A method for shale gas target body identification and high drilling encounter control

Abstract

The present invention discloses a method for shale gas target identification and high drilling encounter control, which relates to the technical field of unconventional oil and gas stimulation and enhancement, and specifically includes the following steps: Step S1: Determine the target position of the shale gas horizontal well fracture network fracturing; Step S2: Select the drilling method according to the well conditions; Step S3: Control the drilling encounter situation of the target according to the geological characteristics and drilling characteristics to obtain a high drilling encounter rate; Step S4: Carry out differential completion hole layout for the horizontal section where the target is missed; In the present invention, the stress difference index and the brittleness index are used for target identification, and a method for controlling the drilling of high drilling encounter targets is formed by using the relationship between the stress difference index curve, the brittleness index curve morphology and the gamma logging curve, realizing the identification and drilling of the optimal target window of the horizontal well, and improving the single-well production of the shale gas horizontal well.

Description

Technical Field

[0001] The present invention relates to the technical field of unconventional oil and gas stimulation and transformation, and particularly relates to a method for shale gas target body identification and high drilling encounter control. Background Art

[0002] Developing shale gas is currently the most effective way to achieve large-scale production of natural gas in China; current statistical results show that marine shale gas in the Sichuan Basin has the most mining value; however, 86% of the shale gas in the basin is concentrated in areas with relatively large burial depths (depth greater than 3500 m), which brings many problems to the drilling and completion engineering. For example, as the burial depth increases, the bottom hole temperature increases, and the temperature adaptation conditions for drilling and completion tools are more demanding; the in-situ stress is greater, the difference in in-situ stress is more obvious, and the difficulty of effectively transforming the reservoir by hydraulic fracturing increases.

[0003] The identification of the target body is the basic guarantee measure to achieve high production in the fracture network fracturing of shale gas horizontal wells; at present, a large number of domestic scholars have conducted research in this area; documents such as "Analysis of influencing factors of shale gas horizontal well production", "Identification of sweet spots in shale gas reservoirs using comprehensive geophysical prediction methods - Taking the Lower Silurian Longmaxi Formation in Changning Block of Sichuan Basin as an example", "Brittleness evaluation and'sweet spot layer' prediction of Wufeng Formation - Longmaxi Formation in Sichuan Basin", "Comprehensive logging evaluation of shale gas reservoir quality", etc., and patents such as "A method for selecting target windows of shale gas horizontal wells", "A method for selecting target windows of marine shale gas horizontal wells based on high-frequency sequence stratigraphy", etc. mainly use static geological parameters to select the target body, following the target body identification idea of conventional oil and gas reservoirs, and failing to achieve the decision-making of shale gas geological engineering integration; documents such as "A new method for evaluating the compressibility of shale gas reservoirs", "New brittleness factors and their application in the prediction of mud shale reservoirs" consider engineering parameters, but require more parameters and the calculation process is more cumbersome, and it is difficult to guarantee the timeliness in actual field applications; moreover, most of the current target body identification methods and technologies fail to consider the geological conditions and engineering conditions of the location where the shale gas horizontal well is located, that is, they fail to form corresponding methods and technologies for drilling the target body well and drilling the target body accurately, resulting in frequent off-target phenomena in the field drilling process, and the production of a large number of wells is generally low due to the low proportion of encountering the target body.

[0004] In addition, due to technological advancements, shale gas horizontal wells are trending towards increasing horizontal section lengths. The length of horizontal wells has increased from 1000m to an average of 1800 - 2000m. The increase in the length of the horizontal section and the burial depth has caused the sum of the vertical section, build section, and horizontal section of the entire shale gas horizontal well to generally exceed 4500m, resulting in higher requirements for the drilled length of the target body. At the same time, challenges are posed in terms of drill string wear and drilling efficiency. Also, even if the target body is identified, it is difficult to ensure a high drilling encounter rate. During pre-drilling and drilling operations in the field, data on the reservoir is mostly obtained through pre-drilling coring, mud logging during drilling, and logging while drilling. The coring data is discontinuous and cannot be directly used to guide drilling and completion. With the current fast-paced construction process, the data volume from mud logging and logging while drilling may not be sufficient to obtain all the parameter indicators mentioned in the aforementioned literature and patents, making it difficult to apply existing methods in practice. Summary of the Invention

[0005] The object of the present invention is to address the problems that for most current target body identification methods and technologies, corresponding methods and technologies for successfully drilling and accurately drilling the target body have not been formed in a supporting manner. This has led to frequent target miss phenomena during the drilling process in the field, low production rates for a large number of wells due to a low proportion of encountering the target body, and with the increasing length of the horizontal section of shale gas horizontal wells as technology progresses, it is not always possible to obtain all the parameter indicators mentioned in the aforementioned literature and patents, making it difficult to apply existing methods in practice. The present invention provides a shale gas target body identification and high drilling encounter control method to solve these problems.

[0006] The technical solution of the present invention is as follows:

[0007] A shale gas target body identification and high drilling encounter control method includes the following steps:

[0008] Step S1: Determine the target body position for hydraulic fracturing of the shale gas horizontal well;

[0009] Step S2: Select the drilling method according to the well conditions;

[0010] Step S3: Control the drilling encounter situation of the target body according to geological characteristics and drilling characteristics to obtain a high drilling encounter rate;

[0011] Step S4: Conduct differential completion hole placement for the horizontal section with target miss.

