Safety crossing method for L-shaped well drilling through mylonitic broken well section

Abstract

The application discloses a kind of L type well drilling safety crossing methods of meeting schistosity broken well section, it is related to ground gas control well field, including the following steps: construction vertical well section and transition well section, down technical casing, stop after meeting resistance position in broken zone;Configuration cement slurry, determine the amount of cement slurry into well;Build grouting system, first injection isolation fluid, then inject cement slurry;Build pressurization system, with technical casing as stop slurry pipe, cement slurry is pressurized, so that cement slurry is extruded and diffused into broken zone formation;After cement slurry diffuses to broken zone formation, wait for a certain time;Down drilling tool probe plug face, drill open cement that the strength of mixed slurry area is insufficient and circulate and return, then carry out again grouting and extrusion, multiple circulation is carried out;After ensuring that the well section through broken zone is stable, construction remaining well section.The application has the advantages that L type well drilling meets the safety, smooth crossing of schistosity broken well section.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of ground gas control well, in particular to a safe crossing method for L-shaped well drilling in a mylonitic broken well section. BACKGROUND

[0002] For the mine area with high gas content of coal seam group, large coal seam gas pressure, high ground stress and serious coal mine gas disaster threat, the ground gas control well breaks through the traditional underground gas control mode, realizes the change from underground to ground gas control, and is the concept improvement and technology upgrading of comprehensive coal mine gas control.

[0003] One type of ground gas control well is L-shaped well. The patent document with publication number CN105134286A discloses a L-shaped well goaf gas extraction method, which uses a ground gas extraction pump to extract the goaf gas of the working face through the L-shaped well. The transition section from the vertical well to the horizontal well of the L-shaped well is the most complex well section in construction technology, which has the characteristics of large vertical depth distance and complex drilling structure. When the L-shaped well is drilled in the fault with a large range of broken zone during construction, it is easy to cause unstable well wall and well wall collapse. For the L-shaped well drilling in the mylonitic broken well section, the conventional backfilling and sidetracking measures cannot form a safe well wall, so the safe crossing cannot be realized. SUMMARY

[0004] The technical problem to be solved by the present application is how to realize the safe crossing of the L-shaped well drilling in the mylonitic broken well section.

[0005] The present application solves the above technical problems by the following technical means: a safe crossing method for L-shaped well drilling in a mylonitic broken well section, comprising the following steps:

[0006] Step one, constructing the vertical well section and the transition well section, and lowering the technical casing during the construction process, and stopping at the position where the broken zone is met;

[0007] Step two, configuring cement slurry and determining the amount of cement slurry into the well;

[0008] Step three, constructing a grouting system, first injecting isolation fluid, and then injecting cement slurry;

[0009] Step four, after grouting is completed, constructing a pressurizing system, using the technical casing as a grouting pipe, pressurizing the cement slurry, and making the cement slurry diffuse into the broken zone stratum under extrusion;

[0010] Step five, after the cement slurry diffuses into the broken zone stratum, waiting for a certain time;

[0011] Step six, after waiting for a certain time, lowering the drilling tool to probe the plug surface, drilling the cement with insufficient strength in the grouting area and circulating it back out, and then performing re-grouting and extrusion, and repeating the process multiple times.

[0012] Step seven, ensure that the well section of the broken zone is stable, and the remaining well section is constructed.

[0013] The technical casing plays a role in sealing the complex formation, and provides protection for the subsequent reinforcement of the broken zone, avoiding the complex risks brought by repeated well passing. The cement slurry is used to reinforce the broken zone and is pressurized, and the process is repeated multiple times to ensure that the well section passing through the broken zone can form a safe well wall, realizing safe and smooth crossing of the broken zone in the L-shaped well.

[0014] Preferably, in step two, the cement slurry is configured with water, cement, a fluid loss additive and a retarder, and a cement slurry thickening test is performed in advance to determine the addition ratio of the fluid loss additive and the retarder. The setting of the fluid loss retarder cement slurry can ensure the reinforcement range.

