A method for predicting rock drillability in a shale gas horizontal well

Abstract

The application discloses a shale gas horizontal well rock drillability prediction method and relates to the technical field of shale gas horizontal wells. The application analyzes the influence law of mineral components, confining pressure, formation dip angle and acoustic time difference on reservoir rock drillability through rock drillability micro drilling experiments and mineral component analysis experiments, establishes a relationship between rock drillability grade value and each parameter, establishes a drillability grade value prediction model under the influence of multiple parameters, firstly, rock drillability experiments are carried out, the influence of mineral components, acoustic time difference, bottom hole confining pressure and formation dip angle on shale reservoir drillability is analyzed, and a relationship between rock drillability grade value and each parameter is established, and secondly, a nonlinear fusion model of drillability grade value and multiple parameters is established based on the least square method and by using matlab programming, so that better drillability prediction application is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of shale gas horizontal well, in particular to a shale gas horizontal well rock drillability prediction method. BACKGROUND

[0002] Rock drillability refers to the difficulty of drilling underground rock, which is closely related to the hardness, compressive strength, abrasiveness, elastic-plasticity and structural characteristics of the formation, and is a basic factor for selecting appropriate drill bit structure, drilling means and drilling parameters and determining drilling efficiency.

[0003] In 2006, Liang Qiming, Zou Deyong and others studied the influence of lithology, density and shale content on rock drillability through laboratory experiments, established a new comprehensive rock drillability prediction model based on the existing drillability and acoustic time difference relationship model, and considered the influence of different lithology, density and shale content on the drillability level value. Although Liang Qiming and others considered the influence of different lithology, density and shale content on the drillability level value, the method can meet the drillability level value prediction of most wells, but it cannot accurately predict the drillability level value of horizontal well reservoir sections.

[0004] The wells in the Betrua block of North American oilfields are horizontal wells with no well logging data in the reservoir section, and the lithology of the reservoir section is shale. The shale lithology has the characteristics of strong formation heterogeneity and large rock drillability variation, so different degrees of drilling difficulty will be encountered during drilling, such as drill bit wear, sticking, diameter reduction and other problems when drilling more than 2000 meters, which cannot be drilled to the bottom, increasing the drilling cost and prolonging the drilling period, seriously affecting the mechanical drilling speed and rock breaking efficiency. Therefore, evaluating the horizontal drillability of the reservoir is one of the necessary tasks before shale exploration and development. SUMMARY

[0005] The present application provides a shale gas horizontal well rock drillability prediction method to solve the existing problems of drill bit wear, sticking, diameter reduction and other problems, which cannot be drilled to the bottom, increasing the drilling cost and prolonging the drilling period, seriously affecting the mechanical drilling speed and rock breaking efficiency.

[0006] To achieve the above-mentioned purpose, the present application provides the following technical scheme: a shale gas horizontal well rock drillability prediction method, at least comprising the following steps:

[0007] S1: first, by means of scanning electron microscopy, XRD analysis, acoustic tester and triaxial drillability tester, the influence of shale mineral composition, acoustic time difference, bottom hole pressure, formation dip and drillability is analyzed, and second, the influence degree of sandy, calcareous, argillaceous content, acoustic time difference, confining pressure and formation dip on rock drillability is comprehensively obtained, and a rock drillability multi-fusion model is obtained;

[0008] The rock drillability multi-fusion model in S1 is at least composed of the relationship between different mineral components and drillability, the relationship between acoustic time difference and drillability, different bottom hole pressure drillability test and different drilling angle drillability test;

[0009] The different bottom hole pressure drillability test is to test shale body under different simulated confining pressures, so as to obtain the influence feedback of confining pressure on drillability level value, and the test effect provides basic data support for establishing the fusion model of rock drillability, and the simulated confining pressure is at least 0MPa, 15MPa and 30MPa;

[0010] The different drilling angle drillability test is to test the influence of different drilling angles on drillability, and the different drilling angles are at least 0°, 15°, 30°, 45°, 60°, 75° and 90°;

[0011] S2: the relationship analysis between multi-parameters and drillability is composed of the uniaxial drillability prediction model of mineral composition, the relationship between acoustic time difference and uniaxial drillability, the influence of confining pressure on drillability and the influence of drilling angle on drillability;

[0012] S3: the comprehensive multi-parameter reservoir drillability prediction model is composed of shale reservoir drillability prediction model and drillability model verification.

