Striped area gas extraction ultra-short radius multi-lateral well drilling and completion method

Abstract

The application discloses a strip area gas extraction ultra-short radius multi-lateral well drilling and completion method, which comprises the following steps: step 1, obtaining coal seam exploration data and adjacent well data of a target coal seam in a strip area, and calculating a lateral angle of the multi-lateral well according to the obtained data; step 2, determining an analytical radius of the multi-lateral well according to the data obtained in step 1, and taking the determined analytical radius as an optimal interval of adjacent ultra-short radius multi-lateral wells; step 3, constructing a main well according to a set main well drilling track, and completing the main well drilling; and step 4, completing the drilling and completion of the ultra-short radius multi-lateral well on both sides of the main well according to the lateral angle of the multi-lateral well determined in step 1 and the optimal interval of the adjacent ultra-short radius multi-lateral wells determined in step 2. The method realizes the drilling and completion of the ultra-short radius multi-lateral horizontal well, the multi-lateral well track constructed by the method is controllable, the effective control area is large, the coal seam gas desorption effect is good, and the problems of uncertain hydraulic fracturing cracks and non-obvious stimulation effect are solved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of coalbed methane development, and particularly relates to a method for drilling and completing a strip area gas extraction ultra-short radius multi-lateral well. BACKGROUND

[0002] In China, coalbed methane reservoirs have poor geological conditions, it is difficult to increase production, and single well production is low, and the whole is in a low-efficiency development stage. Meanwhile, coalbed methane (gas) is a major safety hazard in the process of underground roadway excavation and coal resource exploitation. By deploying ground drilling along the coal roadway strip area to develop coalbed methane and realize gas pre-extraction, waste can be turned into treasure to fully utilize resources, and the requirements of gas outburst elimination in the coal roadway strip area can also be met.

[0003] Increasing single well gas production is a key problem in current coalbed methane development. There are mainly two types of existing technical approaches. One is to take technical measures to reform the reservoir and improve the permeability of the coal seam, and the technical measure is mainly hydraulic sand fracturing. The defects are that due to the weak cementation degree of the coal seam, low mechanical strength and elastic modulus, and high Poisson's ratio, it is difficult to form stable long cracks in the coal reservoir after sand fracturing, the crack communication capacity is limited, the pressure drop funnel formed around the wellbore is small, and ultimately the effective reform area is small. The other is to improve the coalbed methane well drilling and completion technology. At present, the coalbed methane exploration and development mainly uses straight wells or single and multi-lateral horizontal wells, and the three types of wells have certain defects and cannot fully meet the needs of coalbed methane development. Specifically, the control area of conventional straight wells is small, coal powder production leads to frequent well repair, and gas production is low. The effect of single lateral horizontal well application in strip area pre-extraction is not ideal. In the process of drilling, the well wall of the coal seam section is easy to collapse, and in the process of drainage and production, coal powder will enter the wellbore, causing coal powder particle pump sticking accidents, frequent well repair, and high drilling cost.

[0004] After the coalbed methane well is completed, drainage and pressure reduction must be performed first. At present, the drainage and gas production technology mainly uses rod pumps such as pumping units and electric submersible pumps, rodless pumps such as screw pumps, and other rodless pumps to drain water from the wellbore. The above processes have some defects to varying degrees: the liquid production of the rod pump is small, the coal powder adaptability is poor, and it is not suitable for horizontal well drainage. Electric submersible pumps, screw pumps, jet pumps, and diaphragm pumps have serious sticking, gas locking, and other phenomena. Therefore, a technology that is not limited by well type and coal seam water production and can meet the requirements of drainage and gas production technology is highly concerned.

