CN1598529A - Stress sheath demage predicting method - Google Patents

Abstract

The invention discloses a forecasting method for stress damage. Its character lies in: at first, the radius strain of and ground stress are supervised; secondly, takes no account of affection of sleeve pipe axis stress, the sleeve pipe is considered as ring stress problem in condition of plane, deduces out the radius strain formula generated by the ring plastic deformation and the sleeve pipe plastics intensity formula, works out the stress carrier and correspondent limit intensity according to the two formulas. Finally, through the comparison of sleeve stress carrier and sleeve limit intensity, it judges the probability of damage.

Description

The stress cover decreases Forecasting Methodology

Technical field:

The present invention relates to the Forecasting Methodology of oil field oil, well cover damage, belong to the stress cover and decrease Forecasting Methodology.

Background technology:

Cover decrease be meant influence the field produces pipe production, improper damage or distortion, the prediction that oil field oil, well cover decrease, at home and abroad each elephant does not find that all relevant technology is reported and application; The monitoring method of casing stress load change, be to utilize existing cased well cable diameter gauge device, be acoustic caliper device, magnetic method hole diameter instrument and mechanical caliper device etc., come the monitoring sleeve radial strain to change, if the footpath strain along the circumferential direction is uniform, compare with original sleeve pipe, hole diameter enlarges can judge that the external applied load type is interior pressure, and hole diameter dwindles can judge that the external applied load type is a uniform external; If the footpath strain along the circumferential direction is heterogeneous, can judge that casing load is non-homogeneous external applied load; And the monitoring that reservoir stress changes, can utilize the dipole acoustic log instrument of oil companies such as Si Lunbeixie or Atlas to monitor the variation of terrestrial stress, this instrument only carried out application aspect hole stability control and the pressure break prediction during drilling well, at the report that does not also have success aspect the prediction of cover damage.

The anti-evenly formula of outer crowded intensity of four calculating sleeve pipes is arranged in 1984 editions, 1994 editions 5C3 formula of american petroleum IEEE (API) standard, and these four formula calculate with different formulas by the radius-thickness ratio different mining.The internal pressure strength formula is the formula of thin walled tube wall thickness by 0.875 correction in the API standard, and the elastoplasticity strength formula of sleeve pipe is not reported.

Summary of the invention:

Can only monitoring sleeve strain and reservoir stress in order to overcome existing logging instrumentation, and can not decrease the problem of predicting to cover, the invention provides a kind of stress cover and decrease Forecasting Methodology, the measurable cover of this method decreases the possibility that takes place, before cover decreases generation, sleeve pipe is adopted remedial measures, can slow down or avoid cover to decrease and take place, reduce the cost of repairs significantly.

The technical solution adopted for the present invention to solve the technical problems is:

1, last-period forecast method realizes by following step:

A, utilize the radial strain of cased well cable diameter gauge device monitoring sleeve;

B, casing stress load inversion method: do not considering quill under the situation of stress influence, sleeve pipe is regarded as the stressed problem of annulus under the planar condition, under polar coordinates (r, θ), casing stress satisfies following equation:

$\left\{\begin{array}{c}\frac{{\∂\mathrm{\σ}}_r}{\∂r}+\frac{1}{r}\frac{{\∂\mathrm{\τ}}_{\mathrm{\θr}}}{\∂\mathrm{\θ}}+\frac{{\mathrm{\σ}}_r-{\mathrm{\σ}}_{\mathrm{\θ}}}{r}=0\\ \frac{{\∂\mathrm{\τ}}_{\mathrm{r\θ}}}{\∂r}+\frac{1}{r}\frac{{\∂\mathrm{\σ}}_{\mathrm{\θ}}}{\∂\mathrm{\θ}}+\frac{{2\mathrm{\τ}}_{\mathrm{r\θ}}}{r}=0\end{array}\right.---\left(1\right)$

In the formula: σ _r-radial stress, σ _θ-tangential stress, τ _{R θ}, τ _{θ r}-shear stress; Stress boundary condition:

