CN116432399A - Experimental evaluation method for leakage control efficiency of fractured stratum drilling fluid - Google Patents
Experimental evaluation method for leakage control efficiency of fractured stratum drilling fluid Download PDFInfo
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- G06F30/00—Computer-aided design [CAD]
- G06F30/20—Design optimisation, verification or simulation
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- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B47/00—Survey of boreholes or wells
- E21B47/10—Locating fluid leaks, intrusions or movements
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- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B49/00—Testing the nature of borehole walls; Formation testing; Methods or apparatus for obtaining samples of soil or well fluids, specially adapted to earth drilling or wells
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Abstract
The invention discloses a method for experimental evaluation of control efficiency of leakage of a drilling fluid in a fractured stratum, which belongs to the technical field of reservoir protection of fractured oil and gas reservoirs and comprises the following steps: determining the type of drilling fluid leakage of a target well; determining control indexes of the target well leakage control effect and weights of the control indexes according to the leakage type, and establishing a fitness calculation model; performing a leakage control efficiency evaluation experiment and optimizing indoor evaluation experiment parameters according to the fit degree; and performing a formula evaluation experiment to select a plugging formula through the optimized experimental parameters. The method can effectively solve the problems of poor plugging efficiency and low primary success rate caused by insufficient leakage control evaluation of the current fractured formation drilling fluid, and has important significance on the leakage control efficiency and reservoir protection of the fractured formation drilling fluid.
Description
Technical Field
The invention relates to the technical field of drilling fluid leakage control, in particular to a method for experimental evaluation of the drilling fluid leakage control efficiency of a fractured stratum.
Background
The fractured hydrocarbon reservoirs have great development potential due to huge geological reserves. The existence of cracks is beneficial to the efficient development of oil and gas resources, but greatly increases the difficulty of controlling the leakage of the working solution. The occurrence of lost circulation causes long well construction period, great economic loss caused by consumption of drilling fluid and plugging materials, serious reduction of reservoir permeability caused by loss of the drilling fluid, and personnel safety problem caused by easy drilling sticking and collapse accidents. The current common indoor drilling fluid leakage control evaluation method is mostly based on industry standard SY/T5840-2007 'method for testing bridging plugging materials for drilling fluids indoors', which prescribes a basic method for bridging plugging experiments for indoor drilling fluids, but does not distinguish the types of drilling fluid leakage and the differences between the indoor experiments and the field environment, so that the field has poor plugging effect on underground cracks, and the plugging leakage control effect is not ideal.
The geological features of the fractured stratum are complex, and engineering operation is difficult, high in risk, high in cost and long in time consumption. The conventional leakage control method is difficult to evaluate the leakage control efficiency, or is too single without considering the complex fracture environment. Aiming at the most serious reservoir damage mode in the drilling and completion process of working fluid leakage, the drilling fluid leakage is effectively prevented and controlled, the drilling fluid leakage control efficiency is efficiently and reasonably evaluated, and the method has important significance for oil and gas reservoir exploration and development.
Disclosure of Invention
The invention provides an experimental evaluation method for the leakage control efficiency of a fractured formation drilling fluid, which aims to solve the problem of the leakage control efficiency evaluation of a single imperfect fractured formation drilling fluid. According to the method, drilling fluid leakage is divided into three types based on leakage causes, main control factors of different leakage types and weight proportion thereof are defined, the indoor experimental method with the highest degree of fit is selected to evaluate the drilling fluid leakage control efficiency of different leakage types by comparing the indoor and on-site drilling fluid leakage control efficiency degrees, scoring is carried out according to the weight proportion of the main control factors, and finally, the accurate optimization of a leakage stopping formula can be realized through a quantitative scoring formula, so that the leakage stopping formula leakage control efficiency is improved. The system establishes the method for evaluating the leakage control efficiency of the working fluid of the fractured reservoir, and has important significance for the leakage control of the drilling fluid of the fractured reservoir and the reservoir protection.
The technical scheme of the invention is as follows:
a method for evaluating leakage control efficiency experiment of a fractured stratum drilling fluid comprises the following steps:
s1, determining the type of drilling fluid leakage of a target well; the drilling fluid leakage type is one of induced fracture type, crack extension type and natural crack type. For specific judgment, refer to patent application number CN202210485263.0, named a deep well and ultra-deep well drilling fluid leakage type diagnosis method, and will not be described in detail herein.
