Method for changing goaf vertical well into pre-pumping vertical well

Abstract

The invention aims to provide a method for changing a gob-out vertical well into a pre-extraction vertical well, and belongs to the technical field of gas extraction, and the transformation thought of the method is as follows: a ground gob-out vertical well in which lower group coal is firstly mined is transformed, and fracturing transformation is carried out on an upper group coal seam section which is not excavated. And partial backfilling and sealing are carried out on a third-opening well section of an original mining-out vertical well, a reservoir is transformed in a directional perforation and hydraulic fracturing transformation mode, and a top drive screw pump is adopted for drainage and mining. By means of the method, gas extraction can be smoothly completed.

Description

Technical Field

[0001] The invention belongs to the technical field of gas extraction, and in particular relates to a method for converting an empty vertical well into a pre-drainage vertical well. Background Art

[0002] Some high-gas coal mines in China usually mine the lower coal seam first and then the upper coal seam. This mining order is conducive to decompression and extraction of gas in the upper coal seam. Gas extraction from surface coalbed methane wells has become an effective way to control gas underground in high-gas coal mines. Gob wells are used to drain coalbed methane in the gob area of ​​coal mines to reduce the safety risks caused by gas accumulation. Gob wells generally have problems such as fast gas volume attenuation, relatively short extraction life, relatively high investment cost, and poor comprehensive benefits. Summary of the invention

[0003] In view of the above problems, a scheme for transforming an empty vertical well into a pre-pumping vertical well is proposed, which can realize multiple uses of one well, extend the service life of a single well, and achieve the purpose of reducing costs and increasing efficiency. The purpose of the present invention is to provide a method for transforming an empty vertical well into a pre-pumping vertical well. The transformation idea is as follows: transform the empty vertical well on the ground that first mines the lower coal group, and perform fracturing transformation in the coal seam section of the upper coal group that has not yet been mined. Partially backfill and seal the three-opening well section of the original empty vertical well, use directional perforation + clean water fracturing transformation to transform the reservoir, and use a top drive screw pump for drainage.

[0004] The present invention adopts the following technical solution: A method for converting an empty vertical well into a pre-pumping vertical well comprises the following steps: The first step is to install the equipment on site; The second step is to run a φ73mm pipe string in the completed three-well section, record the location of the obstruction, connect the air compressor, and blow out the water accumulated in the well; The third step is to blow away the accumulated water in the well, lower the peep instrument, conduct a peep downhole, check the casing downhole, and make a record; The fourth step is to carry out the well cleaning operation: if the well is completed by screen pipe, first lift the screen pipe out of the wellhead, and then lower the drilling tool + drill bit; if the well is completed by open hole, directly lower the drilling tool + drill bit, use clean water circulation, and repeatedly pull and clean the open hole section from the third opening position of the original vertical well to 40m below the upper coal floor; The fifth step is to fill the sand from the bottom of the original vertical well to 40m below the upper coal floor by segmented sand filling after the well-drilling operation is completed, and then compact it with drilling tools; Step 6: Install a Φ139.7mm, 7.72mm thick, P110 steel grade casing to 40m below the upper coal floor, and inject cement slurry to seal the 139.7mm casing and the three-opening annulus; The seventh step is to use cement with different densities of low density in the upper part and high density in the lower part to reduce the pressure load on the bottom of the well caused by the entire well section, while ensuring the compressive strength of the bottom of the well. The whole well is cemented with G-grade petroleum cement. After 48 hours of cementing, the cementing quality is tested. If the cementing quality is unqualified, remedial work is carried out. After passing the test, the cementing pressure test is required to be no less than 20MPa, the pressure is maintained for 30 minutes, and the pressure drop is less than 0.5MPa; Step 8, perforating and fracturing the upper coal seam section according to conventional hydraulic fracturing; Step 9: Install drainage equipment.

[0005] Furthermore, in the second step, the air compressor blows water into the chamber, a wellhead device is installed at the wellhead, and is connected to the solid control tank or the water outlet is placed below the liquid surface of the sedimentation tank or mud pool through a pipeline. Water cannot be blown directly into the air or onto the ground to prevent environmental pollution.