[0012] Furthermore, the detailed steps of step S1 are as follows:

[0013] Step S1a: Ensure that there is at least 1 vertical well near the planned horizontal well;

[0014] Step S1b: Select one vertical well closest to the pre-drilled horizontal well, collect the burial depths and rock densities corresponding to each measuring point of the vertical well, and calculate the in-situ stress magnitudes and stress difference coefficients of each measuring point;

[0015] Step S1c: Collect the uranium-free gamma data corresponding to each measuring point of the vertical well selected in Step S1b, and calculate the mechanical brittleness magnitudes of each measuring point;

[0016] Step S1d: Collect the mass fractions of siliceous minerals and carbonate minerals corresponding to each measuring point of the vertical well selected in Step S1b, and calculate the mineral brittleness magnitudes of each measuring point;

[0017] Step S1e: Calculate the fracturing index based on the mechanical brittleness magnitudes and mineral brittleness magnitudes of each measuring point;

[0018] Step S1f: Based on the stress difference coefficient calculated in Step S1b and the fracturing index calculated in Step S1e, plot the logging interpretation curves of the stress difference coefficient and the fracturing index of the vertical well selected in Step S1b;

[0019] Step S1g: Compare the peaks of the logging interpretation curves of the stress difference coefficient and the fracturing index, and identify the corresponding measuring points as different types of targets according to different comparison results.

[0020] Further, the identification rules in Step S1g are as follows:

[0021] When the peaks of the two curves completely overlap, identify the measuring point corresponding to the peak as a Type A target;

[0022] When the peaks of the two curves partially overlap, identify the measuring point corresponding to the intersection position of the two curves as a Type B target;

[0023] When the peaks of the two curves do not overlap and the distance between the peaks of the two curves is less than the thickness of the peak in the longitudinal direction, identify the measuring point corresponding to the middle position between the peaks of the two curves as a Type C target;

[0024] When the peaks of the two curves do not overlap and the distance between the peaks of the two curves is greater than the thickness of the peak in the longitudinal direction, use the measuring point corresponding to the peak of the logging interpretation curve of the stress difference coefficient as the target.

[0025] Further, the selection rules for Step S2 are as follows:

[0026] When the sum of the vertical section length a, the build section length b, and the horizontal section length c of the pre-drilled horizontal well is less than 4500 m, the horizontal section of the pre-drilled horizontal well is drilled using the rotary steerable + logging-while-drilling drilling method;

[0027] When the sum of the vertical well section length a, the build section length b, and the horizontal section length c of the pre-drilled horizontal well is greater than 4500m; if the sum of the vertical well section length a and the build section length b is less than 4500m, the horizontal section length c is divided into the front part length c1 and the rear part length c2 of the horizontal section. Among them, the sum of the front part length c1 of the horizontal section, the vertical well section length a, and the build section length b is equal to 4500m. Then, the front part of the horizontal section of the pre-drilled horizontal well is drilled using the rotary steerable + logging-while-drilling drilling method, and the rear part of the horizontal section is drilled using the conventional positive displacement motor + logging-while-drilling drilling method; if the sum of the vertical well section length a and the build section length b is greater than 4500m, then the horizontal section of the pre-drilled horizontal well is drilled using the conventional positive displacement motor + logging-while-drilling drilling method;

[0028] When the buried depth of the horizontal section of the pre-drilled horizontal well exceeds 3500m, or the bottom hole temperature is higher than 130°C, the conventional positive displacement motor + logging-while-drilling drilling method is used for drilling, and a surface drill string torsional oscillation system + all-metal high-temperature resistant hydraulic oscillator is also required for assistance.

[0029] Furthermore, the detailed steps of step S3 are as follows:

[0030] Step S3a: Collect the gamma data corresponding to each logging point of the vertical well selected in step S1b;

[0031] Step S3b: Draw a gamma logging interpretation curve based on the collected gamma data;

[0032] Step S3c: Identify the peak position of the gamma logging curve;

[0033] Step S3d: Denote the buried depth corresponding to the middle position of the wave peak corresponding to the peak position of the gamma curve as h1, and the buried depth corresponding to the middle position of the identified target as h0. When h1 < h0, it indicates that the target is below the gamma peak. During drilling, focus on drilling at the position of |h1 - h0| below the gamma curve peak; when h1 > h0, it indicates that the target is above the gamma peak. During drilling, focus on drilling at the position of |h1 - h0| above the gamma curve peak; when h1 = h0, then drill at the position where the gamma peak is located.

[0034] Furthermore, the detailed steps of step S4 are as follows:

[0035] Step S4a: When the length of a single off-target horizontal section is less than 5m, no differential completion hole layout measures are taken;

[0036] Step S4b: When the length of a single off-target horizontal section is between 5m and 40m, then split this part of the horizontal section into two parts of the same length and distribute them equally to the adjacent left and right fracturing sections for fracturing operations;

[0037] Step S4c: When the length of a single off-target horizontal section is greater than 40 m, this part of the horizontal section is taken as an independent fracturing section for fracturing operations, and directional perforation layout is carried out simultaneously; when the off-target position is above the target body, directional downward perforation operations are adopted, and when the off-target position is below the target body, directional upward perforation operations are adopted.

