Shale gas horizontal well horizontal section borehole and casing type selection evaluation method

Abstract

The invention provides a shale gas horizontal well horizontal section borehole and casing model selection evaluation method, which comprises the following steps of: 1, aiming at shale gas horizontal wells in different work areas, combining burial depth, fracture pressure coefficient, deployment horizontal section length and fracturing transformation requirements, and selecting a casing model for the shale gas horizontal wells in different work areas; carrying out correlation analysis on different borehole open hole extension capability, drilling extension capability, running capability of different sizes of casing pipes and well cementation cement sheath meeting fracturing requirements, determining differences of the different sizes of casing pipes and boreholes, and finishing theoretical model selection of the casing pipes and the boreholes; 2, economic and feasibility evaluation is carried out in combination with the existing sleeve and drill bit downhole tool matching capacity, and finally the horizontal section borehole and sleeve type selection evaluation process is constructed. Theoretical calculation analysis is combined with economic and feasibility analysis, optimal sleeve and borehole type selection is obtained, type selection analysis is comprehensive, cost control is accurate, and the method is suitable for large-scale popularization and application. And reference is provided for model selection of horizontal section casing pipes and wellbores of all the blocks.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas drilling engineering, and in particular to a method for selecting and evaluating a wellbore and casing for a horizontal section of a shale gas horizontal well. Background Art

[0002] As shale oil and gas exploration and development gradually shifts to deep, normal pressure, complex structural areas and other blocks, the EUR production of single wells has decreased. In order to ensure the realization of efficient development, it is necessary to continuously reduce drilling costs and achieve efficient development and mobilization of low-yield areas by reducing engineering investment costs. After analyzing the wellbore structure and supporting technologies of horizontal wells in domestic shale oil and gas development, it is found that the existing conventional wellbore structure has inherent defects in continuous cost reduction. For example, the drill bits, screws and other tools required for large-scale rock breaking in each wellbore are large in size, with high drilling pressure requirements, high overall energy consumption, and a bottleneck in the continuous improvement of mechanical drilling speed; the amount of rock cuttings generated after rock breaking due to large-sized wellbore is large, especially after the use of oil-based drilling fluid in the target layer, the amount of oil-based drill cuttings is large, the processing cost is high, and the environmental and safety risks are high; the wellbore wall area of ​​large-sized wells is large, which is easy to encounter leakage during drilling, and at the same time, the drilling fluid contact area is large and the consumption per meter is higher, resulting in high drilling fluid costs; large-sized wells correspond to larger drill tool combinations, casing usage and load, requiring the use of higher-level drilling rigs, making it difficult to reduce equipment investment and casing costs; the gap between large-sized wells and casing annulus is too large, and the large annulus volume consumes a lot of cement, making it difficult to reduce the overall cementing cost, making it difficult to meet the efficient development of normal pressure and low-abundance shale oil and gas, restricting the efficient use of a large number of low-yield blocks. At the same time, with the adjustment of development technology policies, as well as the changes in fracturing process sections, clusters, process parameters and formation stress fields, the pump pressure of fracturing construction in new and old areas is quite different, and there are new changes in the requirements for the casing size and pressure resistance level of the horizontal section of the completion well; some new well exploration wells require the maximum development and transformation to fully discover oil and gas resources, so the casing requirements are high. At the same time, the residual gas adjustment wells of old wells require the development cost to be reduced as much as possible. Affected by factors such as formation and fracture length, the pump pressure and displacement are low, and the casing requirements are relatively low. Therefore, it is urgent to invent a method for selecting and evaluating the wellbore and casing of the horizontal section of shale horizontal wells based on the actual development of unconventional oil and gas, so as to provide a reference for the selection of casing and wellbore of the horizontal section of each block. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a method for selecting and evaluating the wellbore and casing of a horizontal section of a shale gas horizontal well in response to the above-mentioned problems.

[0004] The embodiment of the present application is implemented as follows:

[0005] The present application provides a method for selecting and evaluating the wellbore and casing of a horizontal section of a shale gas horizontal well, which is characterized by comprising the following steps:

[0006] Step 1: For shale gas horizontal wells in different work areas, combined with the burial depth, fracture pressure coefficient, horizontal section length and fracturing transformation requirements, conduct relevant analysis on the open hole extension capacity, drilling extension capacity, casing running capacity of different sizes and cementing cement sheath meeting the fracturing requirements of different wellbores, clarify the differences between casing and wellbores of different sizes, and complete the theoretical selection of casing and wellbores;

[0007] Step 2: Combine the existing casing, drill bit and downhole tool matching capabilities to conduct economic and feasibility evaluations, and ultimately build a horizontal wellbore and casing selection evaluation process.

