Cooling capacity simulation device and calculation method for cooling material used in drilling fluid

Abstract

The present invention discloses a cooling capacity simulation device and calculation method for cooling materials used in drilling fluids, and the calculation method comprises the following steps: S1: preparing a drilling fluid base slurry for an experiment, and injecting it into a liquid storage tank after stirring evenly; S2: filling the drilling fluid base slurry with a wellbore simulation system; S3: heating to a target drilling fluid temperature; S4: circulating the liquid phase fluid, and recording the time to reach the phase change temperature and the phase change endothermic saturation time during the circulation process; S5: emptying; S6 and S7: conducting a drilling fluid endothermic simulation experiment with different weight ratios of cooling materials at different displacements and well depths, and recording the time and temperature parameters during the simulation experiment; S8: establishing a temperature calculation equation, solving the temperature calculation equation, and obtaining the cooling capacity of the target cooling material during the drilling process. The present invention can more accurately determine the cooling capacity of the cooling material used in the drilling fluid, and provide technical support for improving the control accuracy of the drilling fluid temperature.

Description

Technical Field

[0001] The invention relates to the technical field of high-temperature drilling of oil and natural gas, and in particular to a cooling capacity simulation device and a calculation method of a cooling material used for drilling fluid. Background Art

[0002] With the continuous deepening of oil and gas exploration activities, drilling operations in complex geological environments such as deep water, high temperature and high pressure have become an important technical challenge. In order to ensure the safety and efficiency of drilling operations, various factors need to be accurately controlled and adjusted. Among them, the temperature control of drilling fluid is a key link.

[0003] The traditional cooling method is to indirectly reduce the bottom hole temperature by lowering the injection temperature of drilling fluid. Although this method can achieve certain results, it has problems such as poor effect and high cost. The traditional natural cooling method can no longer meet the needs. Using cooling materials for cooling is a technology with potential application value. It can adjust the temperature by absorbing or releasing heat through the phase change of cooling materials, thereby achieving the purpose of cooling.

[0004] According to public literature, the current analysis of the cooling effect of cooling materials in the well is mostly achieved through computer simulation. However, the simple use of theoretical calculations cannot well analyze the cooling characteristics of cooling materials. The cooling effect of cooling materials during drilling is affected by many factors, including the content of cooling materials, phase change temperature, drilling fluid flow, pumping pressure, drilling depth, etc. Therefore, a cooling capacity simulation device and calculation method for cooling materials used in drilling fluids are urgently needed to help drilling experts more accurately control the temperature of drilling fluids and improve drilling efficiency and safety. Summary of the invention

[0005] In view of the above problems, the present invention aims to provide a device and a method for simulating the cooling capacity of a cooling material for drilling fluid.

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

[0007] On the one hand, a device for simulating the cooling capacity of a cooling material for drilling fluid is provided, comprising a wellbore simulation system, a drilling fluid circulation system, a temperature simulation system, and a data acquisition system;

[0008] The wellbore simulation system includes a wellbore and a drill string disposed in the wellbore;

[0009] The drilling fluid circulation system includes a liquid storage tank, a positive circulation liquid phase delivery pipeline, and a reverse circulation liquid phase delivery pipeline;

[0010] The positive circulation liquid phase delivery pipeline comprises an input pump 1, a pipeline 1 and a pipeline 2, wherein the input end of the input pump 1 is connected to the liquid reservoir, the output end of the input pump 1 is connected to the pipeline 1, the other end of the pipeline 1 is connected to the wellbore, and the two ends of the pipeline 2 are respectively connected to the wellbore and the liquid reservoir; a control valve 1 is provided on the end of the pipeline 1 close to the input pump 1;

[0011] The reverse circulation liquid phase delivery pipeline includes input pump 2, pipeline 3 and pipeline 4. The input end of input pump 2 is connected to pipeline 3, the output end of input pump 2 is connected to the liquid reservoir, the other end of pipeline 3 is connected to the wellbore, and the two ends of pipeline 4 are respectively connected to the wellbore and the atmosphere; a control valve 2 is provided on one end of pipeline 3 close to input pump 2;

[0012] The temperature simulation system includes a heating device, and the heating device is connected to the wellbore simulation system;

[0013] The data acquisition system is used to collect the temperature inside the wellbore simulation system and the flow rate and pressure of the drilling fluid circulation system.

[0014] Preferably, the wellbore and the drill string are both length-adjustable structures, and the lengths of the wellbore and the drill string are adjustable to the same extent.

[0015] Preferably, the data acquisition system comprises a computer and a temperature sensor 1, a temperature sensor 2, a flow meter 1, a flow meter 2, a pressure sensor 1, and a pressure sensor 2 respectively connected to the computer;

[0016] The temperature sensor 1 is arranged on the drill string and is used to monitor the temperature inside the wellbore simulation system;

[0017] The second temperature sensor is arranged on the pipeline of the drilling fluid circulation system to monitor the temperature outside the wellbore;

[0018] The flow meter 1 and the pressure sensor 1 are arranged on the pipeline 1, and an overflow valve 1 is arranged between the two, and the flow meter 1 is arranged at one end close to the control valve 1;

[0019] The second pressure sensor and the second flow meter are arranged on the second pipeline, and a second overflow valve is arranged between the two. The second pressure sensor is arranged at one end close to the wellbore.

[0020] Preferably, the input pump 1 and the input pump 2 use the same self-priming variable frequency screw pump, and the self-priming variable frequency screw pump is connected to the pipeline 1 and the pipeline 3 through the pipeline 5 and the three-way valve; two temperature sensors 1 are provided, respectively located at the lower part and the middle part of the drill string.

