CN109858147A - A kind of borehole well instability quantifying risk evaluation method based on Reliability Theory - Google Patents
A kind of borehole well instability quantifying risk evaluation method based on Reliability Theory Download PDFInfo
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Abstract
The borehole well instability quantifying risk evaluation method based on Reliability Theory that the invention discloses a kind of, it is the following steps are included: S1, the basic data according to drilled strata；S2, according to the input Parameter uncertainties statistical form established in step S1；S3, cave-in and shaft wall fracture unstability limiting condition model are established；S4, the borehole well instability limiting condition model according to step S3 solve cave-in pressure value and shaft wall fracture pressure value under basic random variables limit respectively；S5, given wellbore pressure mean value and the coefficient of variation, and the wellbore pressure value under given mean value and the coefficient of variation is generated using Monte Carlo simulation；S6, statistics calculated result are to obtain cave-in and rupture the quantitative assessment result of unstability risk.The beneficial effects of the present invention are: can borehole well instability risk under the influence of quantitative assessment parameter uncertainty, more accurate and effective decision-making foundation can be provided for drilling technology personnel and construction personnel.
Description
Technical field
The present invention relates to the technical field that borehole wall stability in oil drilling is evaluated, a kind of boreholes wall based on Reliability Theory
Unstability quantifying risk evaluation method.
Background technique
Currently, fine and close oil gas, coal bed gas, shale oil gas, ocean deepwater oil gas etc. are non-with the exhaustion of conventional gas and oil resource
Conventional gas and oil resource is gradually taken seriously.For this kind of unconventional petroleum resources of effective exploitation, more and more directional wells, level
The inclined shafts such as well, extended reach well are widely adopted.For example, beach sea oil gas is developed using extended reach well, it can be to avoid construction offshore drill
Well platform；Using orientation well development marine oil and gas, it is possible to reduce the quantity of required drilling platforms；Using the fine and close oil of horizontal well development
Gas, coal bed gas and shale oil gas not only can effectively increase the drainage area that pit shaft is contacted with reservoir, but also be conducive to segmentation pressure
Transformation is split, the rate of oil and gas recovery is finally improved.But the relative complex deviated well drilling of this class formation is but faced with lot of challenges, such as
Borehole well instability risk is high, drill string frictional resistance/torque is high, wellbore cleaning is difficult, casing tripping in is difficult, casing eccentricity leads to cementing quality
Bad, casing wear is serious etc., these all will lead to drilling well nonproductive time, drilling period and drilling cost and increase.Wherein, well
Wall destabilization problems are one of drilling engineering focus of attention problems, and borehole well instability is usually expressed as cave-in and wellbore leakage,
Wellbore pressure is accurately controlled higher than caving pressure and lower than fracture pressure, it is possible to prevente effectively from borehole well instability accident, can also keep away
Exempt to induce the undergrounds such as blowout, leakage, well slough, the bit freezing generated complexity and accident.
Currently, domestic and foreign scholars have carried out more in-depth study for Wellbore Stability, establish a variety of empirical models,
The focus of analytic modell analytical model and method for numerical simulation, research focuses primarily upon constitutive model and failure criteria.In terms of constitutive model
Formd linear elasticity analytic solutions, plasticity model, elastic-plastic model, poroelasticity model, hole thermoelastic model, chemical hole
A variety of models such as elastic model, chemical hole thermoelastic model, formd in terms of failure criteria Mohr-Coulomb criterion,
Drucker-Prager criterion, Mogi-Coulomb criterion, amendment Lade criterion, amendment Wiebols-Cook criterion, Hoek-
A variety of criterion such as Brown criterion.However,
Due to the concealment and uncertainty of deep formation geological conditions, geophysical log and its means of interpretation are equal in addition
There are certain error so that stratum geomechanics parameter (crustal stress, pore pressure), rock mechanics parameters etc. show it is stronger
Uncertainty, determination will be difficult to by carrying out when wellbore stability analysis accurately enters parameter；It, will if inputting parameter certain deviation occurs
Wellbore stability analysis result is caused deviation occur, in some instances it may even be possible to serious error occur.The research of foreign scholar is it has been shown that input
Parameter has extremely strong uncertainty, and produces the influence of highly significant to wellbore stability.Reliability Theory is reliability
One of the most important basic theory of research, it mainly studies the mathematical method and mathematical modulo with the various integrity problems of solution
Type studies the quantitative rule of reliability.
