Well cementation annulus fluid mixing safety risk quantitative prediction method

Abstract

The invention discloses a well cementation annulus fluid blending safety risk quantitative prediction method, which belongs to the technical field of petroleum and natural gas engineering, and is characterized in that a plurality of parameters influencing blending pollution are quantified according to a statistical function method based on a mixed slurry pollution fluidity experiment in combination with a computational fluid dynamics numerical simulation method; and obtaining a blending safety risk factor. According to the method, the development process of the displacement interface of the well cementation fluid is simulated through computer numerical values, the formation and development characteristics of the three-dimensional displacement interface are truly represented, the annular fluid mixing risk prediction method is summarized and summarized in combination with field experience and test data, fluid mixing pollution is visually and quantitatively described, and the risk prediction accuracy is improved. Therefore, a unified prediction method is formed, well cementation construction risks are proposed in advance, construction scheme adjustment and construction plan making are guided, and the method plays an important role in preventing complex accidents of well cementation mixed slurry pollution.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of oil and gas engineering, and particularly relates to a method for quantitatively predicting safety risks of annular fluid mixing in well cementing. BACKGROUND

[0002] During well cementing, the displacement process of cement slurry, spacer fluid and drilling fluid is very complex, and the displacement effect is restricted by many factors such as the rheological property of well cementing fluid, the geometric condition of wellbore, the centralization degree of casing and the deviation angle. Especially in the complex deep well of Sichuan and Chongqing regions, the displacement of high-density drilling fluid in the annulus has the risk of three-phase mixed slurry. The mixed slurry has a serious impact on the safety of well cementing. The sharp increase in the consistency of mixed slurry leads to high pump pressure, and in severe cases, the thickening time of mixed slurry is only tens of minutes, which may cause serious tailpipe cementing accidents. It is very critical to understand the pollution risk of three-phase mixing of cement slurry, spacer fluid and drilling fluid in the annulus and to quantitatively calculate the pollution risk to ensure the safety of mixed slurry operation in the well.

[0003] At present, there is no method to quantitatively predict the pollution risk of annular fluid in well cementing. The "R value test method" of Schlumberger abroad evaluates the fluid compatibility by analyzing the change of rheological property of mixed slurry with different mixing ratios, which cannot directly reflect the cementing risk after slurry pollution. The domestic pollution experiment evaluation method tests the thickening time of multi-phase fluid mixed slurry and qualitatively evaluates the construction risk, but it cannot quantitatively evaluate the construction risk, and the final construction decision also depends on experience.

[0004] In summary, it is necessary to provide a method for quantitatively predicting the safety risk of annular fluid mixing in well cementing, which combines theory and experience to quantitatively describe the mixing pollution of annular fluid in well cementing, considers various factors affecting the mixing pollution such as eccentricity, fluid fluidity and fluid thickening time, and uses the method of statistical function to form a unified measurement index according to the weight ratio of the above factors. The method can not only truly reflect the actual mixing condition in the well, but also make up for the deficiency of the existing technical method that cannot quantitatively describe the mixing pollution risk, so as to ensure that the design of field process parameters is more reasonable and scientific, thereby guiding the field construction operation. SUMMARY

[0005] The application discloses a method for quantitatively predicting the safety risk of annular fluid mixing in well cementing. The development process of the displacement interface of well cementing fluid is simulated by a computer, the formation and development characteristics of the three-dimensional displacement interface are truly reproduced, a set of annular fluid mixing risk prediction method is summarized by combining field experience and test data, the fluid mixing pollution is quantitatively described, and thus a unified prediction method is formed. The method can predict the well cementing construction risk in advance, guide the adjustment of construction scheme and the preparation of construction plan, and has an important role in preventing complex accidents caused by slurry pollution in well cementing.

[0006] The purpose of the application is achieved by the following technical solutions.

[0007] A cementing annulus fluid blending safety risk quantification prediction method, based on the slurry contamination fluidity experiment, combined with the computational fluid dynamics numerical simulation method, according to the statistical function method, a plurality of parameters affecting the blending contamination are quantified, and the blending safety risk factor is obtained.

[0008] Preferably, the computational fluid dynamics numerical simulation method takes three-dimensional unsteady component multiphase flow equation as control equation, and the development process of the displacement interface of the cementing fluid is simulated by computer, so that the formation and development characteristics of the three-dimensional displacement interface can be truly reproduced, and combined with the field experience and test data, the fluid blending contamination can be quantitatively described.

[0009] Preferably, the method comprises the following steps:

[0010] Step (1), establishing a well diameter, well depth, well deviation, casing eccentricity, displacement, drilling fluid performance, preflush performance, cement slurry performance parameter corresponding array;

[0011] Step (2), according to the well diameter, well depth, well deviation, casing eccentricity array, using fluid mechanics numerical simulation program, geometric modeling and grid division are carried out according to well section;

[0012] Step (3), constructing an annulus drilling fluid-preflush-cement slurry three-phase interface motion model, according to the well diameter, well depth, well deviation, casing eccentricity, displacement, drilling fluid performance, preflush performance, cement slurry performance array data, relying on fluid mechanics calculation program, numerical calculation is carried out to solve, and the drilling fluid-preflush, preflush-cement slurry interface motion process is tracked in real time;

[0013] Step (4), constructing a cement slurry, preflush, drilling fluid three-phase volume fraction proportion array at typical node positions such as top well depth and third type well diameter;

[0014] Step (5), according to the three-phase volume fraction proportion, indoor slurry fluidity, slurry thickening experiment results, target block complex accident well statistical data, solving the annulus fluid blending safety risk coefficient, predicting the cementing construction risk.