[0005] In summary, a coalbed methane development technology suitable for strip area gas extraction is urgently needed to solve the technical difficulties of coalbed methane reservoir reform and drainage and gas production in the prior art, to achieve efficient development of coalbed methane, to meet the requirements of gas outburst elimination in the coal roadway strip area, and to ensure safe and efficient excavation of the roadway. SUMMARY

[0006] In view of the defects and shortcomings in the prior art, the strip area gas extraction ultra-short radius multi-lateral well drilling and completion method is provided to solve the technical problems of low single-well gas production and unsatisfactory drainage gas recovery in the strip area coal bed methane in the prior art.

[0007] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0008] A strip area gas extraction ultra-short radius multi-lateral well drilling and completion method, characterized in that it comprises the following steps:

[0009] Step 1: Obtain the coal seam exploration data and adjacent well data of the target coal seam in the strip area, wherein the adjacent well data includes pre-drilling coal seam flow pressure and branch well bottom hole flow pressure, and the coal seam exploration data includes coal seam elevation data, coal seam inclination data, coal seam inclination, coal seam three-dimensional stress data, coal seam porosity and coal seam permeability; then set the main well drilling trajectory according to the obtained data;

[0010] The coal seam three-dimensional stress data includes the minimum horizontal principal stress σ h , the maximum horizontal principal stress σ H , and the branch well axis vertical principal stress σ V .

[0011] When σ H > σ h > σ V or σ H > σ V > σ h , the branch well azimuth is calculated according to the obtained three-dimensional stress data;

[0012] Step 2: Determine the analytical radius of the branch well according to the data obtained in step 1, and use the determined analytical radius as the optimal spacing of the adjacent ultra-short radius multi-lateral well;

[0013] Step 3: Construct the main well according to the set main well drilling trajectory, and during the last drilling before the completion of the main well, connect a strong magnetic sub near the drill bit, and install a magnetic ranging probe pipe at the predetermined communication point of the coal mine roadway, so as to realize the communication between the horizontal well toe and the coal mine roadway by means of the rotating magnetic ranging system, and complete the well completion by using a screen pipe, and temporarily block the horizontal well toe by using a packer and a casing valve, thus completing the drilling of the main well;

[0014] Step 4: Complete the drilling and completion of the ultra-short radius branch well on both sides of the main well according to the branch well azimuth determined in step 1 and the optimal spacing of the adjacent ultra-short radius multi-lateral well determined in step 2.

[0015] The present application also has the following technical features:

[0016] Specifically, the branch well azimuth in step 1 is determined by the following formula:

[0017]

[0018] wherein:

[0019] θ is the azimuth angle of the branch well, in °;

[0020] σ H is the maximum horizontal principal stress, in MPa;

[0021] σ h is the minimum horizontal principal stress, in MPa;

[0022] σ V is the vertical principal stress of the axis of the branch well, in MPa.

[0023] Further, the analytical radius in step 2 is determined by the following formula:

[0024]

[0025] wherein:

[0026] γ B is the radius of the wellbore of the branch well, in m;

[0027] p is the pre-drilling coal seam flow pressure, in MPa;

[0028] p C is the critical desorption pressure, in MPa;

[0029] p VHP is the bottom hole flow pressure of the branch well, in MPa;

[0030] β is the drainage index of the formation water, dimensionless.

[0031] Further, the drainage index of the formation water is determined by the following formula:

[0032]

[0033] wherein:

[0034] β is the drainage index of the formation water, dimensionless;

[0035] t is the drainage time, in d (days);

[0036] k is the permeability of the coal seam, in md;

[0037] is the porosity of the coal seam, in %.

[0038] Further, the step 1 further comprises: taking the coal seam with a coal seam inclination less than 0° as a target coal seam according to the obtained coal seam elevation data and the coal seam inclination data, and then taking the highest point of the target coal seam as a build-up section entry point to complete the design of the build-up section of the main well.

[0039] Further, the main well drilling trajectory set in the step 1 should meet the following condition: the elevation of any point on the main well drilling trajectory is lower than the elevation of the entry point.

[0040] Further, the parameters of the construction of the ultra-short radius branch well in the step 4 comprise: the curvature radius of the ultra-short radius branch well borehole is 2-3 m, and the horizontal extension distance of the ultra-short radius branch well in the target coal seam is 20-30 m.