[0013] Preferably, the relationship between different mineral components and drillability at least includes analyzing the main minerals in the region and XRD mineral content test;

[0014] The analysis of the main minerals in the region uses scanning electron microscopy to directly observe the surface morphology and mineral composition of the reservoir rock, and combines X-ray energy spectrum to quantitatively or semi-quantitatively analyze the composition, so as to obtain the main mineral composition of the regional shale;

[0015] The XRD mineral content test is to determine the structure and composition of the substance by measuring the diffraction mode of x-rays and the interaction between x-rays and the substance.

[0016] Preferably, the relationship between acoustic time difference and drillability at least includes the following steps:

[0017] The acoustic emission system in the rock acoustic parameter tester is used to excite the wafer vibration by emitting electric pulse, thereby generating acoustic waves, which are propagated to the receiving system through the rock sample, and the receiving system converts the acoustic waves into weak electric signals, which are amplified and displayed as waveforms on the screen, and the hardness of the shale is obtained through the waveforms;

[0018] The formula for calculating the transverse / longitudinal wave velocity of the rock sample is:

[0019]

[0020] In the formula, The transverse / longitudinal wave velocity of the rock sample is m / s;

[0021] The length of the rock sample is m;

[0022] The time required for the electric signal to be emitted and returned is μs;

[0023] The time of the acoustic wave passing through the transducer is μs.

[0024] Preferably, the prediction model of the mineral component on the uniaxial drillability comprises at least the following steps:

[0025] The sandy parameter, the argillaceous parameter and the calcareous parameter are taken as single parameters;

[0026] The relationship between the rock drillability level value and the single parameter is analyzed, and the function form of the rock drillability and the single parameter is obtained, which lays a foundation for the multivariate function fitting of the rock drillability;

[0027] According to the rock drillability data obtained by the micro-drill experiment and the sandy content of the corresponding rock, the relationship between the rock drillability level value and the sandy content is nonlinearly fitted, so as to obtain the relationship between the rock drillability level value and the sandy content, and the relationship between the rock drillability level value and the sandy content is fitted as follows:

[0028]

[0029] In the formula, The sandy content of the rock is %;

[0030] =-9.7, =7.07, =6.1, =0.36, =0.37 is the correlation coefficient;

[0031] The original data has strong discreteness, and the fitting residual is large, but the overall distribution belongs to the above exponential distribution, the fitting correlation is 0.65, and the drilling relationship trend can be basically expressed;

[0032] Similarly, the uniaxial drillability level value of the rock and the calcareous content are nonlinearly fitted, so as to obtain the relationship between the uniaxial drillability level value and the calcareous content:

[0033]

[0034] Among them, =8.97, =5.51, W=0.136, A=-9.17, The calcareous content is %;

[0035] The original data has strong discreteness, and the fitting residual is large, but the overall distribution belongs to the above logarithmic normal distribution, the fitting correlation is 0.70, and the drilling relationship trend with the calcareous content can be basically expressed;

[0036] The uniaxial drillability level value of the rock and the shale content are nonlinearly fitted, so as to obtain the relationship between the uniaxial drillability level value and the shale content:

[0037]

[0038] Among them, =4.15, =2.05, =3.74, P=34.9, The shale content is %.

[0039] The original data has strong discreteness, and the fitting residual is large, but the overall distribution belongs to the above exponential distribution, and the fitting correlation is 0.71.

[0040] Preferably, the formula of the relationship between the acoustic travel time and the uniaxial drillability is as follows:

[0041]

[0042] Among them, =205, =-5.02, =-2.08, =9.67, =0.13, =0.2, =0.23, AC is the acoustic travel time, and the unit is us / m;

[0043] The interval transit time is a key parameter for representing the mineral property and the rock density, and therefore, the relationship between the rock drillability level value and the interval transit time is correlated and fitted.

[0044] Preferably, the formula of the influence of the confining pressure on the drillability is as follows:

[0045]

[0046] wherein A=0.287, n=2.45, is the confining pressure, and the unit is MPa.

[0047] Preferably, the formula of the influence of the drilling angle on the drillability is as follows:

[0048]

[0049] The rock drillability level value and the drilling angle are nonlinearly fitted, so as to obtain the relationship between the rock drillability level value and the drilling angle.

[0050] Preferably, the formula of the shale reservoir drillability prediction model is as follows:

[0051] .

