CN108104804A - A kind of hard brittle shale Fracturing Pressure Prediction method - Google Patents
A kind of hard brittle shale Fracturing Pressure Prediction method Download PDFInfo
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- 238000000034 method Methods 0.000 title claims abstract description 17
- 239000011435 rock Substances 0.000 claims abstract description 54
- 230000015572 biosynthetic process Effects 0.000 claims abstract description 19
- 241001269238 Data Species 0.000 claims abstract description 4
- 230000015556 catabolic process Effects 0.000 claims abstract description 4
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 19
- 230000000694 effects Effects 0.000 claims description 17
- 238000005553 drilling Methods 0.000 claims description 11
- 239000007788 liquid Substances 0.000 claims description 10
- 230000006835 compression Effects 0.000 claims description 9
- 238000007906 compression Methods 0.000 claims description 9
- 239000012528 membrane Substances 0.000 claims description 7
- 238000004364 calculation method Methods 0.000 claims description 5
- 239000011148 porous material Substances 0.000 claims description 5
- 238000012669 compression test Methods 0.000 claims description 4
- 239000012153 distilled water Substances 0.000 claims description 3
- 238000002474 experimental method Methods 0.000 claims description 3
- 238000007654 immersion Methods 0.000 claims description 3
- 238000001764 infiltration Methods 0.000 claims description 3
- 230000008595 infiltration Effects 0.000 claims description 3
- 239000004744 fabric Substances 0.000 claims 1
- 238000009826 distribution Methods 0.000 abstract description 3
- 238000010276 construction Methods 0.000 abstract description 2
- 239000012530 fluid Substances 0.000 description 5
- 230000036571 hydration Effects 0.000 description 3
- 238000006703 hydration reaction Methods 0.000 description 3
- 238000009828 non-uniform distribution Methods 0.000 description 3
- 235000015076 Shorea robusta Nutrition 0.000 description 1
- 244000166071 Shorea robusta Species 0.000 description 1
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- 230000009286 beneficial effect Effects 0.000 description 1
- 239000003245 coal Substances 0.000 description 1
- 238000000205 computational method Methods 0.000 description 1
- 239000012141 concentrate Substances 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000005065 mining Methods 0.000 description 1
- 238000002791 soaking Methods 0.000 description 1
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- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B49/00—Testing the nature of borehole walls; Formation testing; Methods or apparatus for obtaining samples of soil or well fluids, specially adapted to earth drilling or wells
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- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
- E21B43/25—Methods for stimulating production
- E21B43/26—Methods for stimulating production by forming crevices or fractures
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Abstract
A kind of hard brittle shale Fracturing Pressure Prediction method, it first passes through indoor aquation triaxial tests and obtains the rock parameter of hard brittle shale, the detecting earth stress data for obtaining mud shale stratum are tested by live formation breakdown again, then other routine datas needed for calculating are collected, plastoelasticity and rock mechanics theory are based on again, calculate the stress distribution for the vertical well borehole wall surrounding formation for considering seepage flow；Then the effective tangential stress considered under the action of aquation is calculated；Finally according to maximum tensional stress criterion, the fracture pressure model on hard brittle shale stratum is obtained, the present invention can more effectively, more accurately predict the fracture pressure of mud shale stratum, so as to provide high-precision basic data for pressing crack construction design.
Description
Technical field
The present invention relates to oil exploration formation fracture pressure prediction technical field more particularly to a kind of hard brittle shales
Fracturing Pressure Prediction method.