[0041] Compared with the prior art, the present application has the beneficial technical effects that:

[0042] (1) The present application realizes the drilling and completion of the ultra-short radius multi-branch horizontal well, the branch well trajectory constructed by the present application is controllable, has a large effective control area, and has a good coalbed methane desorption effect, thereby solving the problems of uncertain hydraulic fracturing cracks and non-obvious stimulation effect.

[0043] (2) The main borehole obtained by the present application is connected with the roadway, after the completion, by regulating the opening and closing of the casing valve arranged on the casing, the coal seam water in the wellbore can be discharged into the roadway manifold, so as to achieve the purpose of pressure reduction and accelerate the desorption and production of the coalbed methane.

[0044] (3) The diameter size of the completed borehole obtained by the present application can reach more than 200 mm, has a larger drainage area, the drilling torque can reach 30 kN·m, the drilling speed is high, the average drilling speed of the coal seam can reach 30 m / h, the wellbore liquid column pressure can balance the formation flow pressure, and the soft coal seam well wall collapse is avoided, thereby effectively solving the technical problems of small hole diameter, slow drilling speed, poor hole wall stability and difficult hole forming in the roadway drilling in the prior art. BRIEF DESCRIPTION OF DRAWINGS

[0045] Figure 1 is the flow chart of the present application method;

[0046] Figure 2 is the horizontal section view of the main borehole and the branch borehole in Example 1;

[0047] Figure 3 is the vertical section view of the wellbore in Example 1.

[0048] The present application will be specifically described below in combination with the drawings and specific embodiments in the specification. DETAILED DESCRIPTION

[0049] Following the above technical solutions, specific embodiments of the present invention are given below. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent modifications made based on the technical solutions of this application fall within the protection scope of the present invention.

[0050] The technical terms involved in this invention are explained as follows:

[0051] Ultra-short radius branch wells: effective curvature radius of 2-5m, multi-branch wells that become horizontal after turning 90°.

[0052] Desorption radius: Within the pressure drop funnel of a coalbed methane well, the area where the coal seam water pressure is lower than the gas desorption pressure is called the desorption radius. The distance from the edge of this area to the center of the wellbore is called the desorption radius.

[0053] Wellbore Collapse Prevention Principles: Coal seam in-situ stress is the main external force causing wellbore deformation and damage. The magnitude and direction of in-situ stress have a significant impact on the stability of the coal seam surrounding the wellbore and are important factors leading to wellbore collapse. Current technology cannot modify coal seam in-situ stress. Therefore, through theoretical calculations, the azimuth angle of branch wellbores is optimized to minimize the damage of in-situ stress to the wellbore.

[0054] The design concept of this invention is as follows: along the strip area of ​​the coal roadway, a surface horizontal well is drilled from the high point of the coal seam dip angle to the low point. The well structure of the surface horizontal well is three sections: the first section is a vertical section, the second section is a directional drilling section, and the third section is a horizontal section. After completing the drilling of the directional and horizontal sections, ultra-short radius branch wells are constructed along both sides of the main well at the target stratum using flexible drilling tools. Finally, two sets of oppositely arranged comb-shaped branch wells are formed in the coal seam. The branch wells uniformly cover the entire gas pre-drainage area, realizing the elimination of gas outbursts and the development and utilization of coalbed methane, thereby solving the technical problems of small hole diameter, slow drilling speed, poor hole wall stability, and difficult hole formation in existing technologies.

[0055] The present invention will be further described in detail below with reference to the embodiments.

[0056] Example 1

[0057] like Figure 1 As shown, this embodiment provides a drilling and completion method for ultra-short radius multi-branch wells for strip-area gas extraction, including the following steps:

[0058] Step 1: Obtain coal seam exploration data and adjacent well information for the target coal seam in the strip area. The adjacent well information includes pre-drilling coal seam flowing pressure and bottom hole flowing pressure of branch wells. The coal seam exploration data includes coal seam elevation data, coal seam dip angle data, coal seam dip angle, three-dimensional geostress data of coal seam, coal seam porosity, and coal seam permeability. Then, set the main well drilling trajectory based on the obtained data.

