CN1916359B - Method for realizing repeated fracturing to create new seam - Google Patents

Abstract

The invention relates to a method for realizing repeated fracturing and new crack creation in a low-permeability oilfield, which describes a primary fracturing artificial crack by an oval crack, combines a tensile failure criterion and a shear failure criterion, provides a theoretical criterion for repeated fracturing and new crack creation, and provides characteristics and conditions which are required by the critical bottom hole extension pressure and the target stratum crustal stress field and rock mechanical parameters and are required by the repeated fracturing and new crack creation according to the theoretical criterion. The characteristics and conditions of the critical bottom hole extension pressure required by new seam construction, the ground stress field of the target stratum and the rock mechanical parameters are realized. No matter what fracturing technology is adopted, new joints can be manufactured as long as construction conditions can meet the theoretical criterion, and meanwhile, whether new joints are generated in the field repeated fracturing process can be judged. The method can guide the repeated fracturing transformation of a low-permeability oil field, dig the residual oil to a greater extent and improve the recovery ratio.

Description

A kind of refracturing of realizing is made the method for new seam

Technical field

The present invention relates to oil-gas reservoir fracturing volume increase modification measures, particularly propose a kind of low permeability oil field refracturing of realizing and made the theoretical method of new seam, this theoretical method can efficiently instruct the refracturing transformation of low permeability oil field, and the remaining oil of taping the latent power to a greater degree improves recovery ratio.

Background technology

Refracturing is the important channel of realizing the volume increase of low permeability oil field stable yields, make new seam if can realize refracturing, just can in oil-gas Layer, open new gas stream passage, link up the oil-gas Layer that first fracturing artificial slit is not employed more broadly, increase oil and gas production significantly, further improve the development effectiveness of oil-gas reservoir.Yet refracturing is made new seam mechanism and is still lacked system, deep research.The analysis that refracturing is made new seam at present both at home and abroad nearly all is based upon geostatic stress and turns on the basis.And, also just rest on theoretical research and numerical simulation stage at present about the research that geostatic stress turns to, and can not get the field trial support, therefore there is not feasible, practical refracturing to make new seam method and technology.

Summary of the invention

The objective of the invention is provides a kind of refracturing of realizing to make the method for new seam for low permeability oil field fracturing transformation, utilize this method can increase oil and gas production significantly, further improve the development effectiveness of oil-gas reservoir, both can predict in advance and make the condition that new seam institute should satisfy, and can be used for again judging that on-the-spot refracturing was constructed whether has produced new seam.

Technical scheme of the present invention is: design a kind of refracturing of realizing and make the method for new seam, its method is: it describes first fracturing artificial slit with the ellipse seam, in conjunction with opening property failure criterion and shear failure criterion, provided refracturing at home and abroad first and made the theoretical criterion of new seam, according to theoretical criterion provided realize refracturing make new seam the critical shaft bottom extending pressure that should satisfy and target zone stress field and rock mechanics the parameter feature and the condition that should possess.

Described realization refracturing make new seam the critical shaft bottom extending pressure that should satisfy and target zone stress field and the rock mechanics parameter feature that should possess be: the operation pressure condition satisfies the p in the theoretical criterion _Inj〉=σ _H2+ T ₀, ${\mathrm{<figure-callout\; id="0"\; label="T"\; filenames="S05196443620051216E000011.png"\; state="\{\{state\}\}">T</figure-callout>}}_0>\frac{({\mathrm{\&sigma;}}_{h1}-{\mathrm{\&sigma;}}_{h2})}{4}$ Or $p_{\mathrm{inj}}\&GreaterEqual;\frac{1}{2}[({\mathrm{\&sigma;}}_{h1}+{\mathrm{\&sigma;}}_{h2})-{({\mathrm{\&sigma;}}_{h1}-{\mathrm{\&sigma;}}_{h2})}^2/{8T}_0],$ ${\mathrm{<figure-callout\; id="0"\; label="T"\; filenames="S05196443620051216E000011.png"\; state="\{\{state\}\}">T</figure-callout>}}_0<\frac{({\mathrm{\&sigma;}}_{h1}-{\mathrm{\&sigma;}}_{h2})}{4},$ Be that decidable refracturing process has produced new draw crack, wherein p _InjBe the shaft bottom extending pressure, σ _H1Be maximum horizontal principal stress, σ _H2Be minimum level main stress bar, T ₀Be tensile strength; In like manner, if satisfy theoretical criterion $p_{\mathrm{inj}}\&GreaterEqual;\frac{{(1+\sin \frac{1}{2}\mathrm{\&theta;}-m+m\sin \frac{1}{2}\mathrm{\&theta;})(L_f/2r)}^{\frac{1}{2}}\cos \frac{1}{2}{\mathrm{\&theta;\&sigma;}}_{h2}-{\mathrm{\&sigma;}}_C}{1-m+(1+\sin \frac{1}{2}\mathrm{\&theta;}-m+m\sin \frac{1}{2}\mathrm{\&theta;}){(L_f/2r)}^{\frac{1}{2}}\cos \frac{1}{2}\mathrm{\&theta;}}$ And p _Inj＜σ _H2, then can judge to have produced new shear crack, wherein L _fBe the fracture half-length, (r θ) is the plane polar coordinates of certain the some P crack tip near, σ _CBe rock uniaxiality strength, m=tg ²α, α are new shear fracture face normal direction and σ _H1The angle of direction, α=45 °+φ/2, φ is an internal friction angle of rock.