S2, determining a representation system of the target well leakage control effect according to the leakage type, and determining weights of all control indexes in the representation system by adopting a hierarchical analysis method;
s21, determining a drilling fluid leakage control effect characterization system;
the drilling fluid leakage control efficiency is the comprehensive embodiment of the strength, the formation efficiency and the structural compactness of the formed crack plugging layer, and is characterized by the pressure bearing capacity, the initial leakage amount and the accumulated leakage amount during indoor experiments. The larger the bearing capacity is, the stronger the crack plugging layer is in the capability of resisting external force, and the more stable the structure is, the inventor determines that the crack plugging layer is the main control factor of crack expansion type and natural crack type leakage control efficiency through research; the initial leakage amount refers to the leakage amount of drilling fluid before the plugging layer is formed after plugging materials enter the cracks, the leakage amount is characterized by the leakage amount of 1min before the plugging layer is formed, the smaller the initial leakage amount is, the shorter the time for bridging the plugging materials and forming the crack plugging layer is, the higher the plugging efficiency is, and the inventor determines that the leakage amount is a main control factor for inducing the cracking type and the crack expansion type leakage control efficiency through research; the accumulated leakage amount refers to the leakage amount of drilling fluid from the time of entering a crack to the time of damaging a crack plugging layer by a plugging material, the smaller the accumulated leakage amount is, the more compact the structure of the crack plugging layer is, and the inventor determines that the accumulated leakage amount is a main control factor of the natural crack leakage control efficiency through research.
Of course, other control indexes can be adopted to represent the leakage control effect in the specific implementation.
S22, establishing a leakage control effect hierarchical structure and a judgment matrix according to a drilling fluid leakage control effect representation system;
comparing the relative importance degrees of the control indexes in the same layer by two by using a unified standard, and establishing a judgment matrix; the judgment matrix of the drilling fluid leakage control effect is as follows:
wherein the scale of the importance ratio among the control indexes is shown in the following table:
table 1 scale of importance ratio among control indexes
| Scale with a scale bar | Degree of importance between |
| 1 | The control index i and the control index j have the same importance |
| 3 | The control index i is slightly more important than the |
| 5 | The control index i is obviously important than the control index j |
| 7 | The control index i is more important than the control index j |
| 9 | The control index i is extremely important than the |
| 2、4、6、8 | When the relative importance is between the adjacent importance, the median is taken |
S23, carrying out consistency test on the constructed judgment matrix;
consistency ratio calculation formula:
wherein R is I Is an average random consistency index;
C I is a consistency coefficient, and is related to the order n and the maximum feature root of the matrix;
λ max judging the maximum eigenvalue of the matrix;
n is the order of the judgment matrix;
wherein C is I Representing a consistency parameter, R I The parameters representing random consistency are shown in the following table;
table 2 average random concordance index and judgment matrix order mapping relationship table
When C R <When 0.1, the inconsistency degree of the judgment matrix is considered to be within the allowable range, at the moment, the feature vector of the judgment matrix is the weight vector, otherwise, the step S22 is returned to, and the judgment value of the relative importance degree of the two elements is adjusted until the consistency condition is met;
s24, determining the feature vector of the judgment matrix according to the maximum feature value:
wherein B is a judgment matrix, E is an identity matrix with the same order as B,
is a feature vector;
s25, will
And normalizing to obtain the weight of the control index, wherein the vector in W is the weight of the control index, and the normalization formula is as follows:
in the method, in the process of the invention,
is->
J is an integer greater than 0.
As a specific embodiment of the invention, the bearing capacity, the initial leakage amount and the accumulated leakage amount are selected to characterize the leakage control efficiency of the drilling fluid.