[0052] Compared with the prior art, the present application has the beneficial effects that:

[0053] The present application analyzes the influence law of the mineral component, the confining pressure, the formation dip angle and the interval transit time on the reservoir rock drillability through the rock drillability micro-drilling experiment and the mineral component analysis experiment, establishes the relationship between the rock drillability level value and each parameter, and establishes the drillability level value prediction model under the influence of multiple parameters. Firstly, the rock drillability experiment is carried out, the influence of the mineral component, the interval transit time, the bottom hole confining pressure and the formation dip angle on the shale reservoir drillability is analyzed, the relationship between the rock drillability level value and each parameter is established, and secondly, the nonlinear fusion model of the drillability level value and multiple parameters is established based on the least square method and using the matlab programming, so as to achieve better drillability prediction application. BRIEF DESCRIPTION OF DRAWINGS

[0054] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiment description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without any creative effort.

[0055] Figure 1 It is a schematic diagram of the mineral component content diagram of the present application;

[0056] Figure 2A shale longitudinal wave velocity test result schematic diagram of the present application;

[0057] Figure 3 A confining pressure influence on rock drillability regularity schematic diagram of the present application;

[0058] Figure 4 A different drilling angle micro-drill core sample schematic diagram of the present application;

[0059] Figure 5 A sandy content and uniaxial drillability correlation relationship schematic diagram of the present application;

[0060] Figure 6 A sandy content fitting data residual error schematic diagram of the present application;

[0061] Figure 7 A calcareous content and uniaxial drillability correlation relationship schematic diagram of the present application;

[0062] Figure 8 A calcareous content and uniaxial drillability fitting data residual error schematic diagram of the present application;

[0063] Figure 9 A argillaceous content and rock drillability correlation relationship schematic diagram of the present application;

[0064] Figure 10 A argillaceous content and rock drillability fitting data residual error schematic diagram of the present application;

[0065] Figure 11 A acoustic travel time and rock drillability correlation relationship schematic diagram of the present application;

[0066] Figure 12 A acoustic travel time and rock drillability fitting residual error relationship schematic diagram of the present application;

[0067] Figure 13 A rock drillability influence degree schematic diagram of the present application;

[0068] Figure 14 A confining pressure and rock drillability fitting data residual error schematic diagram of the present application;

[0069] Figure 15 A formation dip angle and rock drillability relationship schematic diagram of the present application. DETAILED DESCRIPTION

[0070] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application.

[0071] Please refer to Figure 1 - Figure 15A shale gas horizontal well rock drillability prediction method, at least comprising the following steps:

[0072] S1: First, the influence of North American X area shale mineral composition, acoustic time difference, bottom hole pressure, formation dip and drillability is analyzed by means of scanning electron microscope, XRD analysis, acoustic tester and triaxial drillability tester. Secondly, the influence degree of sandy, calcareous and argillaceous content, acoustic time difference, confining pressure and formation dip on rock drillability is obtained to obtain a rock drillability multi-fusion model.

[0073] The rock drillability multi-fusion model in S1 is at least composed of the relationship between different mineral components and drillability, the relationship between acoustic time difference and drillability, different bottom hole pressure drillability test and different drilling angle drillability test.

[0074] Referring to Figure 4 In order to establish a confining pressure prediction model for shale drillability, the drillability level value under simulated confining pressures of 0 MPa, 15 MPa and 30 MPa is tested (see Table 1 for detailed data), and the test results show that the confining pressure has a significant effect on the drillability level value of the shale in Duowei, Canada. When the simulated confining pressure increases to 30 MPa, the drillability level value increases by about 2-3 levels. The test data provide basic data support for subsequent establishment of the fusion model of rock drillability.

[0075] Table 1 Test results of shale drillability of Duowei shale in Canada under different confining pressures

[0076]

[0077] In order to verify whether this correlation is the same, the drillability level value of domestic Longmaxi shale under different confining pressures is also tested. It can be found that the drillability level value increases with the increase of confining pressure.

[0078] Table 2 Test results of shale drillability of Sichuan Longmaxi shale under different confining pressures

[0079]

[0080] Referring to Figure 5 When drilling, the angle between the drill bit axis and the rock bedding plane is called the drilling angle. The influence of different drilling angles (0°, 15°, 30°, 45°, 60°, 75° and 90°) on drillability is tested. It can be seen from the experimental results that for shale with obvious bedding characteristics, when the drill bit is drilled vertically to the bedding direction ( =0°) direction, the micro-drill is the smallest and the drillability is the best. When the drill bit is drilled along the parallel bedding direction ( =90°), the micro-drill is the largest and the drillability is the worst. The micro-drill when drilling at 45° is greater than that when drilling at 15° and 30°.

