A method for changing a depleted straight well into a pre-drainage straight well

Abstract

The purpose of the present application is to provide a method for transforming a goaf straight well into a pre-drainage straight well, which belongs to the technical field of gas extraction. The transformation idea of the present application is as follows: the ground goaf straight well for first mining the lower group coal is transformed, and the upper group coal seam section which has not been mined is fractured and transformed. The original goaf straight well three-opening well section is partially backfilled and fixed, the reservoir is transformed by using the directional perforation + fresh water fracturing transformation mode, and the top drive screw pump is used for drainage. By using the method of the present application, the gas extraction can be successfully completed.

Description

Technical Field

[0001] This invention belongs to the field of gas extraction technology, specifically relating to a method for converting a goaf vertical well into a pre-extraction vertical well. Background Technology

[0002] In some high-gas coal mines in China, the lower coal seam is typically mined first, followed by the upper coal seam. This mining sequence facilitates the decompression and extraction of gas from the upper coal seam. Surface coalbed methane wells have become an effective method for underground gas control in high-gas coal mines. Goaf wells are used to extract coalbed methane from the goaf area of ​​coal mines to reduce the safety risks caused by gas accumulation. However, goaf wells generally suffer from problems such as rapid gas decay, relatively short extraction lifespan, relatively high investment costs, and poor overall efficiency. Summary of the Invention

[0003] To address the aforementioned problems, a scheme for converting a goaf vertical well into a pre-drainage vertical well is proposed. This allows for multiple uses of a single well, extends its service life, and achieves cost reduction and efficiency improvement. The purpose of this invention is to provide a method for converting a goaf vertical well into a pre-drainage vertical well. The conversion strategy is as follows: The surface goaf vertical well that has been mined from the lower coal seam is converted by fracturing the unmined upper coal seam. Partial backfilling and sealing are performed on the original three-section goaf vertical well. The reservoir is then modified using directional perforation + water fracturing. Finally, a top-drive screw pump is used for drainage.

[0004] The present invention adopts the following technical solution:

[0005] A method for converting a goaf vertical well into a pre-drainage vertical well includes the following steps:

[0006] The first step is the on-site installation of equipment;

[0007] The second step is to run a φ73mm tubing string in the completed three-section well section, record the location of the obstruction, connect an air compressor, and blow out the water accumulated in the well.

[0008] The third step is to blow out the water accumulated in the well, then lower a sighting instrument to inspect the well casing and make a record.

[0009] The fourth step is well cleaning: If it is a screen pipe completion, first pull the screen pipe out of the wellhead, and then run the drill string and drill bit; if it is an open hole completion, run the drill string and drill bit directly, use clean water circulation, and repeatedly pull and draw the open hole section from the original goaf vertical shaft third opening position to 40m below the bottom plate of the upper coal group to clean the well.

[0010] The fifth step is to start from the bottom of the original goaf vertical shaft and fill it with sand in sections up to 40m below the bottom of the upper coal seam, and then compact it with drilling tools.

[0011] The sixth step is to lower a Φ139.7mm, wall thickness 7.72mm, steel grade P110 casing to a position 40m below the upper group coal floor, and to cement the 139.7mm casing and the three open annuli;

[0012] The seventh step is to use upper low and lower high different density cement for cementing, to reduce the bearing load of the whole well section to the well bottom, and to ensure the well bottom compression strength. G grade petroleum cement is used for cementing, cementing quality detection is carried out after 48h of cementing, remedial operation is carried out if the cementing quality is unqualified, cementing pressure test is carried out after the cementing quality is qualified, the pressure test pressure is required to be not less than 20MPa, the pressure is required to be stable for 30min, and the pressure drop is required to be less than 0.5MPa;

[0013] The eighth step is to carry out perforation and fracturing on the upper group coal seam section according to the conventional hydraulic fracturing.

[0014] The ninth step is to install the drainage and extraction equipment.

[0015] Further, the step of blowing out the water accumulated in the well in the second step is as follows: a wellhead device is installed at the wellhead, the water outlet of the wellhead device is connected with a solid control tank or the water outlet is placed below the liquid surface of a sedimentation tank or a slurry tank through a pipeline, and the water cannot be directly blown to the air or the ground to prevent environmental pollution.