Background technology
In the mining operations of oil/gas well, prediction is carried out to formation fracture pressure and is very important.In the prior art
In, model has according to model, anderson model, exlog models, Huang Shi models etc., wherein according to a model consider Poisson's ratio with
The relation of depth；Anderson model considers the influence of borehole wall stress concentration, introduces stress, the strain of elastic porous medium
Relation；The problem of exlog models consider tectonic stress, and done hypothesis of the even level to tectonic stress；Huang Shi models
Primarily directed to what is proposed in general reservoir, the influence of various factors is generally considered, considering not only rock stratum overlying should
Power is the function of depth, the influence of borehole wall stress concentration, but also the work of the tectonic stress in view of underground non-uniform Distribution
With and the factors such as rock strength.Therefore, it can be suitably used for the area of different condition, and the fracture pressure predicted also will be compared with
Other patterns are more accurately and reliably.However, the pattern does not account for the influence of rock porosity, seepage flow and aquation.
It is tight to establish the model for considering that Hydrogeochemical anomaly calculates fracture pressure, the model on the basis of Huang Shi models on the sunny side
It is the function of depth, the effect of tectonic stress of underground non-uniform Distribution and seepage flow and hole not account for rock stratum overlying stress
The influence of degree.Deng Jingen etc. establishes the new mould of high temperature and pressure formation fracture pressure calculating for considering temperature and seepage effect
Type, but this model primarily directed to stratum be sandstone, do not account for the influence of hydration.Luo Limin etc., which is established, to be contained
The prediction before drilling method of confidence level formation fracture pressure, Main Analysis sea deep-well harshness formation fracture pressure.East such as shakes at the utilizations
Theory of Fracture Mechanics derives fractured reservoir fracture pressure calculation formula, with reference to point shape rock mechanics theory with establishing Fractured
Layer fracture pressure analytic modell analytical model, proposes a kind of fracture pressure computational methods of practicality, is primarily directed to coal petrography.Li Chuanliang gives
Go out the fracture pressure computation model under the conditions of perforation completion, however how to obtain continuous contact porosity parameter profile,
Also it is a yet unresolved issue.Li Peichao is corrected the perforation completion fracture pressure model of Li Chuanliang, introduces perforation
Depth parameter finally obtains vertical well perforation completion fracture pressure calculation formula, only accounts for stress concentration caused by drilling well,
Secondary stress caused by ignoring perforation concentrates the influence to fracture pressure.
To sum up, consider that multifactor, more effective, more accurately method carries out hard brittle shale there is presently no a kind of
The prediction of layer fracture pressure.
The content of the invention
The shortcomings that in order to overcome the above-mentioned prior art, the object of the present invention is to provide a kind of ruptures of hard brittle shale to press
Force prediction method, on the basis of Huang Shi models, it is contemplated that Radial Flow Through Porous Media of the drilling well percolate in formation pore is enclosed in the borehole wall
The influence of additional profiled bar, the porosity of rock and drilling fluid hydration caused by rock, it is contemplated that many factors calculate
Simplicity can more effectively, more accurately predict the fracture pressure of mud shale stratum, high-precision so as to be provided for pressing crack construction design
The basic data of degree.
In order to achieve the above object, the technical solution taken of the present invention is：
A kind of hard brittle shale Fracturing Pressure Prediction method, comprises the following steps:
1) rock parameter of hard brittle shale is obtained by indoor aquation triaxial tests, the compression strength including rock,
Elasticity modulus and Poisson's ratio；
2) the detecting earth stress data for obtaining mud shale stratum are tested by live formation breakdown, are had including maximum horizontal
Efficacy σ1, minimum level effective stress σ2, overlying stress σv, tensile strength of rock StWith the compression strength of rock；
3) other routine datas needed for calculating are collected, including geological structure stress coefficient, Hydrogeochemical anomaly, poroelasticity
Constant, permeable membrane efficiency, gas constant, pure water partial molar volume, activity and mud into water in stratum liquid activity, mud shale
Shale porosity；
4) based on plastoelasticity and rock mechanics theory, the vertical well borehole wall surrounding formation of consideration seepage flow is calculated
Stress distribution；
Wherein：σrFor radial stress, Mpa；σθFor tangential stress, Mpa；σrθFor shear stress, Mpa；σzFor vertical stress,
Mpa；σvFor overburden pressure, Mpa；piFor drilling well liquid columnpressure, Mpa；ppFor prime stratum pore pressure, Mpa；For
Effective stress coefficient；μ is Poisson's ratio；σ1Horizontal maximum crustal stress, Mpa；σ2For horizontal minimum crustal stress, Mpa；R is maximum well
Eye radius, m；R be wellbore radius, m；δ is infiltration coefficient；φ is mud shale porosity；
5) the effective tangential stress considered under the action of aquation is calculated：
Wherein：σ'θFor effective tangential stress, Mpa；ImFor permeable membrane efficiency；R ' is gas constant；T is absolute temperature；For
Pure water partial molar volume；(Aw)mTo enter stratum liquid activity；(Aw)shFor the activity of water in mud shale；φ is mud shale hole
Degree；
6) according to maximum tensional stress criterion, the fracture pressure model on hard brittle shale stratum is obtained：
P in formulaFFor formation fracture pressure, MPa；α, β are geological structure stress coefficient；
S is overlying stress, MPa；StFor the tensile strength of rock, MPa.