$\left\{\begin{array}{c}{\mathrm{\&sigma;}}_r{|}_{r=\mathrm{<figure-callout\; id="1"\; label="r"\; filenames="A20041004380300121.png"\; state="\{\{state\}\}">r</figure-callout>}1}=-P_i;\\ {\mathrm{\&tau;}}_{\mathrm{r\&theta;}}{|}_{r=\mathrm{<figure-callout\; id="1"\; label="r"\; filenames="A20041004380300121.png"\; state="\{\{state\}\}">r</figure-callout>}1}=0;\\ {\mathrm{\&sigma;}}_r{|}_{r=r2}=-P_o-\frac{S}{2}(1-\cos 2\mathrm{\&theta;});\\ {\mathrm{\&tau;}}_{\mathrm{r\&theta;}}{|}_{r=r2}=-\frac{S}{2}\sin 2\mathrm{\&theta;};\end{array}\right.---\left(2\right)$

In the formula: P _i-sleeve pipe initial internal pressure, P _oThe initial external pressure of-sleeve pipe, the non-homogeneous external applied load of S-.The radial strain of trying to achieve the generation of annulus elastic-plastic deformation by boundary condition is:

$u_r=\frac{(1-{\mathrm{\&mu;}}^2)P_p}{\mathrm{Er}}[-\frac{A}{(1-\mathrm{\&mu;})r_p}+\frac{2(1-2\mathrm{\&mu;}){\mathrm{Br}}_p}{1-\mathrm{\&mu;}}-(\frac{{2A}_1{r}_p}{1-\mathrm{\&mu;}}-\frac{{4\mathrm{\&mu;B}}_1{r}_p^3}{1-\mathrm{\&mu;}}-\frac{{2C}_1}{(1-\mathrm{\&mu;})r_p^3}$

$-\frac{{4D}_1}{r_p}\left)\cos 2\mathrm{\&theta;}\right]+\frac{(1-{\mathrm{\&mu;}}^2)}{\mathrm{Er}}[-\frac{{\mathrm{\&delta;}}_1}{(1-\mathrm{\&mu;})r_p}+\frac{2(1-2\mathrm{\&mu;}){\mathrm{\&delta;}}_2{r}_p}{1-\mathrm{\&mu;}}]---\left(3\right)$

In the formula:

A＝(S _o-S _i+S/2)A′ B＝S _iB′-(S _o+S/2)C′

${\mathrm{<figure-callout\; id="1"\; label="A"\; filenames="A20041004380300121.png"\; state="\{\{state\}\}">A</figure-callout>}}_1=-\frac{1+k^2+4k^4}{4{(1-k^2)}^3},{\mathrm{<figure-callout\; id="1"\; label="B"\; filenames="A20041004380300121.png"\; state="\{\{state\}\}">B</figure-callout>}}_1=\frac{k^2}{2r_2^2{(1-k^2)}^3}$

${\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="A20041004380300121.png"\; state="\{\{state\}\}">C</figure-callout>}}_1=-\frac{r_p^4(1+k^2)}{4{(1-k^2)}^3},{\mathrm{<figure-callout\; id="1"\; label="D"\; filenames="A20041004380300121.png"\; state="\{\{state\}\}">D</figure-callout>}}_1=\frac{r_p^2(1+k^3)(1+k+k^2)}{2{(1-k)}^3{(1+k)}^4}$

$k=\frac{r_p}{r_2},A^{\&prime;}=\frac{r_p^2{r}_2^2}{r_2^2-r_p^2}$

$B^{\&prime;}=\frac{r_p^2}{2(r_2^2-r_p^2)},C^{\&prime;}=\frac{r_2^2}{2(r_2^2-r_p^2)}$

$\mathrm{\&delta;}=-\frac{2}{\sqrt{3}}{\mathrm{\&sigma;}}_s\log \frac{{\mathrm{<figure-callout\; id="1"\; label="r\; p\; r"\; filenames="A20041004380300121.png"\; state="\{\{state\}\}">r</figure-callout>}}_p}{r_{}}$ δ ₁＝-δA′+(P _o-P _i)A′