[0016] Further, the wellhead device comprises a φ377mm casing collar one connected with the wellhead, a φ244.5mm casing collar two arranged above the casing collar one, a casing head capable of bearing pressure above 45MPa arranged above the casing collar two, the casing head is connected with the casing collar two through a double public short joint, a φ139.7mm casing collar three is arranged in the casing head, a 1.6MPa pressure gauge one is arranged on one side of the casing head, a wellhead cap is arranged at the top end of the casing head, and a 0.6MPa pressure gauge two is arranged on the wellhead cap.

[0017] Further, the way of using upper low and lower high different density cement for cementing in the seventh step is sectional cementing: the cementing cement density is 1.3-1.45g / cm 3 in the upper half well section, the cementing cement is returned to the ground, the cementing cement density is 1.75-1.85g / cm 3 in the lower half well section, and the cementing cement is returned to the middle position of the well section.

[0018] Further, the pressure of 15MPa for 15min with less than 0.5MPa pressure drop is required for the cementing pressure test in the seventh step.

[0019] The beneficial effects of the present application are as follows: the present application realizes the multipurpose of one well for goaf and pre-extraction, achieves the effect of one well for multiple coal seam gas extraction, improves the comprehensive gas production effect, and achieves the purpose of cost reduction and benefit increase.

[0020] By using the method of the present application, the ground coal gas well can be used for multiple purposes, the secondary drilling in the same area is avoided, and the production investment cost is reduced; the caving of the overlying strata of the lower group coal gob has a certain disturbance to the upper group coal, the upper group coal can form a crack, which is beneficial to the later reconstruction of the pre-drainage well and the drainage effect, and the overall single well gas production comprehensive effect can be improved. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 It is a three-opening wellbore structure schematic diagram;

[0022] Figure 2 It is a gob straight well to pre-drainage straight well structure schematic diagram;

[0023] Figure 3 It is a wellhead device structure schematic diagram;

[0024] Wherein: 1 - one opening; 2 - two openings; 3 - three openings; 4 - casing coupling one; 5 - casing coupling two; 6 - casing head; 7 - double male short section; 8 - casing coupling three; 9 - pressure gauge one; 10 - wellhead cap; 11 - pressure gauge two. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0026] A method for converting a gob straight well into a pre-drainage straight well, comprising the following steps:

[0027] First step, equipment approach installation;

[0028] Second step, φ73mm pipe column is lowered in the three-opening well section, the position of resistance encountered is recorded, the air compressor is connected, and the water accumulated in the well is blown out;

[0029] Third step, after the water accumulated in the well is blown clean, the viewing instrument is lowered, the downhole viewing is carried out, the downhole casing condition is checked, and the record is made;

[0030] Fourth step, well-through operation: if the screen pipe completion is used, the screen pipe is first pulled out of the wellhead, and then the drill + drill bit is lowered; if the open hole completion is used, the drill + drill bit is directly lowered, the water circulation is used, and the open hole section between the three-opening position of the original gob straight well and 40m below the bottom of the upper group coal is repeatedly pulled and drawn to pass through the well;

[0031] Fifth step, after the well-through operation is completed, the segmented sand filling is used from the artificial bottom of the original gob straight well to 40m below the bottom of the upper group coal, and the drill is used for compaction;

[0032] Step 6, lower Φ139.7mm, wall thickness 7.72mm, steel grade P110 casing to the position 40m below the bottom of the upper group coal seam, cement slurry is injected to seal the 139.7mm casing and the third open annulus;

[0033] Step 7, use upper low and lower high different density cement for cementing, to reduce the pressure load on the bottom of the well, and ensure the compressive strength of the bottom of the well. G-grade petroleum cement is used for cementing the whole well, and the cementing quality is detected after 48h of cementing. If the cementing quality is unqualified, remedial operation is carried out, and if it is qualified, cementing pressure test is carried out, which requires that the test pressure is not less than 20MPa, the pressure is stable for 30 minutes, and the pressure drop is less than 0.5MPa;

[0034] Step 8, according to the conventional hydraulic fracturing, perforation and fracturing are carried out on the upper group coal seam section;

[0035] Step 9, install drainage equipment.