In Chinese patent, disclosed in Publication No. CN105740583A a kind of suitable for carbonate formation wellbore stability
Property Logging Evaluation Method, comprising the following steps: obtain formation pore pressure using effective stress theorem, established using well-log information
Formation collapse prediction model can obtain formation collapsed pressure equivalent mud density in conjunction with formation pore pressure, to obtain mud
Pulp density safe range is compared with actual well drilled liquid density value and mud density safe range, if in mud density safe range
Interior, then wellbore stability, otherwise the borehole wall is unstable.However, the technical solution can only solve current traditional evaluation method adaptability
It is narrow, be not enough to solve the problems, such as all borehole well instabilities.Therefore need a kind of basis by property theory can quantitative assessment parameter it is not true
Borehole well instability risk under qualitative effect can provide more accurate and effective decision for drilling technology personnel and construction personnel
Foundation.
Summary of the invention
It is an object of the invention to overcome the deficiencies in the prior art, providing one kind being capable of quantitative assessment Parameter uncertainties
Borehole well instability risk under the influence of property, can be provided for drilling technology personnel and construction personnel more accurate and effective decision according to
According to the borehole well instability quantifying risk evaluation method based on Reliability Theory.
The purpose of the present invention is achieved through the following technical solutions: a kind of borehole well instability risk based on Reliability Theory is fixed
Measure evaluation method, it the following steps are included:
S1, the basic data according to drilled strata, building input Parameter uncertainties statistical form, the input parameter includes hanging down
To stress, maximum horizontal crustal stress, minimum level crustal stress, porosity, Poisson's ratio, cohesive force, internal friction angle, hole angle, well
The mean value and the coefficient of variation of rectangle parallactic angle, Biot coefficient, infiltration coefficient and avalanche width parameter；
S2, according to the input Parameter uncertainties statistical form established in step S1, generated using Monte Carlo method each
Basic random variables, the basic random variables include vertical stress, maximum horizontal crustal stress, minimum level crustal stress, hole
Degree, Poisson's ratio, cohesive force, internal friction angle and Biot coefficient, the basic random variables select uniformly to divide according to the actual situation
Cloth, angular distribution, normal distribution, logarithm normal distribution, beta distribution, Geng Beier distribution, Weibull distribution and Gamma distribution
In any one distribution function；
S3, according to by distribution function basic random variables generated, establishing cave-in in step S2 and the borehole wall is broken
Split unstability limiting condition model；
S4, the borehole well instability limiting condition model according to step S3 are solved respectively under basic random variables restriction
Cave-in pressure value and shaft wall fracture pressure value；
S5, given wellbore pressure mean value and the coefficient of variation, and given mean value and variation lines are generated using Monte Carlo simulation
Wellbore pressure value under several；
S6, the cave-in pressure value according to obtained in step S4 and S5, shaft wall fracture pressure value and wellbore pressure value, system
Meter calculated result is to obtain cave-in and rupture the quantitative assessment result of unstability risk.
The invention has the following advantages that the present invention overcomes the prior arts can not consider asking for parameter uncertainty influence
Topic, conventional borehole wall Method of Stability Analysis can not evaluate the influence that input parameter and construction parameter uncertainty may cause, and
Reliability theory can borehole well instability risk under the influence of quantitative assessment parameter uncertainty, can be drilling technology personnel and Shi
Worker person provides more accurate and effective decision-making foundation.
Detailed description of the invention
Fig. 1 is calculation flow chart of the invention；
Fig. 2 is failure probability and reliability relational graph；
Fig. 3 a is slopes wall coordinate transform schematic diagram；
Fig. 3 b is well week unstability area schematic；
Fig. 4 is vertical stress analog result statistic histogram；
Fig. 5 is maximum horizontal crustal stress analog result statistic histogram；
Fig. 6 is rock cohesive force analog result statistic histogram；
Fig. 7 is internal friction angle of rock analog result statistic histogram；
Fig. 8 is straight well cave-in and slip gradient density function and accumulative reliability interference pattern；
Fig. 9 is that slopes wall collapses and slip gradient density function and accumulative reliability interference pattern；
Figure 10 is horizontal well cave-in and slip gradient density function and accumulative reliability interference pattern；
Figure 11 is three kinds of well type comparative result figures.
