A method for determining the horizontal trajectory of a horizontal well in the roof of a surface coal seam

Abstract

The present invention discloses a method for determining the trajectory of a horizontal section of a horizontal well in a surface coal seam roof, comprising drawing a predicted geological profile of the horizontal section of the horizontal well based on collected geological data; determining the landing point of the horizontal section of the horizontal well, the spacing between preset fracturing positions, and the spacing between reserved sidetracking points based on the drawn predicted geological profile, thereby determining the pre-fracturing positions, the reserved sidetracking points, and the trajectory to be drilled of the horizontal section of the horizontal well; correcting the predicted geological profile based on measurement while drilling data and comprehensive logging data collected during coal exploration drilling to obtain an actual drilling geological profile; determining the distance between each actual fracturing position and the coal seam roof to complete the determination of the trajectory of the horizontal section of the horizontal well in the surface coal seam roof. The method of the present invention first constructs a predicted geological profile, and then, during drilling according to the predicted geological profile, uses the measurement while drilling data and comprehensive logging data acquired in real time to timely adjust the drilling direction of the drill bit and correct the predicted geological profile in real time.

Description

Technical Field

[0001] The invention belongs to the technical field of coalbed methane exploration and development, and relates to a method for determining the horizontal section trajectory of a horizontal well in a surface coal seam roof. Background Art

[0002] Surface horizontal well gas extraction or coalbed methane development is a highly effective gas control technology in coal mining areas. In soft and crushed coal seams, laying horizontal wells within the seam presents challenges such as horizontal seam collapse, drill bit sticking and burial, difficulty in running casing, difficulty controlling cementing quality, and coal reservoir contamination. These issues limit the methods and scale of reservoir stimulation and, consequently, the effectiveness of gas control. Roof horizontal wells effectively address these issues by placing the horizontal section trajectory within the roof strata of the target coal reservoir and employing reservoir stimulation measures such as downward directional perforating and large-scale staged hydraulic fracturing.

[0003] However, due to the influence of sedimentary environment and tectonic evolution, the undulation, thickness and lithology of the coal seam roof present a complex situation. For example, due to the influence of sedimentary microfacies, the roof lithologic combination is complex and changeable; the marker layer for delineating the coal seam is unstable; the differences in the lithologic and physical properties between the coal seam and its roof are not obvious, etc., making it very difficult to accurately control the wellbore trajectory. Therefore, the roof horizontal well technology also has technical difficulties. The existing technology mostly uses azimuthal gamma logging while drilling to control the horizontal section trajectory geological guidance. This method is derived from the horizontal well geological guidance technology in coal seams and cannot meet the needs of determining the horizontal section wellbore trajectory of roof horizontal wells. In the actual identification process, it can only be determined whether the trajectory is in the coal seam, but it cannot be determined the vertical position and distance of the coal seam where the trajectory is located. Summary of the Invention

[0004] In response to the defects and shortcomings in the existing technology, the present invention provides a method for determining the horizontal section trajectory of a horizontal well in the roof of a ground coal seam, so as to solve the technical problem in the existing technology that the longitudinal position and distance of the coal seam described in the wellbore trajectory cannot be clearly determined when performing roof horizontal well trajectory detection.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A method for determining a horizontal trajectory of a horizontal well in a surface coal seam roof comprises the following steps:

[0007] Step 1: Collect geological data of the target mining area and draw the expected geological profile of the horizontal section of the horizontal well based on the collected geological data;

[0008] Step 2: Determine the landing point of the horizontal section of the horizontal well, the spacing between the preset fracturing positions, and the spacing between the reserved sidetracking points based on the drawn expected geological profile, and then determine the pre-fracturing positions, the reserved sidetracking points, and the drilling trajectory of the horizontal section of the horizontal well;

[0009] Step 3: Starting from the landing point, the horizontal section of the horizontal well is drilled according to the drilling trajectory determined in Step 2, and the expected geological profile is corrected based on the measurement while drilling data and comprehensive logging data collected during the coal exploration drilling process to obtain the actual drilling geological profile;

[0010] Step 4: Mark the location of the exploration wellbore in the actual drilling geological profile, and determine the distance between each fracturing position and the coal seam roof to complete the horizontal section trajectory determination of the horizontal well on the ground coal seam roof.

[0011] The present invention also has the following technical features:

[0012] Specifically, step 1 specifically includes: according to the horizontal section projection orientation, longitudinal scale and transverse scale, in combination with geological data, outlining the undulating contours and structural positions of each rock layer above the coal seam roof, and then filling in the corresponding lithology symbols and structural symbols in each outlined rock layer to draw the expected geological profile of the horizontal section of the horizontal well.