Evaluating the importance degree of each control index in different leakage types according to an importance degree proportion table among each control index, and establishing a judgment matrix;
TABLE 3 induced crack type leakage control efficacy control index judgment matrix
| B1 | Pressure bearing capacity | Initial leakage quantity | Cumulative leakage |
| |
1 | 1/2 | 3 |
| |
2 | 1 | 5 |
| |
1/3 | 1/5 | 1 |
Table 4 crack extension type leakage control efficiency control index judgment matrix
| B2 | Pressure bearing capacity | Initial leakage quantity | Cumulative leakage |
| |
1 | 5 | 7 |
| |
1/5 | 1 | 3 |
| |
1/7 | 1/3 | 1 |
TABLE 5 Natural fracture type leakage control Performance control index judgment matrix
| B3 | Pressure bearing capacity | Initial leakage quantity | Cumulative leakage |
| |
1 | 7 | 6 |
| |
1/7 | 1 | 1/3 |
| |
1/6 | 3 | 1 |
Consistency test is carried out on the constructed judgment matrix, and the maximum characteristic value of the judgment matrix is obtained, as shown in the following table;
table 6 statistical table of determination matrix consistency test results
| Consistency | Inducing cracks | Crack extension type | Natural crack type |
| λ max | 3.0026 | 3.0649 | 3.0999 |
| C I | 0.0013 | 0.0324 | 0.0500 |
| R I | 0.5800 | 0.5800 | 0.5800 |
| C R | 0.0025 | 0.0324 | 0.0961 |
Determining the feature vector of the judgment matrix according to the maximum feature value
Will->
Normalizing to obtain the weight of the control index, wherein the vector in W is the weight of the control index, and the specific calculation result is shown in the following table:
table 7 weight table of various types of drilling fluid loss control performance control indicators
S3, establishing a fitness calculation model according to the weight of each characterization index in the leakage type; performing a leakage control efficiency evaluation experiment on a target well, wherein the leakage control efficiency evaluation experiment comprises an indoor experiment and a field experiment, and optimizing indoor experiment parameters according to the fit degree of the indoor experiment and the field experiment;
s31, determining initial experimental parameters of indoor experiment
Specifically, the experimental parameters include fracture height, fracture inclination/length, fracture surface roughness, pressurization mode, single pressure increment and pressure stabilization time;
the parameters of the initial experiment can be given according to experience, different initial experiment values can influence the fitness of the initial experiment, the experiment is carried out after the experiment parameters are modified for many times when the initial fitness is smaller, so that the higher fitness can be obtained on the basis of fine adjustment of the experiment parameters in the later period when the better initial experiment parameters are adopted, the time and the cost are saved, and the following experience values of the initial experiment parameters with higher fitness are obtained by the inventor through long-term experiments.
For induced fracture drilling fluid loss control efficacy experiments, when the fracture height: crack entrance width = 6:1, the fit degree of the leakage control efficiency of the indoor and on-site drilling fluid is high, and the evaluation result of the leakage control efficiency of the drilling fluid is good; when the inclination angle of the crack is smaller and is 0.5 degrees, the fit degree of the leakage control efficiency of the indoor and on-site drilling fluid is higher, and the evaluation result of the leakage control efficiency of the drilling fluid is better; the rougher the crack surface is, the higher the fit degree of the leakage control efficiency of the indoor and on-site drilling fluid is, and the better the evaluation result of the leakage control efficiency of the drilling fluid is; the pressurization mode has no obvious influence on the evaluation of the drilling fluid leakage control efficiency; when the single pressure increment is larger and is 5MPa, the control efficiency fit of the indoor and on-site drilling fluid leakage is higher, and the evaluation result is better; and when the pressure stabilizing time is 2min, the fit degree of the indoor and on-site drilling fluid leakage control efficiency is high, and the drilling fluid leakage control efficiency evaluation result is good.
For a crack extension type drilling fluid leakage control efficiency experiment, when the height of a crack: crack entrance width = 6:1, the fit degree of the leakage control efficiency of the indoor and on-site drilling fluid is high, and the evaluation result of the leakage control efficiency of the drilling fluid is good; when the inclination angle of the crack is smaller and is 0.5 degrees, the fit degree of the leakage control efficiency of the indoor and on-site drilling fluid is higher, and the evaluation result of the leakage control efficiency of the drilling fluid is better; the rougher the crack surface is, the higher the fit degree of the leakage control efficiency of the indoor and on-site drilling fluid is, and the better the evaluation result of the leakage control efficiency of the drilling fluid is; the step-type pressurizing mode is selected, the fit degree of the leakage control efficiency of the indoor and on-site drilling fluid is high, and the evaluation result of the leakage control efficiency of the drilling fluid is good; when the single pressure increment is 5MPa, the fit degree of the leakage control efficiency of the indoor and on-site drilling fluid is high, and the evaluation result of the leakage control efficiency of the drilling fluid is good; the pressure stabilizing time is moderate, and when the pressure stabilizing time is 4min, the fit degree of the indoor and on-site drilling fluid leakage control efficiency is high, and the drilling fluid leakage control efficiency evaluation result is good.