Compression strength, elasticity modulus, the Poisson's ratio of test rock, comprise the following steps in the step 1)：
1.1) standard cylinder rock sample is prepared：It is prepared according to International Society of Rock Mechanics (ISRM) proposed standard, it will
The mud shale rock core taken out is processed into the cylindrical standard sample of diameter 25.4mm, a height of 50mm, and the flatness of end face is
0.1mm；
1.2) standard cylinder rock sample prepared by 3 groups of steps 1.1) is immersed in distilled water, impregnate respectively 1d, 3d and
Then 5d weighs and calculates corresponding moisture content；
Moisture content calculation formula is ωc=(mω- m)/m, wherein, m is the quality after impregnating；mωFor the quality before immersion；
1.3) confining pressure is carried out respectively again as the triaxial compression test under 15MPa, 20MPa and 25MPa：
1. starting MTS Wikis control electro-hydraulic servo rock triaxial pressure experimental machine, the parameter setting of control program is carried out；
2. sample is wrapped up with thermal shrinkable sleeve, pressure chamber base is fixed on, extensometer is installed；
3. balancing gate pit's cover is loaded onto, oiling discharge gas；After oil is full of, to triaxial chamber plus confining pressure, with 1MPa per minute or so
Rate be loaded into predetermined confining pressure value, then with axial strain rate 10-6The rate of/s carries out loading experiment；
4. being loaded into sample to destroy suddenly, system is automatically stopped.
The tensile strength S of disrupted beds rock in the step 2)tIt is on the basis of live burst test graph is obtained
It is estimated.
The other basic parameters collected in the step 3) are considered as constant value in oilfield internal these coefficients.
Beneficial effects of the present invention are：
The present invention is based on plastoelasticity and rock mechanics correlation theory, using maximum tensional stress criterion, it is contemplated that rock stratum
Overlying stress is the influence of the relation of depth, borehole wall stress concentration, the effect of the tectonic stress of underground non-uniform Distribution and rock
Layer intensity, Radial Flow Through Porous Media of the drilling well percolate in formation pore is in additional profiled bar caused by Sidewall Surrounding Rock, the hole of rock
The many factors such as the influence of porosity and drilling fluid hydration, example show that Fracturing Pressure Prediction model of the present invention is surveyed with scene
The data difference 3.65% that well data are calculated, it is more more accurate than Forecasting Methodology before, and calculate easy, this hair
Bright method is particularly suitable for hard brittle shale stratum.
Description of the drawings
Fig. 1 is the FB(flow block) of the present invention.
Fig. 2 is curve of the fracture pressure of the embodiment of the present invention with change in depth.
Specific embodiment
With reference to embodiment, the present invention is described in detail.