[0081] At the same time, the influence of different confining pressures was tested. The influence of drilling angle on rock drillability was high (the average amplitude was 1.46) under the confining pressure of 0-10 MPa. When the confining pressure was more than 10 MPa, the influence of drilling angle on rock drillability was weakened.

[0082] Table 3 Influence of drilling angle on rock drillability under different confining pressures

[0083]

[0084] According to the rock drillability determination and classification standard for oil and gas drilling engineering (SY / T 5426-2016), the rock drillability grade value was calculated according to the following formula.

[0085]

[0086] In the formula:

[0087] Drillability grade value;

[0088] Drilling time average, unit: second (s);

[0089] Equivalent conversion grade value;

[0090] Drilling pressure grade (first grade =0; second grade =1; third grade =3).

[0091] Table 4 Influence of different drilling angles on rock uniaxial drillability

[0092]

[0093] At the same time, the influence of drilling angle on drillability under confining pressure was tested, and triaxial drillability experiment was designed. As can be seen from Table 5, under the condition of low confining pressure (0-10 MPa), the influence of drilling angle on rock drillability was high (the average amplitude was 1.46). When the confining pressure was improved (20 MPa-30 Mpa), the influence of different drilling angles on rock drillability was weakened.

[0094] Table 5 Influence of drilling angle on drillability under confining pressure

[0095]

[0096] S2: The relationship analysis between multiple parameters and drillability is composed of the prediction model of uniaxial drillability by mineral components, the relationship between acoustic time difference and uniaxial drillability, the influence of confining pressure on drillability and the influence of drilling angle on drillability;

[0097] S3: Establishing a comprehensive multi-parameter reservoir drillability prediction model from the shale reservoir drillability prediction model and the drillability model verification.

[0098] The relationship between different mineral components and drillability at least includes analyzing the main minerals in the region and XRD mineral content testing;

[0099] The main minerals in the region are analyzed by using a scanning electron microscope (SEM) to visually observe the surface morphology and mineral composition of the reservoir rock, and quantitative or semi-quantitative component analysis is performed by combining an X-ray energy spectrometer (EDS), thereby obtaining the main mineral components of the shale in the region. The results show that the main mineral components of the shale in the North American X region include quartz (Quartz), potassium feldspar (K-spar), plagioclase (Plag), calcite (Calcite), iron dolomite (Dolomite Fe / Ca+), and dolomite (Dolomite);

[0100] Referring to Figure 1 , XRD mineral content testing is a method that uses the characteristics of the interaction between x-rays and matter to determine the structure and composition of matter by measuring the diffraction pattern of x-rays on matter. According to the XRD analysis results, the main mineral components of the shale in the shale reservoir of the North American X block are quartz, feldspar, calcite, and clay minerals. The quartz content is 20.3-65%, with an average of 47.9%. The feldspar content is 3-12%, with an average of 7%. The clay mineral content is 14.3-52.8%, with an average of 29.7%. The calcite content is 2.1-21.8%, with an average of 8.63%. The pyrite content is 1.5-4.7%, with an average content of 2.66%;

[0101] Referring to Figure 3 , the relationship between acoustic travel time and drillability at least includes the following steps:

[0102] The acoustic emission system in the rock acoustic parameter tester is used to excite the wafer vibration by emitting an electric pulse, thereby generating acoustic waves, which propagate through the rock sample to the receiving system. The receiving system converts the acoustic waves into weak electrical signals. These signals are amplified and displayed as waveforms on the screen. The hardness of the shale is obtained by analyzing the waveforms;

[0103] The results show that the shale in this block belongs to a dense sedimentary rock, which is a relatively high hardness shale;

[0104] The formula for calculating the transverse and longitudinal wave velocities of the rock sample is:

[0105]

[0106] In the formula, is the transverse and longitudinal wave velocity of the rock sample, with a unit of m / s;

[0107] Length of the rock sample, in meters;

[0108] Time required for the electrical signal to travel from the transmitter to the receiver, in microseconds;

[0109] Time for the acoustic wave to travel through the transducer, in microseconds

[0110] The test results are shown in Figure 5 As can be seen from the figure, the acoustic time difference of the shale is between 150-300us / m, and most of them are distributed around 250us / m. Shale belongs to dense sedimentary rock, and the acoustic velocity of shale in this block can only reach 250us / m, which belongs to high hardness shale.

