Ultra-deepwater drilling well leakage double-leakage layer positioning method

Abstract

The invention discloses an ultra-deepwater drilling well leakage double-leakage layer positioning method, which comprises the following steps: acquiring the basis of each well section, calculating hydraulic parameters such as the flow velocity of drilling fluid in an annulus, calculating the Reynolds number of the drilling fluid in the annulus, judging the flow state, and selecting a corresponding annulus friction resistance coefficient formula according to the flow state; judging whether well leakage is returned or not according to whether drilling fluid returns from a well mouth, and selecting a model to calculate the depth of the double-leakage layer according to whether the well leakage is returned or not; determining the maximum value Kmax of the annulus pressure consumption distribution coefficient according to the fact that the first leakage layer depth is smaller than the second leakage layer depth, and enabling the annulus pressure consumption distribution coefficient to circulate within the range of (0, Kmax); and substituting the obtained first leakage layer depth and the second leakage layer depth into a post-well-leakage circulating vertical pressure expression to calculate post-well-leakage circulating vertical pressure, and when the post-well-leakage circulating vertical pressure is close to a post-well-leakage actually-measured vertical pressure value and the relation between the leakage layer depth and the length of the drill column meets the model requirement, ending the circulation. And obtaining a final double-leakage-layer leakage horizon calculation result.

Description

Technical Field

[0001] The present invention belongs to the field of oil drilling engineering. Specifically, it relates to a method for locating double lost circulation zones in ultra-deep water drilling based on hydrodynamic principles. Background Art

[0002] During deep water and ultra-deep water drilling operations, the formation is fragile and prone to collapse, the drilling fluid properties are poor, and the loss rate is high. Moreover, factors such as the pressure, flow velocity, and viscosity of the drilling fluid can all affect the loss. Once lost circulation occurs, it will increase non-productive time, reduce production efficiency, and increase drilling costs. Therefore, before plugging the lost circulation, how to quickly and accurately detect and locate the lost circulation zone has become one of the difficulties in drilling operations.

[0003] At present, a large number of scholars have conducted relevant research on lost circulation zone location technology. However, some commonly used methods at home and abroad generally have problems such as low accuracy, high cost, and complex operation. In the actual process of deep water drilling exploration and development, as the degree of ultra-deep water drilling and production increases, the formation conditions become more complex, the pressure systems gradually increase, and multiple pressure systems from abnormally low pressure to abnormally high pressure may alternately appear. Coupled with the influence of formation lithology, there may be a phenomenon where two lost circulation zones exist simultaneously. However, most of the current research on lost circulation zone location methods is based on single lost circulation zones, and there is less research on double lost circulation zone location. Summary of the Invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art. For this purpose, the present invention provides a method for locating double lost circulation zones in ultra-deep water drilling, aiming to establish a calculation model for the lost circulation zone of double lost circulation zones in ultra-deep water drilling based on hydrodynamic principles, determine the positions of the double lost circulation zones after lost circulation in ultra-deep water drilling, and provide suggestions for subsequent lost circulation plugging work.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for locating double lost circulation zones in ultra-deep water drilling includes the following steps:

[0007] Step 1: Obtain the basic parameters of each well section, where the basic parameters include bit diameter, inner and outer diameters of the drill string, drill string length, drilling fluid displacement before lost circulation, standpipe pressure before lost circulation, drilling fluid displacement after lost circulation, loss amount distribution coefficient of the double lost circulation zones, reading of the Fann viscometer at 600 r / min, reading of the Fann viscometer at 300 r / min, reading of the Fann viscometer at 3 r / min, and drilling fluid density, etc.:

[0008] Step 2: Calculate the flow velocity of the drilling fluid in the wellbore annulus before and after lost circulation:

[0009]

[0010] In the formula, Vai is the flow rate of the drilling fluid in the i-th section of the wellbore annulus; Q ai is the drilling fluid outlet flow rate before and after lost circulation; D i is the inner diameter of the i-th annulus; d i is the outer diameter of the drill string in the i-th section.

[0011] Step 3: Calculate the flow behavior index and consistency coefficient of the drilling fluid in the wellbore annulus:

[0012]

[0013] In the formula, n ai is the flow behavior index of the drilling fluid in the i-th section of the wellbore annulus; K ai is the consistency coefficient of the drilling fluid in the i-th section of the wellbore annulus; R 600 is the reading of the Fann viscometer at 600 r / min; R 300 is the reading of the Fann viscometer at 300 r / min; R 3 is the reading of the Fann viscometer at 3 r / min.

