Method and device for reducing bottom hole circulating temperature of deep shale gas horizontal well

Abstract

This invention discloses a method and apparatus for reducing the bottom-hole circulating temperature of deep shale gas horizontal wells, relating to the field of drilling engineering technology. It addresses the technical problem of unsatisfactory cooling effects when using existing surface cooling methods. The method includes the following steps: Step S1: Obtain the three-pressure profile of the well to be drilled and obtain the underpressure value range; Step S2: Determine the underbalanced drilling process based on the underpressure value range; Step S3: Obtain first relationship information and predict the bottom-hole circulating temperature of the well to be drilled. Based on the bottom-hole circulating temperature, the first relationship information, the three-pressure profile, and the underbalanced drilling process, optimize the drilling fluid density in the drilling process. This invention can effectively reduce the bottom-hole circulating temperature during deep shale gas drilling, ensure stable instrument operation, reduce the number of tripping operations, and guarantee efficient drilling of horizontal wells.

Description

Technical Field

[0001] This invention relates to the field of drilling engineering technology, and more specifically to a method and apparatus for reducing the bottom-hole circulating temperature of deep shale gas horizontal wells. Background Technology

[0002] In the shale gas areas of Jiaoshiba, Weirong, Yongchuan, Luzhou, and Yuxi in Sichuan, the reservoir depth is greater than 3500m. During horizontal drilling, the average circulating temperature at the bottom of the well exceeds 145℃, with a maximum of 167℃. This exceeds the temperature resistance limit (150℃) of commonly used rotary steerable drilling tools and other downhole measurement tools, leading to frequent failures of downhole measurement tools and hindering the achievement of the φ215.9mm wellbore single-trip drilling footage and the "one-trip drilling" target. Taking the Luzhou block as an example, the target layer is the Longmaxi Formation of the Silurian system, with a vertical depth of 3500-4300m and a geothermal gradient of about 3℃ / 100m. The Longmaxi Formation is drilled using oil-based drilling fluid, which has a low specific heat capacity and a heat preservation effect. During horizontal drilling, the measured temperature at the bottom of the well can reach more than 145℃, which causes the electronic components in the rotary steering system MWD / LWD module to fail, resulting in frequent tripping and replacement of rotary steering tools. This seriously affects the drilling speed and efficiency of deep shale gas horizontal wells. Therefore, it is very necessary to study a method to continuously reduce the bottom hole circulation temperature to ensure efficient drilling of long horizontal wells.

[0003] Currently, most methods for reducing the bottom-hole circulation temperature of deep shale gas horizontal wells employ surface cooling, as illustrated by patents with publication numbers CN110763050B and CN111927394B. This involves lowering the drilling fluid's inlet temperature to cool the drilling fluid within the wellbore. However, calculations and analysis of field data show that surface cooling only slightly reduces the bottom-hole circulation temperature, resulting in unsatisfactory cooling effects. Further optimization of drilling methods and processes is needed to achieve a greater reduction in downhole circulation temperature. Therefore, there is an urgent need for a method utilizing underbalanced drilling to reduce the bottom-hole circulation temperature of deep shale gas horizontal wells, filling a gap in drilling engineering technology. Summary of the Invention

[0004] The purpose of this invention is to solve the above-mentioned technical problems by providing a method and apparatus for reducing the bottom-hole circulation temperature of deep shale gas horizontal wells.