[0021] On the other hand, a method for calculating the cooling capacity of a cooling material for drilling fluid is also provided, wherein a cooling capacity simulation device for a cooling material for drilling fluid described in any one of the above is used to perform a cooling capacity simulation experiment of the cooling material, and parameters in the simulation process are obtained, and the cooling capacity of the cooling material is calculated based on the parameters. The cooling capacity calculation method comprises the following steps:

[0022] S1: preparing a drilling fluid base slurry for the experiment according to the drilling fluid used in the on-site drilling, stirring it evenly and injecting it into the liquid storage tank;

[0023] S2: Turn on the input pump 1 and the control valve 1 to allow the drilling fluid slurry to fill the wellbore simulation system;

[0024] S3: closing the input pump 1 and the control valve 1, and opening the temperature simulation system, so that the temperature inside the wellbore simulation system reaches the drilling fluid temperature at the depth of the target well;

[0025] S4: Turn on the input pump 1 and the control valve 1 to circulate the liquid phase fluid, and record the temperature inside the wellbore simulation system, the time when the target cooling material reaches the phase change temperature, and the phase change endothermic saturation time during the circulation process;

[0026] S5: close the input pump 1 and the control valve 1 to stop the circulation of the liquid phase fluid; open the input pump 2 and the control valve 2 to drain the liquid phase fluid;

[0027] S6: adding different weight percentages of target cooling materials to the experimental drilling fluid base slurry, and using different displacements less than the displacement limit value, repeating steps S1-S5 respectively, completing the drilling fluid heat absorption simulation experiment with different weight percentages of cooling materials at different displacements, and recording the time and temperature parameters during the simulation experiment;

[0028] S7: adding different weight percentages of target cooling materials to the experimental drilling fluid base slurry, and using wellbore simulation systems with different well depths, repeating steps S1-S5 respectively, completing the drilling fluid heat absorption simulation experiment with different weight percentages of cooling materials at different well depths, and recording the time and temperature parameters during the simulation experiment;

[0029] S8: Establishing a temperature calculation equation, solving the temperature calculation equation, and obtaining the cooling capacity of the target cooling material during the drilling process.

[0030] Preferably, in step S2, when the drilling fluid base slurry fills the wellbore simulation system, the injection displacement is adjusted to the displacement limit value of the cooling capacity simulation device, and the displacement limit value of the cooling capacity simulation device is calculated by the following formula:

[0031]

[0032] Where: Q 1,m is the displacement limit value of the cooling capacity simulation device, m 3 / s;Q 1,s is the displacement of the drilling pump during the actual drilling operation, m 3 / s; R w,m is the wellbore radius of the cooling capacity simulation device, m; R p,m is the drill string radius of the cooling capacity simulation device, m; R w,s is the wellbore radius in actual situation, m; R p,s is the actual drill string radius, m.

[0033] Preferably, in step S8, the temperature calculation equation includes a temperature calculation equation for the drilling fluid in the drill string containing cooling material, a temperature calculation equation for the drill string wall, a temperature calculation equation for the drilling fluid in the annulus containing cooling material, a temperature calculation equation for the well wall, and a temperature calculation equation for the formation;

[0034] The temperature calculation equation of the drilling fluid in the drill string containing the cooling material is:

[0035]

[0036] Where: Q m is the heat source of the liquid in the drill string, W / m 3 ρ 0 is the density of drilling fluid in the drill string, kg / m 3 ;c g 、c f 、c y are the specific heat capacity of the drilling fluid containing cooling material before phase change, the specific heat capacity of the drilling fluid containing cooling material during phase change, and the specific heat capacity of the drilling fluid containing cooling material after phase change; r 0 is the inner radius of the drill string; T 0 , T 1 are respectively the drilling fluid temperature in the drill string and the drill string wall temperature, °C; t is the time step, s; q is the displacement, m 3 / s; z is the spatial step length, m; λ 0 is the thermal conductivity of drilling fluid, W / (m·℃); Nu g1 、Nu f1 、Nu y1 are the Nu number of the inner wall of the drill string before phase change, the Nu number of the inner wall of the drill string during phase change, and the Nu number of the inner wall of the drill string after phase change; L is the characteristic length, m; T is the real-time drilling fluid temperature, °C; T m is the phase transition temperature of the cooling material, ℃; ΔT is the temperature range of phase transition, ℃;

[0037] The temperature calculation equation of the drill string wall is:

[0038]

[0039] Where: 1 is the thermal conductivity of the drill string, W / (m·℃); r 1 is the outer radius of the drill string, m; ρ 1 is the density of drill string, kg / m 3 ;c 1 is the specific heat capacity of the drill string; Nu g2 、Nu f2 、Nu y2 They are respectively the Nu number of the outer wall of the drill string before phase change, the Nu number of the outer wall of the drill string during phase change, and the Nu number of the outer wall of the drill string after phase change;

[0040] The temperature calculation equation of the drilling fluid in the annulus containing the cooling material is:

[0041]

[0042] Where: 2 is the drilling fluid density in the annulus, kg / m 3 ; T 2 , T 3 are the annulus drilling fluid temperature and wellbore wall temperature, °C; Q a is the liquid heat source in the annulus, W / m 3 ; r 2 is the radius of the wellbore, m; Nu g3 、Nu f3 、Nu y3 They are the Nu number of the wellbore wall before phase change, the Nu number of the wellbore wall during phase change, and the Nu number of the wellbore wall after phase change;

[0043] The temperature calculation equation of the well wall is:

[0044]

[0045] Where: 2 is the thermal conductivity of the well wall, W / (m·℃); T 3 , T 4 are wellbore temperature and formation temperature, respectively, °C; ρ 3 is the wellbore density, kg / m 3 ;c 3 is the specific heat capacity of the well wall; r 3 、r 4 are the diameter of the wellbore wall and the diameter of the formation unit, m;

[0046] The temperature calculation equation of the formation is:

[0047]

[0048] Where: Ti is the formation temperature, °C; r is the diameter of the formation unit, m; r i is the diameter of the i-th layer unit, m; ρ i is the formation density, kg / m 3 ;c i is the formation specific heat capacity; i is the thermal conductivity of the formation, W / (m·℃).

[0049] Preferably, the Nu number in the temperature calculation equation is calculated by the following formula:

[0050]

[0051] Where: Q is the total heat exchange, W; A is the heat exchange area of ​​the cooling capacity simulation device, m 2 ; T v is the average temperature of the heating device, °C; T a is the backward temperature of the drilling fluid flowing through the heating area of ​​the heating device, ℃; R w is the thermal resistance between the heating device and the wellbore wall, ℃ / W; R w,m is the wellbore radius of the cooling capacity simulation device, m.