[0038] Further, the in-situ stress magnitudes at each measuring point in step S1b are calculated using the following method:

[0039] Step S1b-a: Calculate the P-wave to S-wave ratio at each measuring point based on the rock density at each measuring point. The formula for calculating the P-wave to S-wave ratio at each measuring point is as follows:

[0040]

[0041] In the formula,

[0042] R—the P-wave to S-wave ratio at each measuring point;

[0043] ρ—the rock density at each measuring point;

[0044] e—a mathematical constant;

[0045] Step S1b-b: Calculate the Poisson's ratio corresponding to each measuring point based on the P-wave to S-wave ratio. The formula for calculating the Poisson's ratio corresponding to each measuring point is as follows:

[0046]

[0047] In the formula,

[0048] ν—the Poisson's ratio corresponding to each measuring point;

[0049] Step S1b-c: Calculate the pore pressure and vertical stress at each measuring point based on the burial depth; the formulas for calculating the pore pressure and vertical stress are as follows:

[0050] σp = ρoverburdengH

[0051] σz = ρgH

[0052] In the formula,

[0053] σ p —the pore pressure at each measuring point;

[0054] ρ overburden —the rock density of the overlying strata;

[0055] g—the acceleration due to gravity;

[0056] H—the burial depth at each measuring point;

[0057] σ z —the vertical stress at each measuring point;

[0058] Steps S1b-d: Calculate the maximum and minimum horizontal principal stresses at each measuring well point according to the acoustic wave data, Poisson's ratio, pore pressure, and vertical stress using the following formula:

[0059]

[0060]

[0061] In the formula,

[0062] σ y — The maximum horizontal principal stress at each measuring well point;

[0063] σ x — The minimum horizontal principal stress at each measuring well point;

[0064] DTC — The acoustic wave at each measuring well point;

[0065] Steps S1b-e: Calculate the horizontal principal stress difference at each measuring well point based on the maximum and minimum horizontal principal stresses, and calculate using the following formula:

[0066] Δσ = σ y - σ x

[0067] In the formula,

[0068] Δσ — The horizontal principal stress difference at each measuring well point;

[0069] Steps S1b-f: Construct a stress difference index, and the stress difference index is calculated using the following formula:

[0070]

[0071] In the formula,

[0072] P stress — The stress difference index.

[0073] Furthermore, the calculation formula for the mechanical brittleness of each measuring well point in step S1c is as follows:

[0074]

[0075] In the formula,

[0076] B mechanics — The mechanical brittleness of each measuring well point;

[0077] KTH — The uranium-free gamma value of each measuring well point;

[0078] KTH max — The maximum uranium-free gamma value in the measuring well points;

[0079] KTH min — The minimum uranium-free gamma value in the measurement well points;

[0080] Furthermore, the calculation formula for the mineral brittleness of each measurement well point in step S1d is as follows:

[0081] B mineral = B Si + B Ca

[0082] In the formula,

[0083] B mineral — The mineral brittleness of each measurement well point;

[0084] B Si — The mass fraction of siliceous minerals at each measurement well point;

[0085] B Ca — The mass fraction of carbonate minerals at each measurement well point;

[0086] The calculation formula for the fracturing index of each measurement well point in step S1e is as follows:

[0087] Bo = (B mechanics + B mineral ) / 2

[0088] In the formula,

[0089] Bo — The fracturing index of each measurement well point.

[0090] Furthermore, the content of the auxiliary of the surface drill string torsional oscillation system + all-metal high-temperature resistant hydraulic oscillator includes:

[0091] The surface drill string torsional oscillation system drives the drill tool to swing forward and backward continuously by controlling the top drive, so that the upper drill string is in a rotational motion state;

[0092] The all-metal high-temperature resistant hydraulic oscillator generates axial peristalsis along the direction of the pipe string, converts static friction into dynamic friction, and reduces the drill pressure loss and drill string vibration.

[0093] Compared with the existing technology, the beneficial effects of the present invention are:

[0094] 1. A method for shale gas target body identification and high drilling encounter control. Compared with the prior art, the present invention pays more attention to considering the in-situ stress conditions, optimizes the stress difference index, and optimizes the original stress difference index that cannot reflect the differences between shallow burial, low stress and deep burial, high stress; pays more attention to the rapid usability of the method in the field and optimizes the complex calculation process in the original technology; innovates the usage of evaluation indicators, proposes to use the curve shape method, and links it with the gamma logging curve most commonly used in the drilling guidance process to achieve the purpose of rapid identification and rapid adjustment, and can ensure that in the drilling process, the off-target phenomenon can be quickly corrected; finally, supplementary measures for the off-target situation are also provided to ensure the transformation effect; overall, the present invention uses the stress difference index and brittleness index to identify the target body, forms a method for controlling high drilling encounter targets by using the relationship between the stress difference index curve, brittleness index curve shape and gamma logging curve, realizes the identification and drilling of the optimal target window of the horizontal well, and realizes the improvement of the single-well production of the shale gas horizontal well. BRIEF DESCRIPTION OF THE DRAWINGS

[0095] Figure 1 It is a flowchart of a method for shale gas target body identification and high drilling encounter control;

[0096] Figure 2 It is a distribution map of vertical wells and partial horizontal well platforms in the CN block in the southern part of the Sichuan Basin in Example 2;

[0097] Figure 3 It is the basic logging curve in the CN block in the southern part of the Sichuan Basin in Example 2;

[0098] Figure 4 It is the relevant logging interpretation curve in the CN block in the southern part of the Sichuan Basin in Example 2;

[0099] Figure 5 It is a schematic diagram of the test production of each well on the B1 - B7 platforms in the CN block in the southern part of the Sichuan Basin in Example 2. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0100] It should be noted that relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprising", "including" or any other variation thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the phrase "comprising a..." does not exclude the presence of additional identical elements in the process, method, article or device comprising the element.