[0005] To achieve the above objectives, the present invention specifically adopts the following technical solution:

[0006] In a first aspect, the present invention provides a method for reducing the bottom-hole circulation temperature of deep shale gas horizontal wells, comprising the following steps:

[0007] Step S1: Obtain the three-pressure profile of the well to be drilled and obtain the underpressure value range; wherein, the three-pressure profile includes the collapse pressure, pore pressure and fracture pressure, and the underpressure value range is lower than the pore pressure and higher than the collapse pressure;

[0008] Step S2: Determine the underbalanced drilling process based on the underpressure range; wherein, the underbalanced drilling process includes using a rotary blowout preventer to control the bottom hole pressure, so that the bottom hole pressure is less than the pore pressure during the drilling process;

[0009] Step S3: Obtain the first relationship information and predict the bottom hole circulation temperature of the well to be drilled. Based on the bottom hole circulation temperature of the well to be drilled, the first relationship information, the three pressure profiles, and the underbalanced drilling process, optimize the drilling fluid density in the drilling process. The first relationship information is the heating rate of the bottom hole circulation temperature in the horizontal section with the increase of well depth and the influence law of the change of drilling fluid density on the bottom hole circulation temperature.

[0010] Furthermore, obtaining the three-pressure profile in step S1 specifically includes the following sub-steps:

[0011] Step S11: Obtain drilling and logging data of the drilled wells in the target well area and establish a single-well geomechanical model;

[0012] Step S12: Based on the obtained single-well geomechanical model and combined with the seismic attribute inversion data of the target well area, establish a three-dimensional geomechanical model to extract the three-pressure curves along the well for the well that needs to be predicted by the three-pressure profile, and determine the three-pressure profile.

[0013] Furthermore, the calculation model for pore pressure is as follows:

[0014]

[0015] In the formula, P p P is the pore pressure. o The pressure of the overlying strata; P h Normal hydrostatic pressure; Δt n Δt0 is the sonic transit time at the calculation point; Δt0 is the sonic transit time of the normal compaction curve of mudstone corresponding to the calculation point; N is the model exponent.

[0016] Furthermore, the calculation model for collapse pressure is as follows:

[0017]

[0018]

[0019] In the formula, P c S0 is the collapse pressure; η is the nonlinear correction coefficient; H is the depth; S0 is the rock cohesion; α is the Biot coefficient; σ is the collapse pressure. h The maximum horizontal principal stress; σH The minimum horizontal principal stress; It is the internal friction angle.

[0020] Furthermore, the calculation model for the rupture pressure is as follows:

[0021]

[0022] In the formula, P f σ is the rupture pressure; h The maximum horizontal principal stress; σ H The minimum horizontal principal stress is denoted by v; the ratio of ν to Poisson's ratio is denoted by P. p S represents pore pressure. T α is the formation tensile strength; α is the Biot coefficient; δ is a coefficient, which is 0 when the wellbore is impermeable and 1 when the wellbore is permeable; φ is the porosity.

[0023] Furthermore, during the implementation of step S2, if the following situations are encountered, corresponding actions need to be taken, as detailed below:

[0024] a. If a single peak rises significantly after pumping is stopped, the logging team shall reposition the layers and well sections according to the delay time.

[0025] b. If the bottom hole drilling fluid density cannot meet the bottom hole pressure balance after the pump is stopped, calculate the ECD value of the bottom hole pressure balance and the difference in drilling fluid density during the circulation process, control the pressure when the pump is stopped, and record the pressure control data in detail each time.

[0026] c. If the gas measurement value continues to rise and the fluid level rises during the drilling process, the well team should shut down the well in time and add weight. After adding weight, stop drilling, start the pump to circulate and vent the gas, and observe the changes in the gas measurement value.

[0027] d. If subsequent underbalanced drilling operations cannot be carried out, drilling shall be completed according to the lower limit of the drilling fluid density that can balance the bottom hole pressure using the bottom hole ECD;

[0028] e. If the vibrating screen returns large pieces or has abnormal torque, the casing pressure control value should be increased, the equivalent density at the bottom of the well should be increased to prevent further collapse of the well wall, and the reaming of the collapsed section should be increased to ensure that the wellbore is unobstructed.

[0029] f. If increasing the wellhead casing pressure is ineffective, the drilling fluid density can be increased and the mud properties adjusted.