[0006] Furthermore, the wellhead device includes a φ377mm casing coupling 1 connected to the wellhead, a φ244.5mm casing coupling 2 is provided above the casing coupling 1, a casing head capable of bearing a pressure of more than 45MPa is provided above the casing coupling 2, the casing head is connected to the casing coupling 2 through a double male nipple, a φ139.7mm casing coupling 3 is provided inside the casing head, a 1.6MPa pressure gauge 1 is provided on one side of the casing head, a wellhead cap is provided on the top of the casing head, and a 0.6MPa pressure gauge 2 is provided on the wellhead cap.

[0007] Furthermore, the cementing method of using cements of different densities in the seventh step is segmented cementing: in the upper half of the well, the cement density is 1.3-1.45 g / cm 3 The cementing cement is returned to the surface in the lower well section. The density of cementing cement is 1.75-1.85g / cm 3 , cementing cement returns to the middle position of the deep well section.

[0008] Furthermore, in the seventh step, the cementing pressure is required to be 15MPa, and the pressure drop within 15 minutes is less than 0.5MPa to be qualified.

[0009] The beneficial effects of the present invention are as follows: multiple uses of one well for mining and pre-drainage are achieved, gas extraction and drainage effects of multiple coal seams in one well are achieved, comprehensive gas production effects are improved, and the purpose of reducing costs and increasing efficiency is achieved.

[0010] By using the method of the present invention, it is possible to realize multiple uses of one ground coalbed methane well, avoid secondary drilling in the same area, and reduce production investment costs; the collapse of the overlying rock strata in the lower coal goaf area has a certain disturbance on the upper coal seam, and cracks can be formed in the upper coal, which is beneficial to the subsequent transformation of the pre-pumping well drainage effect, and can improve the overall gas production effect of a single well. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a schematic diagram of the wellbore structure for three-well completion; Figure 2 This is a schematic diagram of the structure of converting a vertical well into a pre-pumping vertical well; Figure 3 It is a schematic diagram of the wellhead device structure; Among them: 1- one opening; 2- two openings; 3- three openings; 4- casing coupling one; 5- casing coupling two; 6- casing head; 7- double male nipple; 8- casing coupling three; 9- pressure gauge one; 10- wellhead cap; 11- pressure gauge two. DETAILED DESCRIPTION

[0012] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. 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.

[0013] A method for converting an empty vertical well into a pre-pumping vertical well comprises the following steps: The first step is to install the equipment on site; The second step is to run a φ73mm pipe string in the completed three-well section, record the location of the obstruction, connect the air compressor, and blow out the water accumulated in the well; The third step is to blow away the accumulated water in the well, lower the peep instrument, conduct a peep downhole, check the casing downhole, and make a record; The fourth step is to carry out the well cleaning operation: if the well is completed by screen pipe, first lift the screen pipe out of the wellhead, and then lower the drilling tool + drill bit; if the well is completed by open hole, directly lower the drilling tool + drill bit, use clean water circulation, and repeatedly pull and clean the open hole section from the third opening position of the original vertical well to 40m below the upper coal floor; The fifth step is to fill the sand from the bottom of the original vertical well to 40m below the upper coal floor by segmented sand filling after the well-drilling operation is completed, and then compact it with drilling tools; Step 6: Install a Φ139.7mm, 7.72mm thick, P110 steel grade casing to 40m below the upper coal floor, and inject cement slurry to seal the 139.7mm casing and the three-opening annulus; The seventh step is to use cement with different densities of low density in the upper part and high density in the lower part to reduce the pressure load on the bottom of the well caused by the entire well section, while ensuring the compressive strength of the bottom of the well. The whole well is cemented with G-grade petroleum cement. After 48 hours of cementing, the cementing quality is tested. If the cementing quality is unqualified, remedial work is carried out. After passing the test, the cementing pressure test is required to be no less than 20MPa, the pressure is maintained for 30 minutes, and the pressure drop is less than 0.5MPa; Step 8, perforating and fracturing the upper coal seam section according to conventional hydraulic fracturing; Step 9: Install drainage equipment.