[0015] Preferably, in the step (1),

[0016] The well diameter corresponding array: D w ={d1, d2, d3…d n}(1); In the formula: D w represents the well diameter array, unit m; d1, d2, d3…d n respectively represent the well diameter data corresponding to different space nodes of the target well, unit m;

[0017] The well depth corresponding array: H={h1, h2, h3…hn}(2); where: H represents the well depth array, in meters; h1, h2, h3...h n These represent the well depth data corresponding to different spatial nodes of the target well, in meters;

[0018] The well inclination corresponds to the array: A = {α1, α2, α3…α} n}(3); where: A represents the well inclination array, in degrees; α1, α2, α3…α n These represent the well depth data corresponding to different spatial nodes of the target well, in degrees.

[0019] The casing eccentricity corresponds to the array: E = {ε1, ε2, ε3…ε} n}(4); where: E represents the casing eccentricity array, dimensionless; ε1, ε2, ε3…ε n These represent the casing eccentricity data corresponding to different spatial nodes of the target well, and are dimensionless.

[0020] The displacement corresponds to the array: Q = {q1, q2, q3…q i}(5); where: Q represents the displacement array, m 3 / s; q1, q2, q3…q i These represent the discharge data of the target well at different time points, in meters (m). 3 / s;

[0021] The array corresponding to the drilling fluid properties:

[0022] MUD = {P m ;T m N m ;K m} (6);

[0023] P m ={ρm} (7);

[0024] T m ={τm} (8);

[0025] N m ={nm} (9);

[0026] K m ={km} (10);

[0027] In the formula: MUS represents the drilling fluid performance array; P m This represents an array of drilling fluid densities, in kg / m³. 3 ;T m This represents the dynamic shear force array of drilling fluid, in Pa; N m K represents the drilling fluid flowability index, which is dimensionless; mRepresents the consistency coefficient of drilling fluid, in units of... ρ m This indicates the density of the drilling fluid, in kg / m³. 3 τm represents the drilling fluid dynamic shear force array, in Pa; nm represents the drilling fluid flowability index, dimensionless; km represents the drilling fluid consistency coefficient, in Pa·s. nm ;

[0028] The array corresponding to the performance of the pre-fluid:

[0029] SPA = {P s ;T s N s ;K s} (11);

[0030] P s ={ρs1, ρs2, ρs3…ρs j} (12);

[0031] T s ={τs1, τs2, τs3…τs j} (13);

[0032] N s ={ns1, ns2, ns3…ns} j} (14);

[0033] K s ={ks1,ks2,ks3…ks j} (15);

[0034] In the formula: SPA represents the pre-fluid performance array; P s This represents a pre-fluid density array, in kg / m³. 3 ;T s This represents the array of pre-fluid dynamic shear forces, in Pa; N s K represents the pre-fluidity index, which is dimensionless; s Indicates the consistency coefficient of the pre-fluid, in units of... ρs1, ρs2, ρs3…ρs j This indicates the density of different types of pre-fluid, in kg / m³. 3 ;τs1, τs2, τs3…τs j This represents an array of dynamic shear forces for different types of pre-fluid, in Pa; ns1, ns2, ns3…ns j These represent different types of pre-fluid flowability indices, dimensionless; ks1, ks2, ks3…ks i Indicates the consistency coefficient of different types of pre-fluid, in units of

[0035] The array corresponding to the properties of the cement slurry:

[0036] SPC = {P c ;T c N c ;K c} (16);

[0037] P c ={ρc1, ρc2, ρc3…ρc j} (17);

[0038] T c ={τc1, τc2, τc3…τc j} (18);

[0039] N c ={nc1, nc2, nc3…nc j} (19);

[0040] K c ={kc1;kc2;kc3…kc j} (20);

[0041] In the formula: SPC represents the cement paste performance array; P c This represents an array of cement paste densities, in kg / m³. 3 ;T c This represents the dynamic shear force array of cement grout, in Pa; N c K represents the flowability index of cement slurry, which is dimensionless; c This represents the consistency coefficient of cement paste, in units of... ρc1, ρc2, ρc3…ρc j This indicates the density of different types of cement paste, in kg / m³. 3 ;τc1, τc2, τc3…τc j This represents an array of dynamic shear forces for different types of cement grout, in Pa; nc1, nc2, nc3…nc j kc1, kc2, kc3…kc represent the flowability index of different types of cement paste, dimensionless; j Indicates the consistency coefficient of different types of cement paste, in units of...

[0042] Preferably, in step (2), an arithmetic mean filtering algorithm is used to process the well diameter array to suppress errors caused by the measurement data.

[0043] Preferably, in step (2), the well diameter array D in equation (1) w It consists of n elements, where the j-th element is d. j The filter width is set to m, which is usually 3 to 5. The new well diameter array is D. w0 The j-th element in the array is d0j The calculation method is as follows:

[0044]

[0045] D w0 = {d01, d02, d03…d0 n} (22);

[0046] Then the hole diameters are divided into three categories:

[0047] The first category hole diameter is

[0048] The second category hole diameter is

[0049] The third category hole diameter is

[0050] In the formula, dx1 is the first critical hole diameter expansion rate, usually 5% to 10%; dx2 is the second critical hole diameter expansion rate, usually 10% to 15%.