Described oval seam is meant the oval crack of prolate, and both oval semi-major axis is greater than oval semi-minor axis, and it is used for describing first fracturing artificial slit, its fracture half-length both be oval semi-major axis at 30-100m, the crack half-breadth both had been that oval semi-minor axis is at 1-3mm.

Characteristics of the present invention are:

(1) analyzed refracturing process matrix rock at home and abroad first the condition of destruction has taken place, thereby provided the theoretical criterion of making new seam, promptly realize making the required critical shaft bottom extending pressure of new seam and target zone stress field and rock mechanics parameter the feature and the condition that should possess.

(2) this theory criterion form is easily understood.No matter take which kind of fracturing technology,, can realize making new seam as long as execution conditions can satisfy this theoretical criterion.

(3) this theory criterion can be used for judging whether on-the-spot refracturing process has produced new seam simultaneously.

(4) new crack is divided into two kinds of draw crack and shear cracks, corresponds respectively to the two kinds of basic destruction-tensile failures and the shear failure of rock.Two kinds of fracture orientations all are different from first fracturing artificial slit, and critical shaft bottom extending pressure is the function of stress field and rock mechanics parameter.

The present invention has analyzed all kinds that the refracturing crack turns on the abundant domestic and international pertinent literature of investigation basis, propose to make new seam mechanism and only limit to stress field mentioned above absolutely not and turn to.Refracturing is made rock the breaking once more at the plane of weakness place that have its source in of new seam, rather than so-called geostatic stress counter-rotating, and, analyzed refracturing process matrix rock first the condition of destruction has taken place, thereby provided the theoretical criterion of making new seam in conjunction with rock failure mechanism of rock criterion.The crack turns to and controlled by fracture pressure, even if stress field does not change, the crack also may occur and turn to.

For the refracturing construction, according to above theoretical criterion, observe the operation pressure curve, can judge whether to have produced new crack.In like manner, before refracturing construction,, can predict in advance and make the condition that new seam institute should satisfy according to above theoretical criterion, in case reasonable well and story selecting, and take suitable fracturing technology, new seam is made in realization.Therefore this method can instruct the refracturing transformation of low permeability oil field preferably, and the remaining oil of taping the latent power to a greater degree improves recovery ratio, has very strong practical value.

Description of drawings

Fig. 1 is near some P schematic diagram elongated oval (flat ellipse) crack tip.

Fig. 2 is More-coulomb failure criterion schematic diagram.

Fig. 3 is the stifled temporarily sand fallout pressing crack construction pressure vs. time plot of embodiment 1 well.

Fig. 4 is the stifled temporarily sand fallout pressing crack construction pressure vs. time plots of embodiment 2 wells.

Fig. 5 is embodiment 2 well microseism Crack Monitoring figure.

The specific embodiment:

With the ellipse seam first fracturing artificial slit is described, in conjunction with opening property failure criterion and shear failure criterion, analyze the condition of the new rock failure mechanism of rock of appearance in the low permeability reservoir refracturing process at home and abroad first, thereby provided the theoretical criterion that refracturing is made new seam.Promptly provided and realized making feature and the condition that required critical shaft bottom extending pressure value of new seam and target zone stress field and rock mechanics parameter should possess.New herein crack is divided into two kinds of shear crack and draw cracks, corresponds respectively to the shear failure of rock and opens property destruction.Two kinds of fracture orientations all are different from first fracturing artificial slit, and critical pressure is the function of stress field and rock mechanics parameter.Utilize this theoretical method, both can predict in advance and make the condition that new seam institute should satisfy, rationally carry out the refracturing well and story selecting, and take suitable fracturing technology, new seam is made in realization; Can be used for again judging whether on-the-spot refracturing construction has produced new seam.Therefore this method can efficiently instruct the refracturing transformation of low permeability oil field, and the remaining oil of taping the latent power to a greater degree improves recovery ratio.