[0014] Step 4: Based on the drilling fluid flow rate obtained in Step 2 and the flow behavior index and consistency coefficient of the drilling fluid obtained in Step 3, calculate the effective viscosity of the drilling fluid in the wellbore annulus:

[0015]

[0016] In the formula, μ ai is the effective viscosity of the drilling fluid in the i-th section of the wellbore annulus.

[0017] Step 5: Calculate the Reynolds number of the drilling fluid in the wellbore annulus based on the effective viscosity of the drilling fluid obtained in Step 4, and determine the flow regime of the drilling fluid in the wellbore annulus according to the calculated Reynolds number of the drilling fluid:

[0018]

[0019] In the formula, N Reai is the Reynolds number of the drilling fluid in the i-th section of the wellbore annulus; ρ is the density of the drilling fluid.

[0020] According to the calculated Reynolds number of the drilling fluid, determine the flow regime of the drilling fluid in the wellbore annulus based on the flow regime discrimination criterion: When N Reai <3470 - 1370n ai the flow regime of the drilling fluid is laminar; when N Reai >4270 - 1370n ai the flow regime of the drilling fluid is turbulent; when 3470 - 1370n ai ≤N Reai ≤4270 - 1370n ai the flow regime of the drilling fluid is transitional.

[0021] Step 6: Select the calculation formula of the drilling fluid friction coefficient corresponding to the drilling fluid flow pattern to calculate the drilling fluid friction coefficient in the wellbore annulus:

[0022] ① In the case of laminar flow:

[0023]

[0024] In the formula, f ai is the drilling fluid friction coefficient in the annulus of the i-th section of the wellbore;

[0025] ② In the case of turbulent flow:

[0026]

[0027] In the formula,

[0028] ③ In the case of transitional flow:

[0029]

[0030] In the formula, C 1 = 3470 - 1370n ai , C 2 = 4270 - 1370n ai .

[0031] Step 7: Calculate the annulus pressure loss of the drilling fluid in the wellbore annulus based on the drilling fluid friction coefficient obtained in Step 6:

[0032]

[0033] In the formula, P ai is the annulus pressure loss of the drilling fluid in the annulus of the i-th section of the wellbore; L i is the length of the drill string in the i-th section.

[0034] Step 8: Judge whether the well is lost circulation according to whether there is drilling fluid returning at the wellhead, and select the calculation model for non-loss circulation or the calculation model for lost circulation of the well to calculate the depth of the double lost circulation zones:

[0035] Among them, please refer to Figure 2 , the expression of the calculation model for the position of the double lost circulation zones in the case of non-loss circulation of the well is as follows:

[0036]

[0037] In the formula, L 1 is the depth of the first lost circulation zone; L 2 is the depth of the second lost circulation zone; ΔP 1 is the difference in annulus pressure loss above the first lost circulation zone before and after the well is lost circulation; ΔP 2ΔP is the annulus pressure loss difference between the two lost circulation zones before and after lost circulation; Q is the drilling fluid outlet flow rate before lost circulation; Q 1 is the drilling fluid outlet flow rate after lost circulation; Q 2 is the drilling fluid circulation flow rate in the annulus between the two lost circulation zones after lost circulation; D n is the inner diameter of the annulus in the nth section; d n is the outer diameter of the drill string in the nth section; D m is the inner diameter of the annulus in the mth section; d m is the inner diameter of the drill string in the mth section; f am is the drilling fluid friction coefficient of the flow rate Q in the annulus of the mth section of the wellbore; f' am is the flow rate Q 2 in the annulus of the mth section of the wellbore; f' ai is the flow rate Q 2 in the annulus of the ith section of the wellbore; f" ai is the flow rate Q 1 in the annulus of the ith section of the wellbore; f' an is the flow rate Q 2 in the annulus of the nth section of the wellbore; f" an is the flow rate Q 1 in the annulus of the nth section of the wellbore;

[0038] Please refer to Figure 3 , the expression of the calculation model for the positions of the two lost circulation zones with lost returns is as follows:

[0039]

[0040] In the formula, B is the depth of the dynamic liquid level after lost returns.