[0051] Preferably, according to the classification results, the average values of the first category, the second category and the third category hole diameters are taken respectively, the hole diameters at the nodes belonging to the three categories are processed as the corresponding average values of the hole diameters, and geometric modeling and mesh division are performed; for the third category hole diameter node, the number of radial meshes is encrypted by 1.5 to 2.0 times.

[0052] Preferably, the three-phase volume fraction proportion array corresponding to the node at the top h1 well depth is:

[0053]

[0054] The three-phase volume fraction proportion array corresponding to the third category hole diameter node is:

[0055]

[0056]

[0057]

[0058]

[0059] The node j0 with the largest proportion of cement slurry in formula (28) is selected, and the three-phase volume fraction proportion array corresponding to the third category hole diameter node with the largest proportion of cement slurry is obtained:

[0060] In the formula, x1 is an array of volume fractions of cement slurry, preflush and drilling fluid at the node at the top h1 well depth, dimensionless.

[0061] — Cement slurry volume fraction at the node at the top h1 well depth, dimensionless;

[0062] — Preflush volume fraction at the node at the top h1 well depth, dimensionless;

[0063] — Drilling fluid volume fraction at the node at the top h1 well depth, dimensionless;

[0064] — Array of cement slurry volume fractions at each node position of the third type of hole diameter, dimensionless;

[0065] — Cement slurry volume fractions corresponding to the 1st, 2nd...jth node positions of the third type of hole diameter, dimensionless;

[0066] — Preflush volume fractions corresponding to the 1st, 2nd...jth node positions of the third type of hole diameter, dimensionless;

[0067] — Drilling fluid volume fractions corresponding to the 1st, 2nd...jth node positions of the third type of hole diameter, dimensionless;

[0068] x2— Array of cement slurry, preflush, drilling fluid volume fractions corresponding to the node with the largest cement slurry proportion in the third type of hole diameter, dimensionless;

[0069] — Cement slurry volume fraction corresponding to the node with the largest cement slurry proportion in the third type of hole diameter, dimensionless; — Preflush volume fraction corresponding to the node with the largest cement slurry proportion in the third type of hole diameter, dimensionless; — Drilling fluid volume fraction corresponding to the node with the largest cement slurry proportion in the third type of hole diameter, dimensionless.

[0070] Preferably, the three-phase volume fraction proportions X1 and X2 obtained according to step (4) are used to carry out a cement slurry flowability test and a cement slurry thickening experiment, and the cement slurry flowability L1 and L2 and the thickening time T1 and T2 are measured; if the well does not have a third type of hole diameter, only the cement slurry flowability test and the cement slurry thickening experiment are carried out according to the proportion of X1; the flowability threshold value l1 that meets the requirements of cementing pump injection is defined, and is usually taken as 12-15 cm; the flowability threshold value l2 that meets the requirements of cement slurry stability is defined, and is usually taken as 25-30 cm; the flowability range L that ensures safe construction is [l1, l2]; the cementing injection time is t1, and the thickening experiment deviation time is t2, which is usually taken as 30-60 min; the thickening time range T that ensures safe construction is [t1-t2, 2t1].

[0071] Preferably, the number of problem wells due to contamination caused by mixing in a certain block in the past 10 years is counted; the number of problem wells caused by high pump pressure x, the number of problem wells caused by premature cement slurry setting y, and the number of problem wells caused by simultaneous occurrence of high pump pressure and premature cement slurry setting z, and then the risk factor coefficients θ1, θ2 and θ3 are calculated according to the event frequency as follows:

[0072]

[0073]

[0074]

[0075] The flowability normal distribution function is defined as:

[0076]

[0077] The thickening time normal distribution function is defined as:

[0078]

[0079] The mixing safety risk coefficient F is calculated as follows:

[0080]

[0081] The minimum mixing slurry flowability in L1 and L2 and the shortest mixing slurry thickening time in T1 and T2 are selected and brought into formula (37) for calculation; when the mixing safety risk coefficient F is less than 0.1, the safety risk is small; when the mixing safety risk coefficient F is in the range of 0.1-0.3, the safety risk is small; when the mixing safety risk coefficient F is in the range of 0.3-0.5, the safety risk is medium; and when the mixing safety risk factor exceeds 0.5, the safety risk is high.

[0082] The beneficial effects of the technical solution are as follows:

[0083] 1. The cementing annulus fluid mixing safety risk quantitative prediction method provided by the present application can intuitively quantitatively describe fluid mixing contamination, propose cementing construction risks in advance, guide construction scheme adjustment and construction plan development, and has an important role in preventing cementing slurry contamination complex accidents. In the future 2-3 years, the technology can be applied to special cement slurry experiments and compatibility experiments before cementing, to predict cementing construction fluid mixing safety risks and avoid well cementing complex accidents.