[0111] The prediction model of mineral composition on uniaxial drillability includes at least the following steps:

[0112] The mineral composition in the shale in Duowai, Canada is mainly quartz, feldspar, calcite, clay minerals, etc., with a total content of more than 90%. For example, the quartz content can reach nearly 50%, the clay content is 30%, the calcite content is 10%, and the barite, dolomite, and pyrite are only about 0-3%. In order to reduce the modeling parameters of the drillability level equation and reduce the calculation dimension, the above mineral components are classified into sandy, argillaceous, calcareous, etc. as shown in Table 6. The sandy, argillaceous, and calcareous parameters are used as single parameters, and the relationship between the rock drillability level and the single parameter is analyzed to obtain the function form of the rock drillability and the single parameter, which lays the foundation for the multi-element function fitting of the rock drillability.

[0113] Table 6 Relationship between equivalent mineral content and uniaxial drillability of rock

[0114]

[0115] The sandy parameter, the argillaceous parameter, and the calcareous parameter are used as single parameters;

[0116] The relationship between the rock drillability level and the single parameter is analyzed to obtain the function form of the rock drillability and the single parameter, which lays the foundation for the multi-element function fitting of the rock drillability;

[0117] Referring to Figure 5 and Figure 6 , according to the rock drillability data obtained by the micro-drill experiment and the sandy content of the corresponding rock, the nonlinear fitting of the rock drillability level and the sandy content is carried out, so as to obtain the relationship between the rock drillability level and the sandy content, and the relationship between the rock drillability level and the sandy content is fitted as follows:

[0118]

[0119] wherein, Sand content of rock, unit is %;

[0120] = -9.7, = 7.07, = 6.1, = 0.36, = 0.37 is the correlation coefficient;

[0121] Referring to Figure 7 and Figure 8 Because the original data is strong in discreteness, the fitting residual is large, but the overall distribution belongs to the above exponential distribution, the fitting correlation is 0.65, which can basically show the trend of the drillability relationship;

[0122] Similarly, the uniaxial drillability level value of the rock and the calcareous content are nonlinearly fitted, so as to obtain the relationship between the uniaxial drillability level value and the calcareous content:

[0123]

[0124] Among them, = 8.97, = 5.51, W = 0.136, A = -9.17, The calcareous content is unit %;

[0125] The original data is also strong in discreteness, the fitting residual is large, but the overall distribution belongs to the above logarithmic normal distribution, the fitting correlation is 0.70, which can basically show the trend of the drillability and the calcareous content;

[0126] Referring to Figure 9 and Figure 10 The uniaxial drillability level value of the rock and the shale content are nonlinearly fitted, so as to obtain the relationship between the uniaxial drillability level value and the shale content:

[0127]

[0128] Among them, = 4.15, = 2.05, = 3.74, P = 34.9, The shale content is unit %.

[0129] The original data is also strong in discreteness, the fitting residual is large, but the overall distribution belongs to the above exponential distribution, the fitting correlation is 0.71;

[0130] Referring to Figure 11 and Figure 12 The formula of the relationship between the acoustic travel time and the uniaxial drillability is as follows:

[0131]

[0132] wherein, = 205, = -5.02, = -2.08, = 9.67, = 0.13, = 0.2, = 0.23, AC is acoustic travel time, unit is us / m;

[0133] Since the acoustic travel time is a key parameter for representing the mineral properties and the rock density, the correlation fitting between the rock drillability level value and the acoustic travel time is performed, and the prediction accuracy can reach 0.89, and the prediction accuracy is high.

[0134] Table 7: Corresponding relationship between acoustic travel time and uniaxial drillability level value

[0135]

[0136] Since the acoustic travel time is a key parameter for representing the mineral properties and the rock density, the correlation fitting between the rock drillability level value and the acoustic travel time is performed, and the prediction accuracy can reach 0.89, and the prediction accuracy is high.

[0137] The original data has strong discreteness, and the fitting residual is large, but the overall distribution belongs to the above exponential distribution, the fitting correlation is 0.68, and the fitting accuracy is general.