Temporarily stifled sand fallout fracturing technology is in long celebrating oil field successful Application and popularization, and the Ansai Oilfield instance analysis shows that if the temporarily stifled value of boosting satisfies above theoretical criterion can produce new draw crack, this has further confirmed the on-the-spot practicality of this theoretical method.

This method simple possible is transformed applicable to all hyposmosis, ultra-low permeability oil layer refracturing.When implementing refracturing,,, can realize making new seam as long as this technology can be created the execution conditions that satisfy this theory criterion no matter take which kind of fracturing technology or measure.

1 refracturing is made the theoretical derivation of new seam

After the first pressure break, suppose that artificial major fracture forms, and along major principal stress orientation, far field.Suppose that seam is high constant, consider 2D crack, plane situation, it is oval that the crack is approximately, and this and areal models such as GDK, PKN are supposed similar.The fracture half-length is L _f, Breadth Maximum is b.

When refracturing, there is fracturing fluid to enter again, consider near the stress state of crack wall this moment, carry out rupture Analysis.Suppose that current far field maximum horizontal principal stress and minimum level main stress bar are respectively σ _H1And σ _H2, they and x axle clamp angle are respectively

And β.If current main geostatic stress orientation does not change than principal virgin stress, then $\mathrm{\&beta;}=\frac{\mathrm{\&pi;}}{2}.$ If variation (such as the variation that causes because of first crack unlatching or water filling or oil gas extraction) has taken place current stress field, and known, then β is also known.

In the practice of low permeability oil field pressure break, man-made fracture half long desirable 30-100m, and the desirable 1-3mm of crack half-breadth, so b/L _fVery little.And for elliptical coordinate system, if ξ=ζ is arranged ₀, be oval then corresponding to the response curve in x, the y plane

$\frac{x^2}{c^2{\cosh }^2{\mathrm{\&xi;}}_0}+\frac{y^2}{c^2{\sinh }^2{\mathrm{\&xi;}}_0}=1$

Its semiaxis is

a＝ccoshζ ₀，b＝csinhζ ₀

Tanh ζ is then arranged ₀=b/a.According to above, b/L is minimum, so approximate have a ζ ₀=0, promptly first fracturing artificial slit is elongated oval (flat ellipse) crack, becomes the otch from x=-c to x=c, and c=L _f

The stress state of point P can adopt elliptical coordinate system to analyze (see figure 1) near the flat oval crack tip.

(1) crack wall extension fracture

According to the Florence Griffith classical theory, think that extension fracture (tensile fracture) is to be concentrated by the stress at small griffith crack tip to cause, when near the maximum tension stress the crack tip reaches the characteristic value of material, breaks apart the life of starting.

The shear stress of flat oval fracture faces is:

σ _t＝p+{(σ _h1+σ _h2-2p)sinh2ζ ₀+(σ _h1-σ _h2)[exp(2ζ ₀)×cos2(β-η)

-cos2β]}/{cosh2ζ ₀-cos2β}

Obviously this stress is relevant with β, and visible crack wall stress field and current major principal stress orientation are closely related.

The artificial fracturing of mentioning in the fracturing classical theory all is meant extension fracture, analyzes extension fracture and uses the maximum tension stress criterion usually.

Still adopt the maximum tension stress criterion herein, promptly maximum tension stress (surperficial shear stress) when reaching Tensile Strength of Rock, extension fracture occurs.

The failure criterion that analysis provides is:

(σ _h1-σ _h2) ²-8T ₀(σ _h1+σ _h2-2p _inj)＝0，p _inj＜(σ _h1+3σ _h2)/4；

σ _h2-p _inj+T ₀＝0，p _inj＜(σ _h1+3σ _h2)/4

Promptly

$p_{\mathrm{inj}}=\frac{1}{2}[({\mathrm{\&sigma;}}_{h1}+{\mathrm{\&sigma;}}_{h2})-{({\mathrm{\&sigma;}}_{h1}-{\mathrm{\&sigma;}}_{h2})}^2/{8T}_0],$ ${\mathrm{<figure-callout\; id="0"\; label="T"\; filenames="S05196443620051216E000011.png"\; state="\{\{state\}\}">T</figure-callout>}}_0<\frac{({\mathrm{\&sigma;}}_{h1}-{\mathrm{\&sigma;}}_{h2})}{4};$

p _inj＝σ _h2+T ₀， ${\mathrm{<figure-callout\; id="0"\; label="T"\; filenames="S05196443620051216E000011.png"\; state="\{\{state\}\}">T</figure-callout>}}_0>\frac{({\mathrm{\&sigma;}}_{h1}-{\mathrm{\&sigma;}}_{h2})}{4}$