δ ₂＝δB′+P _iB′-P _oC′

C, with the σ in the equation (1) _r, σ _θSubstitution Von Mises yield condition ${({\mathrm{\&sigma;}}_r-{\mathrm{\&sigma;}}_{\mathrm{\&theta;}})}^2+{\left({\mathrm{\&sigma;}}_{\mathrm{\&theta;}}{-\mathrm{\&sigma;}}_z\right)}^2+{({\mathrm{\&sigma;}}_z-{\mathrm{\&sigma;}}_r)}^2+{6\mathrm{\&tau;}}_{\mathrm{r\&theta;}}^2={2\mathrm{\&sigma;}}_s^2,$ Utilize border, elasto-plastic range (elasto-plastic region) r=r _pPlace's stress is obtained elastoplasticity intensity continuously.Get τ in the equation (1) in the plastic zone _{R θ}=0, sleeve pipe

Elastoplasticity intensity is:

$P_p^{\&prime;}=\frac{{-Q}_{10}+\sqrt{Q_{10}^2-4Q_9{Q}_{11}}}{2Q_9}---\left(4\right)$

In the formula:

$Q_9={\mathrm{<figure-callout\; id="1"\; label="S"\; filenames="A20041004380300121.png"\; state="\{\{state\}\}">S</figure-callout>}}_1^2+Q_5^2+Q_7^2$ Q ₁₀＝2S ₁Q ₃+2Q ₅Q ₆+2Q ₇Q ₈

$Q_{11}=Q_3^2+Q_6^2+Q_8^2+{6\mathrm{\&tau;}}_{\mathrm{r\&theta;}}^2-{2\mathrm{\&sigma;}}_s^2$ S ₁＝σ _θ-σ _r

S ₂＝σ _θ+σ _r $Q_1=\frac{{\mathrm{\&delta;}}_1}{r^2}+2{\mathrm{\&delta;}}_2$

$Q_2=-\frac{{\mathrm{\&delta;}}_1}{r^2}+2{\mathrm{\&delta;}}_2,Q_3=-\frac{{2\mathrm{\&delta;}}_1}{r^2}$

Q ₄＝4δ ₂ Q ₅＝σ _θ-μS ₂

Q ₆＝Q ₂-μQ ₂ Q ₇＝μS ₂-σ _r

Q ₈＝Q ₁-μQ ₄ $\mathrm{\&delta;}=-\frac{2}{\sqrt{3}}{\mathrm{\&sigma;}}_s\log \frac{{\mathrm{<figure-callout\; id="1"\; label="r\; p\; r"\; filenames="A20041004380300121.png"\; state="\{\{state\}\}">r</figure-callout>}}_p}{r_{}}$

δ ₁＝-δA′+(P _o-P _i)A′ δ ₂＝δB′+P _iB′-P _oC′

Symbol description in above-mentioned formula (3), (4):

u _rThe radial displacement of-internal surface of sleeve pipe, P _p-casing stress load, P _p'-sleeve pipe elastoplasticity intensity, μ-Poisson ratio, r ₁-sleeve pipe inside radius, r ₂-sleeve pipe external radius, r _p-elastoplasticity intersection radius, r-measurement point radius, E-Young modulus, P _i-sleeve pipe initial internal pressure, P _oThe initial external pressure of-sleeve pipe, the non-homogeneous external applied load of S-, S _i-anti-inner pressuring load, S _o-anti-even external applied load, other each symbol is an intermediate variable.

D, the radial strain value that monitoring among the step a is obtained are updated in the formula (3), are finally inversed by casing stress load, i.e. P in the formula _p

E, utilize formula (4) to calculate the ultimate strength P of sleeve pipe under the respective loads effect _p';

F, the P that above-mentioned steps d, e are calculated _p, P _p' compare, judge that cover decreases the possibility that takes place;

2, long-range forecasting method realizes by following step:

A, utilize dipole acoustic log instrument monitoring terrestrial stress;

B, utilize the formula (4) in the last-period forecast method to calculate the ultimate strength P of sleeve pipe under the respective loads effect _p';

C, above-mentioned steps a monitoring terrestrial stress that obtains and the ultimate strength that step b calculates are compared, judge that cover decreases the possibility of generation.