Specific embodiment
The present invention will be further described with reference to the accompanying drawing, and protection scope of the present invention is not limited to as described below:
As shown in Figure 1, a kind of borehole well instability quantifying risk evaluation method based on Reliability Theory, it includes following step
It is rapid:
S1, the basic data according to drilled strata, building input Parameter uncertainties statistical form, the input parameter includes hanging down
To stress, maximum horizontal crustal stress, minimum level crustal stress, porosity, Poisson's ratio, cohesive force, internal friction angle, hole angle, well
The mean value and the coefficient of variation of rectangle parallactic angle, Biot coefficient, infiltration coefficient and avalanche width parameter；
S2, according to the input Parameter uncertainties statistical form established in step S1, generated using Monte Carlo method each
Basic random variables, the basic random variables include vertical stress, maximum horizontal crustal stress, minimum level crustal stress, hole
Degree, Poisson's ratio, cohesive force, internal friction angle and Biot coefficient, the basic random variables select uniformly to divide according to the actual situation
Cloth, angular distribution, normal distribution, logarithm normal distribution, beta distribution, Geng Beier distribution, Weibull distribution and Gamma distribution
In any one distribution function；
S3, according to by distribution function basic random variables generated, establishing cave-in in step S2 and the borehole wall is broken
Split unstability limiting condition model；
Steps are as follows for the derivation of the borehole well instability limiting condition model:
(1) Reliability Theory
According to Reliability Theory, the factor that can will affect borehole well instability is divided into the comprehensive amount of two classes, i.e. load stochastic variable Qk
With drag stochastic variable Rk, wherein k can use C and F, respectively represent two kinds of situations of cave-in and shaft wall fracture.If enable load with
Machine variable QkWith drag stochastic variable RkIt is respectively as follows:
Wherein, QkFor load stochastic variable；RkFor drag stochastic variable；K is the subscript of collapsing unstability and rupture unstability, can
Take C and F；XRkiFor load stochastic variable element；XSkiFor drag stochastic variable element；I is the subscript of stochastic variable element number,
I=1,2 ..., n；N is stochastic variable element sum.
Therefore the power function of borehole well instability may be expressed as:
Zk=g (Qk,Rk)=Rk-Qk-----------------------------------(2)
Wherein, ZkFor power function；G is power function.
Due to the difference of external applied load and wellbore pressure, in fact it could happen that Zk>0、Zk=0, Zk< 0 three kind of situation.According to ZkIt is big
It is small, it can be determined that whether wellbore pressure meets the functional requirement of stabilizing borehole, therefore formula (2) can be known as power function, pole
Limit equilibrium state is the basis for carrying out reliability evaluation, and be may be expressed as:
Zk=g (Qk,Rk)=0-------------------------------------------- (3)
Due to load stochastic variable QkWith drag stochastic variable RkIt is influenced by basic random variables, such as crustal stress, hole
Pressure, rock strength, wellbore pressure etc., it is assumed herein that the basic random variables of borehole well instability are (Xk1,Xk2,…,Xkn), then its
Power function can further indicate that are as follows:
Zk=g (Xk1,Xk2,…,Xkn)---------------------------------------(4)
Wherein, XknFor basic random variables element；N is stochastic variable element sum；
According to Reliability Theory, RELIABILITY INDEX be may be expressed as:
Wherein, βkFor RELIABILITY INDEX；μ (x) is stochastic variable x mean value；σ (x) is stochastic variable x standard deviation.
Under normal conditions, the probability that power function is under instability status is known as failure probability, if power function meets
Normal distribution, then failure probability and reliability corresponding to cave-in and shaft wall fracture may be expressed as:
Wherein, PfkFor failure probability；PrkFor reliability；Φ is standard normal distribution function.