[0084] 2. The cementing annulus fluid mixing safety risk quantitative prediction method provided by the present application can greatly reduce the cement slurry mixing experiment workload when cementing is performed, because the displacement process of cement slurry, spacer fluid and drilling fluid is very complex, and the displacement effect is restricted by many factors such as cementing working fluid rheology, wellbore geometry, casing centralization and deviation angle. Attached Figure Description

[0085] Figure 1 This is a graph showing the calculation results of the displacement efficiency of a well in Example 3 of this invention;

[0086] Figure 2 This refers to the replacement efficiency of the top 2619m section in Embodiment 3 of this invention;

[0087] Figure 3 This refers to the proportion of the three fluids at the top 2619m cross-section in Embodiment 3 of this invention. Detailed Implementation

[0088] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto.

[0089] Example 1

[0090] A quantitative prediction method for safety risks of cementing annular fluid mixing is proposed. Based on the fluidity experiment of mixing slurry pollution, combined with the numerical simulation method of computational fluid dynamics, multiple parameters affecting mixing pollution are quantified according to the statistical function method to obtain the mixing safety risk factor.

[0091] The computational fluid dynamics numerical simulation method uses the three-dimensional unsteady multiphase flow equation as the governing equation. By numerically simulating the development process of the displacement interface of cementing fluid through computer, it can realistically reproduce the formation and development characteristics of the three-dimensional displacement interface. Combined with field experience and experimental data, it can intuitively and quantitatively describe the fluid mixing pollution.

[0092] Example 2

[0093] The difference between this embodiment and Embodiment 1 is that it includes the following steps:

[0094] Step (1): Establish the corresponding array of parameters for well diameter, well depth, well inclination, casing eccentricity, displacement, drilling fluid properties, pre-flush fluid properties, and cement slurry properties;

[0095] Step (2): Based on the aforementioned arrays of well diameter, well depth, well inclination, and casing eccentricity, use a fluid dynamics numerical simulation program to perform geometric modeling and mesh generation for each well section.

[0096] Step (3): Construct a three-phase interface motion model of annular drilling fluid-pre-flush fluid-cement slurry. Based on the aforementioned array data of well diameter, well depth, well inclination, casing eccentricity, discharge rate, drilling fluid performance, pre-flush fluid performance, and cement slurry performance, numerical calculation is performed using a fluid dynamics calculation program, and the motion process of the drilling fluid-pre-flush fluid and pre-flush fluid-cement slurry interface is tracked in real time.

[0097] Step (4), constructing cement slurry, preflush, drilling fluid three-phase volume fraction ratio array at typical node positions such as top hole depth, third type of caliper;

[0098] Step (5), according to three-phase volume fraction ratio, indoor slurry fluidity, slurry thickening experiment results, target block complex accident well statistical data, solving annulus fluid blending safety risk coefficient, predicting cementing construction risk.

[0099] In the step (1),

[0100] Caliper corresponding array: D w ={d1, d2, d3…d n}(1); In the formula: D w represents the caliper array, unit m; d1, d2, d3…d n respectively represent the caliper data corresponding to different spatial nodes of the target well, unit m;

[0101] The well depth corresponding array: H={h1, h2, h3…h n}(2); In the formula: H represents the well depth array, unit m; h1, h2, h3…h n respectively represent the well depth data corresponding to different spatial nodes of the target well, unit m;

[0102] The inclination corresponding array: A={α1, α2, α3…α n}(3); In the formula: A represents the inclination array, unit °; α1, α2, α3…α n respectively represent the well depth data corresponding to different spatial nodes of the target well, unit °;

[0103] The casing eccentricity corresponding array: E={ε1, ε2, ε3…ε n}(4); In the formula: E represents the casing eccentricity array, dimensionless; ε1, ε2, ε3…ε n respectively represent the casing eccentricity data corresponding to different spatial nodes of the target well, dimensionless;

[0104] The displacement corresponding array: Q={q1, q2, q3…q i}(5); In the formula: Q represents the displacement array, m 3 / s; q1, q2, q3…q i respectively represent the displacement data corresponding to different time nodes of the target well, unit m 3 / s;

[0105] The drilling fluid performance corresponding array:

[0106] MUD={P m ; T m ; N m;K m} (6);

[0107] P m ={ρm} (7);

[0108] T m ={τm} (8);

[0109] N m ={nm} (9);

[0110] K m ={km} (10);

[0111] In the formula, MUD represents the drilling fluid performance array; P m represents the drilling fluid density array, unit kg / m 3 ; T m represents the drilling fluid dynamic shear force array, unit Pa; N m represents the drilling fluid flow index, dimensionless; K m represents the drilling fluid consistency coefficient, unit ρ m represents the drilling fluid density, unit kg / m 3 ; τm represents the drilling fluid dynamic shear force array, unit Pa; nm represents the drilling fluid flow index, dimensionless; km represents the drilling fluid consistency coefficient, unit Pa·s nm ;

[0112] The preflush performance corresponds to the array:

[0113] SPA={P s ; T s ; N s ; K s} (11) ;

[0114] P s ={ρs1, ρs2, ρs3…ρs j} (12) ;

[0115] T s ={τs1, τs2, τs3…τs j} (13) ;

[0116] N s ={ns1, ns2, ns3…ns j} (14) ;

[0117] K s ={ks1, ks2, ks3…ks j} (15) ;

[0118] In the formula, SPA represents the preflush performance array; Ps ρs1, ρs2, ρs3... ρs 3 ; T s τs1, τs2, τs3... τs s ks1, ks2, ks3... ks s ηs1, ηs2, ηs3... ηs ρs1, ρs2, ρs3... ρs j ρs1, ρs2, ρs3... ρs 3 τs1, τs2, τs3... τs j ks1, ks2, ks3... ks j ηs1, ηs2, ηs3... ηs j ηs1, ηs2, ηs3... ηs

