Well hole cleaning optimization design method

Abstract

The invention belongs to the technical field of oil and gas drilling, and particularly discloses a borehole cleaning optimization design method. The borehole cleaning optimization design method comprises the steps that S1, influence factors possibly influencing the borehole cleaning effect are determined; s2, by calculating the thickness of the cuttings bed, the sensitivity of each influence factor to borehole cleaning is analyzed; s3, main control factors influencing the borehole cleaning effect are recognized by calculating the influence factor of each influence factor, and the influence factors represent the change of the thickness of the cuttings bed corresponding to the value of the unit influence factor; and S4, based on the main control factors, according to the sensitivity analysis conclusion of the main control factors, borehole cleaning optimization design is carried out until the borehole efficient cleaning constraint condition of borehole safety is met. According to the method provided by the invention, comprehensive optimization design can be carried out aiming at influence factors influencing the borehole cleaning effect, and the borehole cleaning effect in the construction process can be guaranteed and improved.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas drilling, and in particular relates to a wellbore cleaning optimization design method. Background Art

[0002] With the continuous increase in the country's demand for energy, the depth, length and difficulty of drilling are constantly increasing, and the demand for drilling high-angle wells and horizontal wells is increasing year by year. The characteristics of high-angle wells and horizontal wells are that the well inclination is large, generally exceeding 56°, the middle large well inclination stable inclination section is long, the displacement is large, and there is a long horizontal section. The wellbore cleaning of high-angle wells and horizontal wells is more difficult than that of conventional directional wells. Wellbore cleaning is a key technology for drilling. Maintaining a good wellbore cleaning condition is of great significance for safe and fast drilling. If the wellbore is not effectively cleaned during the drilling process, pressure holding, torque jamming, and drill sticking may occur, which can easily lead to downhole accidents such as early wear of the drill bit, reduced drilling speed, high torque and high friction resistance, which directly affect the drilling efficiency and safe drilling, and are related to the success or failure of drilling. Ensuring a good wellbore cleaning effect can effectively reduce accidents, improve drilling efficiency, and shorten the drilling cycle. For the drilling concept of "time is money", saving drilling cycles means saving drilling costs.

[0003] Wellbore cleaning in highly deviated wells and horizontal wells is affected by many factors, such as drilling parameters, drilling fluid properties, drilling fluid flow state, drilling fluid return rate, drilling fluid rheology, drilling fluid annulus return rate, drilling fluid displacement and mechanical speed. It is of great significance to optimize the wellbore cleaning design based on these influencing factors to ensure and improve the effect of wellbore cleaning during construction.

[0004] However, in the current existing technology, all patents related to wellbore cleaning are methods for judging and evaluating the degree, condition and effect of wellbore cleaning. The contents cover methods for optimizing drill bit combinations, methods for optimizing parameters related to wellbore cleaning, methods for judging and evaluating the degree, condition and effect of wellbore cleaning, methods for judging the risk of insufficient wellbore cleaning, etc., and do not involve wellbore cleaning optimization design, especially comprehensive optimization design of wellbore cleaning for all influencing factors. Summary of the invention

[0005] The main purpose of the present invention is to provide a wellbore cleaning optimization design method, in particular to provide a wellbore cleaning optimization design method for highly deviated wells and horizontal wells based on main control factor analysis.

[0006] According to the present invention, a wellbore cleaning optimization design method is provided, which comprises the following steps:

[0007] Step S1: determining factors that may affect the wellbore cleaning effect;

[0008] Step S2: Analyze the sensitivity of each influencing factor to wellbore cleaning by calculating the cuttings bed thickness;

[0009] Step S3: identifying the main controlling factors affecting the wellbore cleaning effect by calculating the influencing factor of each influencing factor, wherein the influencing factor represents the change in the thickness of the cuttings bed corresponding to the value of the unit influencing factor;

[0010] Step S4: Based on the main controlling factors and referring to the sensitivity analysis conclusions of the main controlling factors, the wellbore cleaning optimization design is performed until the wellbore efficient cleaning constraint conditions of wellbore safety are met.

[0011] According to one embodiment of the present invention, step S2 includes:

[0012] For each influencing factor, give the value range of the influencing factor;

[0013] Calculate the corresponding cuttings bed thickness within the value range;

[0014] The variation trend of cuttings bed thickness is given when the influencing factors change in an increasing or decreasing trend within the value range.

[0015] According to an embodiment of the present invention, when calculating the corresponding cuttings bed thickness for a certain influencing factor, the remaining influencing factors take fixed values ​​and ensure that the calculated cuttings bed thickness is not zero.

[0016] According to one embodiment of the present invention, the corresponding cuttings bed thickness within the value range is given in the form of a graph.

[0017] According to one embodiment of the present invention, step S3 includes:

[0018] When an influencing factor has more than one value, the influencing factor of the influencing factor is calculated according to the following formula, and the calculated influencing factor is compared with the predetermined value to identify the main controlling factor:

[0019]

[0020] Where, F is the impact factor, mm;

[0021] T cmax1 D is the value of the influencing factor 1 Maximum cuttings bed thickness at , mm;

[0022] T cmax2 D is the value of the influencing factor 2 Maximum cuttings bed thickness at , mm;

[0023] k is a coefficient, the unit is consistent with the influencing factor, and it is set according to the change range of the influencing factor.