[0059] The set main well drilling trajectory should meet the following conditions: the elevation of any point on the main well drilling trajectory is lower than the elevation of the entry point.

[0060] The setting of the main well drilling trajectory comprises: taking a coal seam with a coal seam inclination less than 0° as a target coal seam according to the obtained coal seam elevation data and coal seam inclination data, and then taking the highest point of the target coal seam as a build-up section window point to complete the design of the build-up section of the main well.

[0061] The coal seam three-dimensional ground stress data can be obtained through a hydraulic fracturing experiment, and comprises a minimum horizontal principal stress σ h , a maximum horizontal principal stress σ H , and a branch well axis vertical principal stress σ V .

[0062] It should be noted that the method is only applicable to the case of σ H > σ h > σ V or σ H > σ v > σ h , and when σ H > σ h > σ V or σ H > σ V > σ h , the branch well azimuth is calculated according to the obtained three-dimensional ground stress data; this is because, when σ V > σ H > σ h , that is, the coal seam ground stress in the vertical direction of the branch well axis is the maximum value, no matter how the wellbore azimuth is optimized and deployed, the maximum ground stress that may cause the well wall to collapse is vertically applied to the wellbore.

[0063] The branch well azimuth is determined by the following formula:

[0064]

[0065] In the formula:

[0066] θ is the branch well azimuth, in °;

[0067] σ H is the maximum horizontal principal stress, in MPa;

[0068] σ h is the minimum horizontal principal stress, in MPa;

[0069] σ V is the branch well axis vertical principal stress, in MPa.

[0070] In this embodiment, for coal rock, σ H = 14.43 MPa, σ h = 6.85 MPa, and σV = 8.52 MPa, into the calculation formula, and the solution is θ = 51.22°, that is, the branch wellbore orientation should be 51.22° angle with the maximum horizontal principal stress orientation.

[0071] Step 2, determine the analytical radius of the branch well according to the data obtained in step 1, and determine the optimal spacing of the adjacent ultra-short radius multi-branch well with the determined analytical radius;

[0072] The analytical radius is determined by the following formula:

[0073]

[0074] In the formula:

[0075] γ B is the branch wellbore radius, with the unit of m

[0076] p is the pre-drilling coal seam flow pressure, with the unit of MPa

[0077] p C is the critical desorption pressure, with the unit of MPa

[0078] p VHP is the bottom hole flow pressure of the branch well, with the unit of MPa

[0079] β is the formation water discharge index, dimensionless.

[0080] The formation water discharge index is determined by the following formula:

[0081]

[0082] In the formula:

[0083] β is the formation water discharge index, dimensionless;

[0084] t is the discharge time, with the unit of d (day);

[0085] k is the coal seam permeability, with the unit of md;

[0086] φ is the coal seam porosity, with the unit of %.

[0087] The branch wellbore radius γ B = 0.065 m, the coal seam permeability k = 0.03 mD, the porosity The initial flow pressure of the coal seam p = 3.91 MPa, the critical desorption pressure p C = 2.35 MPa, the bottom hole flow pressure p BHP= 0.825 MPa, after 120 days of drainage, the formula is brought into, and the desorption radius of the branch well is γ = 46.723 m, that is, the optimal spacing of the adjacent super-short radius multi-branch well is 46.723 m.

[0088] Step 3, according to the set main well drilling trajectory, the main well is constructed, and when the last drilling before the main well completion is performed, a strong magnetic sub is connected at the near-bit, and a magnetic ranging probe is installed at the predetermined communication point of the coal mine tunnel, the horizontal well toe end is connected with the coal mine tunnel by means of the rotary magnetic ranging system, the well is completed by using the screen pipe, and the horizontal well toe end is temporarily blocked by using the packer and the casing valve, and thus the main well drilling is completed.