[0036] Example

[0037] Mine-out No. 3 well, which is a directional well in the range of working face of the J group in Pingdingshan mining area, has a design well depth of 766.33m and a design complete drilling horizon of the J group coal mine-out area. The drilling cycle of the well is 26.33 days, the total cycle of well construction is 40.50 days, the actual drilled and completed well depth is 766.00m, and the third open hole is completed.

[0038] The overall well deviation of the well is not large, the maximum well deviation is 14.46°, and it is possible that the pent group coal seam is collapsed and blocked due to mining disturbance and mine-out disturbance. The third open hole formation may also be collapsed under the influence of strata disturbance and soaking of three coal group strata water, which may lead to unsuccessful gas production and high negative pressure at the wellhead.

[0039] I, first opening operation

[0040] Mine-out No. 3 well, which is a directional well in the range of working face of the J group in Pingdingshan mining area. Its purpose is to extract the gas in the J group mine-out area and the pent group coal seam affected by mining. After all the pre-drilling preparations are completed, Φ444.5mm PDC drill bit conventional drilling assembly is used for first opening drilling, and water-based mud drilling is used.

[0041] Drilling to 20.00m, reaching the design requirement of entering 10m of bedrock. The drill bit is out of the well, the first opening drilling is completed, and the completed drilling depth is 20.00m. After completion of drilling, Φ444.5mm centralizer is used to pass through the well, and full circulation is ensured to ensure the smoothness of the wellbore.

[0042] Two roots of Φ377mm, wall thickness 8.70mm, steel grade J55 threaded casing produced in Tianjin, total casing 20.00m, cumulative length 20.00m, casing depth 20.00m. Cementing, injecting 2.00m3 of preflush water, injecting 2.20m3 of cement slurry, using 3t of Weiton G grade cement, average cement slurry density 1.85g / cm3, 1.00m3 of slurry replacement (water), cement slurry returns to the ground, shut-in and waiting for curing.

[0043] Two, two open construction

[0044] The combined roller drill string is lowered, the actual exploration cement plug depth is 8.00m, the plug length is 12.00m, the cement plug is drilled, the second opening is drilled, the Φ311.15mm roller bit is used to drill the pilot hole first, and the drilling depth is 574.00m. The logging section is 20.00-574.00m, the first logging project: inclination, temperature; the second logging project: density, gamma; the third logging project: dual laterolog. Logging interpretation shows that the four 4 coal depth is 583.55-581.20, the thickness is 0.65m (vertical depth 580.27-580.90m, vertical thickness 0.64m); four 3 coal depth is 591.15-592.45m, thickness is 1.30m (vertical depth 587.73-589.00m, vertical thickness 1.27m); four 2 coal depth is 596.35-598.45m, inclined thickness is 2.10m (vertical depth 592.83-594.89m, vertical thickness 2.06m).

[0045] The 320.7mm roller bit is used to pass through the well to 574m. The casing is lowered, the casing specification: Φ273.05mm, steel grade J55, wall thickness 8.89mm, place of production: Tianjin. Float shoe + 51 casings + 1 length-adjusting short casing + connection 0.00m. The total length of the casing string is 573.40m, the depth is 573.40m. Cementing. Cementing operation: injecting 6.00m 3 of preflush, injecting 26.00m 3 (25.80t) of cement slurry, cement grade is Weiton G, average cement slurry density is 1.85g / m 3 , replacing 29.30m 3 of water, cement slurry returns to the ground.

[0046] Three, three open construction

[0047] Combined drill string: Φ241.3mm PDC bit + Φ185mm screw + directional joint + Φ172mm non-magnetic + Φ127mm weighted drill pipe + 127mm drill pipe string, start three open drilling, drill to 766.00m, complete the designed footage, circulation occurs loss, drill up, change the light drill string to drill down and wash the well. Air drilling sweeps the hole, sweeps to 773.00m, clears the hole to no cuttings return, drills up, completes the well.

[0048] Four, modification scheme

[0049] a, re-fracturing in four 2, four 3, four 4 coal seam section.