[0024] According to an embodiment of the present invention, when the influence factor of a certain influence factor is greater than a predetermined value, the influence factor is identified as a main control factor, otherwise, the influence factor is identified as a non-main control factor.

[0025] According to one embodiment of the present invention, step S3 includes:

[0026] When an influencing factor has only one value, the influencing factor is defined as a non-dominant factor.

[0027] According to one embodiment of the present invention, step S4 includes:

[0028] Sort the main controlling factors in descending order of the impact factor values;

[0029] For each main control factor, according to the sensitivity analysis conclusion, the wellbore cleaning design is optimized to give the optimal value of the main control factor;

[0030] Determine whether the efficient wellbore cleaning constraint conditions of wellbore safety can be met when all main control factors take the optimal value. If so, the wellbore cleaning design optimization is completed. If not, the wellbore cleaning design optimization is performed again.

[0031] According to one embodiment of the present invention, the efficient wellbore cleaning constraint condition for wellbore safety is:

[0032] ① Calculate that there is no accumulation of cuttings bed on the well wall.

[0033] ②The concentration of cuttings in the annulus is ≤5%.

[0034] ③ The equivalent density of the drilling fluid cannot exceed the minimum fracture pressure of the formation in the open hole section.

[0035] According to one embodiment of the present invention, the wellbore cleaning optimization design method is applicable to the wellbore cleaning optimization design of highly deviated wells and horizontal wells.

[0036] According to one embodiment of the present invention, the factors that may affect the wellbore cleaning effect include six categories: wellbore trajectory, drilling parameters, drilling fluid performance, bottom hole drill assembly, wellbore quality and other supplementary factors, among which the wellbore trajectory category includes trajectory type, inclination point, inclination rate, inclination increase rate and well inclination angle, the drilling parameter category includes rotation speed and displacement, the drilling fluid performance includes density, plastic viscosity, dynamic shear force, consistency coefficient and φ3 value, the bottom hole drill assembly includes drill pipe size and sand cleaning tools, and the wellbore quality includes wellbore expansion rate.

[0037] According to one embodiment of the present invention, the main controlling factors affecting the wellbore cleaning effect are the inclination point, inclination rate, well inclination angle, rotation speed, displacement, plastic viscosity, dynamic shear force, consistency coefficient and drill pipe size.

[0038] According to one embodiment of the present invention, in step S1, the factors that may affect the wellbore cleaning effect are determined from three aspects: early drilling plan demonstration, drilling engineering design and later drilling construction. Among them, the early drilling plan demonstration includes the wellbore trajectory, the drilling engineering design includes drilling parameters, drilling fluid performance and bottom hole drill bit combination, and the later drilling construction includes the wellbore quality.

[0039] Due to the adoption of the above technical solution, the present invention has the following beneficial effects:

[0040] The present invention is based on wellbore cleaning simulation, performs sensitivity analysis on the factors affecting the wellbore cleaning effect, identifies the main controlling factors according to the definition of the main controlling factors, and optimizes the wellbore cleaning effect based on the main controlling factors to achieve the wellbore efficient cleaning constraint conditions that meet the wellbore safety. The method provided by the present invention can comprehensively optimize the factors affecting the wellbore cleaning effect, which helps to ensure and improve the wellbore cleaning effect during the construction process. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] 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 work.

[0042] Figure 1 A flow chart of the wellbore cleaning optimization design method provided by the present invention;

[0043] Figure 2 is a flow chart of a wellbore cleaning optimization design method provided by an embodiment of the present invention;

[0044] Figure 3 It is the "double increase" trajectory of different deflection points;

[0045] Figure 4 It is the effect of the deflection point on wellbore cleaning;

[0046] Figure 5 It is a "double increase" trajectory with different build rates;

[0047] Figure 6 is the effect of build-up rate on wellbore cleaning;

[0048] Figure 7 It is a "double increase" trajectory with different increase slopes;

[0049] Figure 8 is the effect of increasing slope on wellbore cleaning;

[0050] Fig. 9It is a “single increase” wellbore trajectory;

[0051] Fig.10 The effect of well deviation on wellbore cleaning is shown in Figure (1);

[0052] Fig.11 is the effect of well deviation on wellbore cleaning (2);

[0053] Fig.12 is the effect of rotation speed on wellbore cleaning;

[0054] Fig.13 is the effect of displacement on wellbore cleaning;

[0055] Fig.14 is the effect of plastic viscosity on wellbore cleaning;

[0056] Fig.15 is the effect of dynamic shear force on wellbore cleaning;

[0057] Fig.16 is the effect of consistency factor on wellbore cleaning;

[0058] Fig.17 is the effect of φ3 value on wellbore cleaning;