[0013] Furthermore, step 3 includes the following sub-steps:

[0014] Step 3.1, according to the drilling trajectory determined in step 2, start from the landing point and drill towards the first pre-fracturing position;

[0015] If coal is encountered before drilling to the first pre-fracturing position, and the angle between the wellbore inclination and the coal seam dip is less than or equal to 3°, then the wellbore will be rotated and increased inclination in the downdip direction of the formation from the coal point to continue drilling to the first pre-fracturing position. The location of the well section encountering the coal seam will be determined based on the collected measurement while drilling data and comprehensive logging data, and the expected geological profile will be revised accordingly.

[0016] If coal is encountered before drilling to the first pre-fracturing position, and the angle between the wellbore inclination and the coal seam dip is greater than 3°, the drill string will be withdrawn to the first reserved sidetracking point, and the suspended sidetracking operation will be continued to the first pre-fracturing position. The location of the well section encountering the coal seam will be determined based on the collected measurement while drilling data and comprehensive logging data, and the expected geological profile will be revised accordingly.

[0017] Step 3.2, completing the coal exploration drilling in the fracturing section in sequence according to the drilling trajectory determined in step 2;

[0018] If the coal seam is encountered when the drilling distance of the coal exploration drill in the fracturing section is less than or equal to half of the preset fracturing position spacing, then:

[0019] If the angle between the wellbore inclination and the coal seam dip is less than or equal to 3°, and the distance between the drilled pre-fracturing position and the top of the coal seam is less than or equal to the designed distance between the horizontal section of the horizontal well and the coal seam roof, then the wellbore should be twisted and increased inclination in the downdip direction of the formation from the coal point and the drilling should continue to the next pre-fracturing position. The location of the well section encountering the coal seam should be determined based on the collected measurement while drilling data and comprehensive logging data, and the expected geological profile should be revised accordingly.

[0020] If the angle between the wellbore inclination and the coal seam dip is greater than 3°, or the distance between the drilled pre-fracturing position and the top of the coal seam is greater than the designed distance between the horizontal section of the horizontal well and the coal seam roof, the well section where the coal seam is encountered is determined based on the collected measurement while drilling data and comprehensive logging data, the expected geological profile is revised, and the drill tool is withdrawn to the reserved sidetracking point and suspended sidetracking is carried out to the next pre-fracturing position;

[0021] If the coal seam is encountered when the exploration drilling distance in the fracturing section is greater than half of the preset fracturing position spacing, then:

[0022] The expected geological profile is modified according to the location of the well section where the coal seam is encountered, and then the drill tool is withdrawn to the sidetracking point, and the suspended sidetracking construction is continued to the next pre-fracturing position.

[0023] The designed distance between the horizontal section of the horizontal well and the coal seam roof is 0 to 5 meters.

[0024] Furthermore, the preset fracturing position spacing is 30 to 150 meters.

[0025] Furthermore, the reserved side drilling points are spaced 30 to 100 meters apart.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The method of the present invention first constructs a projected geological profile. Then, during drilling according to the projected geological profile, the drill bit's drilling direction is promptly adjusted using real-time measurement-while-drilling data and comprehensive logging data, as well as by determining the angle between the wellbore inclination and the coal seam dip. The projected geological profile is then corrected in real time. This significantly improves the accuracy of determining the drilling trajectory of the horizontal section of a horizontal well, increases the encounter rate of the horizontal section, and reduces drilling risks caused by insufficient trajectory control accuracy and high coal penetration rates during drilling of the horizontal section of a horizontal well. This significantly reduces the difficulty of staged perforation fracturing construction and improves the fracturing and gas production effects. The method of the present invention is highly operable and low-cost for on-site construction, making it worthy of widespread promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings are used to provide further understanding of the present disclosure and constitute a part of the specification. Together with the following detailed description, they are used to explain the present disclosure, but do not constitute a limitation of the present disclosure.

[0029] Figure 1 is a flow chart of the method of the present invention;

[0030] Figure 2 This is a schematic diagram of the coal exploration process of Example 1.

[0031] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. DETAILED DESCRIPTION

[0032] The embodiments described below are only some of the embodiments of the present invention, not all of the embodiments, and do not limit the present invention in any form. Any technical solution that utilizes this embodiment, including simple changes to this embodiment, falls within the scope of protection of the present invention.