[0119] The cement slurry performance corresponds to the array:

[0120] SPC = {P c ; T c ; N c ; K c} (16) ;

[0121] P c = {ρc1, ρc2, ρc3... ρc j} (17) ;

[0122] T c = {τc1, τc2, τc3... τc j} (18) ;

[0123] N c = {nc1, nc2, nc3... nc j} (19) ;

[0124] K c = {kc1, kc2, kc3... kc j} (20) ;

[0125] In the formula, SPC represents the cement slurry performance array; P c ρc1, ρc2, ρc3... ρc 3 ; T c τc1, τc2, τc3... τc c nc1, nc2, nc3... nc c kc1, kc2, kc3... kc ρc1, ρc2, ρc3... ρc jDc1, Dc2, Dc3…Dc represents the density of different types of cement slurry, unit kg / m 3 ; τc1, τc2, τc3…τc j ; nc1, nc2, nc3…nc represents the dynamic shear force array of different types of cement slurry, unit Pa j ; kc1, kc2, kc3…kc represents the flow index of different types of cement slurry, dimensionless j ; represents the consistency coefficient of different types of cement slurry, unit

[0126] In the step (2), the arithmetic average filtering algorithm is used to process the hole diameter array, and the error caused by the measurement data is suppressed.

[0127] In the step (2), the hole diameter array D w is composed of n elements, and the jth element is d j , the filter width is m, m is usually 3-5, and the new hole diameter array is D w0 , and the jth element in the array is d0 j , and the calculation method is as follows:

[0128]

[0129] D w0 = {d01, d02, d03…d0 n} (22);

[0130] Then the hole diameter is divided into three categories:

[0131] The first type of hole diameter is

[0132] The second type of hole diameter is

[0133] The third type of hole diameter is

[0134] In the formula, dx1 is the first critical hole diameter expansion rate, usually 5%-10%; dx2 is the second critical hole diameter expansion rate, usually 10%-15%.

[0135] Among them, according to the classification results, the average values of the first type, the second type and the third type of hole diameter are taken respectively, the hole diameters at the nodes belonging to the three types of hole diameters are processed as the corresponding average values of the hole diameters, and the geometric modeling and mesh division are carried out; for the third type of hole diameter node, the number of radial meshes is encrypted by 1.5-2.0 times.

[0136] Among them, the three-phase volume fraction array corresponding to the node at the top h1 well depth is:

[0137]

[0138] The third type of well diameter node corresponds to a three-phase volume fraction proportion array:

[0139]

[0140]

[0141]

[0142]

[0143] Select the node j0 with the largest cement slurry proportion in formula (28) to obtain the three-phase volume fraction proportion array corresponding to the third type of well diameter node with the largest cement slurry proportion:

[0144] In the formula: x1 is an array of cement slurry, preflush, and drilling fluid volume fractions at the node at the top h1 well depth, dimensionless;

[0145] x1 is the cement slurry volume fraction at the node at the top h1 well depth, dimensionless;

[0146] x1 is the preflush volume fraction at the node at the top h1 well depth, dimensionless;

[0147] x1 is the drilling fluid volume fraction at the node at the top h1 well depth, dimensionless;

[0148] x2 is an array of cement slurry volume fractions at each node position of the third type of well diameter, dimensionless;

[0149] x2 is the cement slurry volume fraction corresponding to the first, second,..., jth node position of the third type of well diameter, dimensionless;

[0150] x2 is the preflush volume fraction corresponding to the first, second,..., jth node position of the third type of well diameter, dimensionless;

[0151] x2 is the cement slurry volume fraction corresponding to the first, second,..., jth node position of the third type of well diameter, dimensionless;

[0152] x2 is an array of cement slurry, preflush, and drilling fluid volume fractions corresponding to the node with the largest cement slurry proportion in the third type of well diameter, dimensionless;

[0153] x2 is the cement slurry volume fraction corresponding to the node with the largest cement slurry proportion in the third type of well diameter, dimensionless; the volume fraction of the preflush corresponding to the node with the largest proportion of cement slurry in the third type of hole diameter, dimensionless; the volume fraction of the drilling fluid corresponding to the node with the largest proportion of cement slurry in the third type of hole diameter, dimensionless.

[0154] wherein the volume fractions X1 and X2 obtained according to step (4) are used to carry out a cement slurry flowability test and a cement slurry thickening experiment, and the flowability L1 and L2 and the thickening time T1 and T2 are measured; if the well does not have the third type of hole diameter, only the flowability test and the thickening experiment are carried out according to the proportion of X1; the flowability threshold value l1 that meets the cementing pump injection requirement is defined, which is usually 12-15 cm; the flowability threshold value l2 that meets the cement slurry stability requirement is defined, which is usually 25-30 cm; the flowability range L that meets the safe construction requirement is defined, which is l1l2; the cementing injection time t1 is defined, which is usually 30-60 min; the thickening time range T that meets the safe construction requirement is defined, which is t1-t2, 2t1.