[0059] Fig.18 is the effect of drill pipe size on wellbore cleaning;

[0060] Fig.19 The effect of the borehole expansion rate of 311.1 mm and 215.9 mm wells on wellbore cleaning;

[0061] Fig. 20 The dynamic shear force of a 311.1 mm borehole is controlled at 8-11 Pa;

[0062] Fig.21 The dynamic shear force of the 215.9mm wellbore is controlled at 7-12Pa;

[0063] Fig. 22 The control consistency coefficient K≤0.8 for 311.1mm wellbore;

[0064] Fig.23 The control consistency coefficient K≤0.7 for 215.9mm wellbore;

[0065] Fig.24 The plastic viscosity of the 311.1mm wellbore is controlled to be μp≤15cp;

[0066] Fig.25 The plastic viscosity of the 215.9 mm borehole is controlled to be μp≤17;

[0067] Fig.26 It is the vertical projection of the wellbore trajectory (vertical section azimuth 39.52°);

[0068] Fig. 27 It is the clean condition of 311.1mm wellbore;

[0069] Fig.28 It is the clean condition of 215.9mm wellbore;

[0070] Fig.29 is the thickness of the wellbore cuttings bed of 311.1 mm;

[0071] Fig.30 is the cuttings concentration in the annulus of a 311.1 mm wellbore;

[0072] Fig.31 It is 311.1mm borehole ECD;

[0073] Fig.32 is the thickness of the wellbore cuttings bed of 215.9 mm;

[0074] Fig.33 is the cuttings concentration in the annulus of a 215.9 mm wellbore;

[0075] Fig.34 It is 215.9mm borehole ECD. DETAILED DESCRIPTION

[0076] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0077] According to the present invention, a wellbore cleaning optimization design method is provided, such as Figure 1 As shown, the method comprises the following steps:

[0078] Step S1: determining factors that may affect the wellbore cleaning effect;

[0079] Step S2: Analyze the sensitivity of each influencing factor to wellbore cleaning by calculating the cuttings bed thickness;

[0080] Step S3: identifying the main controlling factors affecting the wellbore cleaning effect by calculating the influencing factor of each influencing factor, wherein the influencing factor represents the change in the thickness of the cuttings bed corresponding to the value of the unit influencing factor;

[0081] Step S4: Based on the main controlling factors and referring to the sensitivity analysis conclusions of the main controlling factors, the wellbore cleaning optimization design is performed until the wellbore efficient cleaning constraint conditions of wellbore safety are met.

[0082] The method of the invention is particularly suitable for the optimization design of wellbore cleaning of highly deviated wells and horizontal wells.

[0083] In step S1, the factors that may affect the effect of wellbore cleaning can be determined from three aspects: early drilling program demonstration, drilling engineering design and later drilling construction. Specifically, it can be divided into six categories: wellbore trajectory, drilling parameters, drilling fluid performance, bottom hole assembly (BHA), wellbore quality and other supplementary factors. Expert consultation, group discussion and other forms can be used to brainstorm and brainstorm to list the factors that may affect the effect of wellbore cleaning in highly deviated wells and horizontal wells. Among them, the categories of wellbore trajectory include trajectory type, inclination point, inclination rate, slope increase rate and well inclination angle, the categories of drilling parameters include speed and displacement, the properties of drilling fluid include density, plastic viscosity, dynamic shear force, consistency coefficient and φ3 value, the bottom hole assembly includes drill pipe size and sand cleaning tools, and the quality of wellbore includes wellbore expansion rate.

[0084] In step S2, the sensitivity of each influencing factor to wellbore cleaning is analyzed by calculating the cuttings bed thickness, including: for each influencing factor, giving the value range of the influencing factor; calculating the corresponding cuttings bed thickness within the value range; and giving the changing trend of the cuttings bed thickness when the influencing factor changes in an increasing or decreasing trend within the value range. Specifically:

[0085] 1) Calculation conditions

[0086] ① Annular return velocity: The annular return velocity requirement for the open hole section of a φ215.9mm wellbore is >1m / s (when the wellbore expansion rate is 10%, the displacement is >29L / s);

[0087] ②Drilling fluid flow pattern: turbulent flow;

[0088] ③Rock cuttings size: 5mm.

[0089] ④Well diameter expansion rate: the average well diameter expansion rate of the corresponding number of actual drillings of the same well type in the same block, or 10%-15%.

[0090] ⑤ Mechanical drilling speed: the average mechanical drilling speed of the corresponding number of actual drillings of the same well type in the same block.

[0091] 2) Wellbore cleaning calculation

[0092] ① According to the actual situation, a reasonable value range and value change step size are given for each wellbore cleaning influencing factor listed in step S1.

[0093] ② Calculate the corresponding cuttings bed thickness (unit: mm) within the value range of all wellbore cleaning influencing factors (the calculation results can be given in the form of a graph). When calculating a certain influencing factor, the other influencing factors take fixed values ​​and ensure that the calculated cuttings bed thickness is not zero.