[0033] The technical terms involved in the present invention are explained below:

[0034] Reserved side drilling point: According to the requirements of coal exploration, a lateral drilling point (section) is reserved in advance at a certain depth on the main wellbore, with the following characteristics: the side drilling point inclination is greater than the well inclination of the adjacent side drilling point section on the main wellbore, or the azimuth of the side drilling point is inconsistent with the azimuth of the adjacent side drilling point section on the main wellbore.

[0035] Example 1

[0036] Following the above technical solution, such as Figure 1 As shown, this embodiment provides a method for determining the horizontal section trajectory of a horizontal well in the roof of a surface coal seam, wherein A is the landing point, and B and C are both pre-fracturing positions.

[0037] The following steps are involved:

[0038] Step 1: Collect geological data of the target mining area and draw the expected geological profile of the horizontal section of the horizontal well based on the collected geological data;

[0039] The collection of geological data of the target mining area can provide a basis for the drawing of the expected geological profile of the horizontal section of the horizontal well. The geological data mainly include the coal seam floor contour map, exploration line geological profile map and single-hole column map, etc. The analysis obtains the lithologic combination characteristics, physical property characteristics, natural gamma curve characteristics and wellbore curve characteristics of the coal seam roof and floor within 20 to 30 meters of the coal seam roof and floor in the projection direction of the horizontal section. Then, according to the projection orientation, vertical scale and horizontal scale of the horizontal section, the undulating contours and structural positions of each rock layer above the coal seam roof are outlined, and then the corresponding lithologic symbols and structural symbols are filled in the outlined rock layers to draw the expected geological profile of the horizontal section of the horizontal well.

[0040] Step 2: Determine the landing point of the horizontal section of the horizontal well, the spacing between the preset fracturing positions, and the spacing between the reserved sidetracking points based on the drawn expected geological profile, and then determine the pre-fracturing positions, the reserved sidetracking points, and the drilling trajectory of the horizontal section of the horizontal well;

[0041] As a preferred solution of this embodiment, the design distance between the horizontal section of the horizontal well and the coal seam roof is 0 to 5 meters, the preset fracturing position spacing is 30 to 150 meters, and the reserved side drilling point spacing is 30 to 100 meters.

[0042] Step 3: Start from the landing point and drill the horizontal section of the horizontal well according to the drilling trajectory determined in step 2.

[0043] When drilling before the first pre-fracturing location, drill according to the expected geological profile and designed trajectory. If no coal is found after the first pre-fracturing location and the exploration coal drilling distance is less than or equal to half of the preset fracturing stage spacing, drill in the updip direction of the formation at a full-angle change rate of 1° / 30m to 4° / 30m to the coal point. If the exploration coal drilling distance is greater than half of the preset fracturing stage spacing, drill in the updip direction of the formation at the maximum deflection capacity of the drill bit to the coal point. The expected geological profile is then corrected based on the measurement while drilling data and comprehensive logging data collected during the exploration coal drilling process to obtain the actual drilling geological profile.

[0044] During on-site construction, measurement while drilling data include well inclination, azimuth and azimuth gamma. Comprehensive logging data are mainly obtained through engineering parameter logging, drilling time logging, simple hydrological logging, cuttings logging and gas logging, including suspended weight, bit weight, drilling time, displacement, drilling fluid consumption, cuttings, total hydrocarbon value, component value and non-hydrocarbon value. The location and condition of the coal seam section encountered can be determined based on the obtained measurement while drilling data and comprehensive logging data.

[0045] Step 3.1, according to the drilling trajectory determined in step 2, start from the landing point and drill towards the first pre-fracturing position;

[0046] Normally, the coal seam will not be encountered before drilling to the first pre-fracturing position. However, if coal is encountered before drilling to the first pre-fracturing position, and the angle between the wellbore inclination and the coal seam dip is less than or equal to 3°, then the wellbore will be twisted and increased inclination in the downdip direction of the formation from the coal point to continue drilling to the first pre-fracturing position. The location of the well section where the coal seam is encountered is determined based on the collected measurement while drilling data and comprehensive logging data, and the expected geological profile is then revised.

[0047] The distance between the drill bit and the coal seam can be determined based on the detection range of the measurement-while-drilling instrument. If the total hydrocarbon value and hydrocarbon composition values ​​measured by the gas logging system increase, drilling time increases, the drilling pressure decreases, and the returned rock cuttings are coal cuttings, coal is considered to have been encountered.