[0052] Preferably, when solving the temperature calculation equation, the temperature calculation equation is discretized using a fully implicit format to obtain a discrete form of the temperature calculation equation, and then the discrete form is iteratively solved;

[0053] The discrete formula of the temperature calculation equation of the drilling fluid in the drill string containing the cooling material is:

[0054]

[0055] Where: superscript n represents time; subscript j represents depth; A 0 , B 0 , C 0 , D 0 They are all constant terms in the temperature calculation equation of the drilling fluid in the drill string containing cooling materials;

[0056] The discrete form of the temperature calculation equation of the drill string wall is:

[0057]

[0058] Where: A 1 , B 1 , C 1 , D 1 、E 1 They are all constant terms in the temperature calculation equation of the drill string wall;

[0059] The discrete formula of the temperature calculation equation of the drilling fluid in the annulus containing the cooling material is:

[0060]

[0061] Where: A 2 , B 2 , C 2 , D 2 、E 2 They are all constant terms in the temperature calculation equation of the drilling fluid in the annulus containing cooling materials;

[0062] The discrete form of the temperature calculation equation of the well wall is:

[0063]

[0064] Where: A 3 , B 3 , C 3 , D 3 、E 3 They are all constant terms in the temperature calculation equation of the wellbore wall;

[0065] The discrete form of the temperature calculation equation of the formation is:

[0066]

[0067] Where: A i , B i , C i , D i 、E i They are all constant terms in the formation temperature calculation equation.

[0068] Preferably, when the discrete formula is iteratively solved, the number of iterations of the cooling material phase change endothermic time is calculated by the following formula:

[0069] t 1 =h 1,m *3600 / Δt (13)

[0070]

[0071] Where: t 1 h is the number of iterations of the cooling material phase change endothermic time; 1,m is the phase change endothermic saturation time of the cooling material during the actual drilling operation, h; Δt is the time step; h 1,s is the phase change endothermic saturation time of the cooling material during the simulation experiment, h; ΔT 2 is the temperature difference between the formation temperature and the drilling fluid temperature during drilling, °C; R w,s is the wellbore radius in actual situation, m; h yis the convective heat transfer coefficient of drilling fluid during drilling, W / (m 2 ℃); ΔT 1 is the temperature difference between the wellbore outside temperature and the drilling fluid temperature during the simulation experiment, ℃; R w,m is the wellbore radius of the cooling capacity simulation device, m; h x is the convective heat transfer coefficient of drilling fluid during the simulation experiment, W / (m 2 ·℃).

[0072] The beneficial effects of the present invention are:

[0073] The present invention can simulate the cooling capacity of cooling materials used for drilling fluid, and then calculate and obtain a more accurate cooling capacity of the cooling materials used for drilling fluid, thereby helping drilling experts to more accurately control the temperature of the drilling fluid, improve drilling efficiency and safety, and promote the application and development of cooling materials in the field of oil and gas exploration. BRIEF DESCRIPTION OF THE DRAWINGS

[0074] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0075] Figure 1 It is a structural schematic diagram of a device for simulating the cooling capacity of a cooling material for drilling fluid according to the present invention;

[0076] Figure 2 It is a partial structural schematic diagram of a wellbore simulation system of a cooling capacity simulation device for a cooling material for drilling fluid according to the present invention;

[0077] Figure 3 It is a physical model diagram of the heat exchange process of the drilling fluid containing cooling material during the drilling process;

[0078] Figure 4 A schematic diagram of the calculation results of the cooling capacity of cooling materials with different weight ratios for a specific embodiment of a cycle of 6 hours;

[0079] Figure 5 A schematic diagram of the calculation results of the cooling capacity of cooling materials with different weight ratios for 8 hours of circulation in a specific embodiment;

[0080] Figure 6 A schematic diagram of the calculation results of the cooling capacity of cooling materials with different weight ratios for a specific embodiment of a cycle of 10 hours;

[0081] Figure 7This is a schematic diagram of the calculation results of the cooling capacity of cooling materials with different weight ratios after a 12-hour cycle in a specific embodiment.

[0082] Numbers in the figure: 1-wellbore, 2-drill string, 3-liquid storage tank, 4-input pump 1, 5-pipeline 1, 6-pipeline 2, 7-control valve 1, 8-pipeline 3, 9-control valve 2, 10-heating device, 11-temperature sensor 1, 12-temperature sensor 2, 13-flow meter 1, 14-flow meter 2, 15-pressure sensor 1, 16-pressure sensor 2, 17-overflow valve 1, 18-overflow valve 2, 19-pressure sensor 3, 20-pipeline 5, 21-three-way valve, 22-insulation layer 1. DETAILED DESCRIPTION

[0083] The present invention is further described below in conjunction with the accompanying drawings and embodiments. It should be noted that, in the absence of conflict, the embodiments in this application and the technical features in the embodiments can be combined with each other. It should be noted that, unless otherwise specified, all technical and scientific terms used in this application have the same meanings as those generally understood by those of ordinary skill in the art to which this application belongs. The words "including" or "comprising" and the like used in the disclosure of the present invention mean that the elements or objects appearing before the word cover the elements or objects listed after the word and their equivalents, without excluding other elements or objects.

[0084] In the present invention, unless otherwise stated, the terms "first", "second", etc. are used to distinguish similar objects, rather than to describe a specific order or sequence. It should be understood that the terms used in this way; the terms "upper", "lower", "left", "right", etc. are usually used in relation to the directions shown in the drawings, or in relation to the components themselves in the vertical, perpendicular or gravity direction; similarly, for ease of understanding and description, "inner", "outer", etc. refer to the inside and outside relative to the outline of each component itself. However, the above-mentioned directional words are not used to limit the present invention.