[0030] Furthermore, the prediction of the bottom hole circulation temperature in step S3 includes:

[0031] Obtain drilled well parameter information, and use this information to correct the drilling fluid heat transfer model in the drill string and the drilling fluid heat transfer model in the annulus. Then, combine this information with the parameter information of the well to be drilled to predict the bottom hole circulation temperature of the well to be drilled. The drilled well parameter information includes the bottom hole circulation temperature, inlet and outlet drilling fluid temperatures, and drilling fluid density of the drilled well. The well to be drilled parameter information includes the vertical depth, inclination depth, well trajectory, machine speed, displacement, drilling fluid rheological parameters, and drilling fluid thermophysical parameters of the well to be drilled.

[0032] Furthermore, the calculation formula for the drilling fluid heat transfer model within the annulus is as follows:

[0033]

[0034] The calculation formula for the drilling fluid heat transfer model inside the drill string is as follows:

[0035]

[0036] In the formula, ρ is the drilling fluid density; q is the drilling fluid volumetric flow rate; C p T represents the specific heat capacity of the drilling fluid. a T represents the drilling fluid temperature within the annulus. w T represents the drill pipe wall temperature. f The near-wellbore formation temperature; r a r is the outer radius of the drill string assembly; o r is the wellbore radius; p h is the inner radius of the drill pipe. p h is the convective heat transfer coefficient of the inner wall of the drill pipe. a The convective heat transfer coefficient within the annulus.

[0037] Furthermore, optimizing the drilling fluid density in step S3 includes:

[0038] In optimizing the drilling process, the drilling fluid density may be reduced. If the drilling process parameters are consistent with those before the last reduction in drilling fluid density, the density can be further reduced, at a rate of 0.02 g / cm³ per cycle. 3 The drilling was stopped and the density was reduced by circulation.

[0039] Secondly, the present invention provides an apparatus for reducing the bottom-hole circulating temperature of deep shale gas horizontal wells, comprising:

[0040] The acquisition module is used to acquire the three-pressure profile of the well to be drilled and obtain the underpressure value range; wherein, the three-pressure profile includes collapse pressure, pore pressure and fracture pressure, and the underpressure value range is lower than pore pressure and higher than collapse pressure;

[0041] The module is used to determine the underbalanced drilling process based on the underpressure range; the underbalanced drilling process includes using a rotary blowout preventer to control the bottom hole pressure, so that the bottom hole pressure is less than the pore pressure during the drilling process.

[0042] The optimization module is used to obtain the first relationship information and predict the bottom hole circulation temperature of the well to be drilled. Based on the bottom hole circulation temperature of the well to be drilled, the first relationship information, the three pressure profiles, and the underbalanced drilling process, the drilling fluid density in the drilling process is optimized. The first relationship information is the heating rate of the bottom hole circulation temperature in the horizontal section with the increase of well depth and the influence law of the change of drilling fluid density on the bottom hole circulation temperature.

[0043] The beneficial effects of this invention are as follows:

[0044] This invention proposes a method and apparatus for reducing the bottom-hole circulating temperature of deep shale gas horizontal wells. The method optimizes the drilling fluid density during drilling by utilizing the bottom-hole circulating temperature of the wellbore to be drilled, the first relationship information, the three-pressure profile, and the underbalanced drilling process. By optimizing the drilling fluid density, the solid content in the drilling fluid is reduced, lowering the convective heat transfer coefficient of the fluid within the annulus and drill string, and reducing the heat generated by friction during drilling. This effectively reduces the bottom-hole circulating temperature during deep shale gas drilling, ensuring stable instrument operation, reducing the number of tripping operations, guaranteeing efficient drilling of horizontal wells, providing guidance for on-site construction, and is of great significance for improving the overall timeliness and speed of shale gas drilling. Attached Figure Description

[0045] Figure 1 This is a schematic diagram illustrating the effect of drilling fluid density on bottom hole circulation temperature in deep shale gas horizontal wells according to the present invention. Detailed Implementation

[0046] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0047] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0048] Example 1

[0049] like Figure 1 As shown, this embodiment provides a first aspect: the present invention provides a method for reducing the bottom-hole circulation temperature of deep shale gas horizontal wells, comprising the following steps:

[0050] Step S1: Obtain the three-pressure profile of the well to be drilled and obtain the underpressure value range; wherein, the three-pressure profile includes the collapse pressure, pore pressure and fracture pressure, and the underpressure value range is lower than the pore pressure and higher than the collapse pressure;

[0051] Step S2: Determine the underbalanced drilling process based on the underpressure range; wherein, the underbalanced drilling process includes using a rotary blowout preventer to control the bottom hole pressure, so that the bottom hole pressure is less than the pore pressure during the drilling process;

[0052] Step S3: Obtain the first relationship information and predict the bottom hole circulation temperature of the well to be drilled. Based on the bottom hole circulation temperature of the well to be drilled, the first relationship information, the three pressure profiles, and the underbalanced drilling process, optimize the drilling fluid density in the drilling process. The first relationship information is the heating rate of the bottom hole circulation temperature in the horizontal section with the increase of well depth and the influence law of the change of drilling fluid density on the bottom hole circulation temperature.

[0053] It should be noted that underbalanced drilling refers to a drilling technique in which the bottom hole pressure is lower than the pore pressure during drilling, and the fluid from the ground enters the wellbore in a controlled manner and circulates to the surface.

[0054] As one possible implementation, obtaining the three-pressure profile in step S1 specifically includes the following sub-steps:

[0055] Step S11: Obtain drilling and logging data of the drilled wells in the target well area and establish a single-well geomechanical model;

[0056] Step S12: Based on the obtained single-well geomechanical model and combined with the seismic attribute inversion data of the target well area, establish a three-dimensional geomechanical model to extract the three-pressure curves along the well for the well that needs to be predicted by the three-pressure profile, and determine the three-pressure profile.

[0057] It should be noted that single-well geomechanical models are the main method for obtaining the three-pressure profile of drilled wells, while three-dimensional geomechanical models are the main means of obtaining the three-pressure profile of wells to be drilled.

[0058] Drilling data includes wellhead coordinates and wellbore trajectory. Wellhead coordinates clearly indicate the location of the drilled well, while the wellbore trajectory determines its depth, inclination, and azimuth. Logging data primarily includes gamma ray, rock density, and P-wave and S-wave velocities. Based on this logging data, a single-well geomechanical model can be established, yielding curves for Young's modulus, Poisson's ratio, uniaxial compressive strength, internal friction angle, pore pressure, fracture pressure, and collapse pressure.

[0059] The seismic attribute inversion data volume includes Young's modulus, Poisson's ratio, rock density, wave impedance, and P-wave and S-wave velocity attributes.

[0060] Specifically, Young's modulus and Poisson's ratio are calculated using longitudinal and transverse wave velocities, while uniaxial compressive strength is calculated using the acoustic wave method.

[0061] Furthermore, the calculation model for pore pressure is as follows:

[0062]

[0063] In the formula, P p P is the pore pressure. o The pressure of the overlying strata; P h Normal hydrostatic pressure; Δt n Δt0 is the sonic transit time at the calculation point; Δt0 is the sonic transit time of the normal compaction curve of mudstone corresponding to the calculation point; N is the model exponent.

[0064] Furthermore, the calculation model for collapse pressure is as follows:

[0065]

[0066]

[0067] In the formula, P c S0 is the collapse pressure; η is the nonlinear correction coefficient; H is the depth; S0 is the rock cohesion; α is the Biot coefficient; σ is the collapse pressure. h The maximum horizontal principal stress; σ H The minimum horizontal principal stress; It is the internal friction angle.

[0068] Furthermore, the calculation model for the rupture pressure is as follows:

[0069]

[0070] In the formula, P f σ is the rupture pressure; h The maximum horizontal principal stress; σ H The minimum horizontal principal stress is denoted by v; the ratio of ν to Poisson's ratio is denoted by P. p S represents pore pressure. T α is the formation tensile strength; α is the Biot coefficient; δ is a coefficient, which is 0 when the wellbore is impermeable and 1 when the wellbore is permeable; φ is the porosity.