For the natural fracture type drilling fluid leakage control efficiency experiment, when the fracture height: crack entrance width ≡ 3:1, the fit degree of the leakage control efficiency of the indoor and on-site drilling fluid is high, and the evaluation result of the leakage control efficiency of the drilling fluid is good; when the inclination angle of the crack is smaller and is 0.5 degrees, the fit degree of the leakage control efficiency of the indoor and on-site drilling fluid is higher, and the evaluation result of the leakage control efficiency of the drilling fluid is better; the rougher the crack surface is, the higher the fit degree of the leakage control efficiency of the indoor and on-site drilling fluid is, and the better the evaluation result of the leakage control efficiency of the drilling fluid is; the step-type pressurizing mode is selected, the fit degree of the leakage control efficiency of the indoor and on-site drilling fluid is high, and the evaluation result of the leakage control efficiency of the drilling fluid is good; the step-type pressurizing mode is selected, the fit degree of the leakage control efficiency of the indoor and on-site drilling fluid is high, and the evaluation result of the leakage control efficiency of the drilling fluid is good; the single pressure increment is moderate, when the single pressure increment is 2.5MPa, the fit degree of the indoor and on-site drilling fluid leakage control efficiency is high, and the drilling fluid leakage control efficiency evaluation result is good; the pressure stabilizing time is moderate, and when the pressure stabilizing time is 4min, the fit degree of the indoor and on-site drilling fluid leakage control efficiency is high, and the drilling fluid leakage control efficiency evaluation result is good.
S32, carrying out fit degree analysis on the indoor experimental evaluation and the field test result;
the establishment of a fit calculation model according to the weight of each characterization index in each loss type obtained in the step S2 is as follows:
wherein u is i (x) For the leak-off type judging function, i represents the leak-off type, i E (1, 2, 3), when the leak-off type is the ith, then u i (x) =1, otherwise 0; n is the total amount of the characterization index; w (W) ij The weight of the j-th characterization index in the i-th leakage type is represented; x is X 2j A value representing a j-th characterization index obtained by field experiments; x is X 1j The value of the j-th characterization index obtained by the indoor experiment is shown.
As a specific implementation mode of the invention, when the bearing capacity, the initial leakage and the accumulated leakage are selected as the characterization indexes in the step S2, the weight of each characterization index is obtained first, and then a fitness calculation model is established as follows:
wherein X1, Y1 and Z1 are respectively the pressure-bearing capacity, the initial leakage and the accumulated leakage obtained by indoor experiments; x2, Y2 and Z2 are respectively the pressure-bearing capacity, the initial leakage amount and the accumulated leakage amount obtained by field experiments;
s33, optimizing the indoor evaluation experiment parameters through the analysis result of the fit degree of the indoor experiment evaluation and the field test result, re-experiment can be carried out by adjusting the indoor experiment parameters when the fit degree is low, the purpose of optimization is achieved after the final fit degree reaches a preset threshold value, and the higher the fit degree is, the higher the approach degree of the indoor and field experiments is, therefore, the preset threshold value is not unique, for example, 90% or 95% can be adopted.
S4, performing an indoor evaluation experiment on each plugging formula by adopting the optimized indoor experiment parameters, and selecting a plugging formula according to an evaluation experiment result;
s41, quantifying indexes of drilling fluid leakage control efficiency, such as pressure bearing capacity, initial leakage amount and accumulated leakage amount;
table 8 quantitative Standard Table for bearing Capacity, initial leakage and cumulative leakage
S42, comprehensively scoring leakage control capacity of the plugging formula by combining the leakage type of the drilling fluid and the weight ratio of the control factors of the leakage control effect of the drilling fluid;
table 9 leakage control ability evaluation table for different leakage type leakage blocking formulations
S43, optimizing the plugging formula according to the comprehensive score of each plugging formula, and optimizing the plugging formula when the comprehensive score is low until the score meets the requirement.
Table 10 leakage control capability hierarchy for plugging formulations
| Comprehensive score R | ＞9.5 | 8～9.5 | 6.5～8 | 5～6.5 | ＜5 |
| Ranking results | Good (good) | Preferably, it is | In general | Poor quality | Difference of difference |
The beneficial effects of the invention are as follows:
the invention provides a method for experimental evaluation of leakage control efficiency of a fractured stratum drilling fluid, which can accurately evaluate material rationality and field applicability of a plugging formula and provide theoretical basis for the design of the plugging formula.