[0085] On the one hand, if Figure 1-2 As shown, the present invention provides a cooling capacity simulation device for cooling materials used in drilling fluids, including a wellbore simulation system, a drilling fluid circulation system, a temperature simulation system, and a data acquisition system;

[0086] The wellbore simulation system comprises a wellbore 1 and a drill string 2 arranged in the wellbore 1;

[0087] The drilling fluid circulation system includes a liquid storage tank 3, a positive circulation liquid phase delivery pipeline, and a reverse circulation liquid phase delivery pipeline;

[0088] The positive circulation liquid phase delivery pipeline includes an input pump 14, a pipeline 15 and a pipeline 26. The input end of the input pump 14 is connected to the liquid reservoir 3, the output end of the input pump 14 is connected to the pipeline 15, the other end of the pipeline 15 is connected to the wellbore 1, and the two ends of the pipeline 26 are respectively connected to the wellbore 1 and the liquid reservoir 3; a control valve 17 is provided on the end of the pipeline 15 close to the input pump 14;

[0089] The reverse circulation liquid phase delivery pipeline includes an input pump 2 (not shown in the figure), a pipeline 3 8 and a pipeline 4 (not shown in the figure), the input end of the input pump 2 is connected to the pipeline 3 8, the output end of the input pump 2 is connected to the liquid reservoir 3, the other end of the pipeline 3 8 is connected to the wellbore 1, and the two ends of the pipeline 4 are respectively connected to the wellbore 1 and the atmosphere; a control valve 2 9 is provided on the end of the pipeline 3 8 close to the input pump 2;

[0090] The temperature simulation system includes a heating device 10, and the heating device 10 is connected to the wellbore simulation system;

[0091] The data acquisition system is used to collect the temperature inside the wellbore simulation system and the flow rate and pressure of the drilling fluid circulation system.

[0092] In a specific embodiment, the wellbore 1 and the drill string 2 are both length-adjustable structures, and the wellbore 1 and the drill string 2 have the same degree of length adjustment. Optionally, the wellbore 1 is composed of a plurality of wellbore segments that are detachably connected, and the drill string 2 is composed of a plurality of drill string segments that are detachably connected. It should be noted that, in addition to the structure of this embodiment, other length-adjustable structures in the prior art may also be applicable to the present invention. In addition, an integrated wellbore and drill string of different lengths may also be used directly for simulation experiments.

[0093] In a specific embodiment, the data acquisition system includes a computer (not shown in the figure) and a temperature sensor 11, a temperature sensor 12, a flow meter 13, a flow meter 14, a pressure sensor 15, and a pressure sensor 16 respectively connected to the computer; the temperature sensor 11 is arranged on the drill string 2, and is used to monitor the temperature inside the wellbore simulation system; the temperature sensor 12 is arranged on the pipeline of the drilling fluid circulation system, and is used to monitor the temperature outside the wellbore; the flow meter 13 and the pressure sensor 15 are arranged on the pipeline 5, and an overflow valve 17 is arranged between the two, and the flow meter 13 is arranged at one end close to the control valve 7; the pressure sensor 16 and the flow meter 14 are arranged on the pipeline 6, and an overflow valve 18 is arranged between the two, and the pressure sensor 16 is arranged at one end close to the wellbore 1.

[0094] In a specific embodiment, the overflow valve 17 and the overflow valve 2 18 are respectively connected to the computer, and two temperature sensors 11 are provided, which are respectively located at the lower part and the middle part of the drill string 2.

[0095] In a specific embodiment, the data acquisition system also includes a pressure sensor three 19 connected to the computer, and the pressure sensor three 19 is arranged on the pipeline one 5 between the pressure sensor one 15 and the wellbore 1, and is located close to one end of the wellbore 1.

[0096] In a specific embodiment, the input pump 1 4 and the input pump 2 use the same self-priming variable frequency screw pump, and the self-priming variable frequency screw pump is connected to the pipeline 1 5 and the pipeline 3 8 through the pipeline 5 20 and the three-way valve 21; the pipeline 2 6 and the pipeline 4 use the same pipeline, and the end of the pipeline away from the wellbore 1 is located above the liquid reservoir 3; when the pipeline is used for the positive circulation liquid phase delivery pipeline, the output liquid phase is directly delivered to the liquid reservoir 3; when the pipeline is used for the reverse circulation liquid phase delivery pipeline, the atmosphere is sucked in to empty the liquid phase in the wellbore 1. Optionally, the self-priming variable frequency screw pump is connected to the computer. In this embodiment, by sharing the input pump and sharing part of the pipeline, the structure of the present invention can be made simpler and the cost can be reduced.

[0097] In a specific embodiment, the temperature simulation system also includes an insulation layer 1 22 and an insulation layer 2 (not shown in the figure), the insulation layer 1 22 is used to insulate the wellbore 1, and the insulation layer 2 is used to insulate the pipeline of the drilling fluid circulation system.

[0098] On the other hand, a method for calculating the cooling capacity of a cooling material for drilling fluid is also provided, wherein a cooling capacity simulation device for a cooling material for drilling fluid described in any one of the above is used to perform a cooling capacity simulation experiment of the cooling material, and parameters in the simulation process are obtained, and the cooling capacity of the cooling material is calculated based on the parameters. The cooling capacity calculation method comprises the following steps:

[0099] S1: Prepare the drilling fluid base slurry for the experiment according to the drilling fluid used in the on-site drilling, stir it evenly and then inject it into the liquid storage tank 3.

[0100] S2: Open the input pump 4 and the control valve 7 to allow the drilling fluid slurry to fill the wellbore simulation system.

[0101] In a specific embodiment, when the drilling fluid base slurry fills the wellbore simulation system, the injection displacement is adjusted to the displacement limit value of the cooling capacity simulation device, so that the drilling fluid base slurry can fill the wellbore simulation system more quickly. Optionally, the displacement limit value of the cooling capacity simulation device is calculated by the following formula:

[0102]

[0103] Where: Q 1,m is the displacement limit value of the cooling capacity simulation device, m 3 / s;Q 1,s is the displacement of the drilling pump during the actual drilling operation, m 3 / s; R w,m is the wellbore radius of the cooling capacity simulation device, m; R p,m is the drill string radius of the cooling capacity simulation device, m; R w,s is the wellbore radius in actual situation, m; R p,s is the actual drill string radius, m.

[0104] S3: close the input pump 4 and the control valve 7, and start the temperature simulation system to make the temperature inside the wellbore simulation system reach the drilling fluid temperature at the depth of the target well.

[0105] S4: Turn on the input pump 4 and the control valve 7 to circulate the liquid phase fluid, and record the temperature inside the wellbore simulation system, the time when the target cooling material reaches the phase change temperature, and the phase change endothermic saturation time during the circulation process.

[0106] In a specific embodiment, the time when the phase change temperature exceeds a certain interval threshold is recorded as the phase change endothermic saturation time of the target cooling material. Optionally, the interval threshold is 2°C or 5°C. It should be noted that the phase change endothermic saturation time cannot be obtained by observation. Therefore, in this embodiment, by setting a temperature interval, the time exceeding the temperature interval is used as the phase change endothermic saturation time, and the temperature interval can change the set value as needed.