[0008] In some optional implementation schemes, the theoretical selection of casing and wellbore in step 1 specifically includes the following contents:

[0009] Step S1), the impact of casing size changes on fracturing displacement or transformation:

[0010] Combined with the fracturing construction pressure calculation model, the calculation was performed with the existing production casing and fracturing equipment pressure limit as constraints. At the same time, combined with the requirements for displacement of reasonable reservoir transformation in different shale gas blocks, the analysis of the impact of production casing reduction on fracturing construction pump pressure and displacement was carried out;

[0011] Step S2), the impact of casing size changes on casing running capability:

[0012] Based on the existing extension capacity calculation model, simulation is carried out to analyze the impact of casing size changes on casing running capacity in the same fixed wellbore;

[0013] Step S3), casing selection:

[0014] Through the calculation and analysis of the above steps, the casing running capacity meets the horizontal section length, and the casing pressure resistance meets the fracturing transformation displacement requirements, which are the main factors in casing selection. The casing size is obtained when both factors are met at the same time;

[0015] Step S4), the impact of horizontal wellbore size changes on open hole extension capacity:

[0016] Based on the open hole extension limit, that is, under the premise that the circulating equivalent density of the bottom hole drilling fluid is less than the fracture pressure coefficient, considering the exclusion of the influence of rock carrying factors, the same flow rate and drilling tool combination are used for calculation according to wells of different sizes, and the open hole extension capacity of the same drilling tool under different wellbore sizes is analyzed;

[0017] Step S5), the impact of the matching of horizontal section wellbore size and casing size on cementing:

[0018] Based on the existing elastic-plastic mechanical model of casing-cement-formation combination, the equivalent stress of different wellbore gaps is obtained, the corresponding cementing hydraulic stone performance index requirements are obtained, and the influence of cement ring gap reduction on cement stone mechanical properties and the requirements for gaps to meet fracturing are analyzed;

[0019] Step S6), wellbore selection:

[0020] According to the analysis of steps S4 and S5, after the casing size is selected, the equivalent stress of the cement sheath and the open hole extension capacity are the main factors, and the wellbore size is obtained when the above two factors are satisfied at the same time.

[0021] In some optional implementation schemes, the fracturing construction pressure calculation model in step S1 is as follows:

[0022] P wh =P wf -P h +ΔP wh +ΔP perf

[0023] Where: P wh , P wf are wellhead pressure and bottom hole pressure respectively; P h is the static column pressure of the fracturing fluid; ΔP wh , ΔP perf They are respectively the friction along the way and the friction of the hole;

[0024] The friction along the way is expressed by the formula: ΔP wh =δ(ΔP 0 )

[0025] ΔP 0 =1.386×10 12 D -4.8 Q 1.8 L,

[0026] Where: δ is the drag reduction ratio, dimensionless; ΔP 0 is the friction resistance of the clean water pipe string; D is the inner diameter of the pipe string; Q is the construction displacement; L is the pipe length;

[0027] The calculation formula of the drag reduction ratio δ adopts the experimental data regression formula proposed by Lord et al.:

[0028]

[0029] Where: G is the concentration of thickener; C is the concentration of proppant;

[0030] The hole friction is expressed by the formula:

[0031] Where: Q is the construction displacement; ρ is the liquid density: np is the number of holes; d p is the hole diameter; C d is the correction coefficient, the value is 0.8-1.0;

[0032] Bottom hole pressure P wf Obtained based on the extended pressure of implemented wells;

[0033] Hydrostatic column pressure: P h =ρgH, where: ρ is the density of the fracturing fluid; H is the vertical depth of the gas well.

[0034] In some optional implementation schemes, the final selection of casing and wellbore described in step 2 includes the following: the casing and wellbore are calculated according to the theoretical selection process, and are determined in combination with the current status of industrial supporting facilities and construction technical capabilities, and then the upper opening wellbore structure is designed according to the conventional process, and finally the quota is calculated according to the requirements to select the most economical option.

[0035] In some optional embodiments, the extension capacity calculation model in step S2 includes the following contents:

[0036] The extension limit includes the drill string operation limit and the casing running limit, which depends on the drilling steering mode, the string strength, and the ground drilling rig load. The objective function of the wellbore extension limit is:

[0037]

[0038] Among them, L is the target well depth function; L(.) is the overall force model of the downhole tubular; p represents the constraint parameter, specifically the hook load, bit drilling pressure, and bit torque parameters; d represents the design parameter, specifically the tubular combination, wellbore trajectory, and drag reduction joint parameters; P is the allowable space of the constraint parameter p, and the specific form is given in the form of constraint conditions; P* is the optimal constraint parameter, and the well depth obtains the maximum value under the optimal constraint parameter; c represents the specific operating conditions, including the lifting and lowering of the tubular under sliding and rotation modes;

[0039] For a specific drilling rig, the axial tension during the hook lifting process has an upper limit, and its constraint conditions are:

[0040] During the lowering process of the big hook, the axial tension on the big hook has a lower limit value, and the corresponding constraint condition is:

[0041] The constraints corresponding to the rated torque of the ground turntable are:

[0042] Where: -F H is the axial force on the pipe string at the ground location; is the rated pulling load of the drilling rig; The minimum lifting load for lowering the big hook, usually this value is zero, that is, the state of complete lowering; M TH is the torque on the pipe string at the surface; is the rated torque of the turntable;

[0043] During the process of sliding and lifting the pipe string, the occurrence of pipe sticking will cause resistance in lifting. A lifting resistance is applied at the drill bit position to simulate the pipe sticking in the well, and the corresponding constraint condition is: B =T stuck ;

[0044] The drill may get stuck during the process of rotating and lifting the pipe string. In this case, not only the above constraints exist on the axial force, but also the torque constraints are as follows: M B =M T stuck ;

[0045] When the pipe string is lowered and the drill bit is breaking the rock, the drilling pressure needs to exceed a certain threshold value. The constraint conditions are:

[0046] Since there is an approximately linear relationship between the drilling pressure and torque on the drill bit, the rock breaking threshold drilling pressure also corresponds to the threshold drill bit torque, and its constraint condition is:

[0047] Among them: F B is the axial force on the pipe string at the drill bit position N; T stuck M is the drill bit sticking resistance; B M is the torque on the pipe string at the drill bit position; T stuck Select the resistance torque at the drill bit position; The rock breaking threshold drilling pressure; is the threshold torque; k is the approximate proportionality coefficient between the threshold torque and the threshold drilling pressure;

[0048] The axial force on the pipe string causes a uniform axial stress on the pipe string section. The calculation formula is:

[0049] The constraint condition for the drill string not to buckle is:

[0050] Where: t is the true axial stress of the pipe string; Ft is the true axial force of the pipe string; AS is the cross-sectional area of ​​the pipe string; F is the equivalent axial force considering the hydraulic effect; σ m is the axial stress considering the hydraulic effect; σ is the equivalent stress on the pipe string; [σ] is the allowable equivalent stress; σ s is the yield of the pipe material; n4 is the safety factor;

[0051] According to the axial movement direction of the pipe string, it is divided into lifting and lowering. According to whether the pipe string rotates, it is divided into sliding mode and rotation mode. For the sliding mode, the extension limit is the minimum value of sliding lifting and sliding lowering. For the rotation mode, the extension limit is the minimum value of rotation lifting and rotation lowering.

[0052] In some optional implementation schemes, the elastic-plastic mechanical model of the casing-cement-formation assembly in step S5 includes the following contents:

[0053] Theoretically, the strength of the casing string with cement sheath can be analyzed as a thick-walled cylinder composed of two different materials. Considering the actual working state of the cement sheath casing double-layer combination structure near the wellhead, it should belong to the plane strain state. Assume that: a, b, c, d are the inner radius and outer radius of the first layer of casing and the inner radius and outer radius of the second layer of casing respectively, and Ec, Es are the elastic modulus of cement and steel respectively; c, s are the Poisson's ratio of cement and steel respectively; P i , P 1 , P2 and P o The internal pressure and external squeezing force of the first layer of casing and the internal pressure and external squeezing force of the second layer of casing respectively;

[0054] for:

[0055]

[0056] The radial deformation of cement sheath is:

[0057]

[0058] The radial deformation of the second layer of casing is:

[0059]

[0060] Substitute r = b into the radial deformation formula of the first layer of casing and the radial deformation formula of the cement sheath, and make them equal; substitute r = c into the radial deformation formula of the cement sheath and the radial deformation formula of the second layer of casing, and make them equal, and we can get the following equation about P 1 and P 2 The system of equations, where Pi and P o As is known, solve for P 1 and P 2 The value of

[0061] The radial and tangential stress equations are:

[0062]

[0063] According to the boundary conditions:

[0064] When r = a,

[0065] When r = b,

[0066] The stress equation of the inner casing can be obtained:

[0067]

[0068] Where: is the tangential stress of the casing;

[0069] On the inner wall, when r = a, the stress is maximum, and the corresponding von Mises equivalent stress is:

[0070]

[0071] if The casing is safe; where: s is the yield stress and n is the safety factor.

[0072] In some optional embodiments, the constraint conditions include two types, one is that the casing internal pressure resistance performance does not exceed 80%, and the second is that it does not exceed the pressure limit of the fracturing equipment.

[0073] In some optional embodiments, the pump pressure of the fracturing construction at the same displacement in step S1 increases exponentially as the casing size decreases.

[0074] In some optional embodiments, the smaller the size of the casing at the same well location in step S2, the smaller the extension capacity.

[0075] In some optional implementation schemes, the equivalent stress will increase as the cement sheath gap decreases in step S5.

[0076] The beneficial effects of the present application are as follows: the present application provides a method for evaluating the selection of wellbore and casing for the horizontal section of a shale gas horizontal well, which clarifies the differences between casings and wellbores of different sizes through an analysis of the influence of wellbore size and casing size on relevant factors that meet fracturing requirements, and completes the theoretical selection of casing and wellbore; combined with economic and feasibility evaluations, the horizontal section wellbore and casing selection is finally completed, providing a reference for the selection of casing and wellbore for the horizontal section of each block. BRIEF DESCRIPTION OF THE DRAWINGS

[0077] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0078] Figure 1It is a pump pressure curve diagram under different casing sizes of the embodiment of the present application;

[0079] Figure 2 A bar chart showing the extension capabilities of casings of different sizes in a 215.9 mm wellbore according to an embodiment of the present application;

[0080] Figure 3 This is a flowchart of the casing selection process in an embodiment of the present application;

[0081] Figure 4 A bar graph showing the extension conditions under different borehole clearances according to an embodiment of the present application;

[0082] Figure 5 A line diagram of the open hole extension limit under different wellbore spacings according to an embodiment of the present application;

[0083] Figure 6 A physical model diagram of a horizontal well in an embodiment of the present application;

[0084] Figure 7 A flowchart of the theoretical selection process of casing and wellbore in the embodiment of the present application;

[0085] Figure 8 A flowchart of the casing and wellbore selection and evaluation process of an embodiment of the present application;

[0086] Fig. 9 A route map for selecting a casing and a wellbore size for the solution of the embodiment of the present application;

[0087] Fig.10 A selection roadmap for matching casing and wellbore size for solution 2 of the embodiment of the present application;

[0088] Fig.11 This is a bar chart of cost calculation for different casing sizes according to an embodiment of the present application. DETAILED DESCRIPTION

[0089] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. The components of the embodiments of the present application described and shown in the drawings here can be arranged and designed in various different configurations.