[0101] The features and performance of the present invention will be further described in detail below in conjunction with the embodiments.

[0102] Embodiment 1

[0103] Please refer to Figures 1-3 , a shale gas target recognition and high drilling encounter control method, comprising the following steps:

[0104] Step S1: Determine the target position for the fracturing of the shale gas horizontal well with a network of fractures; the main purpose of step S1 is to optimize the target position most suitable for the fracturing of the shale gas horizontal well with a network of fractures;

[0105] Step S2: Select the drilling method according to the well conditions; the main purpose of step S2 is to optimize the most suitable drilling method according to the conditions of different shale gas horizontal wells;

[0106] Step S3: Control the drilling encounter situation of the target according to the geological characteristics and drilling characteristics to obtain a high drilling encounter rate;

[0107] Step S4: Perform differential completion hole layout for the off-target horizontal section and prepare for fracturing.

[0108] The detailed steps of step S1 are as follows:

[0109] Step S1a: Ensure that there is at least 1 vertical well near the pre-drilled horizontal well; it should be ensured that there is at least 1 vertical well within 10 km of the pre-drilled horizontal well. If there is no vertical well, the conditions for target recognition and high drilling encounter control are not available, and relevant operations such as vertical well drilling should be preferentially carried out;

[0110] Step S1b: Select the vertical well closest to the pre-drilled horizontal well, collect the buried depth, rock density, and acoustic wave data corresponding to each measuring point of the vertical well, and calculate the in-situ stress magnitude and stress difference coefficient of each measuring point;

[0111] Specifically, the in-situ stress magnitude of each measuring point in step S1b is calculated by the following method:

[0112] Step S1b-a: Calculate the P-wave to S-wave ratio of each measuring point according to the rock density of each measuring point. The calculation formula for the P-wave to S-wave ratio of each measuring point is as follows:

[0113]

[0114] In the formula,

[0115] R—the P-wave to S-wave ratio of each measuring point, dimensionless;

[0116] ρ—the rock density of each measuring point, unit: g / cm 3 ;

[0117] e—Mathematical constant;

[0118] Step S1b-b: Calculate the Poisson's ratio corresponding to each measuring point according to the P-wave to S-wave ratio. The calculation formula for the Poisson's ratio corresponding to each measuring point is as follows:

[0119]

[0120] In the formula,

[0121] ν—Poisson's ratio corresponding to each measuring point, dimensionless;

[0122] Step S1b-c: Calculate the pore pressure and vertical stress of each measuring point according to the burial depth. The calculation formulas for the pore pressure and vertical stress are as follows:

[0123] σ p =ρ overburden gH (3)

[0124] σ z =ρgH (4)

[0125] In the formula,

[0126] σ p —Pore pressure of each measuring point, unit: MPa;

[0127] ρ overburden —Rock density of overlying strata, unit: g / cm 3 ;

[0128] g—Acceleration of gravity, unit: N / kg

[0129] H—Burial depth of each measuring point, unit: m;

[0130] σ z —Vertical stress of each measuring point, unit: MPa;

[0131] Step S1b-d: Calculate the maximum and minimum horizontal principal stresses of each measuring point according to the acoustic wave data, Poisson's ratio, pore pressure, and vertical stress using the following formula:

[0132]

[0133]

[0134] In the formula,

[0135] σ y —Maximum horizontal principal stress of each measuring point;

[0136] σ x —Minimum horizontal principal stress of each measuring point;

[0137] DTC - Acoustic wave at each measurement well point;

[0138] Steps S1b - e: Calculate the horizontal principal stress difference at each measurement well point based on the maximum and minimum horizontal principal stresses, and calculate using the following formula:

[0139] Δσ = σ y - σ x (7)

[0140] In the formula,

[0141] Δσ—Horizontal principal stress difference at each measurement well point;

[0142] Steps S1b - f: Construct a stress difference index, and the stress difference index is calculated using the following formula:

[0143]

[0144] In the formula,

[0145] P stress —Stress difference index.