[0094] 3) Sensitivity analysis

[0095] After the calculation is completed, the changing trend of the cuttings bed thickness is given when the influencing factors change in an increasing or decreasing trend within the value range, and the corresponding conclusion is given.

[0096] In step S3, the main controlling factors affecting the wellbore cleaning effect are identified by calculating the influencing factors of each influencing factor, including: when the influencing factor has only one value, the influencing factor is defined as a non-main controlling factor; when the influencing factor has more than one value, the influencing factor of the influencing factor is calculated according to the following formula, and the calculated influencing factor is compared with a predetermined value to identify the main controlling factor. When the influencing factor of a certain influencing factor is greater than the predetermined value, the influencing factor is identified as the main controlling factor, otherwise the influencing factor is identified as a non-main controlling factor:

[0097]

[0098] Where, F is the impact factor, mm;

[0099] T cmax1 D is the value of the influencing factor 1 Maximum cuttings bed thickness at , mm;

[0100] T cmax2 D is the value of the influencing factor 2 Maximum cuttings bed thickness at , mm;

[0101] k is a coefficient, the unit is consistent with the influencing factor, and it is set according to the change range of the influencing factor.

[0102] In the present invention, the influencing factor is defined to quantitatively describe the degree of influence of the influencing factor on wellbore cleaning, assuming that within the value range of the influencing factor, the cuttings bed thickness is not zero.

[0103] In the present invention, the coefficient k is defined to make the value of the unit influencing factor meaningful in the actual design. For example, when studying the inclination point, because the variation interval of the inclination point is generally ≥30m in the actual wellbore trajectory design, if the variation interval is too small, such as 1m, the impact on the trajectory is small and the practical significance is not great. At this time, according to the actual situation, the value of k≥30 should be taken, so that the value of the influencing factor calculated in this way is more in line with the actual situation. The k value is equivalent to the step length of the influencing factor value.

[0104] In one embodiment, the predetermined value is 2 mm. That is, when the influence factor F of a certain influencing factor is greater than 2 mm, the influencing factor is identified as the main controlling factor.

[0105] In step S4, based on the main control factors and referring to the sensitivity analysis conclusions of the main control factors, the wellbore cleaning optimization design is performed until the wellbore efficient cleaning constraint conditions of wellbore safety are met, specifically including: sorting the main control factors in descending order of the values ​​of the influencing factors; for each main control factor, according to the sensitivity analysis conclusions, the wellbore cleaning design optimization is performed to give the optimal value of the main control factor; determining whether the wellbore efficient cleaning constraint conditions of wellbore safety can be met when all the main control factors take the optimal value, if so, the wellbore cleaning design optimization is completed, if not, the wellbore cleaning design optimization is performed again.

[0106] The constraints for efficient wellbore cleaning for wellbore safety are:

[0107] ① It is calculated that there is no accumulation of cuttings bed on the well wall, that is, the thickness of the cuttings bed is 0.

[0108] ②The concentration of cuttings in the annulus is ≤5%.

[0109] ③ The equivalent density of drilling fluid (ECO for short) cannot exceed the minimum fracture pressure of the formation in the open hole section.

[0110] Wellbore cleaning optimization design includes bottom hole drilling tool combination optimization, and bottom hole drilling tool combination optimization includes the optimization of sand cleaning drill pipe placement and quantity. Specifically: The calculation method for the placement and quantity of sand cleaning drill pipes is as follows:

[0111] 1) Calculation of placement location

[0112] Perform hydraulic simulation to calculate the corresponding depth MD when the cuttings bed is formed in a certain annular space closest to the previous opening 0 The corresponding depth MD when the cuttings bed thickness closest to the drill bit reaches the maximum 1 , then the length of the sand-cleaning drill pipe is ΔMD=MD 1 -MD 0 , in MD 1 The first sand cleaning drill rod is placed at

[0113] 2) Calculation of placement quantity

[0114] According to the references, based on the modified reference of Moore's sliding terminal velocity formula and the flow field analysis of the wellbore cleaning tool, the tool placement spacing calculation formula is proposed:

[0115]

[0116] in,

[0117] α——carrying factor of the tool, α=1-2;

[0118] β——acceleration factor of the tool, β=flow field velocity increase ratio;

[0119] θ——well inclination angle;

[0120] D h ——annulus diameter;

[0121] v h ——Annular return speed;

[0122] v sx ——The sliding speed of cuttings particles in the wellbore.

[0123] Then the placement quantity n=ΔMD / L. When n is a decimal, round it down.

[0124] The present invention is based on the wellbore cleaning simulation of highly deviated wells and horizontal wells, conducts sensitivity analysis on the factors affecting wellbore cleaning, identifies the main controlling factors according to the definition of the main controlling factors, optimizes the wellbore cleaning effect based on the main controlling factors from aspects such as wellbore trajectory parameters, hydraulic parameters, drilling fluid performance, drill bit combination, the number and position of auxiliary sand cleaning tools, and wellbore quality, so as to achieve the wellbore efficient cleaning constraint conditions that meet the wellbore safety.