[0050] b, drilling modification: partial backfill and cementation to the original well three open well section, 40m sand pocket is reserved under the four 2 coal seam floor, the artificial well bottom is 638.45m.

[0051] c, reservoir modification: using directional perforation + water fracturing modification method.

[0052] d, drainage method: top drive screw pump drainage.

[0053] Five, drilling modification

[0054] 1, equipment investment

[0055] Due to the limitation of the mined-out 3 well site, it is recommended to use truck-mounted drilling rig for workover modification operation. This workover operation plan invests TZJ25 / 1000Y type truck-mounted drilling rig 1, which is equipped with RL3NB-1300 mud pump 1 as the main workover equipment, and its capacity can fully meet the needs of this workover.

[0056] 2, modification process

[0057] (1) equipment installation

[0058] a, before the equipment enters the field, the fence, monitoring equipment, extraction equipment, etc. of the mined-out 3 well are removed for power off to facilitate the entry of the truck-mounted drilling rig.

[0059] b, after the truck-mounted drilling rig enters the field, it is placed in place according to the original wellhead center as the reference, and the truck-mounted drilling rig derrick, mast and wellhead are required to be "three points in a line".

[0060] c, after the truck-mounted drilling rig is placed in place, according to the actual situation on site, prevent circulating tank, try to do not dig mud; if it is necessary to dig mud pool, it must avoid underground cable and pipeline.

[0061] d, after the equipment is installed in place, it can be used for workover operation after acceptance and approval by the first party.

[0062] (2) downhole inspection

[0063] a, lower Φ73mm pipe column, record the resistance position, connect air compressor, and blow out the water accumulated in the well.

[0064] b, before the air compressor blows water, the wellhead device must be installed at the wellhead, the water outlet of the wellhead device is connected with the solid control tank, or the water outlet is placed below the liquid level of the sedimentation tank or mud tank through the pipeline, the water cannot be directly blown to the air or ground to prevent environmental pollution.

[0065] The wellhead device comprises a φ377mm casing collar one connected with an inlet, a φ244.5mm casing collar two arranged above the casing collar one, a casing head capable of bearing pressure of 45MPa or above arranged above the casing collar two, the casing head is connected with the casing collar two through a double public short section, a φ139.7mm casing collar three is arranged in the casing head, a 1.6MPa pressure gauge one is arranged on one side of the casing head, a wellhead cap is arranged at the top end of the casing head, and a 0.6MPa pressure gauge two is arranged on the wellhead cap.

[0066] c. After the water accumulated in the well is blown dry, the downhole viewer is lowered into the well to perform downhole viewing, check the downhole casing, and make a record.

[0067] (3) Well passing

[0068] a. After the screen pipe is pulled out of the wellhead, a Φ89mm drilling tool + drill bit is lowered, and clean water circulation is adopted to repeatedly pull and draw the open hole section between 574.00m and 640m of the second opening well bottom to pass the well.

[0069] b. In order to ensure the effect of coal reservoir reconstruction in the later period, it is suggested to adopt clean water circulation to reduce the pollution and damage to the coal reservoir.

[0070] (4) Cementing design

[0071] a. After the screen pipe passing operation is completed, starting from the original artificial well bottom 766.00m, the section sand filling method is adopted to fill to the well depth of 640m, and the drilling tool is lowered for compaction.

[0072] b. A Φ139.7mm, wall thickness 7.85mm, steel grade P110 casing is lowered to the well depth of 640m, and cement slurry is injected to seal the 139.7mm casing and the third opening annulus.

[0073] c. The cementing method adopts variable density cementing, and "G grade" petroleum cement is required for the whole well. The cementing pressure is required to be 15MPa, and the pressure drop of 15 minutes is less than 0.5MPa. The cementing quality is detected after 48 hours of cementing, and the cementing quality needs to be remedied if it is unqualified. After the cementing is qualified, the cementing pressure test is carried out, and the test pressure is required to be not less than 20MPa, and the pressure drop is less than 0.5MPa after 30 minutes of pressure stabilization.