[0155] wherein the number of problem wells caused by contamination in a certain block in the past 10 years is counted; the number of problem wells caused by high pump pressure is x wells, the number of problem wells caused by premature cement slurry setting is y wells, and the number of problem wells caused by both high pump pressure and premature cement slurry setting is z wells, and the risk factor coefficients θ1, θ2 and θ3 are calculated according to the event frequency as follows:

[0156]

[0157]

[0158]

[0159] The flowability normal distribution function is defined as:

[0160]

[0161] The thickening time normal distribution function is defined as:

[0162]

[0163] The contamination safety risk coefficient F is calculated as follows:

[0164]

[0165] The minimum fluidity of the mixed slurry in L1 and L2 and the shortest thickening time of the mixed slurry in T1 and T2 are selected to be brought into formula (37) for calculation; when the blending safety risk coefficient F is less than 0.1, the safety risk is small; when the blending safety risk coefficient F is in the range of 0.1-0.3, the safety risk is small; when the blending safety risk coefficient F is in the range of 0.3-0.5, the safety risk is moderate; and when the blending safety risk factor exceeds 0.5, the safety risk is high.

[0166] Example 3

[0167] A solid well annulus fluid blending safety risk quantitative prediction method described in Example 2 is used to predict the blending safety risk of a Φ177.8mm+184.15mm tail pipe hanging cementing of a well in Sichuan Basin. The Φ244.5+250.83mm technical casing of the well is lowered to a depth of 3017.03m, a Φ215.9mm drill bit is drilled to a depth of 5428.00m, the hole diameter range is 220-228mm, the average hole diameter is 225mm, a Φ177.8mm+184.15mm tail pipe is lowered for hanging cementing, the casing is lowered to a depth of 2619.00-5428.00m, the average eccentricity of the casing is 0.42. The drilling fluid density is 2200kg / m 3 , the dynamic shear force is 2.3Pa, the flow index is 0.82, and the consistency coefficient is 0.23Pa·s 0.82 . The spacer fluid (prepad fluid) density is 2250kg / m 3 , the dynamic shear force is 1.6Pa, the flow index is 0.73, and the consistency coefficient is 0.32Pa·s 0.73 . The cement slurry density is 2300kg / m 3 , the dynamic shear force is 5.4Pa, the flow index is 0.75, and the consistency coefficient is 0.62Pa·s 0.75 . The cementing construction discharge is 0.017m 3 / s. The cementing construction time is 220min.

[0168] According to step (1), the corresponding arrays of hole diameter, hole depth, hole inclination, casing eccentricity, discharge, drilling fluid performance, prepad fluid performance, and cement slurry performance are established. The longitudinal direction is divided into 100 nodes, the time is divided into 2400 nodes, D w ={225, 222, 227…224}, H={2619, 2619.28, 2619.56…5428}, A={0, 0, 0…0}, E={0.42, 0.42, 0.42…0.42}, Q={0.017, 0.017, 0.017…0.017}, MUD={2200; 2.3; 0.82; 0.23}, SPA={2250; 1.6; 0.73; 0.32}, and CEM={2300; 5.4; 0.75; 0.62}.

[0169] Next, following step (2), use a fluid dynamics calculation program to perform geometric modeling and mesh generation. The well diameter is uniform with minimal fluctuations, belonging to the first type of well diameter, D. w0 ={224, 224, 224…226}. The mesh generation method has 10,000 nodes vertically, 10 nodes radially, and 120 nodes circumferentially, for a total of 12,000,000 nodes.

[0170] Next, following step (3), based on the array data of well diameter, well depth, well inclination, casing eccentricity, discharge rate, drilling fluid properties, pre-flush fluid properties, and cement slurry properties, numerical calculations are performed using a fluid dynamics calculation program.

[0171] Next, following step (4), construct the three-phase volume fraction arrays of cement slurry, pre-filled fluid, and drilling fluid at typical node locations such as the top well depth and the third type of well diameter. This well has no third type of well diameter. Through numerical solution, the three-phase volume fraction array at the top 2619m is obtained: X1=[72;15;13].

[0172] In the final step (5), the fluidity of the mixed slurry was tested at 95℃ according to the ratio of cement slurry: pre-fluid: drilling fluid = 72:15:13, and the thickening of the contaminant was tested at 115℃. The experimental results showed that the fluidity of the mixed slurry was 16cm and the thickening time of the contaminant was 260min. In the past 10 years, there have been 85 accidents in complex wells with high pump pressure in the Sichuan Basin, 22 of which were accidents caused by premature setting of cement slurry, and 5 of which were caused by both high pump pressure and premature setting of cement slurry. From formulas (32) to (37), l1 is taken as 12cm and l2 is taken as 28cm, and the safety risk factor of mixing is calculated to be 0.2397. Prediction result: The safety risk caused by the mixing of annular fluid during cementing construction is small.

[0173] like Figures 1-3 As shown, Figure 1 This is a graph showing the calculation results of the displacement efficiency of a well in this implementation example. Different colors represent different displacement efficiencies, and the values ​​represented by each color correspond to the values ​​on the color bars. Figure 2 This is the displacement efficiency of the top 2619m section in this implementation example. Different colors represent different annular fluids: red represents cement slurry, light blue represents isolation fluid, and dark blue represents drilling fluid. Figure Three The figures represent the proportions of the three fluids at the top 2619m section in the implementation example. Red indicates cement slurry, accounting for 72% of the volume; green indicates isolation fluid, accounting for 15% of the volume; and dark blue indicates drilling fluid, accounting for 13% of the volume.