[0146] Steps S1c: Collect the uranium - free gamma data corresponding to each measurement well point of the vertical well selected in Step S1b, and calculate the mechanical brittleness of each measurement well point;

[0147] Specifically, the calculation formula for the mechanical brittleness of each measurement well point in Step S1c is as follows:

[0148]

[0149] In the formula,

[0150] B mechanics —Mechanical brittleness of each measurement well point, dimensionless;

[0151] KTH—Uranium - free gamma value of each measurement well point, unit: API;

[0152] KTH max —The maximum uranium - free gamma value in the measurement well point, unit: API;

[0153] KTH min —The minimum uranium - free gamma value in the measurement well point, unit: API;

[0154] Steps S1d: Collect the mass fraction of siliceous minerals and the mass fraction of carbonate minerals corresponding to each measurement well point of the vertical well selected in Step S1b, and calculate the mineral brittleness of each measurement well point;

[0155] Specifically, the calculation formula for the mineral brittleness of each measurement well point in Step S1d is as follows:

[0156] Bmineral = B Si + B Ca (10)

[0157] Wherein,

[0158] B mineral —Mineral brittleness of each measurement well point, dimensionless;

[0159] B Si —Mass fraction of siliceous minerals at each measurement well point, unit: %;

[0160] B Ca —Mass fraction of carbonate minerals at each measurement well point, unit: %;

[0161] Step S1e: Calculate the fracturing index based on the mechanical brittleness and mineral brittleness of each measurement well point;

[0162] Specifically, the calculation formula of the fracturing index of each measurement well point in step S1e is as follows:

[0163] Bo = (B mechanics + B mineral ) / 2 (11)

[0164] Wherein,

[0165] Bo—Fracturing index of each measurement well point.

[0166] Step S1f: Draw the logging interpretation curve of the stress difference coefficient and the logging interpretation curve of the fracturing index of the vertical well selected in step S1b according to the stress difference coefficient calculated in step S1b and the fracturing index calculated in step S1e;

[0167] Step S1g: Compare the peaks of the logging interpretation curve of the stress difference coefficient and the logging interpretation curve of the fracturing index, and identify the corresponding measurement well points as different types of targets according to different comparison results; The peak shall not be less than 2 m thick and not more than 5 m thick in the vertical direction.

[0168] Specifically, the identification rule in step S1g is:

[0169] When the peaks of the two curves completely overlap, that is, one peak can completely cover the other peak, or the two peaks can cover each other, then the measurement well point corresponding to the peak is identified as type A target;

[0170] When the peaks of the two curves partially overlap, that is, neither of the two peaks can completely cover each other, then the measurement well point corresponding to the intersection position of the two curves is identified as type B target;

[0171] When the peaks of the two curves do not overlap, the following two situations will occur:

[0172] 1. When the peaks of two curves do not overlap and the distance between the peaks of the two curves is less than the thickness of the peak in the longitudinal direction, the logging point corresponding to the middle position between the peaks of the two curves is identified as a Class C target

[0173] 2. When the peaks of two curves do not overlap and the distance between the peaks of the two curves is greater than the thickness of the peak in the longitudinal direction, the logging point corresponding to the peak of the stress difference coefficient logging interpretation curve is used as the target

[0174] The selection rules for step S2 are as follows

[0175] When the sum of the vertical section length a, the build section length b, and the horizontal section length c of the pre-drilled horizontal well is less than 4500 m, the horizontal section of the pre-drilled horizontal well is drilled using the rotary steerable + logging-while-drilling drilling method

[0176] When the sum of the vertical section length a, the build section length b, and the horizontal section length c of the pre-drilled horizontal well is greater than 4500 m; if the sum of the vertical section length a and the build section length b is less than 4500 m, the horizontal section length c is divided into the front horizontal section length c1 and the rear horizontal section length c2, where the sum of the front horizontal section length c1, the vertical section length a, and the build section length b is equal to 4500 m, then the front horizontal section of the pre-drilled horizontal well is drilled using the rotary steerable + logging-while-drilling drilling method, and the rear horizontal section is drilled using the conventional positive displacement motor + logging-while-drilling drilling method; if the sum of the vertical section length a and the build section length b is greater than 4500 m, then the horizontal section of the pre-drilled horizontal well is drilled using the conventional positive displacement motor + logging-while-drilling drilling method

[0177] When the buried depth of the horizontal section of the pre-drilled horizontal well exceeds 3500 m, or the bottom hole temperature is higher than 130 °C, the drilling is carried out using the conventional positive displacement motor + logging-while-drilling drilling method, and a surface drill string torsional oscillation system + all-metal high-temperature-resistant hydraulic oscillator are also required for assistance

[0178] The detailed steps of step S3 are as follows

[0179] Step S3a: Collect the gamma data corresponding to each logging point of the vertical well selected in step S1b

[0180] Step S3b: Draw a gamma logging interpretation curve based on the collected gamma data

[0181] Step S3c: Identify the peak position of the gamma logging curve; the peak corresponding to the peak position of the gamma logging curve is not restricted by the thickness in the longitudinal direction

[0182] Step S3d: Denote the burial depth corresponding to the middle position of the wave crest at the peak position of the gamma curve as h1, and the burial depth corresponding to the middle position of the identified target body as h0. When h1 < h0, it indicates that the target body is below the gamma peak. During the drilling process, focus on drilling at the position of |h1 - h0| below the gamma curve peak; when h1 > h0, it indicates that the target body is above the gamma peak. During the drilling process, focus on drilling at the position of |h1 - h0| above the gamma curve peak; when h1 = h0, then drill at the position where the gamma peak is located.