[0074] The variable density cementing, the cementing cement density of 0-300m well section is 1.3-1.45g / cm 3 , the cementing cement density of 300-650m well section is 1.75-1.85g / cm 3 , and the cementing cement returns to the ground for 300m.

[0075] (5) Casing string design

[0076] 0-638.45 well section, pipe string structure (from top to bottom): float shoe + Φ139.7mm (wall thickness 7.58mm steel grade P110) casing x 1 + float collar + Φ139.7mm (wall thickness 7.58mm steel grade P110) casing string + Φ139.7mm (wall thickness 7.58mm steel grade P110) marker nipple x 1 + Φ139.7mm (wall thickness 7.58mm steel grade P110) casing string.

[0077] The casing collar is required to avoid four 3 and four 2 coal seams, four ３ At 10m of the coal seam roof, one Φ139.7mm marker nipple is lowered, and one centralizer is installed every two casings.

[0078] (6) Casing running operation

[0079] a. The casing running operation shall meet the relevant requirements of SY / T 5412-2016 "Casing Running Operation Procedure".

[0080] b. The casing string into the well must be strictly arranged according to the casing running construction design by the site construction supervisor and the site technical personnel of the cementing company.

[0081] c. The casing length must be re-measured before casing running, and the female buckle must be evenly coated with casing special sealing grease meeting the API standard on site. Before going to the drilling platform, the casing must be checked for internal diameter with the corresponding internal diameter gauge, and the internal diameter gauge must be kept by the on-site staff.

[0082] d. When hoisting the casing to the drilling platform, the female buckle end must be equipped with a protective cap, and the pin should not be collided.

[0083] e. The surface and production casings must be made up by the casing running team using casing hydraulic tongs to ensure the quality of casing makeup, and the torque record data should be archived for reference. When the special type casing is made up on the drilling platform, the casing pin end protective thread must not be allowed to touch the ground and collide, and the damage to the pin end metal sealing surface must be prevented.

[0084] f. During the casing running process, the wellhead must be covered, and the tools used at the wellhead must be cleaned up to prevent things from falling into or out of the casing; personal, downhole and equipment safety must be paid attention to.

[0085] g. According to the requirements of the construction design, all thread connections of the lower casing, cooperating joints and casing accessories must be fixed by 10mm rivets and adhesion in double ways (only riveting is required for metal sealing casing); the original machine pin end of the casing must also be riveted.

[0086] h. When the casing is made up, the thread damage and misalignment must be prevented.

[0087] i. During the casing running process, the drilling fluid must be filled every 20-30 casings (controlling the internal and external pressure difference of the casing <5MPa), and the open hole section must be filled with drilling fluid while the casing is moved to prevent the casing from being stuck.

[0088] j, the casing is leaked in the middle or after the casing is lowered, and the bridging mud and the material which may cause the circulation passage to be blocked are not allowed to be used for plugging.

[0089] k, when the casing is lowered, the casing is strictly controlled to be lifted and dropped, and the time of each casing is not less than 30s in the upper casing, not less than 50s in the upper casing shoe, and controlled to be 30s-1min in the lower well section. If the casing is blocked when the casing is lowered, the driller should not make decisions by himself, but should ask the technical person in charge on site.

[0090] l, the casing centralizer is strictly added according to the requirements of the cementing construction design. The position, quantity and casing friction of the centralizer (steel, elastic) are calculated to ensure that the casing centralization is greater than or equal to 67% and is successfully lowered.

[0091] m, the standard torque value provided by the cementing design is used for the fastening. In principle, the fastening torque value should be controlled between the best and the maximum torque value.

[0092] n, after the casing is lowered, the pump is opened with a small displacement, gradually increased to the normal drilling displacement circulation, and the drilling fluid performance is adjusted according to the requirements of the cementing construction design, and the circulation is not less than 2 weeks.

[0093] Six, fracturing reconstruction

[0094] (1) fracturing layer: four 3-four 2 coal.

[0095] (2) injection method: light casing injection.

[0096] (3) perforation position: four 3 coal seam section 591-593m; four 2 coal seam section 596-599m.

[0097] (4) water fracturing.

[0098] Seven, drainage scheme

[0099] Install top drive screw pump drainage.