[0174] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for quantifying and predicting safety risk of cementing annulus fluid blending, characterized in that: Based on the contamination flow degree experiment of mixed slurry, combined with the computational fluid dynamics numerical simulation method, the parameters affecting the contamination of mixing are quantified according to the statistical function method, and the mixing safety risk factor is obtained.

2. The method of claim 1, wherein: The computational fluid dynamics numerical simulation method takes three-dimensional unsteady component multiphase flow equation as the control equation, and the development process of the displacement interface of cementing fluid is simulated by computer, which can truly reproduce the formation and development characteristics of three-dimensional displacement interface. Combined with field experience and test data, the fluid contamination of mixing can be quantitatively described.

3. The method of claim 2, wherein: The method comprises the following steps: Step (1), establishing the corresponding array of well diameter, well depth, well deviation, casing eccentricity, displacement, drilling fluid performance, preflush performance, and cement slurry performance parameters; Step (2), according to the aforementioned well diameter, well depth, well deviation, and casing eccentricity array, using a fluid mechanics numerical simulation program, geometric modeling and mesh division are performed for each well section; Step (3), constructing a three-phase interface motion model of annular drilling fluid-preflush-cement slurry, according to the aforementioned well diameter, well depth, well deviation, casing eccentricity, displacement, drilling fluid performance, preflush performance, and cement slurry performance array data, relying on a fluid mechanics calculation program, numerical calculation is performed to solve, and the motion process of the drilling fluid-preflush and preflush-cement slurry interface is tracked in real time; Step (4), constructing a three-phase volume fraction proportion array of cement slurry, preflush, and drilling fluid at typical node positions such as the top well depth and the third type of well diameter; Step (5), according to the three-phase volume fraction proportion, indoor mixed slurry flow degree, mixed slurry thickening experiment results, and target block complex accident well statistical data, the annular fluid mixing safety risk coefficient is solved, and the cementing construction risk is predicted.

4. The method of claim 3, wherein: In the step (1), Well diameter corresponding array: D w = {d1, d2, d3...d n n} (1); In the formula: D w represents the well diameter array, unit m; d1, d2, d3...d n n respectively represent the well diameter data corresponding to different spatial nodes of the target well, unit m; The well depth corresponding array: H = {h1, h2, h3…h n}(2); In the formula: H represents the well depth array, unit m; h1, h2, h3…h n respectively represent the well depth data corresponding to different spatial nodes of the target well, unit m; The well inclination corresponding array A = {a1, a2, a3…a n}(3); In the formula: A represents the well inclination array, unit °; a1, a2, a3…a n respectively represent the well depth data corresponding to different spatial nodes of the target well, unit °; The casing eccentricity corresponding array: E = {ε1, ε2, ε3...ε n}(4); In the formula: E represents the casing eccentricity array, dimensionless; ε1, ε2, ε3...ε n respectively represent the casing eccentricity data corresponding to different spatial nodes of the target well, dimensionless; The displacement corresponding array: Q = {q1, q2, q3…q i}(5); In the formula: Q represents the displacement array, m 3 / s; q1, q2, q3…q i Respectively, the displacement data corresponding to different time nodes of the target well, unit m 3 / s; The drilling fluid performance corresponding array: MUD = {P m ; T m ; N m ; K m} (6); P m = {pm} (7); T m = {τm} (8); N m = {nm} (9) K m = {km} (10) where: MUD represents the drilling fluid performance array; P m represents the drilling fluid density array in kg / m 3 ; T m represents the dynamic shear force array of the drilling fluid, unit Pa; N m represents the flow index of the drilling fluid, dimensionless; K m represents the consistency coefficient of the drilling fluid, unit ρ m represents the density of the drilling fluid, unit kg / m 3 ; τm represents the dynamic shear force array of the drilling fluid, unit Pa; nm represents the flow index of the drilling fluid, dimensionless; km represents the consistency coefficient of the drilling fluid, unit Pa·s nm ; The preflush performance corresponding array: SPA = {P s ; T s ; N s ; K s} (11) P s = {ps1, ps2, ps3... ps j} (12); T s = {τs1, τs2, τs3...τs j} (13); N s = {ns1, ns2, ns3... ns j} (14); K s = {ks1, ks2, ks3...ks j} (15); wherein: SPA represents the array of mobile phase properties; P s represents the array of mobile phase densities, in kg / m 3 ; T s τs1, τs2, τs3... τs represents the dynamic shear stress array of different types of leading fluid, unit Pa; ns1, ns2, ns3... ns s ks1, ks2, ks3... ks represents the flow index of different types of leading fluid, dimensionless; K s μs1, μs2, μs3... μs represents the consistency coefficient of different types of leading fluid, unit ρs1, ρs2, ρs3... ρs j ρs1, ρs2, ρs3... ρs represents the density of different types of leading fluid, unit kg / m 3 ; τs1, τs2, τs3... τs j τs1, τs2, τs3... τs represents the dynamic shear stress array of different types of leading fluid, unit Pa; ns1, ns2, ns3... ns j ks1, ks2, ks3... ks represents the flow index of different types of leading fluid, dimensionless; K j μs1, μs2, μs3... μs represents the consistency coefficient of different types of leading fluid, unit The cement slurry performance corresponding array: SPC = {P c ; T c ; N c ; K c} (16); P c = {pc1, pc2, pc3... pc j} (17); T c = {τc1, τc2, τc3...τc j} (18); N c = {nc1, nc2, nc3... nc j} (19); K c = {kci, kc2, kc3... kcn} (19) j} (20); wherein: SPC represents the cement paste property array; P c represents the cement paste density array in kg / m 3 ; T c represents the array of dynamic shear stress of cement paste, unit Pa; N c represents the flowability index of cement paste, dimensionless; K c represents the consistency coefficient of cement paste, unit ρc1, ρc2, ρc3…ρc j represents the density of different types of cement paste, unit kg / m 3 ; τc1, τc2, τc3…τc j represents the array of dynamic shear stress of different types of cement paste, unit Pa; N j represents the flowability index of different types of cement paste, dimensionless; K j represents the consistency coefficient of different types of cement paste, unit 5. The method of claim 4, wherein: In the step (2), the arithmetic average filtering algorithm is used to process the well diameter array to suppress the error caused by the measurement data.