[0183] In step S4, it should be noted that: missing the target means the part where the target body is not encountered during the horizontal section drilling; specifically, the detailed steps of step S4 are as follows:

[0184] Step S4a: When the length of a single horizontal section with missed target is less than 5m, no differential completion perforation measures are taken, and the fracturing operation can be carried out as scheduled;

[0185] Step S4b: When the length of a single horizontal section with missed target is between 5m and 40m, then split this part of the horizontal section into two parts of the same length and distribute them evenly to the adjacent left and right fracturing sections for fracturing operations;

[0186] Step S4c: When the length of a single horizontal section with missed target is greater than 40m, then take this part of the horizontal section as an independent fracturing section for fracturing operations, and at the same time carry out directional perforation arrangement; when the missed target position is above the target body, directional downward perforation operation is adopted, and when the missed target position is below the target body, directional upward perforation operation is adopted.

[0187] Embodiment 2

[0188] Embodiment 2 is the actual application of Embodiment 1 in the CN Block in the southern part of the Sichuan Basin; Figure 2 It is the topographic structure diagram of the CN Block in the southern part of the Sichuan Basin.

[0189] Step S1: Determine the target body position for the shale gas horizontal well fracture network fracturing.

[0190] Step S1a: Ensure that there is at least 1 vertical well near the pre-drilled horizontal well; as Figure 2 shown, there are more than a dozen vertical wells such as Well A and Well B in this area for selection, with the conditions for target body identification and high drilling encounter control;

[0191] Step S1b: Select 1 vertical well closest to the pre-drilled horizontal well, collect the burial depth, rock density, and acoustic wave data corresponding to each logging point of the vertical well, and calculate and obtain the in-situ stress magnitude and stress difference coefficient of each logging point; in this embodiment, Well B is selected as the vertical well used in the specific implementation method, and at the same time, the basic logging parameters that need to be calculated later are sorted out, as shown in the appendix Figure 3; Its distances to 7 platforms such as B1 to B7 are less than 10 km and it is the closest compared to other vertical wells; Collect the burial depths, densities, and acoustic wave data corresponding to each measuring point of this well, calculate the in-situ stress magnitudes at each measuring point of the vertical well, and obtain the stress difference coefficient according to the calculation, see attachment Figure 4 ;

[0192] Step S1b-a: Calculate the P-wave to S-wave ratio at each measuring point according to the rock density of each measuring point; Use formula (1) to calculate the P-wave to S-wave ratio at each measuring point, see attachment Figure 4 ;

[0193] Step S1b-b: Calculate the Poisson's ratio corresponding to each measuring point according to the P-wave to S-wave ratio; Use formula (2) to calculate the Poisson's ratio corresponding to each measuring point, see attachment Figure 4 ;

[0194] Step S1b-c: Calculate the pore pressure and vertical stress at each measuring point according to the burial depth; Use formula (3)(4) to calculate the pore pressure and vertical stress at each measuring point, see attachment Figure 4 ;

[0195] Step S1b-d: Calculate the maximum and minimum horizontal principal stresses at each measuring point according to the acoustic wave data, Poisson's ratio, pore pressure, and vertical stress; Use formula (5)(6) to calculate the maximum and minimum horizontal principal stresses at each measuring point, see attachment Figure 4 ;

[0196] Step S1b-e: Calculate the horizontal principal stress difference at each measuring point according to the maximum and minimum horizontal principal stresses; Use formula (7) to calculate the horizontal principal stress difference at each measuring point, see attachment Figure 4 ;

[0197] Step S1b-f: Construct the stress difference index; Use formula (8) to calculate the stress difference index at each measuring point, see attachment Figure 4 。

[0198] Step S1c: Collect the uranium-free gamma data corresponding to each measuring point of Well B, and calculate the mechanical brittleness magnitude at each measuring point; Use formula (9) to calculate the mechanical brittleness at each measuring point, see attachment Figure 4 ;

[0199] Step S1d: Collect the mass fractions of siliceous minerals and carbonate minerals corresponding to each measuring point of the vertical well selected in Step S1b, and calculate the mineral brittleness magnitude at each measuring point; Use formula (10) to calculate the mineral brittleness magnitude at each measuring point, see attachment Figure 4 ;

[0200] Step S1e: Calculate the fracturing index based on the mechanical brittleness and mineral brittleness of each measurement well point; calculate the fracturing index of each measurement well point using formula (11), see Appendix Figure 4 ;

[0201] Step S1f: Draw the logging interpretation curve of the stress difference coefficient and the logging interpretation curve of the fracturing index for the vertical well selected in Step S1b according to the stress difference coefficient calculated in Step S1b and the fracturing index calculated in Step S1e; see Appendix Figure 4 ;

[0202] Step S1g: Compare the peaks of the logging interpretation curve of the stress difference coefficient and the logging interpretation curve of the fracturing index, and identify the corresponding measurement well points as different types of targets according to different comparison results; in this embodiment, as Figure 4 can be seen, the peaks of the two curves of Well B are in a superposed state, and it is identified as Type A target.

[0203] Step S2: Select the drilling method according to the well conditions; in this embodiment, taking Well B1-1 as an example, this well is one of the pre-drilled horizontal wells, and the total length of the vertical well section and the build section is 3200m, less than 4500m. The designed horizontal section is drilled for 1800m. Then, the first 1300m is drilled using the drilling method of rotary steerable + logging while drilling, and the last 300m is drilled using the drilling method of conventional screw + logging while drilling; the bottom hole temperature of this well is about 80-90°C, and the average buried depth is about 3020m, so the ground drill string torsional oscillation system + all-metal high-temperature resistant hydraulic oscillator is not used for assistance.