[0015] Preferably, in step two, the cement used is G-grade cement, and the density of the configured cement slurry is greater than or equal to 1.9g / cm 3 , which ensures the reinforcement strength.

[0016] Preferably, in step two, the amount of cement slurry entering the well is calculated based on the well diameter expansion rate of 140% to 160% of the open hole section.

[0017] Preferably, in step three, the maximum wellhead pressure during the pressurization process is greater than 15MPa. Combined with the formation fracture pressure, the sufficient cement slurry is pressurized into the broken zone in a controlled amount.

[0018] Preferably, in step three, the waiting time is greater than or equal to 72 hours. This ensures the cement strength.

[0019] Preferably, in step two, the grouting system uses an oil well cementing truck to connect the drill pipe, and the drill pipe is lowered to the bottom of the well through the inside of the technical casing. Grouting is performed through the hollow drill pipe.

[0020] Preferably, in step three, the pressurization system uses an oil well cementing truck to connect the drill pipe, and the drill pipe is connected to the upper end of the technical casing through a variable diameter joint.

[0021] The advantages of the present application are:

[0022] 1. The technical casing plays a role in sealing the complex formation, and provides protection for the subsequent reinforcement of the broken zone, avoiding the complex risks brought by repeated well passing. The cement slurry is used to reinforce the broken zone and is pressurized, and the process is repeated multiple times to ensure that the well section passing through the broken zone can form a safe well wall, realizing safe and smooth crossing of the broken zone in the L-shaped well.

[0023] 2. The high-density, slow-setting G-grade cement slurry is used as the material for reinforcing the broken zone, which ensures the reinforcement range and reinforcement strength, and has a relatively low cost.

[0024] 3. Combined with the formation fracture pressure, sufficient cement slurry is pressed into the fracture zone under high pressure using a controlled pressure method. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a construction trajectory diagram of the crossing method for the existing L-shaped well drilling encountering mylonitic broken well section.

[0026] Figure 2 This is a flow chart of a method for safely traversing a mylonitic and fractured section in an L-shaped well according to an embodiment of the present invention. DETAILED DESCRIPTION

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0028] like Figure 1 As shown in the figure, during the construction of a surface gas control well in Shaft No. 1 of a certain mine, the transition section encountered a fault. The hanging wall of the fault contained a large fracture zone with developed breccia and fault gouge. Initially, the construction team employed conventional backfilling and sidetracking methods to construct branch holes. They then increased the mud density and specific gravity, and later, twisted the azimuth and adjusted the landing point. Despite various attempts, none of them successfully traversed the fault fracture zone. As shown by the curve in the figure, a total of five backfilling and sidetracking attempts were performed. During the construction of the branch hole, a drill bit was lost due to burial. The transition section alone took two months to complete, severely impacting the project's progress.

[0029] Analysis of causes of difficulty:

[0030] (1) Influence of structural fractures: The well passed through the fault at the boundary of the mining area, and the actual drilling analysis showed that the drop was about 20m. The analysis of drill cuttings from the high-density mud circulation during drilling showed that the fault zone was composed of multiple breccias and structural muds, with loose structure and poor stability. During the drilling construction process, the well was easily broken and collapsed due to the cutting of the drill bit and the flushing of drilling fluid.

[0031] (2) Influence of drilling diameter: The lateral pressure of the well wall rock caused by the vertical strata can cause the poorly cemented rock blocks to slide and collapse into the well. The transition well wall rock constitutes a "pressure zone", which changes the original stress field of the formation. In addition, the transition well section has a diameter of φ311.15mm, the well section has a large pressure, and the structural support force is small, resulting in unstable well wall and well wall collapse.

[0032] (3) Influence of drilling depth: Deep formations have large internal stress. During drilling, the drill bit disturbs the formation, causing the original stress to be destroyed. In addition, due to the influence of the well depth, abnormally high temperatures appear, which can easily destroy the mud properties and increase the difficulty of forming mud cakes on the well wall.

