wellbore so that the water-stop ring is located at the bottom of the sandstone aquifer, the grouting hole is located in the sandstone aquifer section, and the cement plug is located below the sandstone bottom plate. S4. Cement grout is injected through the casing. The cement grout enters the annulus through the grouting hole and returns to the ground, forming a cement ring to seal the sandstone aquifer. S5. After allowing the cement plug to cool and solidify, continue cementing operations below the goaf floor to allow the cement slurry to return to the top of the goaf floor, thus completing the cementing and sealing of the goaf section.

[0008] Furthermore, in step S1, a 311.2mm diameter drill bit is used to drill to 20m below the bottom plate of the goaf, and a 444.5mm diameter drill bit is used to enlarge the hole within 10m below the sandstone bottom plate.

[0009] Furthermore, in step S2, the casing has a specification of 273.1mm × 8.89mm, and the total length of the casing covers the entire wellbore. The material is J55 steel grade.

[0010] Furthermore, in step S2, the water-stop ring is a ring-shaped steel plate made of Q235 steel. The water-stop ring is welded to the bottom of the sandstone aquifer on the outer wall of the casing. The plane of the water-stop ring is perpendicular to the axis of the casing, and the horizontal width of the water-stop ring is 100mm.

[0011] Furthermore, in step S2, the water-swellable filler layer has a ring structure and is located in the 0-1m section below the water-stop ring. The water-swellable filler layer is made of high-ratio water-swellable rubber material with an expansion ratio of 200% to 300%, a temperature resistance range of -20℃ to 150℃, and a compressive strength ≥5MPa after expansion.

[0012] Furthermore, in step S2, the water-swellable filling layer is fixed to the outer wall of the sleeve through an annular groove with a width of 150 mm and a depth of 10 mm. The water-swellable filling layer is fixed with butyl rubber adhesive, the shear strength of which is ≥2 MPa, and is reinforced with a 10 mm wide stainless steel binding strap. The outside of the water-swellable filling layer is wrapped with a 0.5 mm thick biodegradable non-woven fabric.

[0013] Furthermore, in step S2, the cement plug uses Grade G oil well cement, the length of the cement plug is 10m, the cement plug is set 10m below the sandstone bottom plate of the inner wall of the casing, and is formed by segmented vibration using a special pouring tool and cured for 24 hours.

[0014] Furthermore, in step S2, the grouting holes are opened in the section of the casing with a vertical depth of 370-400m. The diameter of the grouting holes is 8-12mm. There are a total of 36 grouting holes, which are arranged in three spiral groups of 12 holes each with a phase angle of 120°.

[0015] Furthermore, in step S4, the injected cement slurry is a mixture of G-grade oil well cement and 2% fluid loss reducing agent. The injection rate of the cement slurry is 20-30 m³ / h. After the cement slurry returns to the surface, the wellhead gate is closed, and the annular pressure is maintained at 2.0-2.5 MPa until it cools and solidifies.

[0016] Furthermore, in step S5, after cementing is completed, the cementing quality is detected by sonic variable density logging. The logging results show that the cement bonding strength of the cementing section in the sandstone aquifer is ≥20MPa, there is no channeling phenomenon, the cementing quality of the cementing section in the goaf is stable, and the height of the cement sheath reaches the top plate of the goaf.

[0017] By adopting the above technical solution, the present invention can also bring the following beneficial effects: 1. This invention discloses a method for single-stage cementing and plugging of sandstone aquifers in goaf areas. By adopting a single-stage eccentric drilling and reaming process, cementing operations of sandstone aquifers and goaf areas can be completed in a single drilling process, avoiding the complex process of multiple drilling and repeated cementing in the traditional two-stage process. The procedures are significantly simplified, the construction cycle is shortened by about 77.8%, and the construction efficiency is greatly improved. It has the advantages of simplified construction procedures, short construction cycle and high construction efficiency.