[0138] Referring to Figure 13 and Figure 14 , in order to study the degree of influence of confining pressure on drillability level value, on the basis of drillability level value under different confining pressures, the difference between test results under confining pressure and uniaxial drillability is used to represent the influence of confining pressure on rock drillability, and the test results are shown in Table 8.

[0139] Table 8: Degree of influence of confining pressure on drillability

[0140]

[0141] Through regression analysis of the data in Table 8, the empirical coefficient A is 0.67, the empirical coefficient n is 0.287, and the prediction model of the degree of influence of confining pressure on rock drillability is obtained as follows:

[0142]

[0143] wherein, A = 0.287, n = 2.45, is the confining pressure, unit is MPa.

[0144] Referring to Figure 15, the drillability formula is as follows:

[0145]

[0146] The rock drillability level value and the drilling angle are nonlinearly fitted, so that the relationship between the rock drillability level value and the drilling angle is obtained, and the prediction accuracy can reach 0.93, and the prediction accuracy is higher;

[0147] Shale reservoir drillability prediction model:

[0148] The influence degree of sandy, calcareous, argillaceous content, acoustic travel time, confining pressure, formation dip on rock drillability is obtained, and a rock drillability multi-element fusion model is obtained. Since the influence of bottom hole pressure and formation dip on shale drillability level value is used when establishing the rock drillability comprehensive prediction model, when considering the influence degree of formation pressure and formation dip on rock drillability, it is currently only applicable to the drillability prediction of shale.

[0149] Through the analysis of the above multi-element parameters and the rock drillability level value, a nonlinear fusion model of drillability level value and multi-element parameters is established based on the least square method using matlab programming.

[0150] The formula of shale reservoir drillability prediction model is as follows:

[0151] ;

[0152] The parameters are shown in the following table:

[0153] Table 9 drillability level value equation parameter explanation

[0154]

[0155] Drillability model verification:

[0156] For the drilled reservoir section, the lithology, bottom hole pressure and formation dip of each small layer have been obtained, and the corresponding drillability level value can be calculated according to the established multi-element parameter rock drillability calculation model. By comparing and analyzing with the measured drillability level value in the micro drill experiment, it can be found that the rock drillability level value obtained by indoor test and the rock drillability level value predicted by model has good consistency. This shows that the established prediction model can accurately describe the drillability characteristics of rock, and has certain prediction accuracy and reliability.

[0157] Table 10 shale measured mineral composition and predicted drillability level value

[0158]

[0159] It will be apparent to those skilled in the art that the application is not limited to the details of the above-exemplified embodiments and that the present application can be implemented in other particular forms without departing from the spirit or essential characteristics of the present application. The embodiments should therefore be considered in all respects as illustrative and not restrictive, the scope of the application being indicated by the appended claims rather than by the above description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. No reference signs in the claims should be considered as limiting the scope of the claims with respect to the figures of the patent document.

Claims

1. A method for predicting rock drillability in shale gas horizontal wells, characterized in that: At least the following steps are included: S1: First, using the results measured by scanning electron microscopy, XRD analysis, acoustic wave tester and triaxial drillability tester, we analyze the influence of shale mineral composition, acoustic transit time, bottom hole confining pressure, formation dip angle and drillability. Second, we comprehensively consider the influence of sand, calcium, clay content, acoustic transit time, confining pressure and formation dip angle on rock drillability to obtain a multi-dimensional fusion model of rock drillability. The rock drillability multi-element fusion model in S1 consists of at least the relationship between different mineral components and drillability, the relationship between sonic transit time and drillability, drillability tests with different bottom hole confining pressures, and drillability tests with different drilling angles. The drillability test with different bottom hole confining pressures is to test the shale body with simulated confining pressures of different pressures to obtain feedback on the influence of confining pressure on the drillability grade value. The test results provide basic data support for establishing a fusion model of rock drillability. The simulated confining pressures are at least 0 MPa, 15 MPa and 30 MPa. The drillability test with different drill-in angles was used to test the effect of different drill-in angles on drillability. The different drill-in angles were at least 0°, 15°, 30°, 45°, 60°, 75° and 90°. S2: The relationship between multivariate parameters and drillability is analyzed by the prediction model of mineral composition on uniaxial drillability, the relationship between sonic transit time and uniaxial drillability, the influence of confining pressure on drillability, and the influence of drill angle on drillability. The predictive model for uniaxial drillability of the mineral composition includes at least the following steps: Sandy, muddy, and calcareous parameters are treated as single parameters; The relationship between rock drillability rating and single parameter was analyzed, and the functional form of rock drillability and single parameter was obtained, laying the foundation for multivariate function fitting of rock drillability. Based on the rock drillability data obtained from micro-drilling experiments and the corresponding sand content results, a nonlinear fitting was performed on the rock drillability grade and sand content to obtain the relationship between the rock drillability grade and sand content. in, The content of sand in the rock is expressed as % (%). =-9.7, =7.07, =6.1, =0.36, =0.37 is the correlation coefficient; Because the original data is highly discrete and the fitting residual is large, the overall distribution is an exponential distribution with a fitting correlation of 0.65, which can basically show the trend of the drillability relationship. Similarly, a nonlinear fitting was performed on the uniaxial drillability grade of the rock and its calcium content to obtain the relationship between the uniaxial drillability grade and the calcium content: in, =8.97, =5.51, W=0.136, A=-9.17, Calcium content is expressed in percentages (%). The original data also showed strong dispersion and large fitting residuals, but the overall distribution was log-normal, with a fitting correlation of 0.70, which could basically show the trend of the relationship between drillability and calcium content. A nonlinear fitting was performed on the uniaxial drillability grade of the rock and the clay content to obtain the relationship between the uniaxial drillability grade and the clay content: in, =4.15, =2.05, =3.74, P=34.9, The content of clay is expressed as % (%). The original data also showed strong dispersion and large fitting residuals, but the overall distribution was exponential, with a fitting correlation of 0.