[0107] S5: close the input pump 1 4 and the control valve 1 7 to stop the circulation of the liquid phase fluid; open the input pump 2 and the control valve 2 9 to drain the liquid phase fluid.

[0108] S6: adding different weight percentages of target cooling materials to the experimental drilling fluid base slurry, and using different displacements less than the displacement limit value, repeating steps S1-S5 respectively, completing the drilling fluid heat absorption simulation experiment with different weight ratios of cooling materials at different displacements, and recording the time and temperature parameters during the simulation experiment.

[0109] S7: adding different weight percentages of target cooling materials to the experimental drilling fluid base slurry, and using wellbore simulation systems with different well depths, repeating steps S1-S5 respectively to complete the drilling fluid heat absorption simulation experiment at different well depths with different weight percentages of cooling materials, and recording the time and temperature parameters during the simulation experiment.

[0110] S8: Establishing a temperature calculation equation, solving the temperature calculation equation, and obtaining the cooling capacity of the target cooling material during the drilling process.

[0111] In a specific embodiment, the temperature calculation equation includes a temperature calculation equation for the drilling fluid in the drill string containing cooling material, a temperature calculation equation for the drill string wall, a temperature calculation equation for the drilling fluid in the annulus containing cooling material, a temperature calculation equation for the well wall, and a temperature calculation equation for the formation;

[0112] The temperature calculation equation of the drilling fluid in the drill string containing the cooling material is:

[0113]

[0114] Where: Q m is the heat source of the liquid in the drill string, W / m 3 ρ 0 is the density of drilling fluid in the drill string, kg / m 3 ;c g 、c f 、c y are the specific heat capacity of the drilling fluid containing cooling material before phase change, the specific heat capacity of the drilling fluid containing cooling material during phase change, and the specific heat capacity of the drilling fluid containing cooling material after phase change; r 0 is the inner radius of the drill string; T 0 , T 1 are respectively the drilling fluid temperature in the drill string and the drill string wall temperature, °C; t is the time step, s; q is the displacement, m 3 / s; z is the spatial step length, m; λ 0 is the thermal conductivity of drilling fluid, W / (m·℃); Nu g1 、Nu f1 、Nu y1 are the Nu number of the inner wall of the drill string before phase change, the Nu number of the inner wall of the drill string during phase change, and the Nu number of the inner wall of the drill string after phase change; L is the characteristic length, m; T is the real-time drilling fluid temperature, °C; T m is the phase transition temperature of the cooling material, ℃; ΔT is the temperature range of phase transition, ℃;

[0115] The temperature calculation equation of the drill string wall is:

[0116]

[0117] Where: 1 is the thermal conductivity of the drill string, W / (m·℃); r 1 is the outer radius of the drill string, m; ρ 1 is the density of drill string, kg / m 3 ;c 1 is the specific heat capacity of the drill string; Nu g2、Nu f2 、Nu y2 They are respectively the Nu number of the outer wall of the drill string before phase change, the Nu number of the outer wall of the drill string during phase change, and the Nu number of the outer wall of the drill string after phase change;

[0118] The temperature calculation equation of the drilling fluid in the annulus containing the cooling material is:

[0119]

[0120] Where: 2 is the drilling fluid density in the annulus, kg / m 3 ; T 2 , T 3 are the annulus drilling fluid temperature and wellbore wall temperature, °C; Q a is the liquid heat source in the annulus, W / m 3 ; r 2 is the radius of the wellbore, m; Nu g3 、Nu f3 、Nu y3 They are the Nu number of the wellbore wall before phase change, the Nu number of the wellbore wall during phase change, and the Nu number of the wellbore wall after phase change;

[0121] The temperature calculation equation of the well wall is:

[0122]

[0123] Where: 2 is the thermal conductivity of the well wall, W / (m·℃); T 3 , T 4 are wellbore temperature and formation temperature, respectively, °C; ρ 3 is the wellbore density, kg / m 3 ;c 3 is the specific heat capacity of the well wall; r 3 、r 4 are the diameter of the wellbore wall and the diameter of the formation unit, m;

[0124] The temperature calculation equation of the formation is:

[0125]

[0126] Where: T i is the formation temperature, °C; r is the diameter of the formation unit, m; r i is the diameter of the i-th layer unit, m; ρ i is the formation density, kg / m 3 ;c i is the formation specific heat capacity; i is the thermal conductivity of the formation, W / (m·℃).

[0127] It should be noted that in the temperature calculation equation of the above embodiment, the parameters of the drill string, drill string outer wall, drilling fluid, wellbore, well wall, etc. are all related parameters of the actual target well and the actual drill string.

[0128] In a specific embodiment, the Nu number in the temperature calculation equation is calculated by the following formula:

[0129]

[0130] Where: Q is the total heat exchange, W; A is the heat exchange area of ​​the cooling capacity simulation device, m 2 ; T v is the average temperature of the heating device, °C; T a is the backward temperature of the drilling fluid flowing through the heating area of ​​the heating device, ℃; R w is the thermal resistance between the heating device and the wellbore wall, ℃ / W; R w,m is the wellbore radius of the cooling capacity simulation device, m.

[0131] In a specific embodiment, when solving the temperature calculation equation, the temperature calculation equation is discretized using a fully implicit format to obtain a discrete form of the temperature calculation equation, and then the discrete form is iteratively solved;

[0132] The discrete formula of the temperature calculation equation of the drilling fluid in the drill string containing the cooling material is:

[0133]

[0134] Where: superscript n represents time; subscript j represents depth; A 0 , B 0 , C 0 , D 0 They are all constant terms in the temperature calculation equation of the drilling fluid in the drill string containing cooling materials;

[0135] The discrete form of the temperature calculation equation of the drill string wall is:

[0136]

[0137] Where: A 1 , B 1 , C 1 , D 1 、E 1 They are all constant terms in the temperature calculation equation of the drill string wall;

[0138] The discrete formula of the temperature calculation equation of the drilling fluid in the annulus containing the cooling material is:

[0139]

[0140] Where: A 2 , B 2 , C 2 , D 2 、E 2 They are all constant terms in the temperature calculation equation of the drilling fluid in the annulus containing cooling materials;

[0141] The discrete form of the temperature calculation equation of the well wall is:

[0142]

[0143] Where: A 3 , B 3 , C 3 , D 3 、E 3 They are all constant terms in the temperature calculation equation of the wellbore wall;

[0144] The discrete form of the temperature calculation equation of the formation is:

[0145]

[0146] Where: A i , B i , C i , D i 、E i They are all constant terms in the formation temperature calculation equation.