[0014] Example Goaf No. 3 Well is a goaf directional well within the working face of Group J in Pingdingshan Mining Area. The designed well depth is 766.33m, and the designed drilling layer is the goaf of Group J. The drilling cycle of the well is 26.33 days, the total well construction cycle is 40.50 days, the actual drilling and completion well depth is 766.00m, and the well is completed in three open holes.

[0015] The overall well inclination is not large, with the maximum well inclination of 14.46°. Affected by mining and goaf disturbance, the Group E coal seam may collapse and block the wellbore. The open-hole strata of the third opening may also collapse due to stratum disturbance and immersion in stratum water of the third coal group, resulting in the inability to produce gas smoothly. As a result, gas can be detected at the wellhead but the extraction negative pressure is too high.

[0016] 1. Start construction Goaf No. 3 Well is a goaf directional well within the working face of Group J in Pingdingshan Mining Area. Its purpose is to extract gas from the goaf of Group J and the coal seam of Group E in the mining influence area. All pre-drilling preparations are ready, and a Φ444.5mm PDC drill bit and conventional drilling tool combination are put in for first-opening drilling, using water-based mud for drilling.

[0017] Drilling to 20.00m, reaching the design requirement of 10m into the bedrock. The drill bit exits the well and the drilling is completed. The well depth is 20.00m. After drilling is completed, the well is ventilated with a Φ444.5mm centralizer to ensure full circulation to ensure smooth wellbore.

[0018] Two threaded casings with an outer diameter of Φ377mm, a wall thickness of 8.70mm and a steel grade of J55 were put into the well. The total length of the casing was 20.00m, the cumulative length was 20.00m, and the casing depth was 20.00m. For cementing, 2.00m³ of pre-flushing water was injected, and 2.20m³ of cement slurry was injected. 3t of Weiton G-grade cement was used, and the average density of cement slurry was 1.85g / cm³. 1.00m³ of slurry (clean water) was replaced. The cement slurry was returned to the surface and the well was shut down for solidification.

[0019] 2. Construction The combined roller drill was used to drill the cement plug surface to a depth of 8.00m and a plug section length of 12.00m. The cement plug was drilled and the second drilling was carried out. A Φ311.15mm roller drill bit was used to drill a pilot hole. The drilling was carried out to 574.00m and electrical logging was carried out. The logging section was 20.00~574.00m. The first logging items included: continuous inclination and well temperature; the second logging items included: density and gamma; the third logging items included: dual lateral. Well logging interpretation shows that the depth of the 4th coal in this well is 583.55-581.20, and the thickness is 0.65m (vertical depth 580.27-580.90m, vertical thickness 0.64m); the depth of the 4th coal is 591.15-592.45m, and the thickness is 1.30m (vertical depth 587.73-589.00m, vertical thickness 1.27m); the depth of the 4th coal is 596.35-598.45m, and the inclined thickness is 2.10m (vertical depth 592.83-594.89m, vertical thickness 2.06m).

[0020] Use 320.7mm roller bit and stabilizer to drill the well to 574m. Casing, casing specification: Φ273.05mm, steel grade J55, wall thickness 8.89mm, origin: Tianjin. Float shoe + 51 casings + 1 length-adjustable short sleeve + 0.00m connection. The total length of the casing string is 573.40m, and the depth is 573.40m. Cementing. Cementing operation: inject 6.00m of pre-fluid 3 , cement slurry injection 26.00m 3 (25.80t), cement grade is Weiton G, and the average density of injected cement slurry is 1.85g / m 3 , 29.30m of clean water 3 , cement slurry returns to the ground.

[0021] 3. Three-opening construction Combined drilling tools: Φ241.3mm PDC drill bit + Φ185mm screw + directional joint + Φ172mm non-magnetic + Φ127mm weighted drill pipe + 127mm drill pipe string, started three-opening drilling, drilled to 766.00m, completed the designed footage, lost during circulation, pulled out, changed to light drilling tools to drill and wash the well. Air drilling was carried out to sweep the empty hole, swept to 773.00m, cleaned the hole until no cuttings were returned, pulled out, and completed the well.