[0071] It should be noted that step S2 is as follows:

[0072] During underbalanced drilling, the drilling fluid density should be higher than the collapse pressure and lower than the pore pressure. Based on the three-pressure profile of the well to be drilled and the maximum working pressure of the rotary blowout preventer (BOF), a suitable model of rotary BOP should be selected for bottom hole pressure control during underbalanced drilling operations. The effective free height of the drilling rig needs to reach at least 8.7 meters, and an 18° inclined drill pipe should be used. A dedicated choke manifold should be employed for conventional pressure control and circulating venting.

[0073] Detailed technical measures should be developed for underbalanced drilling operations, including process requirements for drilling, single-joint connection, tripping, and circulation during the underbalanced drilling process; drill string assembly and drilling parameter requirements; well control and blowout prevention drill requirements; technical solutions for handling complex risks; and other precautions.

[0074] Special situations need to be handled during underbalanced drilling. Furthermore, if the following situations are encountered during step S2, corresponding measures need to be taken, as follows:

[0075] a. If a single peak rises significantly after pumping is stopped, the logging team shall reposition the layers and well sections according to the delay time.

[0076] b. If the bottom hole drilling fluid density cannot meet the bottom hole pressure balance after the pump is stopped, calculate the ECD value of the bottom hole pressure balance and the difference in drilling fluid density during the circulation process, control the pressure when the pump is stopped, and record the pressure control data in detail each time.

[0077] c. If the gas measurement value continues to rise and the fluid level rises during the drilling process, the well team should shut down the well in time and add weight. After adding weight, stop drilling, start the pump to circulate and vent the gas, and observe the changes in the gas measurement value.

[0078] d. If subsequent underbalanced drilling operations cannot be carried out, drilling shall be completed according to the lower limit of the drilling fluid density that can balance the bottom hole pressure using the bottom hole ECD;

[0079] e. If the vibrating screen returns large pieces or has abnormal torque, the casing pressure control value should be increased, the equivalent density at the bottom of the well should be increased to prevent further collapse of the well wall, and the reaming of the collapsed section should be increased to ensure that the wellbore is unobstructed.

[0080] f. If increasing the wellhead casing pressure is ineffective, the drilling fluid density can be increased and the mud properties adjusted.

[0081] It should be noted that step S3 is as follows:

[0082] Obtain primary relationship information: Based on the experimental results of oil-based drilling fluid and shale thermophysical properties, determine the thermal conductivity and specific heat capacity of the drilling fluid, and establish a dynamic and static heat transfer model of the wellbore based on the principle of energy balance. Analyze the influence of drilling fluid density on bottom hole circulating temperature, clarify the heating rate of bottom hole circulating temperature in the horizontal section with increasing well depth, and the influence of drilling fluid density changes on bottom hole circulating temperature.

[0083] Predicting the bottom-hole circulation temperature of the well to be drilled: Obtain the drilling parameters, correct the drilling fluid heat transfer model in the drill string and the drilling fluid heat transfer model in the annulus based on the drilling parameters, and then combine them with the drilling parameters to predict the bottom-hole circulation temperature of the well to be drilled. The drilling parameters include the bottom-hole circulation temperature, inlet and outlet drilling fluid temperatures, and drilling fluid density of the well to be drilled. The drilling parameters include the vertical depth, inclination depth, well trajectory, machine speed, displacement, drilling fluid rheological parameters, and drilling fluid thermophysical parameters of the well to be drilled.

[0084] Based on the bottom hole circulating temperature of the wellbore to be drilled, the first relationship information, the three-pressure profile, and the underbalanced drilling process, the drilling fluid density in the drilling process is optimized. During the optimization process, the drilling fluid density will be reduced. If the drilling process parameters are consistent with those before the last reduction in drilling fluid density, the drilling fluid density can be further reduced, at a rate of 0.02 g / cm³ per cycle. 3 The drilling was stopped and the density was reduced by circulation.