[0125] Figure 2 The flowchart of the wellbore cleaning optimization design method provided according to one embodiment of the present invention. As shown in the figure, the method starts from box 11, and then proceeds to box 12. In box 12, the wellbore cleaning influencing factors are analyzed. In box 13, all influencing factors are listed. In box 14, wellbore cleaning calculations are performed. In box 15, sensitivity analysis of influencing factors is performed. In box 16, the main controlling factor is judged. If it is a main controlling factor, proceed to box 18 and identify it as a main controlling factor; if it is not a main controlling factor, proceed to box 17 and identify it as a non-main controlling factor. After identifying all the main controlling factors, proceed to box 19 and optimize the design based on the main controlling factors. Then in box 20, it is determined whether the wellbore cleaning constraint conditions are met. If they are met, it ends in box 21; if not, return to step 19.

[0126] The specific embodiments of the present invention are further described below by way of examples, but the specific embodiments of the present invention are not limited to the following examples.

[0127] (1) Basic Information

[0128] Well CH is a horizontal well in a certain block of an oil field, with a designed vertical depth of 1486m, the target layer is Es, and the completion method is gravel packing. The design adopts this optimization design method to optimize the wellbore for efficient cleaning.

[0129] (2) Optimize the design process

[0130] 1) Analysis of factors affecting wellbore cleaning

[0131] Through expert consultation, group discussion and other forms, brainstorming was carried out to pool ideas and list the factors that may affect the wellbore cleaning effect of highly deviated wells and horizontal wells, as shown in Table 1.

[0132] Table 1 Analysis of factors affecting wellbore cleaning

[0133]

[0134] 2) Sensitivity analysis of influencing factors

[0135] According to the actual situation, the reasonable value range and value change step of each wellbore cleaning influencing factor in Table 1 are given, see Table 2.

[0136] Table 2 Range of factors affecting wellbore cleaning

[0137]

[0138] Calculate the cuttings bed thickness corresponding to the range of values ​​of the factors affecting wellbore cleaning in Table 2. The calculation results are as follows: Figure 3-Figure 19 As shown. Among them, Figure 3 It is the "double increase" trajectory of different deflection points; Figure 4 It is the corresponding diagram of the thickness variation of the cuttings bed within the range of the inclination point value; Figure 5 It is a "double increase" trajectory with different build rates; Figure 6 It is the corresponding diagram of the thickness change of the cuttings bed within the range of the slope value; Figure 7 It is a "double increase" trajectory with different increase slopes; Figure 8 It is the corresponding diagram of the thickness variation of the cuttings bed within the range of the slope increase value; Fig. 9 It is a “single increase” wellbore trajectory; Fig.10 is the corresponding cuttings bed thickness variation diagram within the range of well inclination angle (1); Fig.11 is the corresponding cuttings bed thickness variation diagram within the range of well inclination angle (2); Fig.12 It is the corresponding diagram of the thickness change of the cuttings bed within the range of rotation speed; Fig.13 It is the corresponding diagram of the thickness variation of the cuttings bed within the range of displacement values; Fig.14 is the corresponding diagram of the thickness variation of the cuttings bed within the range of plastic viscosity values; Fig.15 It is the diagram of the thickness variation of the cuttings bed corresponding to the range of dynamic shear force values; Fig.16 It is the corresponding diagram of the thickness variation of the cuttings bed within the range of the consistency coefficient; Fig.17 is the corresponding diagram of the thickness variation of the cuttings bed within the range of φ3 values; Fig.18 It is the corresponding cuttings bed thickness variation diagram within the range of drill pipe size; Fig.19 It is the effect of the borehole expansion rate of 311.1mm and 215.9mm wells on wellbore cleaning.

[0139] For a 311.1 mm borehole with a medium directional difficulty index, a wellbore cleaning simulation was performed. The calculation results are as follows: Figure 11-Figure 18 shown.

[0140] For the 311.1mm and 215.9mm boreholes with relatively large directional difficulty index, wellbore cleaning simulation was performed. The calculation results are as follows: Fig.19 shown.

[0141] Through the above borehole cleaning simulation and sensitivity analysis of influencing factors, the influence of influencing factors on the trend of cuttings bed thickness was found, and the following conclusions were drawn:

[0142] ① Wellbore trajectory type

[0143] In order to meet the needs of saving footage and reducing the difficulty of drilling construction, this well adopts the "double increase" wellbore trajectory type for preliminary scheme demonstration and drilling engineering design.

[0144] ② Inclination point

[0145] As the inclination point deepens, the inclination angle of the middle high-angle stable inclination section increases, the cuttings bed thickness increases, and the wellbore cleaning effect becomes worse. Therefore, when designing the wellbore trajectory, it is advisable to use shallow inclination, and the inclination point is controlled at 120-300m, which helps to reduce the inclination of the high-angle section and improve the wellbore cleaning effect.