[0090] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application for which protection is sought, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0091] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0092] The features and performance of the present application are further described in detail below in conjunction with the embodiments.

[0093] The present invention provides a method for selecting and evaluating the wellbore and casing of a horizontal section of a shale horizontal well:

[0094] Basic ideas for establishing the horizontal wellbore and casing selection evaluation process:

[0095] Step 1: For shale gas horizontal wells in different work areas, combined with the burial depth (m), fracture pressure coefficient (P f ), deployment horizontal section length (L), fracturing transformation requirements (displacement m 3 / min), conduct relevant analysis on the open hole extension capacity, drilling extension capacity, casing running capacity of different sizes and cement sheath meeting the requirements of fracturing in different wellbores, and clarify the differences between casing and wellbores of different sizes.

[0096] Step 2: Combine the existing casing, drill bit and other downhole tool matching capabilities to carry out economic and feasibility evaluations, and ultimately build a horizontal wellbore and casing selection evaluation process.

[0097] (I) Casing and wellbore selection under technical conditions (theoretical selection)

[0098] 1. Impact of casing size changes on fracturing displacement / reconstruction:

[0099] Calculation method: Combined with the calculation model of fracturing construction pressure, the calculation is carried out with the existing common production casing matching (see Table 1) and the pressure limit of fracturing equipment (105MPa fracturing equipment pressure limit is 95MPa, 140MPa fracturing equipment pressure limit is 115MPa) as constraints. At the same time, combined with the requirements for displacement of reasonable reservoir transformation in different shale gas blocks, the impact of reducing production casing on fracturing construction pump pressure and displacement is analyzed.

[0100] (1) Construction pressure calculation model

[0101] P wh =P wf -P h +ΔP wh +ΔP perf

[0102] Where: P wh , P wf are wellhead pressure and bottom hole pressure respectively; P h is the static column pressure of the fracturing fluid; ΔP wh , ΔP perfThey are respectively the friction along the way and the friction of the hole;

[0103] The friction along the way is expressed by the formula: ΔP wh =δ(ΔP 0 )

[0104] ΔP 0 =1.386×10 12 D -4.8 Q 1.8 L,

[0105] Where: δ is the drag reduction ratio, dimensionless; ΔP 0 is the friction resistance of the clean water pipe string; D is the inner diameter of the pipe string; Q is the construction displacement; L is the pipe length;

[0106] The calculation formula of the drag reduction ratio δ adopts the experimental data regression formula proposed by Lord et al.:

[0107]

[0108] Where: G is the concentration of thickener; C is the concentration of proppant;

[0109] The hole friction is expressed by the formula:

[0110] Where: Q is the construction displacement; ρ is the liquid density: n p is the number of holes; d p is the hole diameter; C d is the correction coefficient, the value is 0.8-1.0;

[0111] Bottom hole pressure P wf Obtained based on extended pressure of implemented wells;

[0112] Hydrostatic column pressure: P h =ρgH, where: ρ is the density of the fracturing fluid; H is the vertical depth of the gas well.

[0113] (2) Parameters of casings of different sizes

[0114] Table 1. Performance parameters of common shale gas casing

[0115]

[0116] (3) Simulation calculation

[0117] Simulation conditions: According to the actual construction pressure in a certain area, the fracture extension pressure gradient is estimated to be 0.019-0.023MPa / m, and the fracturing fluid density is selected to be 1.0045g / cm 3 , the drag reduction rate of slick water and linear rubber is 75%, and the fracturing transformation requires 14m 3 Displacement.

[0118] Constraint 1: Not exceeding 80% of the internal pressure resistance of the matching casing;

[0119] Constraint 2: Do not exceed the 115 / 95MPa pressure limit of the 140 / 105MPa fracturing equipment.

[0120] Simulation conclusion: Under the same displacement, the pump pressure of fracturing operation increases exponentially as the casing size decreases (see Figure 1 ), when the casing size is less than 114.3mm, the pump pressure increases significantly, exceeding the construction capacity of the existing 140MPa fracturing equipment and cannot meet the development requirements of Fuling

[0121] 2. Impact of casing size changes on casing running capacity:

[0122] Calculation method: Combined with the extension capacity calculation model, the Wellplan / Sunny Path software was used to simulate and analyze the impact of casing size changes on the extended casing running capacity in the same well location horizontal section length and fixed wellbore.