The invention has the beneficial effects as follows:, can calculate casing stress load and the ultimate strength under the respective loads effect according to this formula because the present invention has derived radial strain formula and sleeve pipe elastoplasticity strength formula that the annulus elastic-plastic deformation produces according to elastic plastic theory.By the comparison of stress loading and ultimate strength, measurable cover decreases the possibility that takes place; Before cover decreases generation, sleeve pipe is adopted remedial measures, can slow down or avoid cover to decrease and take place, reduce the cost of repairs significantly.

Description of drawings:

Fig. 1 is the evenly outer stress model figure of carrying of sleeve pipe of the present invention;

Fig. 2 is the non-homogeneous outer stress model figure of carrying of sleeve pipe of the present invention;

Fig. 3 is the even and non-homogeneous outer acting in conjunction stress model figure of carrying of sleeve pipe of the present invention;

Fig. 4 is that the present invention is internal pressure strength and the corresponding radial deformation figure that example is calculated with 139.7 * 7.72mm sleeve pipe;

Fig. 5 is that the present invention is anti-uniform external intensity and the corresponding radial deformation figure that example is calculated with 139.7 * 7.72mm sleeve pipe;

Fig. 6 is that the present invention is anti-non-homogeneous external pressure strength and the corresponding radial deformation figure that example is calculated with 139.7 * 7.72mm sleeve pipe;

Embodiment:

The present invention is further described below in conjunction with accompanying drawing:

Fig. 1, Fig. 2, Fig. 3 are casing stress illustratons of model of the present invention, and sleeve pipe is regarded as the stressed problem of annulus under the planar condition, and under polar coordinates (r, θ), casing stress satisfies following equation:

$\left\{\begin{array}{c}\frac{{\&PartialD;\mathrm{\&sigma;}}_r}{\&PartialD;r}+\frac{1}{r}\frac{{\&PartialD;\mathrm{\&tau;}}_{\mathrm{\&theta;r}}}{\&PartialD;\mathrm{\&theta;}}+\frac{{\mathrm{\&sigma;}}_r-{\mathrm{\&sigma;}}_{\mathrm{\&theta;}}}{r}=0\\ \frac{{\&PartialD;\mathrm{\&tau;}}_{\mathrm{r\&theta;}}}{\&PartialD;r}+\frac{1}{r}\frac{{\&PartialD;\mathrm{\&sigma;}}_{\mathrm{\&theta;}}}{\&PartialD;\mathrm{\&theta;}}+\frac{{2\mathrm{\&tau;}}_{\mathrm{r\&theta;}}}{r}=0\end{array}\right.---\left(1\right)$

In the formula: σ _r-radial stress, σ _θ-tangential stress, τ _{R θ}, τ _{θ r}-shear stress; Stress boundary condition:

$\left\{\begin{array}{c}{\mathrm{\&sigma;}}_r{|}_{r=\mathrm{<figure-callout\; id="1"\; label="r"\; filenames="A20041004380300121.png"\; state="\{\{state\}\}">r</figure-callout>}1}=-P_i;\\ {\mathrm{\&tau;}}_{\mathrm{r\&theta;}}{|}_{r=\mathrm{<figure-callout\; id="1"\; label="r"\; filenames="A20041004380300121.png"\; state="\{\{state\}\}">r</figure-callout>}1}=0;\\ {\mathrm{\&sigma;}}_r{|}_{r=r2}=-P_o-\frac{S}{2}(1-\cos 2\mathrm{\&theta;});\\ {\mathrm{\&tau;}}_{\mathrm{r\&theta;}}{|}_{r=r2}=-\frac{S}{2}\sin 2\mathrm{\&theta;};\end{array}\right.---\left(2\right)$