There are following relationships with failure probability for reliability:
Prk+Pfk=1----------------------------------------------- (7)
Fig. 2 is the schematic diagram that failure probability and reliability are obtained by probability density, and pressure is general less than 0 blue region in figure
The area that rate density is accumulated by is failure probability, and red color area probability density of the pressure greater than 0 is accumulated by
Area be reliability, the longitudinal coordinate crosspoint that cumulative probability curve and pressure are 0 is failure probability.Therefore, pressure
Bigger less than 0 area, then reliability is lower；Pressure is smaller less than 0 area, then reliability is higher.According to Reliability Theory,
By calculating the size of unstability region presence probability, the qualitative assessment of borehole well instability risk can be realized.
(2) slopes wall stress distribution model
Deep formation rock is considered as uniform, continuous, isotropic elastic fluid, such as Fig. 3 a, according to Bradley
(1979) the well circumferential stress elastic solution provided, takes radial distance r=R that can obtain borehole wall stress distribution model are as follows:
Wherein:
Wherein, σr,σθ,σz,τθzFor the borehole wall components of stress, MPa；A, B, C, D, E, F, G, H, J are coordinate transform coefficient, nothing
Dimension；σv,σH,σhRespectively vertical, minimum and maximum horizontal crustal stress, MPa；pmFor drilling well liquid columnpressure, MPa；δ is to seep
Saturating coefficient, δ=0 when the borehole wall is impermeable, δ=1 when borehole wall infiltration；θ is well round angle, (°)；I is hole angle, (°)；α is
Direction of deflection and maximum horizontal crustal stress orientation angle, (°)；ν is Poisson's ratio；K1For seep effect coefficient, decimal；φ is hole
Degree, %；αpFor Biot coefficient；ppFor pore pressure, MPa.
Since radial stress is a principal stress, and other two principal stress is then in borehole wall θ z tangent plane, according to material
Material theory of mechanics can solve three principal stresses of the borehole wall are as follows:
Wherein, σi,σj,σkFor three principal stresses of the borehole wall, MPa.
Three principal stress sizes are ranked up, borehole wall maximum and minimum principal stress can be obtained, bond strength criterion can
Caving pressure and fracture pressure nonlinear equation needed for solving stabilizing borehole are obtained, solving the equation can be obtained caving pressure
And fracture pressure, further caving pressure equal yield density and fracture pressure equal yield density can be obtained in conversion.
(3) rock failure mechanism of rock criterion
For borehole wall failure by shear, it is Mohr-Coulomb criterion that wellbore stability, which analyzes most common criterion, is considered effective
It may be expressed as: after stress
Wherein, σ1,σ2,σ3- it is respectively maximum, intermediate and minimum principal stress, MPa；C-cohesive force, MPa；- interior friction
Angle, (°).
The condition occurred is destroyed for tension, depends primarily on formation rock tensile strength, tension failure criteria can indicate
Are as follows: σ3-αppp+St=0-------------------------------------------------- (12)
Wherein, StFor tensile strength of rock, MPa.
(4) cave-in unstability limiting condition model
Minimum wellbore pressure needed for maintaining wellbore stability may be defined as caving pressure, and in general, the borehole wall is radial
Stress will be minimum principal stress (σ3=σi), and the σ known to formula (10)j>σk.Therefore, by σ1=σjAnd σ3=σiBringing formula (11) into can
Obtain caving pressure nonlinear equation:
Wherein, pCFor caving pressure, MPa；fCFor caving pressure function；
Function fCExplicit physical meaning: formation rock resistance borehole wall shear stress ability.If fC< 0, it will shear
It destroys；If fC=0, then it is in limiting equilibrium；If fC> 0, then failure by shear will not occur.In general, being needed to solve formula (13)
Identified sign concentrates the critical point of most serious, as shown in Figure 3b, the highest stress A point as in figure, and corresponding well round angle θ=
θmax.But, it is contemplated that practical wellbore allows a degree of avalanche, and the avalanche proposed herein using Zoback (2007) is wide
Model is spent, as shown in Figure 3b, avalanche width is 2 ω, and borehole well instability critical point at this time is B point, corresponding well round angle are as follows:
θ=θmax±ω-------------------------------------------------(14)
Wherein, θmaxThe corresponding well round angle in highest point, (°) are concentrated for borehole wall stress；ω is avalanche width parameter, (°).