[0041] When calculating, define an annulus pressure loss distribution coefficient k for the annulus pressure loss difference before and after lost circulation, that is:

[0042] ΔP 1 = kΔP (14)

[0043] ΔP 2 = (1 - k)ΔP (15)

[0044] In the formula, ΔP is the annulus pressure loss difference before and after lost circulation.

[0045] Step Nine: Determine the maximum annulus pressure loss distribution coefficient K for the depths of the first lost circulation zone and the second lost circulation zone max , and cyclically substitute the annulus pressure loss distribution coefficient within the range of (0, K max ) into the selected calculation model for the positions of the two lost circulation zones without lost returns or the calculation model for the positions of the two lost circulation zones with lost returns to calculate the depth L 1 of the first lost circulation zone and the depth L 2, where the annulus pressure loss distribution coefficient is calculated by the following formula;

[0046]

[0047] In the formula,

[0048]

[0049] Step Ten: Substitute the first lost circulation zone depth L 1 and the second lost circulation zone depth L 2 into the circulating standpipe pressure expression after lost circulation to calculate the circulating standpipe pressure P" after lost circulation. When the circulating standpipe pressure P" after lost circulation approaches the measured standpipe pressure value P' after lost circulation, and the relationship between the lost circulation zone depth and the drill string length meets the model requirements, the circulation ends, and the final calculation result of the double lost circulation zone positions is obtained. The circulating standpipe pressure expression after lost circulation is as follows:

[0050] P' = P st + P b + P a0 + P' a1 + P' q2 (17)

[0051]

[0052]

[0053] In the formula, P' is the circulating standpipe pressure after lost circulation; P st is the pressure loss inside the drill string; P b is the bit pressure loss; P a0 is the annulus pressure loss from the bottom hole before and after lost circulation to the second lost circulation zone; P a1 ' is the annulus pressure loss above the first lost circulation zone after lost circulation; P a2 ' is the annulus pressure loss between the two lost circulation zones after lost circulation.

[0054] Due to the adoption of the above technical solutions, the present invention has the following advantages:

[0055] 1. The present invention can calculate the positions of double lost circulation zones in two cases of lost circulation and non-lost circulation during ultra-deep water drilling, providing theoretical support for subsequent plugging work.

[0056] 2. Starting from the hydraulic principle, the present invention can obtain the parameters required for calculation on the basis of the original ultra-deep water drilling without adding other equipment or devices, saving time and drilling costs compared with other methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the following detailed description of the preferred embodiments. The drawings are only for the purpose of illustrating the preferred embodiments and are not considered to be a limitation of the present invention. Throughout the drawings, the same reference numerals are used to denote the same components. In the drawings:

[0058] Figure 1 is a flowchart of the method for locating double lost circulation zones in ultra-deepwater drilling well leakage provided by the present invention;

[0059] Figure 2 is a schematic diagram of double lost circulation zones in the case of non-loss return of well leakage in ultra-deepwater drilling according to the present invention;

[0060] Figure 3 is a schematic diagram of double lost circulation zones in the case of loss return of well leakage in ultra-deepwater drilling according to the present invention. Detailed Embodiments

[0061] To make the objectives, technical solutions and advantages of the present invention clearer, the following further explains the specific embodiments of the present invention with reference to the drawings. Although the exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0062] The method for locating double lost circulation zones in ultra-deepwater drilling well leakage provided by the present invention includes: obtaining the basics of each well section, calculating hydraulic parameters such as the drilling fluid velocity in the annulus, calculating the Reynolds number of the drilling fluid in the annulus, judging the flow regime, and selecting the corresponding annulus friction coefficient formula according to the flow regime; judging whether there is drilling fluid return at the wellhead to determine whether the well leakage is a loss return, and selecting a model to calculate the depth of the double lost circulation zones according to whether the well leakage is a loss return; determining the maximum value K of the annulus pressure loss distribution coefficient according to the depth of the first lost circulation zone being less than the depth of the second lost circulation zone max , and making the annulus pressure loss distribution coefficient cycle within the range of (0, K max ); substituting the obtained depth of the first lost circulation zone and the depth of the second lost circulation zone into the expression of the circulating standpipe pressure after well leakage to calculate the circulating standpipe pressure after well leakage. When the circulating standpipe pressure after well leakage approaches the measured standpipe pressure value after well leakage, and the relationship between the lost circulation zone depth and the drill string length meets the model requirements, the cycle ends, and the calculation result of the final lost circulation layer position of the double lost circulation zones is obtained.