New tensile fracture orientation (with the angle of x axle) is

If as seen $\mathrm{\&beta;}=\frac{\mathrm{\&pi;}}{2},$ Then new crack will be perpendicular to first fracture orientation.

(2) near the shear fracture the crack tip

Stress state near the some P crack tip as shown in Figure 1, can obtain

${\mathrm{\&sigma;}}_r=2({\mathrm{\&sigma;}}_{h2}-p)\cos \frac{1}{2}\mathrm{\&theta;}(1+{\sin }^2\frac{1}{2}\mathrm{\&theta;}){\sin }^2\mathrm{\&beta;}{(8r/L_f)}^{-1/2}+2({\mathrm{\&sigma;}}_{h1}-p)\cos \frac{1}{2}\mathrm{\&theta;}(1+{\sin }^2\frac{1}{2}\mathrm{\&theta;})$

${\cos }^2\mathrm{\&beta;}{(8r/L_f)}^{-1/2}+({\mathrm{\&sigma;}}_{h2}-{\mathrm{\&sigma;}}_{h1})\sin \frac{1}{2}\mathrm{\&theta;}(1-{3\sin }^2\frac{1}{2}\mathrm{\&theta;})\sin 2\mathrm{\&beta;}{(8r/L_f)}^{-1/2}$

${\mathrm{\&sigma;}}_{\mathrm{\&theta;}}=2({\mathrm{\&sigma;}}_{h2}-p){\cos }^3\frac{1}{2}\mathrm{\&theta;}{\sin }^2\mathrm{\&beta;}{(8r/L_f)}^{-1/2}+2({\mathrm{\&sigma;}}_{h1}-p){\cos }^3\frac{1}{2}\mathrm{\&theta;}{\cos }^2\mathrm{\&beta;}{(8r/L_f)}^{-1/2}$

$-3({\mathrm{\&sigma;}}_{h2}-{\mathrm{\&sigma;}}_{h1})\sin \frac{1}{2}\mathrm{\&theta;}{\cos }^2\frac{1}{2}\mathrm{\&theta;}\sin 2\mathrm{\&beta;}{(8r/L_f)}^{-1/2}$

${\mathrm{\&tau;}}_{\mathrm{r\&theta;}}=2({\mathrm{\&sigma;}}_{h2}-p){\cos }^2\frac{1}{2}\mathrm{\&theta;}\sin \frac{1}{2}\mathrm{\&theta;}{\sin }^2\mathrm{\&beta;}{(8r/L_f)}^{-1/2}+2({\mathrm{\&sigma;}}_{h1}-p){\cos }^2\frac{1}{2}\mathrm{\&theta;}\sin \frac{1}{2}\mathrm{\&theta;}$

${\cos }^2\mathrm{\&beta;}{(8r/L_f)}^{-1/2}+({\mathrm{\&sigma;}}_{h2}-{\mathrm{\&sigma;}}_{h1})\cos \frac{1}{2}\mathrm{\&theta;}({3\cos }^2\frac{1}{2}\mathrm{\&theta;}-2)\sin 2\mathrm{\&beta;}{(8r/L_f)}^{-1/2}$

If main stress bar orientation, far field does not change, then $\mathrm{\&beta;}=\frac{\mathrm{\&pi;}}{2},$ The above formula of substitution can be found in each formula and σ _H1Relevant item all becomes 0, is therefore only contained σ _H2Expression formula:

${\mathrm{\&sigma;}}_r=2({\mathrm{\&sigma;}}_{h2}-p)\cos \frac{1}{2}\mathrm{\&theta;}(1+{\sin }^2\frac{1}{2}\mathrm{\&theta;}){(8r/L_f)}^{-1/2}$

${\mathrm{\&sigma;}}_{\mathrm{\&theta;}}=2({\mathrm{\&sigma;}}_{h2}-p){\cos }^3\frac{1}{2}\mathrm{\&theta;}{(8r/L_f)}^{-1/2}$