[0048] L=R / tan(α)-M

[0049] d=L×sin(α)

[0050] Where:

[0051] R is the detection radius of the measurement while drilling instrument, in m;

[0052] L is the distance between the drill bit and the top of the coal seam, in meters;

[0053] α is the complementary angle of the well inclination, in degrees;

[0054] d is the vertical distance between the drill bit and the top of the coal seam, in m;

[0055] M is the distance between the drill bit and the MWD instrument, in meters

[0056] If coal is encountered before drilling to the first pre-fracturing position, and the angle between the wellbore inclination and the coal seam dip is greater than 3°, the drill string will be withdrawn to the first reserved sidetracking point, and the suspended sidetracking operation will be continued to the first pre-fracturing position. The location of the well section encountering the coal seam will be determined based on the collected measurement while drilling data and comprehensive logging data, and the expected geological profile will be revised accordingly.

[0057] Step 3.2: According to the drilling trajectory determined in step 2, the coal exploration drilling of each fracturing section is completed in sequence from the first pre-fracturing position to the last pre-fracturing position; a fracturing section is formed between two pre-fracturing positions.

[0058] If the coal seam is encountered when the drilling distance of the coal exploration drill in the fracturing section is less than or equal to half of the preset fracturing position spacing, then:

[0059] If the angle between the wellbore inclination and the coal seam dip is less than or equal to 3°, and the distance between the drilled pre-fracturing position and the top of the coal seam is less than or equal to the designed distance between the horizontal section of the horizontal well and the coal seam roof, then the wellbore should be twisted and increased inclination in the downdip direction of the formation from the coal point and the drilling should continue to the next pre-fracturing position. The coal seam section encountered should be determined based on the collected measurement while drilling data and comprehensive logging data, and the expected geological profile should be revised.

[0060] If the angle between the wellbore inclination and the coal seam dip is greater than 3°, or the distance between the drilled pre-fracturing position and the top of the coal seam is greater than the designed distance between the horizontal section of the horizontal well and the coal seam roof, the well section where the coal seam is encountered is determined based on the collected measurement while drilling data and comprehensive logging data, the expected geological profile is revised, and the drill tool is withdrawn to the reserved sidetracking point and suspended sidetracking is carried out to the next pre-fracturing position;

[0061] After the drill string is withdrawn to the suspended sidetracking point, the tool face is set, such as 210° or 150°. A slot is then cut in the well section 10-20 m above the sidetracking point, which takes 2-3 hours. From the sidetracking point, one or two drill strings are then drilled using the previous tool face, with a controlled time of 12-24 hours. After drilling 1.5-2 drill strings with controlled time, if the drill bit has a strong pressure-bearing capacity, normal drilling can be resumed. After drilling 50-150 m, a short-term drill is performed to repair the sidetracking window, ensuring that the drill string can enter the new wellbore without adjusting the tool face.

[0062] If the coal seam is encountered when the exploration drilling distance in the fracturing section is greater than half of the preset fracturing position spacing, then:

[0063] The expected geological profile is modified according to the location of the well section where the coal seam is encountered, and then the drill tool is withdrawn to the sidetracking point, and the suspended sidetracking construction is continued to the next pre-fracturing position.

[0064] Step 4: Mark the location of the exploration wellbore in the actual drilling geological profile, and determine the distance between each fracturing position and the coal seam roof to complete the horizontal section trajectory determination of the horizontal well on the ground coal seam roof.

[0065] By adopting the method of the present invention, during the process of drilling according to the expected geological profile, with the help of real-time acquired measurement while drilling data and comprehensive logging data, as well as by determining the angle between the wellbore inclination and the coal seam inclination, the drilling direction of the drill bit is timely adjusted, and the expected geological profile is corrected in real time. This can greatly improve the accuracy of determining the drilling trajectory of the horizontal section of the horizontal well, improve the drilling rate of the horizontal section, reduce the drilling risk caused by insufficient trajectory control accuracy and high coal penetration rate during the drilling of the horizontal section of the horizontal well, thereby greatly reducing the difficulty of staged perforation fracturing construction and improving the fracturing and gas production effects.

[0066] The various specific technical features described in the above specific embodiments can be combined in any certain way without contradiction, as long as they do not violate the concept of the present invention, and should also be regarded as the content disclosed by the present invention.

[0067] The preferred embodiments of the present disclosure are described in detail above in conjunction with the accompanying drawings. However, the present disclosure is not limited to the specific details of the above embodiments. Within the technical concept of the present disclosure, various simple modifications can be made to the technical solutions of the present disclosure, and these simple modifications all fall within the scope of protection of the present disclosure.

[0068] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any certain way without contradiction. In order to avoid unnecessary repetition, this disclosure will not further explain various possible combinations.

[0069] In addition, the various embodiments of the present disclosure may be arbitrarily combined, and as long as they do not violate the concept of the present disclosure, they should also be regarded as the contents disclosed by the present disclosure.