[0204] Step S3: Control the target encounter situation according to the geological characteristics and drilling characteristics to obtain a high encounter rate;

[0205] Specifically, the detailed steps of Step S3 are as follows:

[0206] Step S3a: Collect the gamma data corresponding to each measurement well point of Well B;

[0207] Step S3b: Draw the gamma logging interpretation curve according to the collected gamma data, see Appendix Figure 3 ;

[0208] Step S3c: Identify the peak position of the gamma logging curve; the peak corresponding to the peak position of the gamma logging curve is not restricted by the vertical thickness;

[0209] Step S3d: Identify the position relationship between the gamma peak position and the target; the middle depth of the gamma peak of Well B is 3172.5m, and the middle position depth of the target is 3169m. Therefore, during the drilling process, keep a distance of 3.5m above the high gamma position for drilling.

[0210] Step S4: Differentiated completion perforation is carried out for the off-target horizontal section, and fracturing is prepared; in this embodiment, Well B1-1 is well implemented according to the above steps without off-target; taking Well B8-2 as an example, this well does not use the above technology for drilling, and part of the horizontal section at 3985-4042 m is off-target to the lower part of the high gamma, with a section length of 4042 - 3985 = 57 m. Therefore, this part is taken as a separate section, and the perforation position is designed to be directed upward.

[0211] Overall, good drilling and completion transformation effects have been achieved on Platforms B1 - B7, and the test production is all above 20×10 4 m 3 / d, see the appendix Figure 4 。

[0212] The above embodiments only represent the specific implementation manners of the present application. The description is relatively specific and detailed, but it should not be construed as a limitation on the protection scope of the present application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the technical solution of the present application, several deformations and improvements can still be made, and these all belong to the protection scope of the present application.

Claims

1. A method for shale gas target identification and high drilling encounter control, characterized in that, It includes the following steps: Step S1: Determine the target position of the shale gas horizontal well fracture network fracturing; Step S2: Select the drilling method according to the well conditions; Step S3: Control the drilling encounter situation of the target according to the geological characteristics and drilling characteristics to obtain a high drilling encounter rate; Step S4: Conduct differential completion hole layout for the off-target horizontal section; The detailed steps of the said Step S1 are as follows: Step S1a: Ensure that there is at least one vertical well near the pre-drilled horizontal well; Step S1b: Select one vertical well closest to the pre-drilled horizontal well, collect the buried depth, rock density and acoustic wave data corresponding to each logging point of the said vertical well, and calculate and obtain the in-situ stress magnitude and stress difference coefficient of each logging point; Step S1c: Collect the natural gamma data corresponding to each logging point of the vertical well selected in Step S1b, and calculate and obtain the mechanical brittleness magnitude of each logging point; Step S1d: Collect the mass fraction of siliceous minerals and the mass fraction of carbonate minerals corresponding to each logging point of the vertical well selected in Step S1b, and calculate and obtain the mineral brittleness magnitude of each logging point; Step S1e: Calculate the fracturing index based on the mechanical brittleness magnitude and mineral brittleness magnitude of each logging point; Step S1f: Based on the stress difference coefficient calculated in Step S1b and the fracturing index calculated in Step S1e, draw the logging interpretation curve of the stress difference coefficient and the logging interpretation curve of the fracturing index of the vertical well selected in Step S1b; Step S1g: Compare the peaks of the stress difference coefficient logging interpretation curve and the fracturing index logging interpretation curve, and identify the corresponding logging points as different types of targets according to different comparison results; The detailed steps of the said Step S3 are as follows: Step S3a: Collect the gamma data corresponding to each logging point of the vertical well selected in Step S1b; Step S3b: Draw the gamma logging interpretation curve based on the collected gamma data; Step S3c: Identify the peak position of the gamma logging curve; Step S3d: Record the burial depth corresponding to the middle position of the wave peak corresponding to the peak position of the gamma curve as h 1, and record the burial depth corresponding to the middle position of the identified target as h 0, when h 1 < h 0, it indicates that the target is below the gamma peak. During the drilling process, focus on drilling at a position below the gamma curve peak. h 1 - h 0 | position; when h 1 > h 0, it indicates that the target is above the gamma peak. During the drilling process, focus on drilling at a position above the gamma curve peak. h 1 - h 0 | position; when h 1 = h 0, then drill at the position where the gamma peak is located. The detailed steps of the said Step S4 are as follows: Step S4a: When the length of a single off-target horizontal section is less than 5m, no differential completion hole layout measures are taken; Step S4b: When the length of a single off-target horizontal section is between 5m and 40m, split this horizontal section into two parts of the same length and evenly distribute them to the adjacent left and right fracturing sections for fracturing operations; Step S4c: When the length of a single off-target horizontal section is greater than 40m, take this horizontal section as an independent fracturing section for fracturing operations, and at the same time conduct directional perforation layout; when the off-target position is above the target, use directional downward perforation operations, and when the off-target position is below the target, use directional upward perforation operations.