${\mathrm{\&tau;}}_{\mathrm{r\&theta;}}=2({\mathrm{\&sigma;}}_{h2}-p){\cos }^2\frac{1}{2}\mathrm{\&theta;}\sin \frac{1}{2}\mathrm{\&theta;}{(8r/L_f)}^{-1/2}$

Utilize the main stress bar formula:

${\mathrm{\&sigma;}}_1=\frac{1}{2}({\mathrm{\&sigma;}}_{\mathrm{xx}}+{\mathrm{\&sigma;}}_{\mathrm{yy}})+{[{\mathrm{\&tau;}}_{\mathrm{xy}}^2+\frac{1}{4}{({\mathrm{\&sigma;}}_{\mathrm{xx}}-{\mathrm{\&sigma;}}_{\mathrm{yy}})}^2]}^{\frac{1}{2}}$

${\mathrm{\&sigma;}}_2=\frac{1}{2}({\mathrm{\&sigma;}}_{\mathrm{xx}}+{\mathrm{\&sigma;}}_{\mathrm{yy}})-{[{\mathrm{\&tau;}}_{\mathrm{xy}}^2+\frac{1}{4}{({\mathrm{\&sigma;}}_{\mathrm{xx}}-{\mathrm{\&sigma;}}_{\mathrm{yy}})}^2]}^{\frac{1}{2}}$

(r, main stress bar θ) is certain point near obtaining crack tip

$({\mathrm{\&sigma;}}_{h2}-p)\cos \frac{1}{2}\mathrm{\&theta;}(1\&PlusMinus;\sin \frac{1}{2}\mathrm{\&theta;}){(L_f/2r)}^{1/2}$

The orientation of this main stress bar is (with σ _rAngle) θ ' is:

${\mathrm{tg}2\mathrm{\&theta;}}^{\&prime;}=\frac{{2\mathrm{\&tau;}}_{\mathrm{xy}}}{{\mathrm{\&sigma;}}_{\mathrm{xx}}-{\mathrm{\&sigma;}}_{\mathrm{yy}}}=\frac{{2\mathrm{\&tau;}}_{\mathrm{r\&theta;}}}{{\mathrm{\&sigma;}}_r-{\mathrm{\&sigma;}}_{\mathrm{\&theta;}}}=\frac{\sin \mathrm{\&theta;}}{1-\cos \mathrm{\&theta;}}$

So ${\mathrm{\&theta;}}^{\&prime;}=\frac{\mathrm{\&pi;}}{4}-\frac{\mathrm{\&theta;}}{4}$ Perhaps

As p＜σ _H2The time, main stress bar is a compressive stress state, considers shear failure.

Briefly introduce the shear failure criterion below.

The Mohr-Coulomb criterion

The most frequently used fracture criteria of shear failure is the Mohr-Coulomb criterion.On any cross section of medium infinitesimal, its shear stress τ _nSize all can not surpass a certain threshold, as | τ _n| when reaching this threshold, material will produce shearing slip.

Fig. 2 is More-coulomb (Mohr-Coulomb) failure criterion schematic diagram, and its two straight lines are the Moht-Coulomb intensity curve, and the straight line medial region is the place of safety, and the straight line exterior lateral area is the failure zone.(σ, τ) with straight line when tangent, shear failure will take place in rock when the circle of stress of rock.

|τ _n|≥C ₀+σ _n′tgφ

$\mathrm{\&sigma;}=\frac{1}{2}({\mathrm{\&sigma;}}_1+{\mathrm{\&sigma;}}_3)+\frac{1}{2}({\mathrm{\&sigma;}}_1-{\mathrm{\&sigma;}}_3)\cos 2\mathrm{\&alpha;}$

$\mathrm{\&tau;}=-\frac{1}{2}({\mathrm{\&sigma;}}_1-{\mathrm{\&sigma;}}_3)\sin 2\mathrm{\&alpha;}$

α＝45°+φ/2

τ _nAnd σ _n' being respectively shear stress and normal stress (normal stress) on the shear fracture face, α is shear fracture face normal direction and major principal stress σ ₁The angle of direction, c ₀Be intrinsic shear strength (cohesion or cohesive strength) that tg φ is a coefficient of internal friction, φ is an angle of internal friction.Shear failure is that the typical case under the compressive stress is broken, and its feature is the shear displacemant along the plane of fracture.

The Mohr-Coulomb criterion also can be expressed with the relational expression between the main stress bar:

σ ₁-p＝m(σ ₃-p)+σ _C

M=tg wherein ²α, σ _C=2c ₀Tg α is uniaxial compressive strength.