[0022] 4. Renovation Plan a. Re-fracturing and reconstruction in the 42, 43 and 44 coal seam sections.

[0023] b. Well drilling transformation: Partially backfill and seal the three-opening section of the original well, reserve a 40m sedimentation pocket under the bottom plate of the 4-2 coal seam, and the artificial well bottom is 638.45m.

[0024] c. Reservoir transformation: directional perforation + clean water fracturing transformation method is adopted.

[0025] d. Drainage method: top drive screw pump drainage.

[0026] 5. Drilling transformation 1. Equipment investment Due to the limitation of the well site of Well No. 3, it is recommended to use a vehicle-mounted drilling rig for well repair and reconstruction operations. This well repair operation plans to invest one TZJ25 / 1000Y vehicle-mounted drilling rig and one RL3NB-1300 mud pump as the main well repair equipment, and its capacity can fully meet the needs of this well repair.

[0027] 2. Transformation process (1) Equipment installation a. Before the equipment enters the site, the fence of Well No. 3, monitoring equipment, extraction equipment, etc. need to be powered off and removed to facilitate the entry of the drill.

[0028] b. After the drill rig enters the site, it is placed in place based on the center of the original wellhead, and the drill rig crane, mast and wellhead are required to be in a "three-point straight line".

[0029] c. After the auger is in place, according to the actual situation on site, avoid circulating the tank and try not to dig mud; if you must dig a mud pool, you must avoid underground cables and pipelines.

[0030] d. After the equipment is installed, it can be inspected and accepted by Party A before the well repair operation can be carried out.

[0031] (2) Underground observation a. Lower the Φ73mm pipe column, record the location of the obstruction, connect the air compressor, and blow out the water accumulated in the well.

[0032] b. Before the air compressor blows water, the wellhead device must be installed at the wellhead and connected to the solid control tank, or the water outlet must be placed below the liquid surface of the sedimentation tank or mud pool through a pipeline. Water cannot be blown directly into the air or on the ground to prevent environmental pollution.

[0033] The wellhead device includes a φ377mm casing coupling 1 connected to the inlet, a φ244.5mm casing coupling 2 is arranged above the casing coupling 1, a casing head capable of bearing a pressure of more than 45MPa is arranged above the casing coupling 2, the casing head is connected to the casing coupling 2 through a double male nipple, a φ139.7mm casing coupling 3 is arranged inside the casing head, a 1.6MPa pressure gauge 1 is arranged on one side of the casing head, a wellhead cap is arranged on the top of the casing head, and a 0.6MPa pressure gauge 2 is arranged on the wellhead cap.

[0034] c. After the accumulated water in the well is blown away, lower the downhole peep instrument to conduct downhole peep, check the downhole casing and its condition, and keep records.

[0035] (3) Tongjing a. After the screen is lifted out of the wellhead, Φ89mm drilling tools + drill bit are lowered, and clean water circulation is used to repeatedly pull and plow the open hole section between 574.00m and 640m at the bottom of the second well.

[0036] b. In order to ensure the transformation effect of the coal reservoir in the later stage, it is recommended to adopt clean water circulation to reduce the pollution and damage to the coal reservoir.

[0037] (4) Cementing design a. After the screen pipe lifting and well clearing operation is completed, starting from the original artificial well bottom of 766.00m, the sand is filled in sections to a well depth of 640m, and compacted with a drill bit.

[0038] b. Install Φ139.7mm, 7.85mm thick, steel grade P110 casing to a depth of 640m, and inject cement slurry to seal the 139.7mm casing and the three-opening annulus.

[0039] c. Variable density cementing is used for cementing, and the whole well is required to be cemented with "G grade" petroleum cement. The cementing pressure is required to be 15MPa, and the pressure drop in 15 minutes is less than 0.5MPa to be qualified. After 48 hours of waiting for cementing, the cementing quality is tested. If the cementing quality is unqualified, remedial work is required. After passing the test, the cementing pressure test is required to be no less than 20MPa, the pressure is stabilized for 30 minutes, and the pressure drop is less than 0.5MPa.