[0018] 2. This invention discloses a method for cementing and plugging a sandstone aquifer in a goaf. It involves installing a water-stop ring at the bottom of the sandstone aquifer on the outer wall of the casing, a water-swellable filling layer below the water-stop ring, prefabricating cement plugs below the sandstone bottom plate on the inner wall of the casing, and opening grouting holes in the sandstone aquifer section. The water-stop ring restricts the flow of cement grout, the water-swellable filling layer expands and fills the fissures in the annulus after encountering water, the cement plugs serve as a physical isolation barrier and load-bearing foundation, and the grouting holes ensure that the cement grout can evenly cover the aquifer section. The synergistic effect of these structures enables the cement grout to accurately plug the target aquifer section, avoiding "top sealing and bottom leakage" or "bottom sealing and top leakage" phenomena, significantly improving the plugging effect, and possessing the advantages of preventing leakage and providing good plugging results.

[0019] 3. This invention discloses a method for segmented cementing and plugging of sandstone aquifers in goaf areas. During the cementing process, G-grade oil well cement combined with a fluid loss reducing agent is used as the grouting system, which can reduce the risk of cement slurry leakage. After cementing, sonic variable density logging tests show that the cement bonding strength of the cemented section in the sandstone aquifer is ≥20MPa, with no channeling. The cementing quality of the goaf cemented section is stable, the cement sheath height reaches the top of the goaf, and there is no leakage. The overall cementing quality is stable over a long period, and the cement sheath compressive strength can reach 15-20MPa, meeting the reliability requirements for long-term use under complex formation conditions. Simultaneously, this method reduces cementing failure rate while lowering construction costs by approximately 30%. Its economic advantages are even more prominent under multi-well concentrated operation conditions, offering the advantages of significantly reduced costs, enhanced stability, and high cementing quality. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of a method for sealing a single-stage cementing well in a sandstone aquifer in a goaf area, as mentioned in this invention. Figure 2 This is a schematic diagram of the connection structure between the casing and the wellbore in this embodiment; In the diagram: 1. Casing; 2. Wellbore; 3. Grouting hole; 4. Water-stop ring; 5. Water-swellable filling layer; 6. Cement plug. Detailed Implementation

[0022] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0023] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments can be combined with each other. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0024] It should be noted that various aspects of embodiments within the scope of the appended claims are described below. It will be apparent that the aspects described herein can be embodied in a wide variety of forms, and any particular structure and / or function described herein is merely illustrative. Based on this invention, those skilled in the art will understand that one aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number of aspects set forth herein can be used to implement the device and / or practice the method. Additionally, this device and / or method can be implemented using other structures and / or functionalities besides one or more of the aspects set forth herein.

[0025] It should also be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. The drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0026] Furthermore, specific details are provided in the following description to facilitate a thorough understanding of the examples. However, those skilled in the art will understand that the described aspects can be practiced without these specific details.

[0027] In one embodiment of this application, such as Figure 1 and Figure 2 As shown, the present invention provides a method for cementing and plugging a single section of sandstone aquifer in a goaf area, comprising the following steps: S1. Drill to the target formation and enlarge the borehole. Drilling rigs were deployed at the target well site. Conventional drilling fluid circulation was used to reduce pressure and maintain the stability of wellbore 2. A 311.2mm diameter drill bit was used to drill to 20m below the bottom plate of the goaf, ensuring the wellbore 2 was connected and removing rock cuttings from the bottom of the well. Within 10m below the sandstone bottom plate (corresponding to the vertical depth of wellbore 2 of 400–410m), a 444.5mm diameter drill bit was used to enlarge the hole, forming a well diameter transition section to facilitate the smooth running of casing 1 and ensure the smooth return flow of cementing slurry.

[0028] S2, Preparation of sleeve 1 S201 uses casing 1 with a specification of 273.1mm×8.89mm. The total length of casing 1 covers the entire section of wellbore 2, and the material is J55 steel grade.

[0029] S202 Weld a water-stop ring 4 at the bottom of the sandstone aquifer. The water-stop ring 4 is a ring-shaped steel plate made of Q235 steel with a width of 100mm. The plane of the water-stop ring 4 is perpendicular to the axis of the sleeve 1, and the weld is continuously sealed.

[0030] S203 A water-swellable filling layer 5 is installed 0–1m below the water-stop ring 4. This filling layer is a high-expansion water-swellable rubber ring with an expansion ratio of 200%–300%, a temperature resistance range of -20℃ to 150℃, and a compressive strength ≥5MPa after expansion. The water-swellable filling layer 5 is fixed to the outer wall of the sleeve 1 through an annular groove 150mm wide and 10mm deep, using butyl rubber adhesive. The shear strength of the adhesive is ≥2MPa. The outside of the filling layer is wrapped with 0.5mm thick biodegradable non-woven fabric and reinforced circumferentially with 10mm wide stainless steel binding straps.