6. The method of claim 5, wherein: In the step (2), the well diameter array D in the formula (1) w consists of n elements, and the jth element is D j , the filter width is m, m is usually 3-5, and the new well diameter array is D w0 , and the jth element in the array is d0 j , and the calculation method is as follows: D w0 = {d01, d02, d03... d0 n} (22); Then the well diameter is divided into three types: The first type of caliper is The second type of caliper is The third type of caliper is In the formula, dx1 is the first critical well diameter expansion rate, which is usually 5% to 10%; dx2 is the second critical well diameter expansion rate, which is usually 10% to 15%.

7. The method of claim 6, wherein: According to the classification results, the average values of the first type, the second type, and the third type of well diameter are taken respectively, the well diameters at the nodes belonging to the three types of well diameters are processed as the corresponding well diameter average values, and geometric modeling and mesh division are performed; for the third type of well diameter node, the radial mesh number is encrypted by 1.5 to 2.0 times.

8. The method of claim 7, wherein: The three-phase volume fraction proportion array corresponding to the node at the top h1 well depth is: The three-phase volume fraction proportion array corresponding to the third type of well diameter node is: Selecting the node j0 with the largest proportion of cement slurry in formula (28), the three-phase volume fraction proportion array corresponding to the third type of well diameter node with the largest proportion of cement slurry is obtained: In the formula: x1 is an array composed of cement slurry, preflush, and drilling fluid volume fractions at the node at the top h1 well depth, dimensionless; x2 is an array composed of cement slurry, preflush, and drilling fluid volume fractions corresponding to the node with the largest proportion of cement slurry in the third type of well diameter, dimensionless; - cement slurry volume fraction at the top h1 well depth node, dimensionless; - frontal fluid volume fraction at the node at the depth of the top well h1, dimensionless; - the dimensionless well fluid volume fraction at the node at the depth h1 in the top well - an array of third-type of normalized annular volume fractions of cement slurry at each node position, dimensionless; - a third type of well diameter, the first, second,... jth node position corresponding to a cement slurry volume fraction, dimensionless; - a third type of well diameter first, second,... jth node position corresponding preflush volume fraction, dimensionless; - a third type of well diameter, the first, second,... jth node position corresponding to a cement slurry volume fraction, dimensionless; ​ - the cement volume fraction, dimensionless, at the node where the cement slurry has the largest share in the third type of caliper, — the volume fraction of the preflush corresponding to the node where the cement slurry has the largest proportion in the third type of caliper, dimensionless; - the drilling fluid volume fraction, dimensionless, at the node where the cement slurry occupies the largest fraction of the third type of hole diameter.

9. The method of claim 8, wherein: The triphase volume fraction proportions X1 and X2 obtained according to step (4) are used to carry out the mixed slurry flowability test and the mixed slurry thickening experiment, and the mixed slurry flowability L1 and L2 and the thickening time T1 and T2 are measured; if the well does not have the third type of caliper, only the mixed slurry flowability test and the mixed slurry thickening experiment are carried out according to the proportion of X1; the flowability threshold value meeting the requirements of the cementing pump injection is defined as l1, which is usually 12-15 cm, and the flowability threshold value meeting the requirements of the cement slurry stability is defined as l2, which is usually 25-30 cm; the flowability range of the safe construction is L∈[l1,l2]; the cementing injection time is t1, and the thickening experiment deviation time is t2, which is usually 30-60 min; and the thickening time range that can guarantee the safe construction is T∈[t1-t2,2t1].

10. The method of claim 9, wherein: The number of problem wells caused by contamination mixing in a certain block in the past 10 years is counted; the number of problem wells caused by high pump pressure is x, the number of problem wells caused by premature cement slurry setting is y, and the number of problem wells caused by both high pump pressure and premature cement slurry setting is z, and then the risk factor coefficients θ1, θ2 and θ3 are calculated according to the event frequency as follows: The flowability normal distribution function is defined as: The thickening time normal distribution function is defined as: The mixing safety risk coefficient F is calculated as follows: The minimum mixed slurry flowability in L1 and L2 and the shortest mixed slurry thickening time in T1 and T2 are selected and brought into formula (37) for calculation; when the mixing safety risk coefficient F is less than 0.1, the safety risk is small; When the mixing safety risk coefficient F is in the range of 0.1-0.3, the safety risk is small; When the mixing safety risk coefficient F is in the range of 0.3-0.5, the safety risk is moderate; When the mixing safety risk factor exceeds 0.5, the safety risk is high.

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