Claims

1. A method for determining the horizontal trajectory of a horizontal well in a surface coal seam roof, characterized in that: The following steps are involved: Step 1: Collect geological data of the target mining area and draw the expected geological profile of the horizontal section of the horizontal well based on the collected geological data; Step 2: Determine the landing point of the horizontal section of the horizontal well, the spacing between the preset fracturing positions, and the spacing between the reserved sidetracking points based on the drawn expected geological profile, and then determine the pre-fracturing positions, the reserved sidetracking points, and the drilling trajectory of the horizontal section of the horizontal well; Step 3: Starting from the landing point, the horizontal section of the horizontal well is drilled according to the drilling trajectory determined in Step 2, and the expected geological profile is corrected based on the measurement while drilling data and comprehensive logging data collected during the coal exploration drilling process to obtain the actual drilling geological profile; Step 4: Mark the location of the exploration wellbore in the actual drilling geological profile, and determine the distance between each actual fracturing position and the coal seam roof to complete the horizontal section trajectory determination of the horizontal well on the surface coal seam roof; Step 3 includes the following sub-steps: Step 3.1, according to the drilling trajectory determined in step 2, start from the landing point and drill towards the first pre-fracturing position; If coal is encountered before drilling to the first pre-fracturing position, and the angle between the wellbore inclination and the coal seam dip is less than or equal to 3°, then the wellbore will be rotated and increased inclination in the downdip direction of the formation from the coal point to continue drilling to the first pre-fracturing position. The location of the well section where the coal seam is encountered will be determined based on the measurement while drilling data and comprehensive logging data collected during the drilling process, and the expected geological profile will be revised accordingly. If coal is encountered before drilling to the first pre-fracturing position, and the angle between the wellbore inclination and the coal seam dip is greater than 3°, the drill string will be withdrawn to the first reserved sidetracking point, and the suspended sidetracking operation will be continued to the first pre-fracturing position. The location of the well section encountering the coal seam will be determined based on the measurement while drilling data and comprehensive logging data, and the expected geological profile will be revised accordingly. Step 3.2, according to the drilling trajectory determined in step 2, complete the coal exploration drilling of each fracturing section in sequence from the first pre-fracturing position to the last pre-fracturing position; If the coal seam is encountered when the drilling distance of the coal exploration drill in the fracturing section is less than or equal to half of the preset fracturing position spacing, then: If the angle between the wellbore inclination and the coal seam dip is less than or equal to 3°, and the distance between the drilled pre-fracturing position and the top of the coal seam is less than or equal to the designed distance between the horizontal section of the horizontal well and the coal seam roof, then the wellbore should be twisted and increased inclination in the downdip direction of the formation from the coal point and the drilling should continue to the next pre-fracturing position. The location of the well section encountering the coal seam should be determined based on the collected measurement while drilling data and comprehensive logging data, and the expected geological profile should be revised accordingly. If the angle between the wellbore inclination and the coal seam dip is greater than 3°, or the distance between the drilled pre-fracturing position and the top of the coal seam is greater than the designed distance between the horizontal section of the horizontal well and the coal seam roof, the well section where the coal seam is encountered is determined based on the collected measurement while drilling data and comprehensive logging data, the expected geological profile is corrected, and the drill tool is withdrawn to the reserved sidetracking point and suspended sidetracking is carried out to the next pre-fracturing position; If the coal seam is encountered when the exploration drilling distance in the fracturing section is greater than half of the preset fracturing position spacing, then: The expected geological profile is modified according to the location of the well section where the coal seam is encountered, and then the drill tool is withdrawn to the sidetracking point, and the suspended sidetracking construction is continued to the next pre-fracturing position.

2. The method for determining the horizontal trajectory of a horizontal well in a surface coal seam roof according to claim 1, wherein: The step 1 specifically includes: outlining the undulating contours and structural positions of each rock layer above the coal seam roof based on the horizontal section projection orientation, longitudinal scale and transverse scale in combination with geological data, and then filling in the corresponding lithology symbols and structural symbols in each outlined rock layer to draw an expected geological profile of the horizontal section of the horizontal well.

3. The method for determining the horizontal trajectory of a horizontal well in a surface coal seam roof according to claim 1, wherein: The designed distance between the horizontal section of the horizontal well and the coal seam roof is 0~5 meters.

4. The method for determining the horizontal trajectory of a horizontal well in a surface coal seam roof according to claim 1, wherein: The preset fracturing position spacing is 30 to 150 meters.

5. The method for determining the horizontal trajectory of a horizontal well in a surface coal seam roof according to claim 1, wherein: The reserved side drilling points are spaced 30 to 100 meters apart.

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