Counter pushing away draws

$p_{\mathrm{inj}}=\frac{{\mathrm{\&sigma;}}_1-{\mathrm{m\&sigma;}}_3-{\mathrm{\&sigma;}}_C}{1-m}$

With above main stress bar substitution shear fracture criterion $p_{\mathrm{inj}}=\frac{{\mathrm{\&sigma;}}_1-{\mathrm{m\&sigma;}}_3-{\mathrm{\&sigma;}}_C}{1-m},$ Obtain critical injection pressure (pore pressure):

$p_{\mathrm{inj}}=\frac{{(1+\sin \frac{1}{2}\mathrm{\&theta;}-m+m\sin \frac{1}{2}\mathrm{\&theta;})(L_f/2r)}^{\frac{1}{2}}\cos \frac{1}{2}{\mathrm{\&theta;\&sigma;}}_{h2}-{\mathrm{\&sigma;}}_C}{1-m+(1+\sin \frac{1}{2}\mathrm{\&theta;}-m+m\sin \frac{1}{2}\mathrm{\&theta;}){(L_f/2r)}^{\frac{1}{2}}\cos \frac{1}{2}\mathrm{\&theta;}}$

And answer p _Inj＜σ _H2

M=tg wherein ²α, σ _C=2C ₀Tg α,

The concrete analysis process whether new shear fracture forms is as follows:

At first judge ${\mathrm{\&sigma;}}_{h2}<\frac{{\mathrm{\&sigma;}}_C}{m-1}$ Whether set up,

$\mathrm{\&Delta;}=(1+\sin \frac{1}{2}\mathrm{\&theta;}-m+m\sin \frac{1}{2}\mathrm{\&theta;}){(L_f/2r)}^{\frac{1}{2}}\cos \frac{1}{2}\mathrm{\&theta;}$

M=tg wherein ²α, σ _C=2c ₀Tg α,

(1) if set up, then investigates the possibility of 1-m+ Δ＞0, if possible, and have ${\mathrm{\&sigma;}}_{h2}>\frac{{\mathrm{\&sigma;}}_C}{\mathrm{\&Delta;}},$ Then shear crack may appear; If impossible, then there is not the seam of shearing.

(2) if be false, then investigate the possibility of 1-m+ Δ＜0, if possible, and satisfy ${\mathrm{\&sigma;}}_{h2}<\frac{{\mathrm{\&sigma;}}_C}{\mathrm{\&Delta;}}$ Then shear crack may appear; If impossible, then there is not the seam of shearing.

If produced new shear crack, then shear fracture face normal direction and current major principal stress orientation θ ' angle should be

Investigate point (r, σ θ) so shear seam with this _rThe angular separation is: Perhaps

The alternatively is because the main stress bar orientation ${\mathrm{\&theta;}}^{\&prime;}=\frac{\mathrm{\&pi;}}{4}-\frac{\mathrm{\&theta;}}{4}$ Perhaps

Can only get one of them.

As seen roughly 30 °～75 ° scopes, promptly new shear crack has also taken place to turn to new plane of fracture normal direction and x axle (being first man-made fracture orientation) angle.

2 The field for example

This patent provides a kind of judgement and realization refracturing to make the theoretical method of new seam.This method simple possible is transformed applicable to all hyposmosis, ultra-low permeability oil layer refracturing.When implementing refracturing,,, can realize making new seam as long as this technology can be created the execution conditions that satisfy this theory criterion no matter take which kind of fracturing technology or measure.

Temporarily stifled at present sand fallout fracturing technology has been brought into play important effect in the volume increase of long celebrating low permeability oil field refracturing is transformed, be widely used, its specific implementation process can be with reference to many open source literatures, such as 2002 " drilling technology " 25 (6): 39～41: " the long 6 oil reservoir end sand fallout crushing tests of Ansai Oilfield " etc.Its core thinking is to utilize sand fallout to control first fracturing artificial slit to continue expansion and extension, in first fracturing artificial slit, adds diverting agent and forms shielding, thus the formation hyperbaric environment.Instance analysis shows, if the temporarily stifled value of boosting satisfies above theoretical criterion, then can produce new draw crack.Below be that the stifled temporarily sand fallout pressure break of the two mouthfuls of wells in Ansai Oilfield Wang Yao district is made new seam analysis.

Wang14-15Jing analyzes

Middle part, this well location Yu Wangyao district is 1 mouthful of test well of middle part change liquid flow path direction.The oval semi-major axis of first fracturing artificial slit prolate is 82.4m, and half-breadth both oval semi-minor axis in crack is 1.6mm.