In the formula: P _i-sleeve pipe initial internal pressure, P _oThe initial external pressure of-sleeve pipe, the non-homogeneous external applied load of S-.The radial strain of trying to achieve the generation of annulus elastic-plastic deformation by boundary condition is:

$u_r=\frac{(1-{\mathrm{\&mu;}}^2)P_p}{\mathrm{Er}}[-\frac{A}{(1-\mathrm{\&mu;})r_p}+\frac{2(1-2\mathrm{\&mu;}){\mathrm{Br}}_p}{1-\mathrm{\&mu;}}-(\frac{2A_1{r}_p}{1-\mathrm{\&mu;}}-\frac{4\mathrm{\&mu;}{B}_1{r}_p^3}{1-\mathrm{\&mu;}}-\frac{2C_1}{(1-\mathrm{\&mu;})r_p^3}$

$-\frac{{4D}_1}{r_p}\left)\cos 2\mathrm{\&theta;}\right]+\frac{(1-{\mathrm{\&mu;}}^2)}{\mathrm{Er}}[-\frac{{\mathrm{\&delta;}}_1}{(1-\mathrm{\&mu;})r_p}+\frac{2(1-2\mathrm{\&mu;}){\mathrm{\&delta;}}_2{r}_p}{1-\mathrm{\&mu;}}]---\left(3\right)$

In the formula:

A＝(S _o-S _i+S/2)A′ B＝S _iB′-(S _o+S/2)C′

$A_1=-\frac{1+k^2+{4k}^4}{4{(1-k^2)}^3},{\mathrm{<figure-callout\; id="1"\; label="B"\; filenames="A20041004380300121.png"\; state="\{\{state\}\}">B</figure-callout>}}_1=\frac{k^2}{{2r}_2^2{(1-k^2)}^3}$

${\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="A20041004380300121.png"\; state="\{\{state\}\}">C</figure-callout>}}_1=-\frac{r_p^4(1+k^2)}{4{(1-k^2)}^3},{\mathrm{<figure-callout\; id="1"\; label="D"\; filenames="A20041004380300121.png"\; state="\{\{state\}\}">D</figure-callout>}}_1=\frac{r_p^2(1+k^3)(1+k+k^2)}{2{(1-k)}^3{(1+k)}^4}$

$k=\frac{r_p}{r_2},A^{\&prime;}=\frac{r_p^2{r}_2^2}{r_2^2-r_p^2}$

$B^{\&prime;}=\frac{r_p^2}{2(r_2^2-r_p^2)},C^{\&prime;}=\frac{r_2^2}{2(r_2^2-r_p^2)}$

$\mathrm{\&delta;}=-\frac{2}{\sqrt{3}}{\mathrm{\&sigma;}}_s\log \frac{{\mathrm{<figure-callout\; id="1"\; label="r\; p\; r"\; filenames="A20041004380300121.png"\; state="\{\{state\}\}">r</figure-callout>}}_p}{r_{}}$ δ ₁＝-δA′+(P _o-P _i)A′

δ ₂＝δB′+P _iB′-P _oC′

With σ _r, σ _θSubstitution Von Mises yield condition ${({\mathrm{\&sigma;}}_r-{\mathrm{\&sigma;}}_{\mathrm{\&theta;}})}^2+{\left({\mathrm{\&sigma;}}_{\mathrm{\&theta;}}{-\mathrm{\&sigma;}}_z\right)}^2+{({\mathrm{\&sigma;}}_z-{\mathrm{\&sigma;}}_r)}^2+{6\mathrm{\&tau;}}_{\mathrm{r\&theta;}}^2={2\mathrm{\&sigma;}}_s^2,$ Utilize border, elasto-plastic range (elasto-plastic region) r=r _pPlace's stress is obtained elastoplasticity intensity continuously.Get τ in the equation (1) in the plastic zone _{R θ}=0, its result causes non-uniform load intensity slightly bigger than normal.Sleeve pipe elastoplasticity intensity is:

$P_p^{\&prime;}=\frac{{-Q}_{10}+\sqrt{Q_{10}^2-{4Q}_9{Q}_{11}}}{2Q_9}---\left(4\right)$