71. S3: A comprehensive multi-parameter reservoir drillability prediction model is established, consisting of a shale reservoir drillability prediction model and a drillability model verification model.

2. The method for predicting rock drillability in shale gas horizontal wells according to claim 1, characterized in that: The relationship between different mineral components and drillability includes at least the analysis of the main minerals in the analytical area and XRD mineral content testing. The main minerals in the analysis area were directly observed by scanning electron microscopy to examine the surface morphology and mineral composition of the reservoir rocks, and quantitative or semi-quantitative component analysis was performed by X-ray energy dispersive spectroscopy to obtain the main mineral components of the shale in the area. The XRD mineral content test utilizes the properties of X-rays interacting with matter to determine the structure and composition of a substance by measuring its diffraction patterns.

3. The method for predicting rock drillability in shale gas horizontal wells according to claim 1, characterized in that: The relationship between acoustic transit time and drillability includes at least the following steps: The acoustic emission system in the rock acoustic parameter tester uses electrical pulses to excite the crystal to vibrate, thereby generating sound waves. These sound waves propagate through the rock sample to the receiving system, which converts the sound waves into weak electrical signals. These signals are amplified and displayed as waveforms on the screen, from which the hardness of the shale can be determined. The formula for calculating the transverse / longitudinal wave velocity of a rock sample is: In the formula, The transverse / longitudinal wave velocities of the rock sample are expressed in m / s. The length of the rock sample is in meters. The time required for an electrical signal to travel from transmission to return, measured in μs; The time it takes for a sound wave to pass through the transducer is expressed in μs.

4. The method for predicting rock drillability in shale gas horizontal wells according to claim 1, characterized in that: The formula relating the acoustic transit time to uniaxial drillability is as follows: in, =205, =-5.02, =-2.08, =9.67, =0.13, =0.2, =0.23, AC is the acoustic transit time, in µs / m; Acoustic transit time is a key parameter characterizing the mineral properties and compactness of rocks. Therefore, a correlation fitting was performed to study the relationship between rock drillability grade and acoustic transit time.

5. The method for predicting rock drillability in shale gas horizontal wells according to claim 1, characterized in that: The formula for the effect of confining pressure on drillability is as follows: Where A = 0.287, n = 2.45, The confining pressure is expressed in MPa.

6. The method for predicting rock drillability in shale gas horizontal wells according to claim 1, characterized in that: The formula for the drill angle and drillability is as follows: A nonlinear fitting was performed on the rock drillability rating and the drilling angle to obtain the relationship between the rock drillability rating and the drilling angle.

7. The method for predicting rock drillability in shale gas horizontal wells according to claim 1, characterized in that: The formula for the shale reservoir drillability prediction model is as follows: ； in, =205; =12; =-8.5; =-0.56; =3.5; =-9.76; =0.7; =3.5; =1.3; =3.54; =0.4; This refers to the time difference of sound waves, measured in µs / m. =0.34; =0.15; To drill into an angle.

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