By θ=θmaxAfter ± ω brings formula (9) into, and cave-in pressure is solved by formula (13), can be obtained allows certain journey
Caving pressure in the case of the avalanche width (2 ω) of degree.
When wellbore pressure is lower than caving pressure, i.e. generation cave-in unstability, then well week centralization of formation stress causes to be to lead
The load of cave-in unstability is caused, and wellbore pressure is the drag for supporting wellbore stability.In view of influencing the factor of cave-in
Including crustal stress, pore pressure, formation rock mechanics parameter, well track, avalanche width etc., then the load of cave-in with
Machine variable QCWith drag stochastic variable RCIt can respectively indicate are as follows:
Therefore, RELIABILITY INDEX, failure probability and reliability corresponding to cave-in unstability limiting condition are respectively as follows:
(5) shaft wall fracture unstability limiting condition model
The borehole wall is prevented to may be defined as fracture pressure by the highest wellbore pressure of pressure break.By formula (10) it is found that σiAnd σjIt is greater than
Zero, only σkIt is likely to occur negative value.Therefore, by σ3=σkFracture pressure nonlinear equation can be obtained by bringing formula (12) into:
fF(pF)=σk-αppp+St=0------------------------------------------- (18)
Wherein, pFFor fracture pressure, MPa；fFFor fracture pressure function.
Function fFExplicit physical meaning: formation rock resistance borehole wall tensile stress ability.If fF< 0, tension will occur
It destroys；If fF=0, then it is in limiting equilibrium；If fF> 0, then tension destruction will not occur.
Similarly, when wellbore pressure is higher than fracture pressure, i.e. generation shaft wall fracture unstability, then wellbore pressure becomes leading to well
The load of wall rupture, and well week ground environment becomes resisting the drag of shaft wall fracture.In view of influencing the factor packet of shaft wall fracture
Crustal stress, pore pressure, formation rock mechanics parameter, well track etc. are included, then the load stochastic variable Q of shaft wall fractureFWith
Drag stochastic variable RFIt can respectively indicate are as follows:
Therefore, RELIABILITY INDEX, failure probability and reliability corresponding to shaft wall fracture unstability limiting condition are respectively as follows:
S4, the borehole well instability limiting condition model according to step S3 are solved respectively under basic random variables restriction
Cave-in pressure value and shaft wall fracture pressure value；
S5, given wellbore pressure mean value and the coefficient of variation, and given mean value and variation are generated using Monte-Carlo simulation
Wellbore pressure value under coefficient；
S6, the cave-in pressure value according to obtained in step S4 and S5, shaft wall fracture pressure value and wellbore pressure value, system
Meter calculated result is to obtain cave-in and rupture the quantitative assessment result of unstability risk.
Specific embodiment
It is analyzed by taking the CW-101X well Xu jiahe stratum of Sichuan Basin oil field as an example, Xu jiahe buried depth of strata
2500~3500m, according to the well logging on bored Xu jiahe stratum and real brill data, stratum vertical stress 52.10-
69.52MPa, 42.55~59.47MPa of maximum horizontal crustal stress (N37.86 ° of E), minimum level crustal stress 35.63~
49.68MPa, pore pressure 26.95~33.24, rock 12.15~18.63MPa of cohesive force, internal friction angle of rock 33.54~
36.67 °, 3.47~5.63MPa of tensile strength of rock, Rock Poisson Ratio Using 0.23~0.27, porosity 0.05~0.16, by system
Meter analysis, constructs input Parameter uncertainties statistical form, and the input parameter includes vertical stress, maximum horizontal crustal stress, most
Small horizontal crustal stress, porosity, Poisson's ratio, cohesive force, internal friction angle, hole angle, drift azimuth, Biot coefficient, infiltration system
Several and avalanche width parameter mean value and the coefficient of variation statistics is as shown in the table:
| No. | Stochastic variable | Mean value | Standard deviation | The coefficient of variation | P10 | P90 |
| 1 | Vertical stress/MPa | 57.82 | 2.89 | 0.05 | 53.22 | 62.42 |
| 2 | Horizontal maximum crustal stress/MPa | 50.05 | 10.01 | 0.20 | 34.12 | 65.98 |