[0033] (4) Influence of exposure time: The time of drilling open hole directly affects the stability of the hole wall, especially in complex formations; the poor quality of the mud cake on the hole wall and long-term exposure to open hole can easily lead to problems such as expansion and collapse.

[0034] (5) Improper drilling technology: Improper operating techniques will create or aggravate the complexity of the situation in the hole; rotating and lifting the drill bit, frequent circulation and well washing, etc. will cause pressure fluctuations in the well; in addition, when the pump is turned on, the mud will flow from static to flowing, which will generate great resistance, causing the pump to be blocked or the mud to be pressed into the formation cracks, and then flow out again during normal circulation, which can easily cause the rock formation to collapse.

[0035] (6) Factors of the inclination section: The transition section is mainly the inclination section, among which the 780-1040m section is greatly affected by the fault fracture zone, with a well inclination of 37° to 89°. The well inclination varies greatly, and the bent drill string in the rotating state has a strong impact and damage effect on the well wall.

[0036] like Figure 2 As shown, the embodiment of the present invention discloses a method for safely traversing a mylonitic fractured section in an L-shaped well, comprising the following steps:

[0037] Step 1: construct the vertical well section and transition well section. During the construction process, the technical casing is lowered to the vertical well section and transition well section and stops when the broken zone is blocked. In this embodiment, the transition well section is 1100m deep. Due to the complex conditions downhole, the technical casing is lowered to Figure 1 At a depth of 900m, an obstruction was encountered at position a, and the technical casing isolated the broken zone of about 120m, which played the role of the technical casing in isolating the complex formation and provided a guarantee for the subsequent reinforcement of the broken zone and the establishment of a cycle, avoiding the complex risks brought by repeated well drilling. When drilling in unstable formations, the drilling cycle should be shortened as much as possible and the technical casing should be quickly lowered to protect the wall.

[0038] Step 2: Prepare cement slurry and determine the amount of cement slurry to be injected into the well. The cement slurry is prepared using water, cement, fluid loss additive and retarder. A cement slurry thickening test is conducted in advance to determine the addition ratio of fluid loss additive and retarder. Slowing down the setting of cement slurry can ensure the reinforcement range. The cement used is Grade G cement, and the density of the prepared cement slurry is greater than or equal to 1.9g / cm 3 , ensuring the reinforcement strength; the volume of cement slurry injected into the well is calculated based on the open hole section well diameter expansion rate of 140% to 160%. In this embodiment, the volume is calculated based on the open hole section drill bit diameter of φ311.15mm and the well diameter expansion rate of 140% to 160%. It is expected that 38m of cement slurry will be injected into the well. 3 The slurry volume exceeds the open hole section volume by 15 to 20 m3 Before grouting, check the wellbore pressure stabilization state and the working condition of each facility to prepare for handling abnormal conditions and tripping out.

[0039] Step three, build a grouting system, connect the drill pipe with the petroleum cementing truck, drill the drill pipe into the well bottom through the inside of the technical casing, and grout through the hollow drill pipe; the petroleum cementing truck has a maximum pressure of 40Mpa and has a G-class cement high-density slurry supply capacity; first, inject clean water as a spacer fluid, and then inject cement slurry.

[0040] Step four, after grouting is completed, build a pressurization system, connect the drill pipe with the petroleum cementing truck, and connect the upper end of the technical casing through the variable-diameter joint; use the technical casing as a cementing pipe to pressurize the cement slurry, so that the cement slurry is diffused into the fractured zone; during the pressurization process, the maximum wellhead pressure is greater than 15Mpa, combined with the formation fracture pressure, the petroleum cementing truck is used to control the amount of pressurization to press a sufficient amount of cement slurry into the fractured zone at high pressure; after the cement slurry diffuses into the fractured zone, the setting time is greater than or equal to 72 hours to ensure the cement strength.