[0085] Optimizing drilling fluid density requires consideration of the wellbore trajectory, vertical depth, and maximum working pressure of the pressure control device to ensure well control safety.

[0086] Among them, the drilling process parameters include the recording of mud inlet and outlet density, cuttings return, total hydrocarbon value, mud tank liquid level, single-cut peak value, friction torque, and vacuum degassing device usage during the drilling process.

[0087] Specifically, the drilling process parameters mentioned above are representations of drilling phenomena during actual drilling operations, used to indicate whether operation can continue.

[0088] Furthermore, the calculation formula for the drilling fluid heat transfer model within the annulus is as follows:

[0089]

[0090] The calculation formula for the drilling fluid heat transfer model inside the drill string is as follows:

[0091]

[0092] In the formula, ρ is the drilling fluid density; q is the drilling fluid volumetric flow rate; C p T represents the specific heat capacity of the drilling fluid. a T represents the drilling fluid temperature within the annulus. w T represents the drill pipe wall temperature. f The near-wellbore formation temperature; r a r is the outer radius of the drill string assembly; o r is the wellbore radius; p h is the inner radius of the drill pipe. ph is the convective heat transfer coefficient of the inner wall of the drill pipe. a The convective heat transfer coefficient within the annulus.

[0093] The following examples illustrate this point:

[0094] Taking well Y101H29 as an example, based on its borehole trajectory, at a vertical depth of 3800m, the collapse pressure, pore pressure, and fracture pressure extracted from the three-dimensional geomechanical model are 60 MPa, 78 MPa, and 105 MPa, respectively, corresponding to a physical density of 2.12 g / cm³. 3 1.62g / cm 3 2.85g / cm 3 The drilling fluid density for underbalanced drilling should be between 1.62 and 2.12 g / cm³. 3 Between; select an FX35-17.5 / 35 rotary blowout preventer with a maximum working pressure of 17.5 MPa. During actual drilling, a back pressure of 3-5 MPa can be applied at the wellhead. Based on the 3800m vertical depth of well Y101H29, an additional 0.14 g / cm³ can be applied. 3 The equivalent density.

[0095] Based on the wellbore trajectory, a two-dimensional horizontal well was adopted with a vertical depth of 3800m and a geothermal gradient of 3℃ / 100m. Drilling parameters of 30L / s displacement, 80RPM rotation speed, and 12000N·m torque were used, with a pH of 1.8-2.0 g / cm³. 3 Within the drilling fluid density range, the temperature rise rate of the bottom-hole circulation in the horizontal section is approximately 1.35℃ / 100m; the drilling fluid density decreases by 0.1g / cm³. 3 The bottom circulation temperature decreases by about 2°C, and the lower the mud density, the greater the decrease in circulation temperature.

[0096] Example 2

[0097] Based on the same inventive concept as in the foregoing embodiments, the present invention provides a second aspect: an apparatus for reducing the bottom-hole circulating temperature of deep shale gas horizontal wells, comprising:

[0098] The acquisition module is used to acquire the three-pressure profile of the well to be drilled and obtain the underpressure value range; wherein, the three-pressure profile includes collapse pressure, pore pressure and fracture pressure, and the underpressure value range is lower than pore pressure and higher than collapse pressure;

[0099] The module is used to determine the underbalanced drilling process based on the underpressure range; the underbalanced drilling process includes using a rotary blowout preventer to control the bottom hole pressure, so that the bottom hole pressure is less than the pore pressure during the drilling process.

[0100] The optimization module is used to obtain the first relationship information and predict the bottom hole circulation temperature of the well to be drilled. Based on the bottom hole circulation temperature of the well to be drilled, the first relationship information, the three pressure profiles, and the underbalanced drilling process, the drilling fluid density in the drilling process is optimized. The first relationship information is the heating rate of the bottom hole circulation temperature in the horizontal section with the increase of well depth and the influence law of the change of drilling fluid density on the bottom hole circulation temperature.