This well was gone into operation in November, 89, day at initial stage produce oil 2.5t, and take effect in June, 91, and a day produce oil rises to 4.0t.In March, 93 water breakthrough, in in February, 99 because of the water logging closing well, accumulative total produce oil 6278t, improve the technical thought of recovery ratio for Westbound in exploring, in metaideophone Wang13-15Jing on May 26th, 2002, carry out and change the test of liquid flow path direction, and 3 mouthfuls of water are on every side flooded oil well reproduce, other two mouthfuls of wells have been seen oil at present, and average day production fluid is at 3.45m ³, and Wang14-15Jing reproduce on July 16th, 2002 after fluid not always.Think that oil reservoir has obstruction, should carry out refracturing.This well carries out stifled temporarily sand fallout pressure break September 29 in 20002, and construction curve is seen Fig. 3, and the oily 3.24t that on average increases day by day, obvious effect of increasing production (seeing Table 1) are gone into operation in blowing after the pressure break.

Utilize the geostatic stress and the rock mechanics parameter data of this well offset well laboratory core test determination, know maximum horizontal principal stress σ _H1With minimum level main stress bar σ _H2Be respectively 25.74,18.44MPa, tensile strength T ₀Be 7.67MPa, then $\frac{({\mathrm{\&sigma;}}_{h1}-{\mathrm{\&sigma;}}_{h2})}{4}=1.83\mathrm{MPa},$ Promptly ${\mathrm{<figure-callout\; id="0"\; label="T"\; filenames="S05196443620051216E000011.png"\; state="\{\{state\}\}">T</figure-callout>}}_0>\frac{({\mathrm{\&sigma;}}_{h1}-{\mathrm{\&sigma;}}_{h2})}{4}.$ Observe refracturing operation pressure curve, the previous work pressure stability is about 15MPa, can judge that first fracturing artificial slit restarts pressure and be about 15MPa, and stifled temporarily boosting to about 23MPa, so the temporarily stifled value of boosting is roughly 8MPa, as seen the temporarily stifled value of boosting is slightly larger than the rock tensile strength, and promptly the operation pressure condition satisfies the p in the theoretical criterion _Inj〉=σ _H2+ T ₀, ${\mathrm{<figure-callout\; id="0"\; label="T"\; filenames="S05196443620051216E000011.png"\; state="\{\{state\}\}">T</figure-callout>}}_0>\frac{({\mathrm{\&sigma;}}_{h1}-{\mathrm{\&sigma;}}_{h2})}{4},$ So decidable refracturing process has produced new draw crack, the latter half of development and change trend of this and operation pressure curve is very identical.And this well blowing and obvious effect of increasing production occur and has also proved effectively and may produce new crack after the pressure break.

Table 1W14-15 well refracturing construction parameter and effect analysis statistics

Pound sign	Layer position	Core intersection (m)	Perforation thickness (m)	Permeability (10 -3μm 2)		Last time pressure break added sand amount (m 3)	Sand fallout pressing crack construction parameter
											Add sand amount (m 3)	Discharge capacity (m 3/min)	Diverting agent amount (kg)	Stifled temporarily boost (MPa)
							W14-15	Long 6	12.2	11					2.427		17	30	1.4-1.6	380	8
Before the measure			1-12 month is average after the measure								Effective fate (my god)		Oil (t) on average increases day by day
							Day production fluid (m 3)	Day produce oil (t)	Moisture (%)	Day production fluid (m 3)					Day produce oil (t)	Moisture (%)
0	0	0	6.26		3.24	37.97											37		3.24

Wang20-017Jing analyzes

Wang20-017Jing adopts temporarily stifled sand fallout fracturing technology construction.The operation pressure curve is seen Fig. 4, and the microseism Crack Monitoring the results are shown in Figure 5.The major fracture orientation is an east northeast to 64.1 degree, and the both oval semi-major axis of fracture half-length is approximately 65 meters, and half-breadth both oval semi-minor axis in crack is 2.0mm.Have at about 60 meters of distance east major fracture one with approximately perpendicular crack of major fracture, about 30 meters of length.

As can be seen from Figure 4, first fracturing artificial slit is restarted pressure and is about 12MPa, then blocks up temporarily and boosts to 15MPa, so the temporarily stifled value of boosting is about 3.0MPa.

Wang Yao district maximum horizontal principal stress azimuth averaging is that east northeast is to 67 °, so the major fracture orientation of refracturing (east northeast is to 64.1 degree) are identical with first fracturing fracture orientation basically, be that refracturing the crack does not take place turns to, stress field turns in other words.