2. The method for shale gas target identification and high drilling encounter control according to claim 1, wherein The identification rules in the said Step S1g are as follows: When the peaks of the two curves completely overlap, identify the logging point corresponding to this peak as Class A target; When the peaks of the two curves partially overlap, identify the logging point corresponding to the intersection position of the two curves as Class B target; When the peaks of the two curves do not overlap and the distance between the peaks of the two curves is less than the thickness of the peak in the longitudinal direction, identify the middle position corresponding to the peaks of the two curves as Class C target; When the peaks of two curves do not overlap and the distance between the peaks of the two curves is greater than the thickness of the peak in the longitudinal direction, the logging point corresponding to the peak of the stress difference coefficient logging interpretation curve is used as the target body.

3. A method for shale gas target body identification and high drilling encounter control according to claim 1, characterized in that, The selection rules of step S2 are as follows: When the sum of the vertical well section length a, the build section length b, and the horizontal section length c of the pre-drilled horizontal well is less than 4500 m, the horizontal section of the pre-drilled horizontal well is drilled by the drilling method of rotary steerable + logging while drilling; When the sum of the vertical well section length a, the build section length b, and the horizontal section length c of the pre-drilled horizontal well is greater than 4500 m; if the sum of the vertical well section length a and the build section length b is less than 4500 m, the horizontal section length c is divided into the front section length c1 of the horizontal section and the rear section length c2 of the horizontal section, where the sum of the front section length c1 of the horizontal section, the vertical well section length a, and the build section length b is equal to 4500 m, then the front section of the horizontal section of the pre-drilled horizontal well is drilled by the drilling method of rotary steerable + logging while drilling, and the rear section of the horizontal section is drilled by the drilling method of conventional screw + logging while drilling; if the sum of the vertical well section length a and the build section length b is greater than 4500 m, then the horizontal section of the pre-drilled horizontal well is drilled by the drilling method of conventional screw + logging while drilling; When the buried depth of the horizontal section of the pre-drilled horizontal well exceeds 3500 m, or the bottom hole temperature is higher than 130 °C, the drilling is carried out by the drilling method of conventional screw + logging while drilling, and it is also necessary to use the surface drill string torsional oscillation system + all-metal high-temperature-resistant hydraulic oscillator for assistance.

4. A method for shale gas target body identification and high drilling encounter control according to claim 1, characterized in that The in-situ stress magnitude of each logging point in step S1b is calculated by the following method: Step S1b-a: Calculate the P-wave to S-wave ratio of each logging point according to the rock density of each logging point. The calculation formula of the P-wave to S-wave ratio of each logging point is as follows: In the formula, R — The P-wave to S-wave ratio of each measurement point; ρ — The rock density of each measurement point; e — Mathematical constant; Step S1b-b: Calculate the Poisson's ratio corresponding to each logging point according to the P-wave to S-wave ratio. The calculation formula of the Poisson's ratio corresponding to each logging point is as follows: In the formula, ν — Poisson's ratio corresponding to each measurement point Step S1b-c: Calculate the pore pressure and vertical stress of each logging point according to the buried depth; the formulas for calculating the pore pressure and vertical stress are as follows: In the formula, σ p — The pore pressure at each measuring point; ρ overburden — Rock density of overlying strata; g — acceleration due to gravity; H — The buried depth of each measuring point σ z — The vertical stress of each measurement point Step S1b-d: Calculate the maximum and minimum horizontal principal stresses of each logging point according to the acoustic data, Poisson's ratio, pore pressure, and vertical stress by the following formula: In the formula, σ y — The maximum horizontal principal stress at each measurement point; σ x — The minimum horizontal principal stress at each measurement point; DTC — The acoustic waves of each measurement point; Step S1b-e: Calculate the horizontal principal stress difference of each logging point according to the maximum and minimum horizontal principal stresses, and calculate it by the following formula: In the formula, Δ σ — Horizontal principal stress difference at each measuring point; Step S1b-f: Construct the stress difference index, and the stress difference index is calculated by the following formula: In the formula, P stress — Stress difference index.

5. A method for shale gas target body identification and high drilling encounter control according to claim 1, characterized in that The calculation formula of the mechanical brittleness of each logging point in step S1c is as follows: In the formula, B mechanics — The mechanical brittleness of each measurement point KTH — The uranium-free gamma value of each measurement point; KTH max — The maximum uranium-free gamma value in the measurement well points; KTH min — The minimum uranium-free gamma value in the measurement well points.

6. The method for shale gas target body identification and high drilling encounter control according to claim 5, characterized in that, The calculation formula of the mineral brittleness of each logging point in step S1d is as follows: In the formula, B mineral — Mineral brittleness of each measuring point; B Si — Mass fraction of siliceous minerals at each measuring point B Ca — Mass fraction of carbonate minerals at each measurement point; The calculation formula of the fracturability index of each logging point in step S1e is as follows: In the formula, B o—Fracturing index of each measuring point.

7. A method for shale gas target identification and high drilling encounter control according to claim 3, characterized in that The content of the surface drill string torsional oscillation system + all-metal high-temperature-resistant hydraulic oscillator for assistance includes: The surface drill string torsional oscillation system drives the drill string to swing forward and backward continuously by controlling the top drive, so that the upper drill string is in a rotational motion state; The all-metal high-temperature-resistant hydraulic oscillator generates axial peristalsis along the direction of the pipe string, converts static friction into dynamic friction, and reduces the drill pressure loss and drill string vibration.

Images