[0101] In summary, this invention proposes a method and apparatus for reducing the bottom-hole circulating temperature of deep shale gas horizontal wells. This method optimizes the drilling fluid density during drilling by utilizing the bottom-hole circulating temperature of the wellbore to be drilled, the first relationship information, the three-pressure profile, and the underbalanced drilling process. By optimizing the drilling fluid density, the solid content in the drilling fluid is reduced, lowering the convective heat transfer coefficient of the fluid within the annulus and drill string, and reducing the heat generated by friction during drilling. This effectively reduces the bottom-hole circulating temperature during deep shale gas drilling, ensuring stable instrument operation, reducing the number of tripping operations, guaranteeing efficient drilling of horizontal wells, and providing guidance for on-site construction. It is of great significance for improving the overall efficiency and speed of shale gas drilling.

Claims

1. A method for reducing the bottom-hole circulating temperature of deep shale gas horizontal wells, characterized in that, Includes the following steps: Step S1: Obtain the three-pressure profile of the well to be drilled and obtain the underpressure value range; wherein, the three-pressure profile includes collapse pressure, pore pressure and fracture pressure, and the underpressure value range is lower than pore pressure and higher than collapse pressure; Step S2: Determine the underbalanced drilling process based on the underpressure range; wherein the underbalanced drilling process includes using a rotary blowout preventer to control the bottom hole pressure, and the bottom hole pressure is less than the pore pressure during the drilling process; Step S3: Obtain the first relationship information and predict the bottom hole circulation temperature of the well to be drilled. Based on the bottom hole circulation temperature of the well to be drilled, the first relationship information, the three pressure profiles and the underbalanced drilling process, optimize the drilling fluid density in the drilling process. The first relationship information is the heating rate of the bottom hole circulation temperature in the horizontal section with the increase of well depth and the influence law of the change of drilling fluid density on the bottom hole circulation temperature. If the following situations occur during the implementation of step S2, appropriate actions need to be taken, as detailed below: a. If a single peak rises significantly after pumping is stopped, the logging team shall reposition the layers and well sections according to the delay time. b. If the bottom hole drilling fluid density cannot meet the bottom hole pressure balance after the pump is stopped, calculate the ECD value of the bottom hole pressure balance and the difference in drilling fluid density during the circulation process, control the pressure when the pump is stopped, and record the pressure control data in detail each time. c. If the gas measurement value continues to rise and the fluid level rises during the drilling process, the well team should shut down the well in time and add weight. After adding weight, stop drilling, start the pump to circulate and vent the gas, and observe the changes in the gas measurement value. d. If subsequent underbalanced drilling operations cannot be carried out, drilling shall be completed according to the lower limit of the drilling fluid density that can balance the bottom hole pressure using the bottom hole ECD; e. If the vibrating screen returns large chunks or has abnormal torque, the casing pressure control value should be increased, the equivalent density at the bottom of the well should be increased to prevent further collapse of the well wall, and the reaming of the collapsed section should be increased to ensure that the wellbore is unobstructed. f. If increasing the wellhead casing pressure is ineffective, the drilling fluid density can be increased and the mud properties adjusted; The step S3 of predicting the bottom hole circulation temperature of the well to be drilled includes: The process involves acquiring drilled well parameter information, revising the drilling fluid heat transfer model within the drill string and the drilling fluid heat transfer model within the annulus based on this information, and then combining it with the well-to-be-drilled parameter information to predict the bottom hole circulation temperature of the well to be drilled. The drilled well parameter information includes the bottom hole circulation temperature, inlet and outlet drilling fluid temperatures, and drilling fluid density. The well-to-be-drilled parameter information includes the vertical depth, inclination depth, wellbore trajectory, machine speed, displacement, drilling fluid rheological parameters, and drilling fluid thermophysical parameters of the well to be drilled. The calculation formula for the drilling fluid heat transfer model in the annulus is as follows: The calculation formula for the drilling fluid heat transfer model inside the drill string is as follows: In the formula, Density of drilling fluid; This refers to the volumetric flow rate of the drilling fluid. Specific heat capacity of drilling fluid; The temperature of the drilling fluid within the annulus; The drill pipe wall temperature; The formation temperature near the wellbore; The outer radius of the drill string assembly; The radius of the wellbore; The inner radius of the drill pipe; The convective heat transfer coefficient of the inner wall surface of the drill pipe; The convective heat transfer coefficient within the annulus; The drilling fluid density in the optimized drilling process described in step S3 includes: In the process of optimizing the drilling process, the drilling fluid density will be reduced. If the drilling process parameters are consistent with those before the last reduction of drilling fluid density, the drilling fluid density can be further reduced by stopping drilling and cyclically reducing the density at a rate of 0.02 g / cm³ per cycle.