[0100] The above only details the preferred embodiments of the present application, but the present application is not limited to the above embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the purpose of the present application, and various changes should be included in the protection scope of the present application.

Claims

1. A method for converting a goaf vertical well into a pre-drainage vertical well, characterized in that: Reconstruct the surface gob vertical well for first mining the lower coal seam, perform fracturing reconstruction in the coal seam section of the upper coal seam that has not been mined and excavated, partially backfill and seal the third open hole section of the original gob vertical well, use the directional perforation + water fracturing reconstruction method to reconstruct the reservoir, and use a top drive screw pump for production drainage; Specifically, it includes the following steps: The first step is to install equipment on site; The second step is to lower a φ73mm pipe string in the completed third open hole section, record the position where resistance is encountered, connect an air compressor, and blow out the accumulated water in the well; The third step is to lower a borescope into the well after the accumulated water in the well is blown out, conduct downhole peeping to check the downhole casing condition, and make records; The fourth step is to conduct hole cleaning operation: if it is a screen completion method, first lift the screen to the wellhead, and then lower the drill string + bit; if it is an open hole completion, directly lower the drill string + bit, use clear water circulation, and repeatedly pull and scrape the open hole section between the third open position of the original gob vertical well and 40m below the bottom plate of the upper coal seam for hole cleaning; The fifth step is to start from the artificial bottom of the original gob vertical well after the hole cleaning operation, fill the section up to 40m below the bottom plate of the upper coal seam in a segmented sand filling manner, and compact it with a drill string; The sixth step is to lower a Φ139.7mm, wall thickness 7.72mm, steel grade P110 casing to 40m below the bottom plate of the upper coal seam, and inject cement slurry to seal the annulus between the 139.7mm casing and the third open hole; The seventh step is to use different density cements with lower density in the upper part and higher density in the lower part for cementing to reduce the pressure-bearing load on the bottom hole caused by the entire well section, and at the same time ensure the compressive strength of the bottom hole; use G-grade oil cement for cementing the whole well. After waiting for 48h for cementing, conduct cementing quality inspection. If the cementing quality is unqualified, carry out remedial operations. After passing, conduct cementing pressure test, requiring the test pressure to be not less than 20MPa, maintaining pressure for 30 minutes, and the pressure drop to be less than 0.5MPa; The method of cementing with cement of different densities, one lower in the upper section and one higher in the lower section, is called segmented cementing: the cement density in the upper half of the well section is 1.3-1.45 g / cm³. 3 The cement was returned to the surface in the lower half of the well section, with a cement density of 1.75-1.85 g / cm³. 3 The cement return section is located in the middle of the well section. The eighth step is to perform perforating fracturing on the coal seam section of the upper coal seam according to conventional hydraulic fracturing; The ninth step is to install production drainage equipment.

2. The method for converting a goaf vertical well into a pre-drainage vertical well according to claim 1, characterized in that: The steps of blowing out the accumulated water in the well described in the second step are as follows: install a wellhead device at the wellhead, connect the water outlet of the wellhead device to a solids control tank or place the water outlet under the liquid level of a sedimentation tank or mud pit through a pipeline, and do not directly blow the water into the air or onto the ground to prevent environmental pollution.

3. The method for converting a goaf vertical well into a pre-drainage vertical well according to claim 2, characterized in that: The wellhead device includes a φ377mm casing collar 1 connected to the wellhead, a φ244.5mm casing collar 2 is provided above the casing collar 1, a casing head with a pressure-bearing capacity of more than 45MPa is provided above the casing collar 2, the casing head is connected to the casing collar 2 through a double male pup joint, a φ139.7mm casing collar 3 is provided inside the casing head, a pressure gauge 1 with a pressure of 1.6MPa is provided on one side of the casing head, and a wellhead cap is provided at the top of the casing head, and a pressure gauge 2 with a pressure of 0.6MPa is provided on the wellhead cap.

4. The method for converting a goaf vertical well into a pre-drainage vertical well according to claim 1, characterized in that: When cementing is bumped in the seventh step, it is required that the pressure is 15MPa and the pressure drop in 15 minutes is less than 0.5MPa to be qualified.

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