[0089] The main well adopts a three-opening wellbore structure, a straight well section is opened in the first opening, a drill tool assembly is used, that is, 12 1 / 4" drill bit + 5" drill rod, and casing cementing is performed; a build-up section is opened in the second opening, a drill tool assembly is used, that is, 8 1 / 2" drill bit + 6 1 / 2" screw drill + 5" heavy drill rod + 5" drill rod, a "single-bend screw drill + wireless while-drilling measurement system" directional drill tool assembly is used in the build-up section, and the drill tool assembly is used in the form of sliding drilling to realize torsional azimuth, build-up and drop-off; the build-up section is stabilized by using composite drilling to effectively improve the drilling speed and the trajectory control accuracy, and the casing is cemented; the main well horizontal section is opened in the third opening, a drill tool assembly is used, that is, 6" drill bit + 4 6 / 8" screw drill + 3 1 / 2" heavy drill rod + 3 1 / 2" drill rod, the main well horizontal section uses the geosteering technology to perform real-time monitoring of the wellbore trajectory, and the main well horizontal section trajectory should be completely in the target coal seam to meet the lateral drilling requirements of the subsequent super-short radius branch well.

[0090] Step 4, according to the branch well azimuth angle determined in step 1 and the optimal spacing of the adjacent super-short radius multi-branch well determined in step 2, drilling and completion of the super-short radius branch well are completed on both sides of the main well, wherein the parameters of the super-short radius branch well include that the curvature radius of the super-short radius branch well is 2-3 m, and the horizontal extension distance of the super-short radius branch well in the target coal seam is 20-30 m.

[0091] Along the horizontal section of the main wellbore which has been drilled, high-curvature lateral drilling is realized at the designed horizon by using the existing flexible drill tool, and lateral drilling points are arranged at equal intervals to meet the subsequent needs of strip area coalbed methane extraction, and finally dozens of stable and long-term effective gas production channels are formed in the coal seam as shown in Figure 2 and Figure 3 The screen pipe and casing cementing combination completion method is used, that is, the upper casing + horizontal well section screen pipe + casing valve + casing outer packer combination form, the upper casing is cemented for half the distance, the upper formation is sealed, the bottom of the well is completely connected with the coal mine tunnel, and the tail pipe is connected with the drainage pipe manifold in the tunnel, the casing valve is adjusted to open and close, the produced water and coal powder in the formation are drained into the coal mine tunnel manifold, and the effect of drainage, pressure reduction and sand removal is achieved.

[0092] In the embodiment, after the ultra-short radius branch wells arranged on both sides of the main well are all completed, the branch wellbores extending in each direction can be stably formed in the coalbed methane reservoir, and the branch direction can be artificially controlled, the length of the ultra-short radius branch well can reach more than 20 meters, the fractures in each direction of the near-wellbore end and the far-wellbore end can be effectively communicated, and the reservoir reconstruction purpose is achieved.

[0093] Compared with the conventional borehole size of 100mm, the theoretical torque of 6kN·m, the average drilling speed of only 10m / h, and the use of only water as the drilling fluid, the diameter of the completed borehole obtained by using the method can reach more than 200mm, has a larger drainage area, the drilling torque can reach 30kN·m, the drilling speed is high, the average drilling speed of the coal seam can reach 30m / h, the wellbore liquid column pressure can balance the formation flow pressure, and the collapse of the well wall in the soft coal seam is avoided.

[0094] The preferred embodiments of the present disclosure are described in detail above in combination with the drawings, but the present disclosure is not limited to the specific details in the above-described embodiments, and various simple modifications can be made to the technical solutions of the present disclosure within the technical concept of the present disclosure, and these simple modifications all belong to the protection scope of the present disclosure.