[0031] S204 A cement plug 6 is poured 10m below the sandstone bottom plate of the inner wall of casing 1 (the vertical depth of casing 1 is about 400m). The cement plug 6 is made of G-grade oil well cement, with a length of 10m. It is formed by segmented vibration using a special pouring tool and cured for 24 hours. It serves as both a physical isolation barrier and a load-bearing foundation for subsequent well cementing in the goaf.

[0032] S205 Grouting holes 3 are opened in the corresponding section of the sandstone aquifer. The diameter of the grouting holes 3 is 8-12mm. There are 36 grouting holes 3, which are arranged in 3 spiral groups of 12 holes each. The phase angle is distributed at 120° to ensure that the cement grout can be uniformly diffused in the circumference to cover the target layer.

[0033] S3, Lower Sleeve 1 and Positioning The casing 1 is lowered into the wellbore 2 as a whole. During the lowering process, drilling fluid circulation is maintained to ensure wellbore stability and remove cuttings from the bottom of the well. The lowering speed and wellhead fluid level are monitored in real time during the lowering process to ensure that the casing 1 is lowered smoothly and to avoid safety hazards caused by excessive speed disturbing the wellbore or fluid fluctuations. The water-stop ring 4 is accurately positioned at the bottom of the sandstone aquifer. The water-swellable filling layer 5 is in close contact with the wellbore to form the first sealing barrier. The cement plug 6 is stabilized 10m below the sandstone bottom plate, serving as the physical isolation body and load-bearing foundation for cementing. The grouting hole 3 corresponds to the sandstone aquifer section and provides a channel for subsequent precise injection and uniform diffusion of grout.

[0034] S4. Inject cement slurry and cement the well. The cement slurry used is a mixture of G-grade oil well cement and 2% fluid loss reducer. The slurry has good fluidity and low fluid loss rate. The cement slurry is injected through casing 1 at a rate of 20–30 m³ / h. The cement slurry enters the annulus of the well wall through grouting hole 3 and flows back to the top of the sandstone aquifer (vertical depth of about 400 m) to form a dense cement annulus, achieving precise sealing of the aquifer. After the cement slurry returns to the surface, the wellhead gate is closed to maintain the annulus pressure at 2.0–2.5 MPa, so that the slurry can fully fill the fractures and prevent early leakage.

[0035] S5, Drill through cement plug 6 and cement the goaf section After the cement slurry is allowed to stand and cool to the specified strength, the initial sealing of the sandstone aquifer section is completed. After the cement plug 6 has solidified, the cement plug 6 is drilled through with a drill bit, and cementing is carried out in the 20m section below the bottom plate of the goaf (vertical depth of wellbore 2 806–826m) to return the cement slurry to the bottom plate position of the goaf (vertical depth 806m), thus completing the cementing operation of the goaf section.

[0036] After cementing is completed, sonic variable density logging is used to test the cementing quality. The test results show that the cement bond strength of the cemented section in the sandstone aquifer reaches ≥20MPa and there is no channeling phenomenon. The cement sheath height of the cemented section in the goaf reaches the top of the goaf and remains stable without leakage. The overall cement sheath compressive strength is 15-20MPa, which can stably seal for a long time and meet the requirements for use under complex formation conditions. Compared with the traditional "two-stage" process, the construction cycle is shortened by about 77.8% and the cost is reduced by about 30%. The economic benefits are particularly prominent under the condition of concentrated construction of multiple wells. This not only significantly improves the overall efficiency and safety of mine construction, but also solves the technical bottlenecks of long cycle, high cost and unsuitability for concentrated operation of multiple wells that are common in existing cementing methods. It reflects the creative advantages of this method in terms of process simplification and economic applicability. In summary, this invention has the advantages of simplifying construction procedures, improving construction efficiency, avoiding slurry leakage, enhancing sealing effect, reducing engineering costs and improving long-term stability.