2. The method for reducing the bottom-hole circulation temperature of deep shale gas horizontal wells according to claim 1, characterized in that, Obtaining the three pressure profiles in step S1 specifically includes the following sub-steps: Step S11: Obtain drilling and logging data of the drilled wells in the target well area and establish a single-well geomechanical model; Step S12: Based on the obtained single-well geomechanical model and combined with the seismic attribute inversion data of the target well area, establish a three-dimensional geomechanical model to extract the three-pressure curves along the well for the well that needs to be predicted by the three-pressure profile, and determine the three-pressure profile.

3. The method for reducing the bottom-hole circulation temperature of deep shale gas horizontal wells according to claim 1, characterized in that, The calculation model for the pore pressure is as follows: In the formula, Pore ​​pressure; This refers to the pressure of the overlying strata. Normal hydrostatic pressure; To calculate the acoustic transit time at the point; The sonic transit time is the normal compaction curve of mudstone corresponding to the calculation point. This is the model index.

4. The method for reducing the bottom-hole circulation temperature of deep shale gas horizontal wells according to claim 1, characterized in that, The calculation model for the collapse pressure is as follows: In the formula, For collapse pressure; These are nonlinear correction coefficients; For depth; It is the cohesive force within the rock; Biot coefficient; This represents the maximum horizontal principal stress. The minimum horizontal principal stress; It is the internal friction angle.

5. The method for reducing the bottom-hole circulation temperature of deep shale gas horizontal wells according to claim 1, characterized in that, The calculation model for the rupture pressure is as follows: In the formula, This is the rupture pressure; This represents the maximum horizontal principal stress. The minimum horizontal principal stress; Poisson's ratio; Pore ​​pressure; Tensile strength of the formation; Biot coefficient; The coefficient is 0 when the well wall is impermeable and 1 when the well wall is permeable. Porosity.

6. An apparatus for reducing the bottom-hole circulating temperature of a deep shale gas horizontal well, capable of implementing the method for reducing the bottom-hole circulating temperature of a deep shale gas horizontal well as described in any one of claims 1-5, characterized in that, include: The acquisition module is used to acquire the three-pressure profile of the well to be drilled and obtain the underpressure value range; wherein, the three-pressure profile includes collapse pressure, pore pressure and fracture pressure, and the underpressure value range is lower than pore pressure and higher than collapse pressure; A formulation module is used to determine an underbalanced drilling process based on the underpressure value range; wherein the underbalanced drilling process includes using a rotary blowout preventer to control the bottom hole pressure, wherein the bottom hole pressure is less than the pore pressure during the drilling process; An optimization module is used to acquire first relationship information and predict the bottom hole circulation temperature of the well to be drilled. Based on the bottom hole circulation temperature of the well to be drilled, the first relationship information, the three pressure profiles, and the underbalanced drilling process, the drilling fluid density in the drilling process is optimized. The first relationship information is the heating rate of the bottom hole circulation temperature in the horizontal section with increasing well depth and the influence of the drilling fluid density change on the bottom hole circulation temperature.

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