[0041] Step five, after the setting time is completed, drill the cement that is insufficient in strength in the grouting area and circulate it back out, and then perform re-grouting and extrusion, and repeat multiple times to ensure that the well section passing through the fractured zone is fully reinforced.

[0042] Step six, after ensuring the stability of the well section passing through the fractured zone, the remaining well section is constructed; for the horizontal well section, the method of small-hole rapid drilling is used to reduce the ground stress, reduce the pressure, reduce the disturbance, and quickly form a hole.

[0043] The present application collects and analyzes geological data of the drilling area, and comprehensively uses the construction technology for dealing with the fractured zone in the drilling construction to explore a technical process for safely passing through the mylonitic fractured well section of the L-shaped complex well type, and successfully passes through the fault fractured zone. The scheme safely and quickly completes the transition well section passing work in the construction of No. 2 well under the same geological conditions, and verifies again that the method for safely passing through the mylonitic fractured well section of the L-shaped well has good operability and generalizability.

[0044] The above examples are only used to illustrate the technical solutions of the present application, but not to limit it; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that they can modify the technical solutions recorded in the foregoing examples, or make equivalent substitutions for part of the technical features; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for safely traversing a mylonitic fractured section in an L-shaped well, characterized by: The following steps are involved: Step 1: construct the vertical well section and transition well section. During the construction process, technical casing is lowered into the vertical well section and transition well section and stopped when the fracture zone encounters resistance. Step 2: Prepare cement slurry and determine the amount of cement slurry to be injected into the well; Step 3: Build a grouting system, inject the spacer fluid first, and then inject the cement slurry; Step 4: After grouting is completed, a pressurizing system is constructed. A cementing truck is used to connect the drill pipe. The drill pipe is connected to the upper end of the technical casing through a reducer. The technical casing is used as a slurry stop pipe to pressurize the cement slurry so that the cement slurry is squeezed and diffused into the fractured zone. Based on the formation fracture pressure, a cementing truck is used to pressurize a sufficient amount of cement slurry into the fractured zone in a controlled manner. Step 5: After the cement slurry spreads to the fractured zone, it is allowed to solidify for a certain period of time; Step 6: After the setting is completed, the drill bit is lowered to explore the plug surface, and the cement with insufficient strength in the slurry area is drilled out and circulated out, and then grouting and extrusion are carried out again, and the cycle is repeated multiple times; Step 7: After ensuring that the well section passing through the broken zone is stable, construct the remaining well sections; In step 2, water, cement, fluid loss additive and retarder are used to prepare cement slurry, and a cement slurry thickening test is carried out in advance to determine the addition ratio of the fluid loss additive and retarder.

2. The method for safely crossing a mylonitic fractured section in an L-shaped well according to claim 1, wherein: In step 2, the cement used is Grade G cement, and the density of the prepared cement slurry is greater than or equal to 1.9 g / cm 3 .

3. The method for safely traversing a mylonitic fractured section in an L-shaped well according to claim 1, wherein: In step 2, the volume of cement slurry injected into the well is calculated based on the open hole section diameter expansion rate of 140% to 160%.

4. The method for safely traversing a mylonitic fractured section in an L-shaped well according to claim 1, wherein: In step three, the maximum wellhead pressure during the pressurization process is greater than 15 MPa.

5. The method for safely crossing a mylonitic fractured section in an L-shaped well according to claim 1, wherein: In step 3, the waiting time for setting is greater than or equal to 72 hours.

6. The method for safely crossing a mylonitic fractured section in an L-shaped well according to claim 1, wherein: In step 2, the grouting system uses an oil cementing truck to connect the drill pipe, the drill pipe is drilled from the inside of the technical casing to the bottom of the well, and grouting is performed through the hollow drill pipe.

7. The method for safely traversing a mylonitic fractured section in an L-shaped well according to claim 1, wherein: In step three, the pressurized system is connected to the drill pipe using an oil cementing truck, and the drill pipe is connected to the upper end of the technical casing through a reducer.

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