[0123] The extension limit includes the drill string operation limit and the casing running limit, which depends on the drilling steering mode, the string strength, and the ground drilling rig load. The objective function of the wellbore extension limit is:

[0124]

[0125] Among them, L is the target well depth function; L(.) is the overall force model of the downhole tubular; p represents the constraint parameter, specifically the hook load, bit drilling pressure, and bit torque parameters; d represents the design parameter, specifically the tubular combination, wellbore trajectory, and drag reduction joint parameters; P is the allowable space of the constraint parameter p, and the specific form is given in the form of constraint conditions; P* is the optimal constraint parameter, and the well depth obtains the maximum value under the optimal constraint parameter; c represents the specific operating conditions, including the lifting and lowering of the tubular under sliding and rotation modes;

[0126] For a specific drilling rig, the axial tension during the hook lifting process has an upper limit, and its constraint conditions are:

[0127] During the lowering process of the big hook, the axial tension on the big hook has a lower limit value, and the corresponding constraint condition is:

[0128] The constraints corresponding to the rated torque of the ground turntable are:

[0129] Where: -F H is the axial force on the pipe string at the ground location; is the rated pulling load of the drilling rig; The minimum lifting load for lowering the big hook, usually this value is zero, that is, the state of complete lowering; M TH is the torque on the pipe string at the surface; is the rated torque of the turntable;

[0130] During the process of sliding and lifting the pipe string, the occurrence of pipe sticking will cause resistance in lifting. A lifting resistance is applied at the drill bit position to simulate the pipe sticking in the well, and the corresponding constraint condition is: B =T stuck ;

[0131] The drill may get stuck during the process of rotating and lifting the pipe string. In this case, not only the above constraints exist on the axial force, but also the torque constraints are as follows: M B =M T stuck ;

[0132] When the pipe string is lowered and the drill bit is breaking the rock, the drilling pressure needs to exceed a certain threshold value. The constraint conditions are:

[0133] Since there is an approximately linear relationship between the drilling pressure and torque on the drill bit, the rock breaking threshold drilling pressure also corresponds to the threshold drill bit torque, and its constraint condition is:

[0134] Among them: F B is the axial force on the pipe string at the drill bit position N; T stuck M is the drill bit sticking resistance; B M is the torque on the pipe string at the drill bit position; T stuck Select the resistance torque at the drill bit position; The rock breaking threshold drilling pressure; is the threshold torque; k is the approximate proportionality coefficient between the threshold torque and the threshold drilling pressure;

[0135] The axial force on the pipe string causes a uniform axial stress on the pipe string section. The calculation formula is:

[0136] The constraint condition for the drill string not to buckle is:

[0137] Where: t is the true axial stress of the pipe string; Ft is the true axial force of the pipe string; AS is the cross-sectional area of ​​the pipe string; F is the equivalent axial force considering the hydraulic effect; σ m is the axial stress considering the hydraulic effect; σ is the equivalent stress on the pipe string; [σ] is the allowable equivalent stress; σ s is the yield of the pipe material; n4 is the safety factor;

[0138] According to the axial movement direction of the pipe string, it is divided into lifting and lowering. According to whether the pipe string rotates, it is divided into sliding mode and rotation mode. For the sliding mode, the extension limit is the minimum value of sliding lifting and sliding lowering. For the rotation mode, the extension limit is the minimum value of rotation lifting and rotation lowering.

[0139] Analysis conclusion: The smaller the casing size is, the smaller the extension capacity is. Taking the extension capacity of different casing sizes in a 215.9mm wellbore as an example, the extension capacity of casings smaller than 114.3mm is reduced to less than 1700m (see Figure 2 ).

[0140] 3. Casing selection process

[0141] Through the previous analysis, the casing running capacity meets the horizontal section length, and the casing pressure resistance meets the fracturing transformation displacement requirements are the main factors in casing selection. Therefore, the casing selection process is constructed as follows: Figure 3 shown.

[0142] 4. The influence of the change of the horizontal section annular gap wellbore size on the open hole extension capacity:

[0143] Calculation method: Based on the open hole extension limit prediction model, the common bottom hole ECD (equivalent circulating density) < P f Considering the exclusion of rock carrying and other factors, SunnyDrilling software was used to calculate the same flow rate and common 127mm drilling tool combination according to different wellbore sizes, and the influence of the same drilling tool on the open hole extension capacity under different wellbore sizes was analyzed (see Figure 4 , Figure 5 ).

[0144] Simulation conclusion: From the simulation results, with a vertical depth of 2400m and a 127mm drill tool size, the extension capacity of a 215.9mm open hole is 4277m under the same drilling fluid performance. As the wellbore clearance is further reduced to 185mm, the open hole extension capacity drops to less than 2000m, and ECD>P f The leaky formation does not meet the well location requirements of the Fuling work area.

[0145] 5. Impact of horizontal section wellbore size and casing size matching on cementing:

[0146] Calculation method: Based on the elastic-plastic mechanical model of casing-cement-stratum combination (see Figure 6), obtain the equivalent stress of different wellbore gaps, obtain the corresponding cementing hydraulic stone performance index requirements, analyze the influence of cement ring gap reduction on the mechanical properties of cement stone and meet the requirements of fracturing for gaps. Theoretically, the strength of the casing string with cement ring can be analyzed as a thick-walled cylinder composed of two different materials; considering the actual working state of the cement ring casing double-layer combination structure near the wellhead, it should belong to the plane strain state. Assume that: a, b, c, d are the inner radius and outer radius of the first layer of casing and the inner radius and outer radius of the second layer of casing respectively, and Ec, Es are the elastic modulus of cement and steel respectively; c, s are the Poisson's ratio of cement and steel respectively; P i , P 1 , P2 and P o The internal pressure and external squeezing force of the first layer of casing and the internal pressure and external squeezing force of the second layer of casing respectively;

[0147] for:

[0148]

[0149] The radial deformation of cement sheath is:

[0150]

[0151] The radial deformation of the second layer of casing is:

[0152]

[0153] Substitute r = b into the radial deformation formula of the first layer of casing and the radial deformation formula of the cement sheath, and make them equal; substitute r = c into the radial deformation formula of the cement sheath and the radial deformation formula of the second layer of casing, and make them equal, and we can get the following equation about P 1 and P 2 The system of equations, where Pi and P o As is known, solve for P 1 and P 2 The value of

[0154] The radial and tangential stress equations are:

[0155]

[0156] According to the boundary conditions:

[0157] When r = a,

[0158] When r = b,

[0159] The stress equation of the inner casing can be obtained:

[0160]

[0161] Where: is the tangential stress of the casing;

[0162] On the inner wall, when r = a, the stress is maximum, and the corresponding von Mises equivalent stress is:

[0163]

[0164] if Then the casing is safe; where: s is the yield stress, n is the safety factor;

[0165] The calculation results are shown in Table 2.