Drawings
FIG. 1 is a leakage rate versus time curve feature layout;
FIG. 2 is a plot of leak rate versus time curve characteristics for the A well;
FIG. 3 is an experimental result of natural fracture type drilling fluid leakage control efficacy experimental evaluation;
fig. 4 is an experimental result of an optimized plugging formulation.
Detailed Description
The technical solution of the present invention will be described in detail below for a clearer understanding of technical features, objects and advantageous effects of the present invention, but should not be construed as limiting the scope of the present invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The invention will be further described with reference to the drawings and examples.
S1, determining the type of drilling fluid leakage of a target well;
s11, collecting geological feature data of the crack stratum site engineering of the K block A well of the Tarim basin, and establishing a corresponding drilling fluid leakage dynamics model; the drilling fluid leakage dynamics model comprises three leakage models of induced fracture type, crack extension type and natural crack type;
induced rupture type leakage dynamics equation:
crack propagation type leakage dynamics equation:
natural fracture-cavity leakage dynamics equation:
wherein: n is a flow pattern index, dimensionless; k is the consistency coefficient, pa.s n The method comprises the steps of carrying out a first treatment on the surface of the x is the coordinate of the crack entrance on the x axis, m; w is the width of the dynamic crack, mm; p is the force per unit area, namely the stress tensor, pa; τ y Is dynamic shear stress, pa; t is time, s; τ y Is dynamic shear stress, pa; f is a crack deformation coefficient, dimensionless; p () is the seam internal pressure, p (0, x) represents the seam internal pressure at the position x in the seam length direction at the initial time; p is p 0 Is the formation pressure, MPa; p is p w Is the pressure of a liquid column of a shaft and MPa; x is x f The depth of invasion of the dynamic drilling fluid is m; w (w) o The crack width, m, is the crack normal stress zero; beta is an empirical coefficient, dimensionless; sigma (sigma) n The normal stress of the crack surface is MPa; p (P) i Fluid pressure in dynamic joint is MPa; ρ is the fluid density, g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the g is a gravity constant, m/s 2 The method comprises the steps of carrying out a first treatment on the surface of the Alpha is crack inclination angle degree; l (L) x 、L y Respectively forming x and y boundaries, mm, of a crack extension type leakage dynamics model in the crack length direction; r is the distance from the radial direction of the crack to the crack entrance, and mm; v is the instantaneous rate of drilling fluid through the fracture cross section, m/s; c (C) t Is a fracture wall drilling fluid loss coefficient, and has no dimension.
S12, solving the drilling fluid leakage dynamics model to obtain drilling fluid leakage rates of the three leakage models at different moments, and manufacturing drilling fluid leakage rate-time characteristic curves of the different leakage models as characteristic layouts, wherein the characteristic layouts are shown in FIG. 1;
s13, recording drilling fluid leakage rate data of an initial drilling fluid leakage occurrence period of the well A, and drawing a drilling fluid leakage rate-time relation curve, wherein the curve is shown in FIG. 2;
the leakage rate-time curve of the drilling fluid of the well A reaches a peak value rapidly when leakage occurs, and the leakage rate is more than 0.4m 3 And/min (being larger than the range of the crack expansion type leakage peak value and smaller than the range of the natural crack hole type leakage peak value), the stratum is proved to have a small opening degree, a leakage-causing crack with short extension, the leakage rate rapidly drops and is wavy after reaching the peak value, and the fluctuation range is large, so that the crack width direction has dynamic change and has an extension trend in the crack length direction along with the progress of drilling fluid leakage, the natural crack hole type leakage and the extension trend of the crack are met, and malignant leakage is caused.
In summary, the target well leak-off type is identified as a natural fracture-cave type.
S2, determining a characterization system of control effects of different leakage types, and determining weights of all control indexes in the characterization system by adopting a analytic hierarchy process;
s21, determining a drilling fluid leakage control effect characterization system;
according to the drilling fluid leakage control effect characterization system, the main control factor of the natural fracture type leakage is the strength of the plugging layer and the compactness of the structure thereof, and the corresponding experimental result is characterized by the pressure bearing capacity and the accumulated leakage.
S22, determining the weight of each characterization system of the natural fracture type leakage.