[0037] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for open subzone sandstone aquifer cementing by section, characterized in that, The method comprises the following steps: S1, drilling a well to a target layer, first drilling to a certain depth below the floor of the goaf, and expanding the hole below the sandstone floor to form a borehole; S2, preparing a casing, welding a water stop ring at a predetermined position on the outer wall of the casing, setting a water-swelling filling layer below the water stop ring, pouring a cement plug at a predetermined position on the inner wall of the casing, and opening a grouting hole corresponding to the casing segment in the sandstone aquifer; S3, lowering the casing into the borehole, so that the water stop ring is located at the bottom of the sandstone aquifer, the grouting hole is located in the sandstone aquifer segment, and the cement plug is located below the sandstone floor; S4, injecting cement slurry through the casing, the cement slurry entering the annulus through the grouting hole and returning to the ground to form a cement sheath to seal the sandstone aquifer; S5, after standing and condensing, drilling through the cement plug, continuing to perform cementing operations below the floor of the goaf, so that the cement slurry returns to the top of the floor of the goaf, and the cementing and plugging of the goaf segment is completed.

2. The open completion method for the mined-out area sandstone aquifer according to claim 1, characterized in that: In the step S1, a drill bit with a diameter of 311.2 mm is used to drill to 20 m below the floor of the goaf, and a drill bit with a diameter of 444.5 mm is used to expand the hole 10 m below the sandstone floor.

3. A method for open sub-fractional cementing and plugging of mined-out areas in sandstone aquifers according to claim 2, characterized in that: In the step S2, the casing has a specification of 273.1 mm x 8.89 mm, the total length of the pipe covers the entire section of the borehole, and the material is J55 steel grade.

4. The open completion method for the mined-out area sandstone aquifer according to claim 3, characterized in that: In the step S2, the water stop ring is a Q235 steel ring-shaped steel plate, the water stop ring is welded to the outer wall of the casing at the bottom of the sandstone aquifer, the plane of the water stop ring is perpendicular to the axis of the casing, and the horizontal width of the water stop ring is 100 mm.

5. A method for open sub-fractional cementing and plugging of mined-out zones in sandstone aquifers according to claim 4, characterized in that: In the step S2, the water-swelling filling layer is ring-shaped, the water-swelling filling layer is arranged 0-1 m below the water stop ring, the water-swelling filling layer is made of high-ratio water-swelling rubber material, the swelling ratio is 200%-300%, the temperature resistance range is -20℃ to 150℃, and the compressive strength after swelling is ≥5MPa.

6. A method for open sub-fractional cementing and plugging of mined-out zones in sandstone aquifers according to claim 5, characterized in that: In the step S2, the water-swelling filling layer is fixed to the outer wall of the casing through a ring-shaped groove with a width of 150 mm and a depth of 10 mm, the water-swelling filling layer is fixed by using butyl rubber adhesive, the shear strength of the adhesive is ≥2MPa, and the water-swelling filling layer is reinforced by a 10 mm wide stainless steel binding belt, and the outside of the water-swelling filling layer is wrapped with 0.5 mm thick degradable non-woven fabric.

7. A method for open sub-fractional cementing and plugging of mined-out areas in sandstone aquifers according to claim 6, characterized in that: In the step S2, the cement plug is made of G-grade oil well cement, the length of the cement plug is 10 m, the cement plug is arranged 10 m below the sandstone floor on the inner wall of the casing, and the cement plug is formed by segmental vibration molding through a special pouring tool and cured for 24 hours.

8. A method for open sub-fractional cementing and plugging of mined-out zones in sandstone aquifers according to claim 7, characterized in that: In the step S2, the grouting hole is opened at a vertical depth of 370-400 m of the casing, the grouting hole has a diameter of 8-12 mm, there are a total of 36 grouting holes, and the multiple grouting holes are arranged in three groups in a spiral manner, each group has 12 grouting holes and the phase angles are distributed at an angle of 120°.

9. A method for open sub-fractional cementing and plugging of mined-out zones in sandstone aquifers according to claim 8, characterized in that: In the step S4, the injected cement slurry is a mixed system of G-grade oil well cement and 2% fluid loss agent, the injection rate of the cement slurry is 20-30 m³ / h, the wellhead gate is closed after the cement slurry returns to the ground, the annulus pressure is maintained at 2.0-2.5 MPa, and the cement slurry is solidified until it is solidified.

10. The method of claim 9, wherein the method is used to cement a depleted sandstone aquifer. In the step S5, the cementing quality is detected by acoustic variable density logging after the cementing is completed.

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