[0147] In a specific embodiment, when the discrete formula is iteratively solved, the number of iterations of the cooling material phase change endothermic time is calculated by the following formula:

[0148] t 1 =h 1,m *3600 / Δt (13)

[0149]

[0150] Where: t 1 h is the number of iterations of the cooling material phase change endothermic time; 1,m is the phase change endothermic saturation time of the cooling material during the actual drilling operation, h; Δt is the time step; h 1,s is the phase change endothermic saturation time of the cooling material during the simulation experiment, h; ΔT 2 is the temperature difference between the formation temperature and the drilling fluid temperature during drilling, °C; R w,s is the wellbore radius in actual situation, m; h y is the convective heat transfer coefficient of drilling fluid during drilling, W / (m 2 ℃); ΔT 1 is the temperature difference between the wellbore outside and the drilling fluid during the simulation experiment, °C; R w,mis the wellbore radius of the cooling capacity simulation device, m; h x is the convective heat transfer coefficient of drilling fluid during the simulation experiment, W / (m 2 ·℃).

[0151] It should be noted that the method of iteratively solving the discrete equation is a prior art, and the specific steps will not be repeated here.

[0152] In a specific embodiment, the cooling capacity calculation method of the cooling material for drilling fluid of the present invention is used to calculate the cooling capacity of a target cooling material. In this embodiment, the physical model of the heat exchange process of the drilling fluid containing the cooling material during the drilling process is as follows: Figure 3 As shown, the target well is located in an oil field, and the well is drilled from a well depth of 3000m to a well depth of 7000m. The phase change temperature of the target cooling material is 140°C. The operating parameters are: drilling fluid density 1.60g / cm 3 , drilling fluid injection temperature 20℃, drilling pump displacement 25L / s. Environmental parameters are: vertical depth 7000m, surface temperature 15℃, geothermal gradient 3.5℃ / 100m. The thermal physical parameters of the target cooling material are shown in Table 1, and the drilling and thermal parameters are shown in Table 2:

[0153] Table 1. Thermophysical properties of target cooling materials

[0154]

[0155] Table 2. Drilling and thermal parameters

[0156]

[0157] The calculation method specifically includes the following sub-steps:

[0158] (1) preparing a drilling fluid base slurry for the experiment according to the drilling fluid used in the on-site drilling, stirring it evenly and injecting it into the liquid storage tank 3; in this embodiment, the drilling fluid base slurry for the experiment is bentonite base slurry;

[0159] (2) Opening the control valve 7, starting the self-priming variable frequency screw pump, and gradually increasing its output power until its injection displacement reaches the displacement limit value of the cooling capacity simulation device, so that the drilling fluid slurry quickly fills the wellbore simulation system;

[0160] (3) Detecting whether the cooling capacity simulation device has leakage, and ensuring that the sealing of the cooling capacity simulation device remains intact;

[0161] (4) closing the control valve 7 and opening the temperature simulation system so that the temperature inside the wellbore simulation system reaches the drilling fluid temperature at the depth of the target well;

[0162] (5) Turn on the self-priming variable frequency screw pump and the control valve 7 to circulate the liquid phase fluid, and record the temperature inside the wellbore simulation system, the time when the target cooling material reaches the phase change temperature, and the phase change endothermic saturation time during the circulation process (1h, 2h, 4h, 6h, 8h, 10h, 12h); in this embodiment, the time when the drilling fluid temperature exceeds the phase change temperature of the target cooling material by 2°C is recorded as the phase change endothermic saturation time;

[0163] (6) closing the control valve 1 7 to stop the circulation of the liquid phase fluid; opening the control valve 2 9 to start the self-priming variable frequency screw pump to reversely drain the liquid phase fluid;

[0164] (7) Add different weight percentages (5%, 10%, 15%) of the target cooling material to the experimental drilling fluid base slurry, and use different displacements (0.015m 3 / s, 0.020m 3 / s, 0.025m 3 / s, 0.030m 3 / s), repeat steps S1-S5 respectively, complete the drilling fluid heat absorption simulation experiment under different displacements with different weight ratios of cooling materials, and record the time and temperature parameters during the simulation experiment;

[0165] (8) adding different weight percentages (5%, 10%, 15%) of the target cooling material to the experimental drilling fluid base slurry, and using wellbore simulation systems with different well depths (5m, 6m, 7m, 8m), repeating steps S1-S5 respectively, completing the drilling fluid heat absorption simulation experiment with different weight percentages of cooling materials at different well depths, and recording the time and temperature parameters during the simulation experiment;

[0166] (9) Establishing the temperature calculation equation shown in equations (2)-(6), discretizing the temperature calculation equation to obtain the discrete equations shown in equations (8)-(12);

[0167] (10) The discrete equations shown in equations (8)-(12) are iteratively solved. When solving, the number of iterations of the cooling material phase change endothermic time is calculated by equations (13)-(14). When the cycle time is 6 h, 8 h, 10 h, and 12 h, respectively, the simulation results obtained by solving are as follows: Figure 4-Figure 7 shown.

[0168] from Figure 4-Figure 7It can be seen that after adding cooling material to the drilling fluid, the cooling material begins to change phase from 5000m, and the circulation temperature is lower than the circulation temperature when no cooling material is added. The more cooling material content, the greater the phase change heat absorption and the greater the cooling amplitude. As the circulation time increases, the cooling amplitude of the cooling material first increases rapidly, reaches the maximum value, and then slowly decreases.

[0169] In summary, the present invention can simulate the cooling capacity of the cooling material used for drilling fluid, more accurately determine the cooling capacity of the cooling material, and thus accurately predict the amount of the cooling material used in the drilling process. Compared with the prior art, the present invention is a significant improvement.