[0063] Next, the method for locating double lost circulation zones in ultra-deepwater drilling well leakage provided by the embodiments of the present invention will be described in detail with reference to the drawings.

[0064] Please refer to Figure 1 , in this embodiment, during the ultra-deepwater drilling process, when there is no loss return of well leakage and there are double lost circulation zones in the case of two drill string assemblies, the calculation of the double lost circulation zone positions includes the following steps:

[0065] Step 1: Obtain basic parameters such as bit diameter, inner and outer diameters of the drill string, drill string length, drilling fluid displacement before lost circulation, standpipe pressure before lost circulation, drilling fluid displacement after lost circulation, loss volume distribution coefficient of the double lost circulation zones, Fann viscometer reading at 600 r / min, Fann viscometer reading at 300 r / min, Fann viscometer reading at 3 r / min, and drilling fluid density.

[0066] Step 2: Calculate the flow velocities of the drilling fluid in the wellbore annulus before and after lost circulation:

[0067]

[0068] Substitute the drilling fluid outlet flow rates, annulus inner diameter, and drill string outer diameter data before and after lost circulation into Equation (1) to calculate the flow velocities V and V' of the drilling fluid in the wellbore annulus before and after lost circulation.

[0069] Step 3: Calculate the flow behavior index and consistency coefficient of the drilling fluid in the wellbore annulus:

[0070]

[0071] Substitute the Fann viscometer reading at 600 r / min, Fann viscometer reading at 300 r / min, and Fann viscometer reading at 3 r / min into Equations (2) and (3) to calculate the flow behavior index n ai and the consistency coefficient K ai .

[0072] Step 4: Calculate the effective viscosity of the drilling fluid in the wellbore annulus:

[0073]

[0074] Substitute the drilling fluid flow velocity calculated in the previous two steps, as well as the flow behavior index and consistency coefficient in the wellbore annulus, into Equation (4) to obtain the effective viscosity of the drilling fluid in the wellbore annulus.

[0075] Step 5: Calculate the Reynolds number of the drilling fluid in the wellbore annulus and determine the flow regime:

[0076]

[0077] Substitute the drilling fluid density, drilling fluid flow velocity, and the effective viscosity of the drilling fluid calculated from Equation (4) into Equation (5) to respectively obtain the Reynolds number of the drilling fluid in the wellbore annulus.

[0078] According to the calculated Reynolds number, determine the drilling fluid flow regime based on the flow regime discrimination criterion: When N Reai <3470 - 1370n ai the drilling fluid flow regime is laminar flow; when N Reai>4270 - 1370n ai When the drilling fluid flow regime is turbulent; when 3470 - 1370n ai ≤ N Reai ≤ 4270 - 1370n ai the drilling fluid flow regime is transitional flow.

[0079] Step Six: Select the friction coefficient calculation formula corresponding to the drilling fluid flow regime to calculate the friction coefficient in the wellbore annulus:

[0080] a. In the case of laminar flow:

[0081] In the annulus:

[0082]

[0083] b. In the case of turbulent flow:

[0084]

[0085] c. In the case of transitional flow:

[0086]

[0087] Step Seven: Calculate the annulus pressure loss of the drilling fluid in the wellbore annulus:

[0088]

[0089] Step Eight: Select the following calculation model for the position of two lost circulation zones in the case of no lost return during well leakage and two drill string combinations. Assume that the two lost circulation zones are not on the same drill string section, and first calculate the position of the two lost circulation zones in this case:

[0090]

[0091] Define an annulus pressure loss distribution coefficient k for the difference in annulus pressure loss before and after well leakage during calculation, that is:

[0092] ΔP 1 = kΔP (12)

[0093] ΔP 2 = (1 - k)ΔP (13)

[0094] Step Nine: Calculate the maximum annulus pressure loss distribution coefficient K of lost circulation zone 1 and lost circulation zone 2 through the following formula max , and substitute the annulus pressure loss distribution coefficient into Equation (10) and Equation (11) in the range of (0, K max ) to calculate the depth L 1 of lost circulation zone 1 and the depth L 2 of lost circulation zone 2;

[0095]