[0166] Table 2 Mechanical properties of cement paste

[0167]

[0168] From the results, it can be seen that after the cement sheath is reduced from 38.1mm to 25.4mm, the compressive stress increases by 9-13%, and the tensile stress remains basically unchanged; if it is further reduced and the performance requirements of cement stone are higher, the difficulty of optimizing the cement slurry formula will increase.

[0169] 6. Wellbore size selection process

[0170] Through the analysis of steps 4-5, after the casing size is selected, the quality of the cement sheath and the performance of the cement slurry, as well as the open hole extension capacity are the main factors. Therefore, the wellbore selection process is constructed as follows: Figure 7 .

[0171] (II) Casing and wellbore selection under economic conditions

[0172] The casing and wellbore are calculated according to the theoretical selection process, and are determined in combination with the current status of industrial supporting facilities and construction technical capabilities (see Table 3). The upper opening wellbore structure is then designed according to the conventional process, and finally the quota is calculated according to the requirements. The one that is more economical is selected.

[0173] Table 3 Supporting and technical capability requirements

[0174] factor Criteria Cementing clearance >19mm Annular space safety (blocking) >13mm Centralizer accessories Yes / No Casing centering ＞67.7％ Cementing Cycle ECD Less than Pf Cementing capacity Return to the ground

[0175] (III) Establishment of horizontal wellbore and casing selection evaluation process

[0176] Based on the above analysis and ideas, the horizontal wellbore and casing selection evaluation process was finally constructed (see Figure 8 ).

[0177] Example 1

[0178] Taking the added value of small casing in 139.7mm casing construction pump pressure as an example, casing selection is carried out in accordance with the most economical and mature matching method.

[0179] Table 4 Prediction of pump pressure in Φ114.3mm casing fracturing construction

[0180]

[0181]

[0182] Conclusion: Combining the post-pressure data statistics and simulation prediction, the deeper the vertical depth and the longer the horizontal section, the higher the construction pump pressure; in the block with a vertical depth of more than 3500m, the construction pump pressure of 127 / 114.3mm casing exceeds the limit pressure (95 / 115MPa) and does not meet the construction requirements.

[0183] Through the above analysis, it is concluded that different sizes of casing can be used in different blocks. 114.3 / 127 / 139.7mm casing can be used for shallower than 3500m, but which one is more suitable needs to be evaluated from the economic and technical perspectives.

[0184] Scheme 1: Φ114.3mm casing: Combined with the comparative analysis of circulating pressure loss, ECD, etc., the horizontal section Φ114.3mm casing is optimally used in the Φ165.1mm wellbore, and a preliminary wellbore structure scheme is formed. The specific selection route map is shown in Fig. 9 The basis for wellbore selection is shown in Table 5.

[0185] Table 5 Φ114.3mm casing horizontal section wellbore selection basis table

[0186]

[0187] Note: 149.23mm wellbore: annular clearance <19mm does not meet cementing requirements;

[0188] 152.4 / 155.57mm wellbore: cementing cycle ECD is high and prone to leaking formation, cement return ability is weak, cement ring is thin and cementing quality is poor;

[0189] 165.1 / 171.5mm wellbore: The annular space is moderate to meet the requirements of cementing, casing running, cement return, etc., and the centralizer is mature.

[0190] Option 2: Φ139.7mm casing: Based on the comparative analysis of circulating pressure loss, ECD, etc., the horizontal section Φ139.7mm casing is optimally used in the Φ190.5mm wellbore, and a preliminary wellbore structure plan is formed. The specific selection route map is shown in Fig.10 The basis for wellbore selection is shown in Table 6.

[0191] Table 6 Φ139.7mm casing horizontal section wellbore selection basis table

[0192]

[0193] Description: 177.8mm / 185mm wellbore: small annular space, high cementing cycle ECD, easy to leak formation, weak cement return ability, thin cement ring, poor cementing quality, difficult to rotate the supporting centralizer, poor casing centering and difficulty in running the casing;

[0194] 190.5 / 195.0mm wellbore: The annular space is moderate to meet the requirements of cementing, casing running, cement return, etc., and the centralizer is mature;

[0195] Wellbores 200.2mm and above: The annular space is relatively large, the drill cuttings increase, and the related centralizers are mature, but the upper wellbore structure is larger in size and the economy is not outstanding.

[0196] Based on quota accounting (see Fig.11 ), compared with conventional wellbore structure, 114.3mm casing is expected to save 20% of the cost of the whole well, and 127mm casing is expected to save 8% of the cost; combined with cost saving and fracturing tool matching, two casing selection schemes for the horizontal section are proposed:

[0197] Option 1 (maximum cost reduction): 114.3 mm casing in the horizontal section; Option 2 (minimum impact of fracturing): 139.7 mm casing in the horizontal section.