According to the indoor rock mechanics parametric measurement result that this well target zone sandstone is cored, the rock tensile strength is 2.9MPa.The average maximum horizontal principal stress σ in Wang Yao district _H1Be 24MPa, minimum level main stress bar σ _H2Be 19MPa, then ${\mathrm{<figure-callout\; id="0"\; label="T"\; filenames="S05196443620051216E000011.png"\; state="\{\{state\}\}">T</figure-callout>}}_0>\frac{({\mathrm{\&sigma;}}_{h1}-{\mathrm{\&sigma;}}_{h2})}{4};$ And the temporarily stifled value of boosting is very approaching and be slightly larger than tensile strength.As seen this well construction condition satisfies p _Inj〉=σ _H2+ T ₀, ${\mathrm{<figure-callout\; id="0"\; label="T"\; filenames="S05196443620051216E000011.png"\; state="\{\{state\}\}">T</figure-callout>}}_0>\frac{({\mathrm{\&sigma;}}_{h1}-{\mathrm{\&sigma;}}_{h2})}{4},$ Be that refracturing will produce new draw crack.According to above analyzing, this well layer stress field does not turn to, promptly $\mathrm{\&beta;}=\frac{\mathrm{\&pi;}}{2},$ So new draw crack should be perpendicular to artificial major fracture.As seen theory analysis conclusion and on-the-spot Crack Monitoring result are in full accord.

Adopt temporarily stifled its fracture half-length of sand fallout fracturing technology construction to have at 35m at other well, the crack half-breadth has at 1.2 meters.Also have the fracture half-length to have at 95m, the crack half-breadth has at 3 meters.Its theory analysis conclusion and on-the-spot Crack Monitoring result are also in full accord.

More than, proved this theoretical method feasibility of application facet at the scene by the stifled temporarily sand fallout fracturing technology instance analysis of Ansai Oilfield.Implement temporarily stifled sand fallout fracturing technology, can create the execution conditions that satisfy this theory criterion, so produced new draw crack.If can take other suitable fracturing technologies certainly, make critical bottom pressure satisfy theoretical criterion, then equally also can realize making new seam.Temporarily stifled at present sand fallout fracturing technology has been brought into play important effect in the volume increase of long celebrating low permeability oil field refracturing is transformed, be widely used.It utilizes sand fallout to control first fracturing artificial slit continuation expansion and extension, adds diverting agent formation shielding in first fracturing artificial slit, thus the formation hyperbaric environment.Instance analysis shows, if the temporarily stifled value of boosting is made the theoretical criterion of new seam more than satisfying, then can produce new draw crack.

Make new seam analysis for refracturing, no matter be to predict in advance or The field that this method all is practicable, so it can effectively instruct the refracturing transformation of low permeability oil field, the remaining oil of taping the latent power to a greater degree, raising recovery ratio.

Claims (1)

1. realize that refracturing makes the method for new seam for one kind, its method is: it describes first fracturing artificial slit with the ellipse seam, in conjunction with opening property failure criterion and shear failure criterion, provided refracturing and made the theoretical criterion of new seam, according to theoretical criterion provided realize refracturing make new seam the critical shaft bottom extending pressure that should satisfy and target zone stress field and rock mechanics parameter feature and the condition that should possess;

Realize refracturing make new seam the critical shaft bottom extending pressure that should satisfy and target zone stress field and the rock mechanics parameter feature that should possess be: the operation pressure condition satisfies the p in the theoretical criterion _Inj≤ σ _H2+ T ₀,

Or

Be that decidable refracturing process has produced new draw crack, wherein p _InjBe the shaft bottom extending pressure, σ _H1Be maximum horizontal principal stress, σ _H2Be minimum level main stress bar, T ₀Be tensile strength; If satisfy theoretical criterion

And p _Inj＜σ _H2, then can judge to have produced new shear crack, wherein L _fBe the fracture half-length, (r θ) is the plane polar coordinates of certain the some P crack tip near, σ _CBe rock uniaxiality strength, m=tg ²α, α are new shear fracture face normal direction and σ _H1The angle of direction, α=45 °+φ/2, φ is an internal friction angle of rock;

Oval seam is meant the oval crack of prolate, and promptly oval semi-major axis is greater than oval semi-minor axis, and it is used for describing first fracturing artificial slit, and its fracture half-length is oval semi-major axis at 30-100m, and the crack half-breadth is oval semi-minor axis at 1-3mm.

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