[0040] The variable density cementing, 0-300m well section, cement density is 1.3-1.45g / cm 3 , cementing cement returns to the surface, 300-650m well section, cementing cement density is 1.75-1.85g / cm 3 , cementing return depth is 300m.

[0041] (5) Casing string design 0-638.45 well section, pipe string structure (from top to bottom): float shoe + Φ139.7mm (wall thickness 7.58mm steel grade P110) casing × 1 piece + float collar + Φ139.7mm (wall thickness 7.58mm steel grade P110) casing string + Φ139.7mm (wall thickness 7.58mm steel grade P110) marker short section × 1 piece + Φ139.7mm (wall thickness 7.58mm steel grade P110) casing string.

[0042] Casing collars are required to avoid the 43 and 42 coal seams. ３ A Φ139.7mm marking short section is lowered into the coal seam at 10m from the roof, and a centralizer is installed for every two casings.

[0043] (6) Casing operation a. The casing lowering operation shall comply with the relevant requirements of SY / T 5412-2016 "Casing Lowering Operation Procedure".

[0044] b. The casing string going into the well must be strictly arranged by the on-site construction manager and the on-site technicians of the cementing company according to the cementing construction design.

[0045] c. Before lowering the casing, the length of the casing must be remeasured. On site, evenly apply special casing sealing grease that meets API standards inside the female buckle. Before going to the drilling platform, the inner diameter of each casing must be measured with the corresponding inner diameter gauge. The inner diameter gauge is kept by a dedicated person on site.

[0046] d. When hanging the casing on the drilling platform, put the protective cap on the female thread end and avoid collision with the thread.

[0047] e. The surface and production casings must be fastened by the casing lowering team using casing hydraulic tongs to ensure the quality of casing fastening, and the torque record data should be archived for future reference. When the special buckle type casing is put on the drilling platform, it is strictly forbidden for the casing male buckle end to collide with the ground to prevent damage to the metal sealing surface of the male buckle end.

[0048] f. During the casing lowering process, the wellhead should be covered and the tools used at the wellhead should be collected and sorted out to prevent objects from falling inside and outside the casing; pay attention to personal safety, underground safety, and equipment safety.

[0049] g. According to the construction design requirements, all threaded connections of the lower casing and matching joints, casing accessories, etc. must be double fixed by carefully riveting and bonding with 10mm rivets (metal sealing casing only needs to be riveted); the original fastening end of the casing must also be riveted.

[0050] h. When fastening the casing together, prevent cross-threading and damage to the thread.

[0051] i. During the casing lowering process, every 20 to 30 casings (control the pressure difference between the inside and outside of the casing to be less than 5MPa) should be filled with drilling fluid. When filling the open hole section with drilling fluid, the casing should be kept movable to prevent the casing from getting stuck.

[0052] j. If leakage occurs during or after casing lowering, in principle, bridge plug mud and other materials that may block the circulation path shall not be used to stop the leakage.

[0053] k. It is strictly forbidden to lift or release the casing violently when lowering the casing. The lowering speed of the casing must be strictly controlled. The lowering time of each casing in the upper casing shall not be less than 30 seconds, and the lowering time of each casing out of the upper casing shoe shall not be less than 50 seconds. The lowering time of each casing in the lower well section shall be controlled within 30 seconds to 1 minute. If there is an obstruction when lowering the casing, the driller of the well team shall not act on his own and must consult the on-site technical person in charge.

[0054] l. Install casing centralizers that meet the requirements strictly according to the cementing construction design requirements. Calculate the position, quantity and friction resistance of the centralizers (rigidity and elasticity) to ensure that the casing centering degree is ≥67% and the casing is lowered smoothly.

[0055] m. Tighten according to the standard torque value provided by the cementing design. In principle, the tightening torque value should be controlled between the optimal and maximum torque values.

[0056] n. After lowering the casing, start the pump at a small displacement, gradually increase the displacement to the normal drilling circulation, and adjust the drilling fluid properties according to the cementing construction design requirements. The circulation should not be less than 2 weeks.