[0096] Step Ten: Substitute the calculated depth L of leakage layer 1 1 and the depth L of leakage layer 2 2 into the annulus pressure loss calculation formula to calculate the annulus pressure loss after lost circulation, and finally substitute it into Equation (15) to calculate the standpipe pressure value after lost circulation:

[0097] P' = P st + P b + P a0 + P' a1 + P' a2 (15)

[0098] Compare the calculated standpipe pressure value after lost circulation with the measured standpipe pressure value after lost circulation to see if it meets the error requirement. If it does not meet the error requirement, continue to loop and calculate different leakage layer depths, that is, change the annulus pressure loss distribution coefficient, and repeat Step Nine; if it meets the error requirement, compare the obtained leakage layer depth with the drill string length to see if it meets the requirement that the two leakage layers are not on the same section of the drill string assumed at the beginning. If it does not meet the requirement, select the calculation model where the two leakage layers are on the same section of the drill string and start the calculation again, that is, repeat Step Eight and Step Nine; if it meets the requirement, the calculated depth L of leakage layer 1 1 and the depth L of leakage layer 2 2 are the final depths of the two leakage layers.

[0099] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application and are not intended to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should all be covered by the scope of the claims and the description of the present application. In particular, as long as there is no structural conflict, the technical features mentioned in each embodiment can be combined in any way. The present application is not limited to the specific embodiments disclosed in the text, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A method for locating double-leakage layers in ultra-deep water drilling, characterized in that: The following steps are involved: Obtain basic parameters of each well section; Calculate the drilling fluid flow rate in the wellbore annulus before and after lost circulation based on the basic parameters obtained; Calculate the drilling fluid flow index and consistency coefficient in the wellbore annulus based on the basic parameters obtained; Based on the obtained drilling fluid flow rate, drilling fluid manifold index and consistency coefficient, the effective viscosity of the drilling fluid in the wellbore annulus is calculated; Calculating the drilling fluid Reynolds number in the wellbore annulus based on the obtained drilling fluid effective viscosity, and determining the flow state of the drilling fluid in the wellbore annulus according to the calculated drilling fluid Reynolds number; Select the drilling fluid friction coefficient calculation formula corresponding to the drilling fluid flow state to calculate the drilling fluid friction coefficient in the wellbore annulus; Calculate the drilling fluid annular pressure loss in the wellbore annulus based on the obtained drilling fluid friction coefficient; Determine whether the well is lost or not according to whether drilling fluid is returned from the wellhead, and select the well loss without loss or not calculation model or the well loss or not calculation model to calculate the double leakage layer depth according to whether the well is lost or not; Determine the maximum annular pressure loss distribution coefficient K of the first leak layer depth and the second leak layer depth max , and the annular pressure loss distribution coefficient is (0, K max ) range is cyclically substituted into the selected well leakage non-return double leakage layer position calculation model or well leakage return double leakage layer position calculation model to calculate the first leakage layer depth and the second leakage layer depth; The obtained first leaky layer depth and second leaky layer depth are substituted into the expression of circulating standing pressure after well leakage to calculate the circulating standing pressure after well leakage. When the circulating standing pressure after well leakage is close to the measured standing pressure value after well leakage, and the relationship between the leaky layer depth and the drill string length meets the model requirements, the cycle ends and the final calculation result of the double leaky layer leakage layer is obtained.

2. The method for locating double leakage layers in ultra-deep water drilling according to claim 1, characterized in that: The calculation formula of the drilling fluid flow rate in the wellbore annulus before and after the well leakage is as follows: Where V ai is the drilling fluid velocity in the annulus of the i-th wellbore; Q ai D is the drilling fluid outlet flow rate before and after lost circulation; i is the inner diameter of the annulus in the i-th section; d i is the outer diameter of the drill string section i.

3. The method for locating double leakage layers in ultra-deep water drilling according to claim 2, characterized in that: The calculation formulas for the drilling fluid manifold index and consistency coefficient in the wellbore annulus are as follows: Where n ai is the drilling fluid manifold index in the i-th wellbore annulus; K ai is the drilling fluid viscosity coefficient in the annulus of the i-th wellbore; R 600 is the reading of the Fann viscometer at 600r / min; R 300 It is the reading of Fann viscometer at 300r / min; R3 is the reading of Fann viscometer at 3r / min.

4. The method for locating double leakage layers in ultra-deep water drilling according to claim 3, characterized in that: The calculation formula of the effective viscosity of the drilling fluid in the wellbore annulus is as follows: In the formula, μ ai is the effective viscosity of the drilling fluid in the annulus of the i-th section of the wellbore.