Claims

1. A method for selecting and evaluating the wellbore and casing of a horizontal section of a shale gas horizontal well, characterized in that: The steps include: Step 1: For shale gas horizontal wells in different work areas, combined with the burial depth, fracture pressure coefficient, horizontal section length and fracturing transformation requirements, conduct relevant analysis on the open hole extension capacity, drilling extension capacity, casing running capacity of different sizes and cementing cement sheath meeting the fracturing requirements of different wellbores, clarify the differences between casing and wellbores of different sizes, and complete the theoretical selection of casing and wellbores; Step 2: Combine the existing casing, drill bit and downhole tool matching capabilities to conduct economic and feasibility evaluations, and ultimately build a horizontal wellbore and casing selection evaluation process.

2. A method for selecting and evaluating the wellbore and casing of a horizontal section of a shale gas horizontal well according to claim 1, characterized in that: The theoretical selection of casing and wellbore described in step 1 specifically includes the following contents: Step S1), the impact of casing size changes on fracturing displacement or transformation: Combined with the fracturing construction pressure calculation model, the calculation was performed with the existing production casing and fracturing equipment pressure limit as constraints. At the same time, combined with the requirements for displacement of reasonable reservoir transformation in different shale gas blocks, the analysis of the impact of production casing reduction on fracturing construction pump pressure and displacement was carried out; Step S2), the impact of casing size changes on casing running capability: Based on the existing extension capacity calculation model, simulation is carried out to analyze the impact of casing size changes on casing running capacity in the same fixed wellbore; Step S3), casing selection: Through the calculation and analysis of the above steps, the casing running capacity meets the horizontal section length, and the casing pressure resistance meets the fracturing transformation displacement requirements, which are the main factors in casing selection. The casing size is obtained when both factors are met at the same time; Step S4), the impact of horizontal wellbore size changes on open hole extension capacity: Based on the open hole extension limit, that is, under the premise that the circulating equivalent density of the bottom hole drilling fluid is less than the fracture pressure coefficient, considering the exclusion of the influence of rock carrying factors, the same flow rate and drilling tool combination are used for calculation according to wells of different sizes, and the open hole extension capacity of the same drilling tool under different wellbore sizes is analyzed; Step S5), the impact of the matching of horizontal section wellbore size and casing size on cementing: Based on the existing elastic-plastic mechanical model of casing-cement-formation combination, the equivalent stress of different wellbore gaps is obtained, the corresponding cementing hydraulic stone performance index requirements are obtained, and the influence of cement ring gap reduction on cement stone mechanical properties and the requirements for gaps to meet fracturing are analyzed; Step S6), wellbore selection: According to the analysis of steps S4 and S5, after the casing size is selected, the equivalent stress of the cement sheath and the open hole extension capacity are the main factors, and the wellbore size is obtained when the above two factors are satisfied at the same time.

3. A method for selecting and evaluating the wellbore and casing of a horizontal section of a shale gas horizontal well according to claim 2, characterized in that: The calculation model of the fracturing construction pressure in step S1 is as follows: P wh =P wf -P h +ΔP wh +ΔP perf Where: P wh , P wf are wellhead pressure and bottom hole pressure respectively; P h is the static column pressure of the fracturing fluid; ΔP wh , They are respectively the friction along the way and the friction of the hole; The friction along the way is expressed by the formula: ΔP wh =δ(ΔP0) ΔP0=1.386×10 12 D -4.8 Q 1.8 L, Where: δ is the drag reduction ratio, dimensionless; ΔP0 is the friction resistance of the clean water string along the way; D is the inner diameter of the string; Q is the construction displacement; L is the pipe length; The calculation formula of the drag reduction ratio δ adopts the experimental data regression formula proposed by Lord et al.: Where: G is the concentration of thickener; C is the concentration of proppant; The hole friction is expressed by the formula: Where: Q is the construction displacement; ρ is the liquid density: n p is the number of holes; d p is the hole diameter; C d is the correction coefficient, the value is 0.8-1.0; Bottom hole pressure P wf Obtained based on the extended pressure of implemented wells; Hydrostatic column pressure: P h =ρgH, where: ρ is the density of the fracturing fluid; H is the vertical depth of the gas well.

4. A method for selecting and evaluating the wellbore and casing of a horizontal section of a shale gas horizontal well according to claim 3, characterized in that: The final selection of casing and wellbore described in step 2 includes the following: the casing and wellbore calculated according to the theoretical selection process, and determined in combination with the current status of industrial supporting facilities and construction technical capabilities, and then the upper opening wellbore structure design is carried out according to the conventional process, and finally the quota is calculated according to the requirements to select the most economical selection.