The specific calculation process has been set forth above and will not be described in detail herein, wherein the pressure bearing capacity weight is 0.75, the initial leak-off weight is 0.08, and the cumulative leak-off weight is 0.17.
S3, carrying out fit analysis on the leakage control efficiency evaluation experiment, and optimizing the indoor evaluation experiment parameters;
s31, determining crack module parameters and experimental steps of an indoor experiment;
experiment plunger: for a crack with a crack width of 3mm-1mm, the crack height of the crack plunger is 18mm, the crack inclination/length is 0.5 °/50mm, and the jrc coefficient is 20.
The experimental steps are as follows: the pressurizing mode is selected to be stepped pressurizing, the single pressure increment is 2.5MPa, and the pressure stabilizing time is 4min.
The plugging formula comprises the following steps: the formula used in the site A well is as follows: oil-based drilling fluid (1.88) +4% NTS-M (medium crude) +7% NTS-S (type II, medium crude) +5% NTS-S (type I, coarse) +2% GYD-coarse+3% GYD-medium crude+5% GYD-fine+10% GT-MF+0.8% NT-2 (1/8 ").
The specific experimental results are shown in fig. 3.
S32, performing fit degree analysis on the indoor experimental evaluation and the field test result;
table 11 results of comparison of the degree of compliance of different indoor evaluation methods with the on-site drilling fluid loss control performance
The method can be used for finding out that the indoor experiment has better conformity with the field test result, so that the parameters can be directly used as optimized experiment parameters.
S4, performing an indoor evaluation experiment on each plugging formula by adopting the optimized indoor experimental parameters, and selecting the plugging formula according to the indoor evaluation experiment result.
S41, indexes of the drilling fluid leakage control efficiency are as follows: quantifying the bearing capacity, the initial leakage and the accumulated leakage;
s42, comprehensively evaluating and grading leakage control capacity of the plugging formula by combining the leakage type of the drilling fluid and the weight ratio of the main control factors of the leakage control effect of the drilling fluid;
table 12 statistical table of experimental results of conventional evaluation method in room
With 3D wedge plungers, r=0.5×3+0.1×7+0.4×5=4.2, the result is rated "bad" according to the leak control ability rating system of the leak slurry formulation.
S43, comprehensively evaluating the leakage control capacity of the plugging formula according to the leakage control capacity of the plugging formula, and optimizing the leakage control capacity of the plugging formula.
According to the comprehensive evaluation method of the natural fracture leakage control capability, the non-ideal plugging formula is optimized. According to the leakage control efficiency evaluation method of the leakage control formula, the leakage control materials aiming at the natural cracks are screened out and the formula is formed.
The formula is optimized as follows:
oil-based drilling fluid (1.88) +3% NTS-M (middle coarse) +3% NTS-S (II type, middle coarse) +5% NTS-S (I type, coarse) +5% GT-MF+0.5% NT-2 (1/8') +2% GT-HS (middle coarse), plugging material concentration is 18.5%, and experimental results are shown in FIG. 4.
Table 13 statistical table of experimental results for optimized formulations
According to the leak type determination result, by combining the leak control ability evaluation methods of the natural fracture type leak-off formulation of table 6, r=0.5×10+0.1×10+0.4×10=10 can be obtained, and the result is classified as "good" according to the leak control ability classification system of the leak-off formulation.
Thus, this formulation was determined to be the preferred lost circulation formulation.
Claims (6)
1. The experimental evaluation method for the leakage control efficiency of the drilling fluid of the fractured stratum is characterized by comprising the following steps of:
s1, determining the type of drilling fluid leakage of a target well; the drilling fluid leakage type is one of an induced fracture type, a crack extension type and a natural crack type;
s2, determining a representation system of the target well leakage control effect according to the leakage type, and determining weights of all control indexes in the representation system by adopting a hierarchical analysis method;
s3, establishing a fitness calculation model according to the weight of each control index; performing a leakage control efficiency evaluation experiment on a target well, wherein the leakage control efficiency evaluation experiment comprises an indoor experiment and a field experiment, and optimizing indoor experiment parameters according to the fit degree of the indoor experiment and the field experiment;
the fitness calculation model is as follows:
wherein u is i (x) For the leak-off type judging function, i represents the leak-off type, i E (1, 2, 3), when the leak-off type is the ith, then u i (x) =1, otherwise 0; n is the total amount of leakage control indicators; w (W) ij A weight indicating a j-th loss control index in the i-th loss type; x is X 2j A value representing a j-th loss control index obtained by field experiments; x is X 1j A value indicating a j-th loss control index obtained by an indoor experiment;
s4, performing an indoor evaluation experiment on each plugging formula by adopting the optimized indoor experimental parameters, and selecting the plugging formula according to the indoor evaluation experiment result.