In the formula:

$Q_9={\mathrm{<figure-callout\; id="1"\; label="S"\; filenames="A20041004380300121.png"\; state="\{\{state\}\}">S</figure-callout>}}_1^2+Q_5^2+Q_7^2$ Q ₁₀＝2S ₁Q ₃+2Q ₅Q ₆+2Q ₇Q ₈

$Q_{11}=Q_3^2+Q_6^2+Q_8^2+{6\mathrm{\&tau;}}_{\mathrm{r\&theta;}}^2-{2\mathrm{\&sigma;}}_s^2$ S ₁＝σ _θ-σ _r

S ₂＝σ _θ+σ _r $Q_1=\frac{{\mathrm{\&delta;}}_1}{r^2}+2{\mathrm{\&delta;}}_2$

$Q_2=-\frac{{\mathrm{\&delta;}}_1}{r^2}+2{\mathrm{\&delta;}}_2,Q_3=-\frac{{2\mathrm{\&delta;}}_1}{r^2}$

Q ₄＝4δ ₂ Q ₅＝σ _θ-μS ₂

Q ₆＝Q ₂-μQ ₂ Q ₇＝μS ₂-σ _r

Q ₈＝Q ₁-μQ ₄ $\mathrm{\&delta;}=-\frac{2}{\sqrt{3}}{\mathrm{\&sigma;}}_s\log \frac{{\mathrm{<figure-callout\; id="1"\; label="r\; p\; r"\; filenames="A20041004380300121.png"\; state="\{\{state\}\}">r</figure-callout>}}_p}{r_{}}$

δ ₁=-δ A '+(P _o-P _i) A ' δ ₂=δ B '+P _iB '-P _oSymbol description in the above-mentioned formula of C ' (3), (4):

u _rThe radial displacement of-internal surface of sleeve pipe, P _pCasing stress load, P _p'-sleeve pipe elastoplasticity intensity, μ-Poisson ratio, r ₁-sleeve pipe inside radius, r ₂-sleeve pipe external radius, r _p-elastoplasticity intersection radius, r-measurement point radius, E-Young modulus, P _i-sleeve pipe initial internal pressure, P _oThe initial external pressure of-sleeve pipe, the non-homogeneous external applied load of S-, S _i-anti-inner pressuring load, S _o-anti-even external applied load, other each symbol is an intermediate variable.

In actual use, available two kinds of methods are decreased cover and are predicted.A kind of method is long-range forecasting, utilizes the dipole acoustic log instrument to monitor terrestrial stress; Then, middle sleeve elastoplasticity strength formula (4) calculates the ultimate strength of sleeve pipe under the respective loads effect according to the present invention.Terrestrial stress and ultimate strength are compared, judge that cover decreases the possibility that takes place; Another kind method is last-period forecast, sharp cased well cable diameter gauge device, be acoustic caliper device, magnetic method hole diameter instrument and mechanical caliper device etc., come the monitoring sleeve radial strain, if the footpath strain along the circumferential direction is uniform, compare with original sleeve pipe, hole diameter enlarges can judge that the external applied load type is interior pressure, and hole diameter dwindles can judge that the external applied load type is a uniform external; If the footpath strain along the circumferential direction is heterogeneous, can judge that casing load is non-homogeneous external applied load, utilize casing stress strain stress relation formula (3) to calculate casing stress load then.At last, utilize sleeve pipe elastoplasticity strength formula (4) to calculate the ultimate strength of sleeve pipe under the respective loads effect; Casing stress load and ultimate strength are compared, judge that cover decreases the possibility that takes place.

Above-mentioned two kinds of methods are decreased the prediction of possibility occurrence to cover, if casing stress load (or reservoir stress) very near the sleeve pipe ultimate strength, then to decrease the possibility that takes place just big for cover; If casing stress load (or reservoir stress) increase is than very fast, then the possibility of cover damage generation is also very big, need pay close attention to load change; If casing stress load (or reservoir stress) is more stable, and compare lessly with the ultimate strength under the respective loads, then the possibility that decrease to take place of cover is also less; Other situation can the rest may be inferred.Two kinds of methods can be used separately, also can use simultaneously, and using simultaneously can be complementary, obtains best prediction effect; Can before cover decreases generation, adopt remedial measures, slow down or avoid cover to decrease and take place, reduce the cost of repairs significantly sleeve pipe.