[0057] 6. Fracturing transformation (1) Fractured layer: 43-42 coal.

[0058] (2) Injection method: optical casing injection.

[0059] (3) Perforation positions: 591-593m in the 43 coal seam section; 596-599m in the 42 coal seam section.

[0060] (4) Clean water fracturing.

[0061] VII. Drainage and mining plan Install a top drive screw pump for drainage.

[0062] Only the preferred embodiments of the present invention are described in detail above, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge scope of ordinary technicians in this field without departing from the purpose of the present invention, and various changes should be included in the protection scope of the present invention.

Claims

1. A method for converting an empty vertical well into a pre-pumping vertical well, characterized in that: The steps include: The first step is to install the equipment on site; The second step is to run a φ73mm pipe string in the completed three-well section, record the location of the obstruction, connect the air compressor, and blow out the water accumulated in the well; The third step is to blow away the accumulated water in the well, lower the peep instrument, conduct a peep downhole, check the casing downhole, and make a record; The fourth step is to carry out the well cleaning operation: if the well is completed by screen pipe, first lift the screen pipe out of the wellhead, and then lower the drilling tool + drill bit; if the well is completed by open hole, directly lower the drilling tool + drill bit, use clean water circulation, and repeatedly pull and clean the open hole section from the third opening position of the original vertical well to 40m below the upper coal floor; The fifth step is to fill the sand from the bottom of the original vertical well to 40m below the upper coal floor by segmented sand filling after the well-drilling operation is completed, and then compact it with drilling tools; Step 6: Install a Φ139.7mm, 7.72mm thick, P110 steel grade casing to 40m below the upper coal floor, and inject cement slurry to seal the 139.7mm casing and the three-opening annulus; Step 7: Use cement with different densities, low in the upper part and high in the lower part, to reduce the pressure load on the bottom of the well caused by the entire well section, while ensuring the compressive strength of the bottom of the well; the whole well is cemented with G-grade petroleum cement, and the cementing quality is tested after waiting for 48 hours. If the cementing quality is unqualified, remedial work is carried out. If it is qualified, cementing pressure test is carried out, and the test pressure is required to be no less than 20MPa, the pressure is maintained for 30 minutes, and the pressure drop is less than 0.5MPa; Step 8, perforating and fracturing the upper coal seam section according to conventional hydraulic fracturing; Step 9: Install drainage equipment.

2. The method for converting an empty vertical well into a pre-pumping vertical well according to claim 1, characterized in that: In the second step, the air compressor blows the water chamber, installs a wellhead device at the wellhead, and connects it to the solid control tank or places the water outlet through a pipeline below the liquid level of the sedimentation tank or mud pool. Water cannot be blown directly into the air or on the ground to prevent environmental pollution.

3. The method for converting an empty vertical well into a pre-pumping vertical well according to claim 2, characterized in that: The wellhead device includes a φ377mm casing coupling 1 connected to the wellhead, a φ244.5mm casing coupling 2 is arranged above the casing coupling 1, a casing head capable of bearing a pressure of more than 45MPa is arranged above the casing coupling 2, the casing head is connected to the casing coupling 2 through a double male nipple, a φ139.7mm casing coupling 3 is arranged inside the casing head, a 1.6MPa pressure gauge 1 is arranged on one side of the casing head, a wellhead cap is arranged on the top of the casing head, and a 0.6MPa pressure gauge 2 is arranged on the wellhead cap.

4. The method for converting an empty vertical well into a pre-pumping vertical well according to claim 1, characterized in that: The cementing method of using cements of different densities in step 7 is segmented cementing: in the upper well section, the cement density is 1.3-1.45g / cm 3 The cementing cement is returned to the surface in the lower well section. The density of cementing cement is 1.75-1.85g / cm 3 , cementing cement returns to the middle position of the deep well section.

5. The method for converting an empty vertical well into a pre-pumping vertical well according to claim 1, characterized in that: The cementing pressure in the seventh step is required to be 15MPa, and the pressure drop within 15 minutes is less than 0.5MPa to be qualified.

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