2. The experimental evaluation method for the leakage control efficacy of the drilling fluid in the fractured formation according to claim 1, wherein the step S2 comprises:
s21, determining a drilling fluid leakage control effect characterization system; the characterization system includes at least one control index;
s22, establishing a leakage control effect hierarchical structure and a judgment matrix according to a drilling fluid leakage control effect representation system;
comparing the relative importance degrees of the control indexes in the same layer by two by using a unified standard, and establishing a judgment matrix; the judgment matrix of the drilling fluid leakage control effect is as follows:
wherein the scale of the importance ratio among the control indexes is shown in the following table:
s23, carrying out consistency test on the constructed judgment matrix;
consistency ratio calculation formula:
wherein R is I Is an average random consistency index;
C I is a consistency coefficient, and is related to the order n and the maximum feature root of the matrix;
λ max judging the maximum eigenvalue of the matrix;
n is the order of the judgment matrix;
wherein C is I Representing a consistency parameter, R I The parameters representing random consistency are shown in the following table;
when C R <When 0.1, the inconsistency degree of the judgment matrix is considered to be within the allowable range, at the moment, the feature vector of the judgment matrix is the weight vector, otherwise, the step S22 is returned to, and the judgment value of the relative importance degree of the two elements is adjusted until the consistency condition is met;
s24, determining the feature vector of the judgment matrix according to the maximum feature value:
wherein B is a judgment matrix, E is an identity matrix with the same order as B,
is a feature vector;
s25, will
And normalizing to obtain the weight of the control index, wherein the vector in W is the weight of the control index, and the normalization formula is as follows:
in the method, in the process of the invention,
is->
J is an integer greater than 0.
3. The experimental evaluation method for the leakage control efficiency of the drilling fluid of the fractured stratum according to claim 2, wherein the leakage control index of the characterization system comprises bearing capacity, initial leakage amount and accumulated leakage amount;
the fitness calculation model is as follows:
wherein X1, Y1 and Z1 are respectively the pressure-bearing capacity, the initial leakage and the accumulated leakage obtained by indoor experiments; x2, Y2 and Z2 are respectively the pressure-bearing capacity, the initial leakage and the accumulated leakage obtained by field experiments.
4. The experimental evaluation method for the leakage control efficiency of the drilling fluid for the fractured formation according to claim 3, wherein the step of selecting the plugging formulation according to the result of the evaluation experiment comprises the following steps:
s31, scoring each performance of each plugging formula according to experimental scoring criteria;
the scoring criteria are as follows:
s32, obtaining the total score of each plugging formula according to the score and the scoring model of each performance of the plugging formula;
the scoring model is as follows:
K＝u 1 (i)(0.29X+0.62Y+0.09Z)+u 2 (i)(0.73X+0.19Y+0.08Z)+u 3 (i)(0.75X+0.08Y+0.17Z)
wherein X, Y, Z is the bearing capacity, initial leakage and accumulated leakage obtained by indoor experiments respectively;
s33, selecting the plugging formula according to the total components of the plugging formulas.
5. The experimental evaluation method for the leakage control efficiency of the drilling fluid for the fractured formation according to claim 4, wherein the plugging formulation with the highest score is selected when the plugging formulation is selected according to the total score of each plugging formulation.
6. The method for evaluating the leakage control performance experiment of the drilling fluid in the fractured stratum according to claim 2, wherein initial experimental parameters of the indoor experiments of different leakage types are as follows:
inducing rupture: seam height: crack entrance width = 6:1, the dip angle of the crack is smaller by 0.5 degrees, and when the single pressure increment is 5MPa, the pressure stabilizing time is 2min;
crack extension type: seam height: crack entrance width = 6:1, the crack inclination angle is smaller by 0.5 degrees, the single pressure increment is 5MPa, and the pressure stabilizing time is 4min;
natural cracking: seam height: crack entrance width = 3:1, the crack dip angle is smaller by 0.5 degrees, the single pressure increment is 2.5MPa, and the pressure stabilizing time is 4min.
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