| 3 | Horizontal minimum crustal stress/MPa | 41.63 | 2.08 | 0.05 | 38.32 | 44.94 |
| 4 | Horizontal maximum crustal stress orientation/(°) | 37.86 | 7.57 | 0.20 | 25.81 | 49.91 |
| 5 | Pore pressure/MPa | 29.50 | 8.85 | 0.30 | 15.42 | 43.58 |
| 6 | Cohesive force/MPa | 16.47 | 6.59 | 0.40 | 5.98 | 26.96 |
| 7 | Internal friction angle/(°) | 34.67 | 6.93 | 0.20 | 23.64 | 45.70 |
| 8 | Tensile strength/MPa | 3.85 | 1.54 | 0.40 | 1.40 | 6.30 |
| 9 | Poisson's ratio | 0.25 | 0.05 | 0.20 | 0.17 | 0.33 |
| 10 | Porosity | 0.10 | 0.02 | 0.20 | 0.07 | 0.13 |
Wherein: P10 and P90 is corresponding confidence interval upper and lower limit when being confidence level 90%
According to the input Parameter uncertainties statistical form established in step S1, generated using Monte-Carlo method each
Basic random variables.Under normal conditions, the geomechanics parameter and rock mechanics parameters that wellbore stability analysis is related to are uncertain
, in Reliability Theory the probabilistic mathematical method of characterising parameter include be uniformly distributed, angular distribution, normal distribution, logarithm
Normal distribution, Beta distribution, Gumbel distribution, Weibull distribution, Gamma distribution etc. are a variety of, most common mainly normal state point
Cloth, logarithm normal distribution, Weibull distribution.It is assumed herein that the geomechanics parameter and rock mechanics parameters on Xu jiahe stratum
Normal distribution is substantially met, the mean value of each parameter is given according to result of log interpretation, calculates phase with reference to the various test methods in scene
Close the coefficient of variation and standard deviation that the possible error range of parameter sets each parameter.It is simulated using Monte-Carlo method to defeated
Enter parameter and carries out grab sample simulation, grab sample analog sample quantity 10000, the statistical result and just of partial parameters simulation
State fitting of distribution curve is as also shown in e.g. figs. 4-7.It is seen that the uncertain regularity of distribution of each parameter meets normal distribution rule
Rule；The coefficient of variation is higher, then the uncertainty of sample data is stronger；Vice versa.For example, the coefficient of variation of rock cohesive force reaches
To 0.40, corresponding to the confidence interval under 90% confidence level is 5.98~26.96MPa；The coefficient of variation of vertical stress is 0.05, right
Answering the confidence interval under 90% confidence level is 53.22~62.42MPa；In contrast, the coefficient of variation is lower, then its confidence interval
Lower for amplitude of variation, i.e., sample data is more concentrated, is uncertain weaker.It can be seen that this more not true than stronger parameter
It is qualitative borehole wall stability to be made a significant impact.
Further, the basic random variables according to generated in step S2 establish cave-in and shaft wall fracture unstability pole
Limit state model；According to borehole well instability limiting condition model described in step S3, solved under basic random variables restriction respectively
Cave-in pressure value and shaft wall fracture pressure value；Given wellbore pressure mean value and the coefficient of variation, and use Monte-Carlo mould
The quasi- wellbore pressure value generated under given mean value and the coefficient of variation；According to cave-in pressure value obtained in step S4 and S5,
Shaft wall fracture pressure value and wellbore pressure value, assessment cave-in and the risk for rupturing unstability, and calculated result is counted
It obtains cave-in and ruptures the quantitative assessment result of unstability risk.In order to disclose the synthesis wind of borehole well instability under different well type
Danger, analyzes under straight well, inclined shaft (45 ° of orientation, 45 ° of hole deviation) and horizontal well (45 ° of orientation, 90 ° of hole deviation) three quasi-representative well type
Cave-in and rupture unstability risk, are set forth cave-in under three quasi-representative well type as a result as shown in Fig. 8~11, in figure
With slip gradient density function and accumulative reliability interference pattern as shown in figs. 8-10 with three quasi-representative well type reliability comparison diagrams such as
Shown in Figure 11.