[0146] ③Building slope

[0147] The commonly used inclination rate is 1.8-3.0° / 30m. As the inclination rate increases, the well inclination in the middle high-inclination stable inclination section decreases, and the thickness of the cuttings bed decreases. The inclination rate has a greater impact on the thickness of the cuttings bed, and 2.4-3.0° / 30m is suitable.

[0148] ④Increase slope

[0149] The commonly used slope increase rate is 2.4-3.0° / 30m. The slope increase rate has little effect on the overall shape of the trajectory, especially the well inclination angle of the middle high-inclination stable well section. Hydraulic simulation shows that the slope increase rate has little effect on the thickness of the cuttings bed and will not significantly affect the wellbore cleaning effect. Considering the problem of deflection capacity of deeper formations and improving deflection efficiency, 3.0° / 30m is suitable.

[0150] ⑤Well inclination angle

[0151] When the well inclination is greater than 40°, the cuttings bed begins to form. As the well inclination angle increases, the thickness of the cuttings bed increases. In the well section with a well inclination of 45°-60°, the cuttings bed forms at a faster rate, and the cuttings accumulate rapidly in the annulus, making it easier to form a cuttings bed and difficult to clean the cuttings. When designing, the middle high-inclination stable inclination well section should try to avoid the well inclination range of 45°-60°.

[0152] ⑥Speed

[0153] As the speed increases, the thickness of the cuttings bed decreases. When the speed is higher than 100rpm, the thickness of the cuttings bed decreases significantly. When designing hydraulic parameters, a high speed of 100-120rpm is suitable.

[0154] ⑦Displacement

[0155] As the displacement increases, the thickness of the cuttings bed decreases. When the displacement is greater than 65L / s, the thickness of the cuttings bed decreases significantly. When designing hydraulic parameters, a large displacement should be used, with a 311.1mm borehole displacement of ≥65L / s and a 215.9mm borehole displacement of ≥32L / s.

[0156] ⑧Drilling fluid density

[0157] The drilling fluid density needs to be determined based on the formation pressure prediction results and the drilling fluid density of adjacent wells.

[0158] ⑨Plastic viscosity

[0159] Reduce plastic viscosity, prevent cuttings from adhering to the well wall, and reduce the accumulation of cuttings beds.

[0160] ⑩ Dynamic shear force

[0161] Increasing the dynamic shear force can reduce the accumulation of cuttings beds.

[0162] Consistency coefficient

[0163] Lowering the consistency coefficient can reduce the accumulation of cuttings beds.

[0164] φ value

[0165] Increasing the φ3 value improves the rock-carrying capacity of the drilling fluid and helps reduce the accumulation of cuttings beds.

[0166] Drill pipe size

[0167] Borehole cleaning simulation shows that the use of 139.7mm drill pipe in BHA has a significantly better rock cleaning effect than the use of 127mm drill pipe. For high-angle wells and horizontal wells in Chenghai 6 area, 139.7mm drill pipe is suitable.

[0168] Sand cleaning tools

[0169] Applying sand removal tools in BHA can improve the efficiency of cuttings removal.

[0170] Well diameter expansion rate

[0171] Under the conditions of specific displacement, rotation speed and mechanical drilling speed, when the borehole diameter expansion rate is greater than a certain critical value, the cuttings bed begins to accumulate. Calculations show that for a 311.1mm borehole, the critical value of the borehole diameter expansion rate is 18%, and for a 215.9mm borehole, the critical value of the borehole diameter expansion rate is 21%.

[0172] 3) Identify the main controlling factors

[0173] By calculating the value of the influencing factor F of each influencing factor, it is found that there are 9 main controlling factors affecting the wellbore cleaning effect of this design well: inclination point, inclination rate, well inclination angle, rotation speed, displacement, plastic viscosity, dynamic shear force, consistency coefficient and drill pipe size, see Table 3.

[0174] Table 3 Identification of main controlling factors

[0175]

[0176]

[0177] 4) Wellbore cleaning optimization design based on main control factors

[0178] According to the value of influencing factor F, the factors that influence the wellbore cleaning effect from large to small are drilling parameters, drilling fluid properties, wellbore trajectory and BHA, as shown in Table 4. The wellbore cleaning design of this well is optimized from these four aspects.

[0179] Table 4 Optimization design based on main control factors

[0180]

[0181] ①Optimize drilling equipment and strengthen drilling parameters

[0182] Add top drive, upgrade mud pump and use large water hole drill pipe, large displacement and high speed to strengthen drilling parameters (Table 5) and strengthen wellbore cleaning.

[0183] Top drive: TDS-450H top drive system, providing high speed of 100-120rpm;

[0184] Optimize mud pumps: Based on the relationship between displacement and pressure loss and mud pump parameters, three F-1600s are preferred, with a displacement of ≥65L / s for the second 311.1mm wellbore and a displacement of ≥32L / s for the third 215.9mm wellbore, and strengthen wellbore cleaning;

[0185] Optimize the drilling tool combination: use rotary steering + LWD / MWD + 139.7mm drill pipe + sand cleaning drill pipe to increase the annular return speed.