[0170] The above description is only a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with the profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. A method for calculating the cooling capacity of a cooling material for drilling fluid, It is characterized in that A cooling capacity simulation device is used to conduct a cooling capacity simulation experiment of the cooling material, and the parameters in the simulation process are obtained, and the cooling capacity of the cooling material is calculated based on the parameters; The cooling capacity simulation device includes a wellbore simulation system, a drilling fluid circulation system, a temperature simulation system and a data acquisition system; The wellbore simulation system includes a wellbore and a drill string disposed in the wellbore; The drilling fluid circulation system includes a liquid storage tank, a positive circulation liquid phase delivery pipeline, and a reverse circulation liquid phase delivery pipeline; The input end of the input pump 1 of the positive circulation liquid phase delivery pipeline is connected to the liquid reservoir, and the output end is connected to the pipeline 1. The other end of the pipeline 1 is connected to the wellbore. The wellbore and the liquid reservoir are connected through the pipeline 2. A control valve 1 is provided at one end of the pipeline 1 close to the input pump 1. The input end of the input pump 2 of the reverse circulation liquid phase delivery pipeline is connected to the pipeline 3, and the output end is connected to the liquid storage tank. The other end of the pipeline 3 is connected to the wellbore. The two ends of the pipeline 4 of the reverse circulation liquid phase delivery pipeline are respectively connected to the wellbore and the atmosphere; the control valve 2 is provided on the end of the pipeline 3 close to the input pump 2; The cooling capacity calculation method comprises the following steps: S1: preparing a drilling fluid base slurry for the experiment according to the drilling fluid used in the on-site drilling, stirring it evenly and injecting it into the liquid storage tank; S2: Turn on the input pump 1 and the control valve 1 to allow the drilling fluid slurry to fill the wellbore simulation system, and adjust the injection displacement to the displacement limit value of the cooling capacity simulation device. The displacement limit value of the cooling capacity simulation device is calculated by the following formula: Where: Q 1,m is the displacement limit value of the cooling capacity simulation device, m 3 / s;Q 1,s is the displacement of the drilling pump during the actual drilling operation, m 3 / s; R w,m is the wellbore radius of the cooling capacity simulation device, m; R p,m is the drill string radius of the cooling capacity simulation device, m; R w,s is the wellbore radius in actual situation, m; R p,s is the drill string radius in actual situation, m; S3: closing the input pump 1 and the control valve 1, and opening the temperature simulation system, so that the temperature inside the wellbore simulation system reaches the drilling fluid temperature at the depth of the target well; S4: Turn on the input pump 1 and the control valve 1 to circulate the liquid phase fluid, and record the time when the target cooling material reaches the phase change temperature and the phase change endothermic saturation time during the circulation process; S5: close the input pump 1 and the control valve 1 to stop the circulation of the liquid phase fluid; open the input pump 2 and the control valve 2 to drain the liquid phase fluid; S6: adding different weight percentages of target cooling materials to the experimental drilling fluid base slurry, and using different displacements less than the displacement limit value, repeating steps S1-S5 respectively, completing the drilling fluid heat absorption simulation experiment with different weight percentages of cooling materials at different displacements, and recording the time and temperature parameters during the simulation experiment; S7: adding different weight percentages of target cooling materials to the experimental drilling fluid base slurry, and using wellbore simulation systems with different well depths, repeating steps S1-S5 respectively, completing the drilling fluid heat absorption simulation experiment with different weight percentages of cooling materials at different well depths, and recording the time and temperature parameters during the simulation experiment; S8: Establishing a temperature calculation equation, solving the temperature calculation equation, and obtaining the cooling capacity of the target cooling material during the drilling process.

2. The method for calculating the cooling capacity of the cooling material for drilling fluid according to claim 1, It is characterized in that In step S8, the temperature calculation equation includes the temperature calculation equation of the drilling fluid in the drill string containing cooling material, the temperature calculation equation of the drill string wall, the temperature calculation equation of the drilling fluid in the annulus containing cooling material, the temperature calculation equation of the well wall, and the temperature calculation equation of the formation; The temperature calculation equation of the drilling fluid in the drill string containing the cooling material is: Where: Q m is the heat source of the liquid in the drill string, W / m 3 ; ρ 0 is the density of drilling fluid in the drill string, kg / m 3 ;c g 、c f 、c y are the specific heat capacity of the drilling fluid containing cooling material before phase change, the specific heat capacity of the drilling fluid containing cooling material during phase change, and the specific heat capacity of the drilling fluid containing cooling material after phase change; r 0 is the inner radius of the drill string; T 0 , T 1 are the drilling fluid temperature in the drill string and the drill string wall temperature, °C; t is the time step, s; q is the displacement, m 3 / s; z is the spatial step length, m; λ 0 is the thermal conductivity of drilling fluid, W / (m·℃); Nu g1 、Nu f1 、Nu y1 are the Nu number of the inner wall of the drill string before phase change, the Nu number of the inner wall of the drill string during phase change, and the Nu number of the inner wall of the drill string after phase change; L is the characteristic length, m; T is the real-time drilling fluid temperature, °C; T m is the phase transition temperature of the cooling material, ℃; ΔT is the temperature range of phase transition, ℃; The temperature calculation equation of the drill string wall is: Where: 1 is the thermal conductivity of the drill string, W / (m·℃); r 1 is the outer radius of the drill string, m; ρ 1 is the density of drill string, kg / m 3 ;c 1 is the specific heat capacity of the drill string; Nu g2 、Nu f2 、Nu y2 They are respectively the Nu number of the outer wall of the drill string before phase change, the Nu number of the outer wall of the drill string during phase change, and the Nu number of the outer wall of the drill string after phase change; The temperature calculation equation of the drilling fluid in the annulus containing the cooling material is: Where: 2 is the drilling fluid density in the annulus, kg / m 3 ; T 2 , T 3 are the annulus drilling fluid temperature and wellbore wall temperature, °C; Q a is the liquid heat source in the annulus, W / m 3 ; r 2 is the radius of the wellbore, m; Nu g3 、Nu f3 、Nu y3 They are the Nu number of the wellbore wall before phase change, the Nu number of the wellbore wall during phase change, and the Nu number of the wellbore wall after phase change; The temperature calculation equation of the well wall is: Where: 2 is the thermal conductivity of the well wall, W / (m·℃); T 3 , T 4 are wellbore temperature and formation temperature, respectively, °C; ρ 3 is the wellbore density, kg / m 3 ;c 3 is the specific heat capacity of the well wall; r 3 、r 4 are the diameter of the wellbore wall and the diameter of the formation unit, m; The temperature calculation equation of the formation is: Where: T i is the formation temperature, °C; r is the diameter of the formation unit, m; r i is the diameter of the i-th layer unit, m; ρ i is the formation density, kg / m 3 ;c i is the formation specific heat capacity; i is the thermal conductivity of the formation, W / (m·℃).