[0095] In addition, it should be noted that each specific technical feature described in the above specific embodiments can be combined in any appropriate manner without contradiction, and in order to avoid unnecessary repetition, the present disclosure will not further describe various possible combination manners.

[0096] In addition, the various different embodiments of the present disclosure can also be combined in any manner, as long as it does not deviate from the idea of the present disclosure, and it should also be considered as the disclosed content of the present disclosure.

Claims

1. A drilling and completion method for ultra-short radius multi-branch wells for strip-area gas extraction, characterized in that, Includes the following steps: Step 1: Obtain coal seam exploration data and adjacent well information for the target coal seam in the strip area. The adjacent well information includes pre-drilling coal seam flowing pressure and bottom hole flowing pressure of branch wells. The coal seam exploration data includes coal seam elevation data, coal seam dip angle data, coal seam dip angle, three-dimensional geostress data of coal seam, coal seam porosity, and coal seam permeability. Then, set the main well drilling trajectory based on the obtained data. The three-dimensional geostress data of the coal seam includes the minimum horizontal principal stress. Maximum horizontal principal stress Vertical principal stress of the branch well axis ; when At that time, the azimuth angle of the branch well is calculated based on the obtained three-dimensional geostress data; Step 2: Determine the analytical radius of the branch wells based on the data obtained in Step 1, and use the determined analytical radius as the optimal spacing between adjacent ultra-short radius multi-branch wells; Step 3: Construct the main shaft according to the set main shaft drilling trajectory. During the last drilling before the main shaft is completed, connect a strong magnetic short section near the drill bit and install a magnetic ranging probe at the predetermined connection point of the coal mine roadway. Use a rotating magnetic ranging system to connect the horizontal shaft toe with the coal mine roadway. Complete the shaft using a screen pipe method. At the same time, temporarily block the horizontal shaft toe with a packer and casing valve. This completes the main shaft drilling. Step 4: Based on the branch well azimuth angle determined in Step 1 and the optimal spacing between adjacent ultra-short radius multi-branch wells determined in Step 2, complete the drilling and completion of ultra-short radius branch wells on both sides of the main well. The azimuth angle of the branch well mentioned in step 1 is determined by the following formula: In the formula: θ is the azimuth angle of the branch well, in degrees; The maximum horizontal principal stress is expressed in MPa. The minimum horizontal principal stress is expressed in MPa. The vertical principal stress along the axis of the branch well is expressed in MPa. The analytical radius mentioned in step 2 is determined by the following formula: In the formula: The radius of the branch wellbore is in meters (m). This refers to the coal seam flow pressure before drilling, in MPa. The critical desorption pressure is expressed in MPa. The bottom hole pressure of the branch well is expressed in MPa. This is the formation water discharge index, which is dimensionless. The formation water discharge index is determined by the following formula: In the formula: This is the formation water discharge index, which is dimensionless. t represents the discharge time, expressed in days (d). Coal seam permeability, in md; The value represents coal seam porosity, expressed as a percentage.

2. The drilling and completion method for ultra-short radius multi-branch wells for strip-area gas extraction as described in claim 1, characterized in that, Step 1 further includes: based on the obtained coal seam elevation data and coal seam dip angle data, taking the coal seam with a dip angle of less than 0° as the target coal seam, and then taking the highest point of the target coal seam as the entry point of the directional section to complete the design of the main shaft directional section.

3. The drilling and completion method for ultra-short radius multi-branch wells for strip-area gas extraction as described in claim 1, characterized in that, The main well drilling trajectory set in step 1 should meet the following conditions: the elevation of any point on the main well drilling trajectory is lower than the elevation of the entry point.

4. The drilling and completion method for ultra-short radius multi-branch wells for strip-area gas extraction as described in claim 1, characterized in that, The parameters for constructing the ultra-short radius branch well in step 4 include: the radius of curvature of the wellbore of the ultra-short radius branch well is 2~3m, and the horizontal extension distance of the ultra-short radius branch well within the target coal seam is 20~30m.

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