Embodiment:

Embodiment 1: burst resistance:

Series 1 is that the sleeve pipe inside and outside differential pressure is 0 o'clock anti-internal pressure stress strain stress relation of sleeve pipe among Fig. 4, sleeve pipe elastoplasticity intensity P _p' be 66MPa, when external applied load (interior pressure) begins to enter elastic-plastic phase when reaching this numerical value, its Changing Pattern no longer is a linear relationship, and its strain variation scope also has only 0.1 millimeter to 0.2 millimeter variation, and it is very difficult that existing cover damage detecting instrument device is monitored its variation.The burst resistance increase is more and more slower, but numerical value is still bigger, and pressure energy power was still bigger in sleeve pipe was anti-, and it is not this that the oil field cover decreases main type.Series the 2,3, the 4th, interior pressure are 10,20, the situation during 30MPa, as seen with interior pressure increase sleeve pipe anti-in pressure energy power reduced.Series the 5,6, the 7th, external pressure are 10,20, the situation during 30MPa, press because external pressure has been offset in the part, and pressure energy power increased in sleeve pipe was anti-.

Embodiment 2: anti-uniform external intensity:

Series 1 is that the sleeve pipe inside and outside differential pressure is 0 o'clock anti-uniform external stress-strain relation of sleeve pipe among Fig. 5, sleeve pipe elastoplasticity intensity P _p' be 66MPa, when reaching this numerical value, external applied load (external pressure) begins to enter elastic-plastic phase, and its Changing Pattern no longer is a linear relationship, and its strain variation scope is from 0.2 millimeter to 2.5 millimeters variation, with the radial strain u of cased well cable diameter gauge device monitoring sleeve _r, can be finally inversed by the casing stress load p by formula of the present invention (3) _pThe increase of the anti-uniform external intensity of sleeve pipe is more and more slower, but numerical value is still bigger, and sleeve pipe critical external compressive resistance ability is still bigger, and the oil field cover decreases main type neither be this.Series the 2,3, the 4th, interior pressure are 10,20, the situation during 30MPa, increase sleeve pipe critical external compressive resistance ability with interior pressure and increase.Series the 5,6, the 7th, external pressure are 10,20, the situation during 30MPa, increase the anti-uniform external ability of sleeve pipe with external pressure and have reduced.

Embodiment 3: anti-non-homogeneous external pressure strength:

Fig. 6 series 1 is that the sleeve pipe inside and outside differential pressure is 0 o'clock anti-non-homogeneous external pressure stress strain stress relation of sleeve pipe, sleeve pipe elastoplasticity intensity is 5.6MPa, less than evenly the time 10%, when external applied load (non-homogeneous external pressure) begins to enter elastic-plastic phase when reaching this numerical value, its Changing Pattern no longer is a linear relationship, the anti-intensity of carrying descends rapidly, and its strain variation scope is from 0.3 millimeter to 15 millimeters variation, with the radial strain u of cased well cable diameter gauge device monitoring sleeve _r, can be finally inversed by the casing stress load p by formula of the present invention (3) _pIt is maximum that such cover decreases harm.Series the 2,3, the 4th, interior pressure are 10,20, the situation during 30MPa, increase the anti-non-homogeneous external pressure ability of sleeve pipe with interior pressure and have reduced.Series the 5,6, the 7th, external pressure are 10,20, the situation during 30MPa, because the external pressure increase has reduced sleeve pipe and carried non-uniform degree outward, the anti-non-homogeneous external pressure ability of sleeve pipe increases.So say exactly, it not is the mistake of water filling that cover decrease to increase, but changes when the structure on stratum, and for example: the slippage on stratum, faulting recurrence and mud stone creep etc. cause the non-homogeneous loading of sleeve pipe, occur cover easily and decrease; Oilfield injection water should be kept a close eye on and inject the water whereabouts, strengthens two monitorings such as profile logging, well bore and stratal configuration variation, and strictness avoids non-homogeneous loading to occur.Why sometimes this has just explained that water injection pressure is not too high and but has been easy to occur cover and decreases, and the damage problem do not occur overlapping and water injection pressure is very big sometimes.