3. The method for calculating the cooling capacity of the cooling material for drilling fluid according to claim 2, It is characterized in that The Nu number in the temperature calculation equation is calculated by the following formula: Where: Q is the total heat exchange, W; A is the heat exchange area of ​​the cooling capacity simulation device, m 2 ; T v is the average temperature of the heating device, °C; T a is the backward temperature of the drilling fluid flowing through the heating area of ​​the heating device, ℃; R w is the thermal resistance between the heating device and the wellbore wall, ℃ / W; R w,m is the wellbore radius of the cooling capacity simulation device, m.

4. The method for calculating the cooling capacity of the cooling material for drilling fluid according to claim 2, It is characterized in that When solving the temperature calculation equation, the temperature calculation equation is discretized using a fully implicit format to obtain a discrete form of the temperature calculation equation, and then the discrete form is iteratively solved; The discrete formula of the temperature calculation equation of the drilling fluid in the drill string containing the cooling material is: Where: superscript n represents time; subscript j represents depth; A 0 , B 0 , C 0 , D 0 They are all constant terms in the temperature calculation equation of the drilling fluid in the drill string containing cooling materials; The discrete form of the temperature calculation equation of the drill string wall is: Where: A 1 , B 1 , C 1 , D 1 、E 1 They are all constant terms in the temperature calculation equation of the drill string wall; The discrete formula of the temperature calculation equation of the drilling fluid in the annulus containing the cooling material is: Where: A 2 , B 2 , C 2 , D 2 、E 2 They are all constant terms in the temperature calculation equation of the drilling fluid in the annulus containing cooling materials; The discrete form of the temperature calculation equation of the well wall is: Where: A 3 , B 3 , C 3 , D 3 、E 3 They are all constant terms in the temperature calculation equation of the wellbore wall; The discrete form of the temperature calculation equation of the formation is: Where: A i , B i , C i , D i 、E i They are all constant terms in the formation temperature calculation equation.

5. The method for calculating the cooling capacity of the cooling material for drilling fluid according to claim 4, It is characterized in that When the discrete formula is iteratively solved, the number of iterations of the cooling material phase change endothermic time is calculated by the following formula: t 1 =h 1,m *3600 / Δt (13) Where: t 1 h is the number of iterations of the cooling material phase change endothermic time; 1,m is the phase change endothermic saturation time of the cooling material during the actual drilling operation, h; Δt is the time step; h 1,s is the phase change endothermic saturation time of the cooling material during the simulation experiment, h; ΔT 2 is the temperature difference between the formation temperature and the drilling fluid temperature during drilling, °C; R w,s is the wellbore radius in actual situation, m; h y is the convective heat transfer coefficient of drilling fluid during drilling, W / (m 2 ℃); ΔT 1 is the temperature difference between the wellbore outside temperature and the drilling fluid temperature during the simulation experiment, ℃; R w,m is the wellbore radius of the cooling capacity simulation device, m; h x is the convective heat transfer coefficient of drilling fluid during the simulation experiment, W / (m 2 ·℃).

6. A cooling capacity simulation device using the cooling capacity calculation method of the cooling material for drilling fluid according to any one of claims 1 to 5, It is characterized in that Including wellbore simulation system, drilling fluid circulation system, temperature simulation system and data acquisition system; The wellbore simulation system includes a wellbore and a drill string disposed in the wellbore; The drilling fluid circulation system includes a liquid storage tank, a positive circulation liquid phase delivery pipeline, and a reverse circulation liquid phase delivery pipeline; The input end of the input pump 1 of the positive circulation liquid phase delivery pipeline is connected to the liquid reservoir, and the output end is connected to the pipeline 1. The other end of the pipeline 1 is connected to the wellbore. The wellbore and the liquid reservoir are connected through the pipeline 2. A control valve 1 is provided at one end of the pipeline 1 close to the input pump 1. The input end of the input pump 2 of the reverse circulation liquid phase transport pipeline is connected to the pipeline 3, and the output end is connected to the liquid storage tank. The other end of the pipeline 3 is connected to the wellbore. The two ends of the pipeline 4 of the reverse circulation liquid phase transport pipeline are respectively connected to the wellbore and the atmosphere; a control valve 2 is provided on the end of the pipeline 3 close to the input pump 2.

7. The cooling capacity simulation device according to claim 6, It is characterized in that The temperature simulation system comprises a heating device, which is connected to the wellbore simulation system; the data acquisition system is used to collect the temperature inside the wellbore simulation system and the flow rate and pressure of the drilling fluid circulation system.

8. The cooling capacity simulation device according to claim 6, It is characterized in that The wellbore and the drill string are both length-adjustable structures, and the lengths of the wellbore and the drill string can be adjusted to the same extent.

9. The cooling capacity simulation device according to claim 6 or 8, It is characterized in that The data acquisition system comprises a computer and a temperature sensor 1, a temperature sensor 2, a flow meter 1, a flow meter 2, a pressure sensor 1, and a pressure sensor 2 respectively connected to the computer; The temperature sensor 1 is arranged on the drill string and is used to monitor the temperature inside the wellbore simulation system; The second temperature sensor is arranged on the pipeline of the drilling fluid circulation system to monitor the temperature outside the wellbore; The flow meter 1 and the pressure sensor 1 are arranged on the pipeline 1, and an overflow valve 1 is arranged between the two, and the flow meter 1 is arranged at one end close to the control valve 1; The second pressure sensor and the second flow meter are arranged on the second pipeline, and a second overflow valve is arranged between the two. The second pressure sensor is arranged at one end close to the wellbore.

10. The cooling capacity simulation device according to claim 9, It is characterized in that The input pump 1 and the input pump 2 use the same self-priming variable frequency screw pump, and the self-priming variable frequency screw pump is connected to the pipeline 1 and the pipeline 3 through the pipeline 5 and the three-way valve; two temperature sensors 1 are provided, respectively located at the lower part and the middle part of the drill string.

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