[0186] Table 5 “Large displacement and high speed” enhanced drilling parameters

[0187]

[0188] ②Optimization and adjustment of drilling fluid performance

[0189] Optimize and adjust the drilling fluid performance, control viscosity, improve dynamic speed ratio, enhance rock carrying capacity and improve inhibition, and enhance the wellbore cleaning effect.

[0190] Improve inhibition: Control the wellbore expansion rate. The wellbore expansion rate of the second opening should be controlled at ≤18%, and the wellbore expansion rate of the third opening should be controlled at ≤21%;

[0191] Enhance rock carrying capacity: Considering the critical value of wellbore expansion rate, the ratio of cuttings bed thickness to open hole diameter is controlled within 10%, ensuring that the cuttings bed thickness of the second opening wellbore is less than 37mm (311.1mm*1.18*0.1) and the cuttings bed thickness of the third opening wellbore is less than 26mm (215.9mm*1.21*0.1).

[0192] Improve dynamic shear force: 311.1mm wellbore dynamic shear force is controlled in the range of 8-11Pa, 215.9mm wellbore dynamic shear force is controlled in the range of 7-12Pa. In summary, dynamic shear force is controlled in the range of 8-11Pa. Fig. 20 and Fig.21 As shown;

[0193] Control viscosity: prevent cuttings from adhering to the well wall.

[0194] The control viscosity coefficient K is ≤ 0.8 for 311.1mm borehole and ≤ 0.7 for 215.9mm borehole. In summary, the control viscosity coefficient K is ≤ 0.7. Fig. 22 and Fig.23 shown.

[0195] 311.1mm borehole controlled plastic viscosity μp≤15cp, 215.9mm controlled plastic viscosity μp≤17cp. In summary, controlled plastic viscosity μp≤15cp, such as Fig.24 and Fig.25 shown.

[0196] ③ Wellbore trajectory design optimization

[0197] Well inclination angle: When the well inclination angle is 45°-60°, the cuttings accumulation rate is fast and the cuttings cleaning is difficult. When designing, the middle large-angle stable inclination well section should try to avoid the well inclination range of 45°-60°.

[0198] Inclination point: Controlled at 120-300m, it helps to reduce the well inclination in high-angle well sections and improve the wellbore cleaning effect.

[0199] Dogleg degree: The slope rate has a greater impact on the thickness of the cuttings bed, so 2.4-3.0° / 30m is used; the slope rate has a smaller impact, so 3.0° / 30m is used.

[0200] In summary, the trajectory type adopts shallow inclination + upper pre-inclination to reserve sufficient space for unused slots to ensure smooth subsequent drilling. Optimize the wellbore trajectory parameters, optimize the inclination angle of the high-inclination long and stable inclination well section, and avoid the inclination range of 45°-60° where cuttings accumulate rapidly. The full trajectory improves directional efficiency. In order to enable the upper well section to quickly leave the anti-collision dangerous area below and near the platform, the inclination rate and upper inclination rate are 3.0° / 30m, and the lower dogleg degree is 3.0° / 30m. The trajectory profile data and vertical projection diagram are shown in Tables 6 and Fig.26 .

[0201] Table 6 Wellbore trajectory design table

[0202]

[0203] ④ Use sand-cleaning drill rod and inverted reamer to assist in rock cleaning

[0204] During the drilling of long stable inclined sections and horizontal well sections, sand-clearing drill rods are placed in the drill bit to assist in rock clearing. During the drilling and pulling out process, the back-reamer and the centralizer are used to cut and trim the wellbore in both directions to eliminate complex factors such as shrinkage, steps, and sand settling. The spacing of the sand-clearing drill rods is calculated according to formula (2). The calculation parameters are shown in Table 7.

[0205] Table 7 Calculation parameters for spacing of sand-cleaning drill rods

[0206]

[0207] 311.1mm borehole: According to the hydraulic simulation results, the first sand-clearing drill pipe is placed 92m away from the drill bit. The calculation results are as follows: Fig. 27 As shown; According to formula (2), the spacing between sand-clearing drill rods is 338m, and 6 drill rods are required;

[0208] 215.9mm borehole: According to the hydraulic simulation results, the first sand-clearing drill pipe is placed 96m away from the drill bit. The calculation results are as follows: Fig.28 As shown; according to formula (2), the spacing between sand-clearing drill rods is 191m, and 6 drill rods are required.

[0209] The optimal values ​​of the main controlling factors are given in Table 8. The wellbore structure and other calculation parameters are shown in Tables 9 and 10.

[0210] Table 8 Optimization design results based on main control factors

[0211]

[0212] Table 9 Wellbore structure

[0213]

[0214]

[0215] Table 10 Other calculation parameters

[0216]

[0217] According to the optimal values ​​of the main control factors given in Table 8, the thickness of the annular cuttings bed, the cuttings concentration and the bottom hole ECD are calculated. The calculation results are as follows: Figure 29-Figure 34 shown.

[0218] The calculation results show that the wellbore cleaning design optimization based on the main controlling factors is completed by meeting the constraints of wellbore safety and efficient wellbore cleaning.