5. A method for selecting and evaluating the wellbore and casing of a horizontal section of a shale gas horizontal well according to claim 4, characterized in that: The extension capacity calculation model in step S2 includes the following contents: The extension limit includes the drill string operation limit and the casing running limit, which depends on the drilling steering mode, the string strength, and the ground drilling rig load. The objective function of the wellbore extension limit is: Among them, L is the target well depth function; L(.) is the overall force model of the downhole tubular; p represents the constraint parameter, specifically the hook load, bit drilling pressure, and bit torque parameters; d represents the design parameter, specifically the tubular combination, wellbore trajectory, and drag reduction joint parameters; P is the allowable space of the constraint parameter p, and the specific form is given in the form of constraint conditions; P* is the optimal constraint parameter, and the well depth obtains the maximum value under the optimal constraint parameter; c represents the specific operating conditions, including the lifting and lowering of the tubular under sliding and rotation modes; For a specific drilling rig, the axial tension during the hook lifting process has an upper limit, and its constraint conditions are: During the lowering process of the big hook, the axial tension on the big hook has a lower limit value, and the corresponding constraint condition is: The constraints corresponding to the rated torque of the ground turntable are: Where: -F H is the axial force on the pipe string at the ground location; is the rated pulling load of the drilling rig; The minimum lifting load for lowering the big hook, usually this value is zero, that is, the state of complete lowering; M TH is the torque on the pipe string at the surface; is the rated torque of the turntable; During the process of sliding and lifting the pipe string, the occurrence of pipe sticking will cause resistance in lifting. A lifting resistance is applied at the drill bit position to simulate the pipe sticking in the well, and the corresponding constraint condition is: B =T stuck ; The drill may get stuck during the process of rotating and lifting the pipe string. In this case, not only the above constraints exist on the axial force, but also the torque constraints are as follows: M B =M T stuck ; When the pipe string is lowered and the drill bit is breaking the rock, the drilling pressure needs to exceed a certain threshold value. The constraint conditions are: Since there is an approximately linear relationship between the drilling pressure and torque on the drill bit, the rock breaking threshold drilling pressure also corresponds to the threshold drill bit torque, and its constraint condition is: Among them: F B is the axial force on the pipe string at the drill bit position N; T stuck M is the drill bit sticking resistance; B M is the torque on the pipe string at the drill bit position; T stuck Select the resistance torque at the drill bit position; The rock breaking threshold drilling pressure; is the threshold torque; k is the approximate proportionality coefficient between the threshold torque and the threshold drilling pressure; The axial force on the pipe string causes a uniform axial stress on the pipe string section. The calculation formula is: The constraint condition for the drill string not to buckle is: Where: t is the true axial stress of the pipe string; Ft is the true axial force of the pipe string; AS is the cross-sectional area of ​​the pipe string; F is the equivalent axial force considering the hydraulic effect; σ m is the axial stress considering the hydraulic effect; σ is the equivalent stress on the pipe string; [σ] is the allowable equivalent stress; σ s is the yield of the pipe material; n4 is the safety factor; According to the axial movement direction of the pipe string, it is divided into lifting and lowering. According to whether the pipe string rotates, it is divided into sliding mode and rotation mode. For the sliding mode, the extension limit is the minimum value of sliding lifting and sliding lowering. For the rotation mode, the extension limit is the minimum value of rotation lifting and rotation lowering.

6. A method for selecting and evaluating the wellbore and casing of a horizontal section of a shale gas horizontal well according to claim 5, characterized in that: The elastic-plastic mechanical model of the casing-cement-formation combination in step S5 includes the following contents: Theoretically, the strength of the casing string with cement sheath can be analyzed as a thick-walled cylinder composed of two different materials. Considering the actual working state of the cement sheath casing double-layer combination structure near the wellhead, it should belong to the plane strain state. Assume that: a, b, c, d are the inner radius and outer radius of the first layer of casing and the inner radius and outer radius of the second layer of casing respectively, and Ec, Es are the elastic modulus of cement and steel respectively; c, s are the Poisson's ratio of cement and steel respectively; P i , P1, P2 and P o The internal pressure and external squeezing force of the first layer of casing and the internal pressure and external squeezing force of the second layer of casing respectively; for: The radial deformation of cement sheath is: The radial deformation of the second layer of casing is: Substitute r = b into the radial deformation formula of the first layer of casing and the radial deformation formula of the cement sheath, and make them equal; substitute r = c into the radial deformation formula of the cement sheath and the radial deformation formula of the second layer of casing, and make them equal, and we get the equation group about P1 and P2, where Pi and P o For known, solve to obtain the values ​​of P1 and P2; The radial and tangential stress equations are: According to the boundary conditions: When r = a, When r = b, The stress equation of the inner casing can be obtained: Where: is the tangential stress of the casing; On the inner wall, when r = a, the stress is maximum, and the corresponding von Mises equivalent stress is: if The casing is safe; where: s is the yield stress and n is the safety factor.

7. A method for selecting and evaluating the wellbore and casing of a horizontal section of a shale gas horizontal well according to claim 2 or 4, characterized in that: The constraint conditions include two types: one is that the casing internal pressure resistance performance does not exceed 80%, and the second is that it does not exceed the pressure limit of the fracturing equipment.

8. The method for selecting and evaluating the wellbore and casing of a horizontal section of a shale gas horizontal well according to claim 5, characterized in that: In step S1, the pump pressure of the fracturing construction at the same displacement increases exponentially as the casing size decreases.

9. A method for selecting and evaluating the wellbore and casing of a horizontal section of a shale gas horizontal well according to claim 8, characterized in that: The smaller the casing size is at the same well location in step S2, the smaller the extension capacity is.

10. A method for selecting and evaluating the wellbore and casing of a horizontal section of a shale gas horizontal well according to claim 9, characterized in that: In step S5, the equivalent stress will increase as the cement sheath gap decreases.

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