(1) in cave-in and slip gradient density function interference pattern, cave-in probability density and shaft wall fracture probability
The lap of density is known as interference region, and interference region is that possible occur collapsing and rupturing the region of unstability: interference region face simultaneously
Product is bigger, then the reliability crept into that succeeds is lower；Interference region area is smaller, then the reliability crept into that succeeds is higher.
(2) cave-in and rupture unstability add up in reliability interference pattern, are collapsing unstability on the left of collapsing reliability curves
Risk area, rupture reliability curves right side is rupture unstability risk area, while avoiding cave-in and rupturing the region of unstability (i.e.
The region that cave-in reliability curves and shaft wall fracture reliability curves lower part are included) represent the safety crept into that can succeed
Region.
(3) for three quasi-representative well type, the security window of straight well, inclined shaft and horizontal well is respectively in the case of reliability 95%
1.19~1.98g/cm3, 1.36~2.18g/cm3With 1.47~2.19g/cm3, illustrate no matter creep into straight well, inclined shaft in the direction
Or horizontal well, there is window wider and reliable ' Safe Density Windows；If by wellbore stability reliability be reduced to 90% or
Lower, then corresponding security window will be wider, but the risk of borehole well instability also can significantly increase；In comparison, if adopting
Collapsing unstability risk with identical wellbore pressure, straight well is lower, and inclined shaft takes second place, and the risk of horizontal well is higher, this with use mean value
The caving pressure distribution trend being calculated is consistent.
(4) the borehole well instability risk evaluation results obtained based on reliability theory are existed with conventional borehole wall stability analysis result
It is still consistent on overall trend, still, conventional borehole wall Method of Stability Analysis can not evaluate input parameter and construction parameter
The influence that uncertainty may cause, and reliability theory being capable of borehole well instability wind under the influence of quantitative assessment parameter uncertainty
Danger, can provide more accurate and effective decision-making foundation for drilling technology personnel and construction personnel.
In conclusion the method overcome the prior arts can not consider the problems of that parameter uncertainty influences, the conventional borehole wall
Method of Stability Analysis, which can not be evaluated, inputs the influence that parameter and construction parameter uncertainty may cause, and reliability theory energy
Borehole well instability risk under the influence of enough quantitative assessment parameter uncertainties, can provide more for drilling technology personnel and construction personnel
Add accurate and effective decision-making foundation.
Claims (1)
1. a kind of borehole well instability quantifying risk evaluation method based on Reliability Theory, it is characterised in that: it the following steps are included:
S1, the basic data according to drilled strata, building input Parameter uncertainties statistical form, the input parameter includes vertical answers
Power, maximum horizontal crustal stress, minimum level crustal stress, porosity, Poisson's ratio, cohesive force, internal friction angle, hole angle, hole deviation side
The mean value and the coefficient of variation of parallactic angle, Biot coefficient, infiltration coefficient and avalanche width parameter；
S2, according to the input Parameter uncertainties statistical form established in step S1, generated using Monte Carlo method each basic
Stochastic variable, the basic random variables include vertical stress, maximum horizontal crustal stress, minimum level crustal stress, porosity, pool
Loose ratio, cohesive force, internal friction angle and Biot coefficient, the basic random variables select to be uniformly distributed according to the actual situation, three
It is any in angle distribution, normal distribution, logarithm normal distribution, beta distribution, Geng Beier distribution, Weibull distribution and Gamma distribution
A kind of distribution function；
S3, according to by distribution function basic random variables generated, establishing cave-in in step S2 and shaft wall fracture loses
Steady limiting condition model；
S4, the borehole well instability limiting condition model according to step S3 solve the borehole wall under basic random variables limit respectively
Caving pressure value and shaft wall fracture pressure value；
S5, given wellbore pressure mean value and the coefficient of variation, and generated under given mean value and the coefficient of variation using Monte Carlo simulation
Wellbore pressure value；
S6, the cave-in pressure value according to obtained in step S4 and S5, shaft wall fracture pressure value and wellbore pressure value, statistics meter
Result is calculated to obtain cave-in and rupture the quantitative assessment result of unstability risk.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| WO2021047328A1 (en) * | 2019-09-10 | 2021-03-18 | 青岛理工大学 | Method for determining maximum strain for wellbore instability breakage |
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