[0219] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention, including the combination of various technical features in any other appropriate manner, these simple variations and combinations should also be regarded as the contents disclosed by the present invention and should be included in the protection scope of the present invention.

Claims

1. A wellbore cleaning optimization design method, characterized in that: The following steps are involved: Step S1: determining factors that may affect the wellbore cleaning effect; Step S2: Analyze the sensitivity of each influencing factor to wellbore cleaning by calculating the cuttings bed thickness; Step S3: identifying the main controlling factors affecting the wellbore cleaning effect by calculating the influencing factor of each influencing factor, wherein the influencing factor represents the change in the thickness of the cuttings bed corresponding to the value of the unit influencing factor; Step S4: Based on the main controlling factors and referring to the sensitivity analysis conclusions of the main controlling factors, the wellbore cleaning optimization design is performed until the wellbore efficient cleaning constraint conditions of wellbore safety are met.

2. The wellbore cleaning optimization design method according to claim 1, characterized in that: Step S2 includes: For each influencing factor, give the value range of the influencing factor; Calculate the corresponding cuttings bed thickness within the value range; The variation trend of cuttings bed thickness is given when the influencing factors change in an increasing or decreasing trend within the value range.

3. The wellbore cleaning optimization design method according to claim 2, characterized in that: When calculating the corresponding cuttings bed thickness for a certain influencing factor, the other influencing factors take fixed values ​​and ensure that the calculated cuttings bed thickness is not zero.

4. The wellbore cleaning optimization design method according to claim 2, characterized in that: The corresponding cuttings bed thickness within the range of values ​​is given in the form of a graph.

5. The wellbore cleaning optimization design method according to claim 1, characterized in that: Step S3 includes: When an influencing factor has more than one value, the influencing factor of the influencing factor is calculated according to the following formula, and the calculated influencing factor is compared with the predetermined value to identify the main controlling factor: Where, F is the impact factor, mm; T cmax1 The maximum cuttings bed thickness when the influencing factor takes the value D1, mm; T cmax2 The maximum cuttings bed thickness when the influencing factor takes the value D2, mm; k is a coefficient, the unit is consistent with the influencing factor, and it is set according to the change range of the influencing factor.

6. The wellbore cleaning optimization design method according to claim 5, characterized in that: When the influence factor of a certain influencing factor is greater than a predetermined value, the influencing factor is identified as a main controlling factor; otherwise, the influencing factor is identified as a non-main controlling factor.

7. The wellbore cleaning optimization design method according to claim 5, characterized in that: Step S3 includes: When an influencing factor has only one value, the influencing factor is defined as a non-dominant factor.

8. The wellbore cleaning optimization design method according to claim 1, characterized in that: Step S4 includes: Sort the main controlling factors in descending order of the impact factor values; For each main control factor, according to the sensitivity analysis conclusion, the wellbore cleaning design is optimized to give the optimal value of the main control factor; Determine whether the efficient wellbore cleaning constraint conditions of wellbore safety can be met when all main control factors take the optimal value. If so, the wellbore cleaning design optimization is completed. If not, the wellbore cleaning design optimization is performed again.

9. The wellbore cleaning optimization design method according to claim 1, characterized in that: The constraints for efficient wellbore cleaning for wellbore safety are: ① Calculate that there is no accumulation of cuttings bed on the well wall. ②The concentration of cuttings in the annulus is ≤5%. ③ The equivalent density of the drilling fluid cannot exceed the minimum fracture pressure of the formation in the open hole section.

10. The wellbore cleaning optimization design method according to claim 1, characterized in that: Applicable to the optimization design of wellbore cleaning in highly deviated wells and horizontal wells.

11. The wellbore cleaning optimization design method according to claim 10, characterized in that: The factors that may affect the wellbore cleaning effect include six categories: wellbore trajectory, drilling parameters, drilling fluid performance, bottom hole assembly, wellbore quality and other supplementary factors. Among them, the wellbore trajectory category includes trajectory type, inclination point, inclination rate, inclination increase rate and well inclination angle; the drilling parameter category includes rotation speed and displacement; the drilling fluid performance includes density, plastic viscosity, dynamic shear force, consistency coefficient and φ3 value; the bottom hole assembly includes drill pipe size and sand cleaning tools; the wellbore quality includes wellbore expansion rate.

12. The wellbore cleaning optimization design method according to claim 11, characterized in that: The main controlling factors affecting the wellbore cleaning effect are the inclination point, inclination rate, well inclination angle, rotation speed, displacement, plastic viscosity, dynamic shear force, consistency coefficient and drill pipe size.

13. The wellbore cleaning optimization design method according to claim 1, characterized in that: In step S1, the factors that may affect the wellbore cleaning effect are determined from three aspects: early drilling plan demonstration, drilling engineering design and later drilling construction. Among them, the early drilling plan demonstration includes wellbore trajectory, the drilling engineering design includes drilling parameters, drilling fluid performance and bottom hole drilling tool combination, and the later drilling construction includes wellbore quality.

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