Claims (2)

1, a kind of stress cover decreases Forecasting Methodology, and it is characterized in that: the last-period forecast method realizes by following step:

A, utilize the radial strain ur of cased well cable diameter gauge device monitoring sleeve;

B, casing stress load inversion method: do not considering quill under the situation of stress influence, sleeve pipe is regarded as the stressed problem of annulus under the planar condition, under polar coordinates (r, θ), casing stress satisfies following equation:

Stress boundary condition:

The radial strain of trying to achieve the generation of annulus elastic-plastic deformation by boundary condition is:

$u_r=\frac{(1-{\mathrm{\&mu;}}^2)P_p}{\mathrm{Er}}[-\frac{A}{(1-\mathrm{\&mu;})r_p}+\frac{2(1-2\mathrm{\&mu;})B{r}_p}{1-\mathrm{\&mu;}}-(\frac{2A_1{r}_p}{1-\mathrm{\&mu;}}-\frac{4\mathrm{\&mu;}{B}_1{r}_p^3}{1-\mathrm{\&mu;}}-\frac{2C_1}{(1-\mathrm{\&mu;})r_p^3}$

$-\frac{{4D}_1}{r_p}\left)\cos 2\mathrm{\&theta;}\right]+\frac{(1-{\mathrm{\&mu;}}^2)}{\mathrm{Er}}[-\frac{{\mathrm{\&delta;}}_1}{(1-\mathrm{\&mu;})r_p}+\frac{2(1-2\mathrm{\&mu;}){\mathrm{\&delta;}}_2{r}_p}{1-\mathrm{\&mu;}}]---\left(3\right)$

C, with the σ in the equation (1) _r, σ _θSubstitution Von Mises yield condition ${({\mathrm{\&sigma;}}_r-{\mathrm{\&sigma;}}_{\mathrm{\&theta;}})}^2+{({\mathrm{\&sigma;}}_{\mathrm{\&theta;}}-{\mathrm{\&sigma;}}_z)}^2+{({\mathrm{\&sigma;}}_z-{\mathrm{\&sigma;}}_r)}^2+6{\mathrm{\&tau;}}_{\mathrm{r\&theta;}}^2=2{\mathrm{\&sigma;}}_s^2,$ Utilize border, elasto-plastic range (elasto-plastic region) r=r _pPlace's stress is obtained elastoplasticity intensity continuously.Get τ in the equation (1) in the plastic zone _{R θ}=0, sleeve pipe elastoplasticity intensity is:

$P_p^{\&prime;}=\frac{-Q_{10}+\sqrt{Q_{10}^2-4Q_9{Q}_{11}}}{2Q_9}--\left(4\right)$

D, the radial strain value that monitoring among the step a is obtained are updated in the formula (3), are finally inversed by casing stress load, i.e. P in the formula _p

E, utilize formula (4) to calculate the ultimate strength P ' of sleeve pipe under the respective loads effect _p

F, the P that above-mentioned steps d, e are calculated _p, P ' _pCompare, judge that cover decreases the possibility that takes place;

2, a kind of stress cover decreases Forecasting Methodology, and it is characterized in that: the long-range forecasting method realizes by following step:

A, utilize dipole acoustic log instrument monitoring terrestrial stress;

B, utilize the formula (4) in the claim 1 to calculate the ultimate strength P ' of sleeve pipe under the respective loads effect _p

The ultimate strength P ' that c, the terrestrial stress that above-mentioned steps a monitoring is obtained and step b calculate _pCompare, judge that cover decreases the possibility that takes place.

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