5. The method for locating double leakage layers in ultra-deep water drilling according to claim 4, characterized in that: The calculation formula of the drilling fluid Reynolds number in the wellbore annulus is as follows: Where N Reai is the drilling fluid Reynolds number in the annulus of the i-th wellbore; ρ is the drilling fluid density; According to the calculated drilling fluid Reynolds number, the flow pattern of the drilling fluid in the wellbore annulus is as follows: According to the calculated drilling fluid Reynolds number, the flow state of the drilling fluid in the wellbore annulus is determined according to the flow state determination criteria: when N Reai <3470-1370n ai When N Reai >4270-1370n ai When the drilling fluid flow is turbulent, when 3470-1370n ai ≤N Reai ≤4270-1370n ai When , the drilling fluid flow state is transitional flow.

6. The method for locating double leakage layers in ultra-deep water drilling according to claim 5, characterized in that: The calculation formula of drilling fluid friction coefficient corresponding to each drilling fluid flow state is as follows: ① In laminar flow conditions: In the formula, f ai is the friction coefficient of drilling fluid in the annulus of the i-th section of the wellbore; ② In turbulent flow conditions: In the formula, ③In the case of transition flow: Where, C1 = 3470-1370n ai , C2=4270-1370n ai .

7. The method for locating double leakage layers in ultra-deep water drilling according to claim 6, characterized in that: The calculation formula of the drilling fluid annular pressure loss in the wellbore annulus is as follows: Where P ai is the annular pressure loss of drilling fluid in the annular space of the i-th wellbore; L i is the length of the drill string section i.

8. The method for locating double leakage layers in ultra-deep water drilling according to claim 7, characterized in that: The expression of the calculation model of the double leakage layer position without loss return is as follows: Where, L1 is the depth of the first leaky layer; L2 is the depth of the second leaky layer; ΔP1 is the annular pressure loss difference above the first leaky layer before and after the well leakage; ΔP2 is the annular pressure loss difference between the two leaky layers before and after the well leakage; Q is the drilling fluid outlet flow rate before the well leakage; Q1 is the drilling fluid outlet flow rate after the well leakage; Q2 is the drilling fluid circulation flow rate in the annulus between the two leaky layers after the well leakage; D n is the inner diameter of the nth annulus; d n is the outer diameter of the drill string in the nth section; D m is the inner diameter of the mth annulus; d m is the inner diameter of the drill string in the mth section; f am f' is the friction coefficient of drilling fluid in the wellbore annulus at the flow rate Q in the mth section; am f' is the friction coefficient of the drilling fluid in the wellbore annulus at the flow rate Q2 in the mth section; ai is the friction coefficient of drilling fluid in the wellbore annulus at the i-th section with flow rate Q2; f" ai f' is the friction coefficient of drilling fluid in the wellbore annulus at the i-th section with flow rate Q1; an is the friction coefficient of drilling fluid in the annular space of the nth section of the wellbore at flow rate Q2; f" an is the friction coefficient of drilling fluid in the annular space of the nth section of the wellbore at flow rate Q1; The expression of the calculation model of the double leakage layer position of the well loss return is as follows: Where, B is the dynamic liquid level depth after the well loss; During the calculation, an annular pressure loss distribution coefficient k is defined for the annular pressure loss difference before and after the well leakage, that is: ΔP1=kΔP (14) ΔP2=(1-k)ΔP (15) Where ΔP is the annular pressure loss difference before and after lost circulation.

9. The method for locating double leakage layers in ultra-deep water drilling according to claim 8, characterized in that: The calculation formula of the annular space pressure loss distribution coefficient is as follows: In the formula, 10. The method for locating double leakage layers in ultra-deep water drilling according to claim 9, characterized in that: The expression of the circulating standing pressure after lost circulation is as follows: P'=P st +P b +P a0 +P' a1 +P' a2 (17) Where, P' is the circulating pressure after well leakage; P st is the pressure loss in the drill string; P b is the drill bit pressure loss; P a0 P is the annular pressure loss between the bottom of the well and the second leaking layer before and after the well leakage; a1 ' is the annular pressure loss above the first leaking layer after the well is lost; P a2 ' is the annular pressure loss between two leaking layers after the well is lost.

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