With reference to Fig. 1, a kind of hard brittle shale Fracturing Pressure Prediction method comprises the following steps:
1) rock parameter of hard brittle shale is obtained by indoor aquation triaxial tests, the compression strength including rock,
Elasticity modulus and Poisson's ratio；
Compression strength, elasticity modulus, the Poisson's ratio of rock are tested, is comprised the following steps：
1.1) standard cylinder rock sample is prepared：It is prepared according to International Society of Rock Mechanics (ISRM) proposed standard, it will
The mud shale rock core taken out is processed into the cylindrical standard sample of diameter 25.4mm, a height of 50mm, and the flatness of end face is
0.1mm；
1.2) standard cylinder rock sample prepared by 3 groups of steps 1.1) is immersed in distilled water, impregnate respectively 1d, 3d and
Then 5d weighs and calculates corresponding moisture content；
Moisture content calculation formula is ωc=(mω- m)/m, wherein, m is the quality after impregnating；mωFor the quality before immersion；
1.3) confining pressure is carried out respectively again as the triaxial compression test under 15MPa, 20MPa and 25MPa：
1. starting MTS Wikis control electro-hydraulic servo rock triaxial pressure experimental machine, the parameter setting of control program is carried out；
2. sample is wrapped up with thermal shrinkable sleeve, pressure chamber base is fixed on, extensometer is installed；
3. balancing gate pit's cover is loaded onto, oiling discharge gas；After oil is full of, to triaxial chamber plus confining pressure, with 1MPa per minute or so
Rate be loaded into predetermined confining pressure value, then with axial strain rate 10-6The rate of/s carries out loading experiment；
4. being loaded into sample to destroy suddenly, system is automatically stopped；
Obtained experimental result is shown in Table 1,
The triaxial compression test result of the different soaking time rock samples of table 1
2) the detecting earth stress data for obtaining mud shale stratum are tested by live formation breakdown, are had including maximum horizontal
Efficacy σ1, minimum level effective stress σ2, overlying stress σv, tensile strength of rock StWith the compression strength of rock, it is specifically shown in
Table 2；
3) other routine datas needed for calculating are collected, including geological structure stress coefficient, Hydrogeochemical anomaly, poroelasticity
Constant, permeable membrane efficiency, gas constant, pure water partial molar volume, activity and mud into water in stratum liquid activity, mud shale
Shale porosity；
Permeable membrane efficiency is I in the present embodimentm=0.1, gas constant is R '=8.314, and absolute temperature T=363K is pure
Water partial molar volume is _ V_=1.8 × 10-5m3mol-1, other parameters are shown in Table 2；Due to general mud shale stratum using clear water or
Slippery water carries out pressure break, then can be (A into stratum liquid activityw)m=0.78, the activity of water is (A in shalew)sh=
0.915, mud shale porosity is φ=18.11%, effective stress coefficientPoisson's ratio μ=0.25, tectonic stress system
Number α=1.40, β=0.46；
4) based on plastoelasticity and rock mechanics theory, the vertical well borehole wall surrounding formation of consideration seepage flow is calculated
Stress distribution.
Wherein：σrFor radial stress, Mpa；σθFor tangential stress, Mpa；σrθFor shear stress, Mpa；σzFor vertical stress,
Mpa；σvFor overburden pressure, Mpa；piFor drilling well liquid columnpressure, Mpa；ppFor prime stratum pore pressure, Mpa；For
Effective stress coefficient；μ is Poisson's ratio；σ1Horizontal maximum crustal stress, Mpa；σ2For horizontal minimum crustal stress, Mpa；R is maximum well
Eye radius, m；R be wellbore radius, m；δ is infiltration coefficient；φ is mud shale porosity；
5) the effective tangential stress considered under the action of aquation is calculated：
Wherein：σ'θFor effective tangential stress, Mpa；ImFor permeable membrane efficiency；R ' is gas constant；T is absolute temperature；For
Pure water partial molar volume；(Aw)mTo enter stratum liquid activity；(Aw)shFor the activity of water in mud shale；φ is mud shale hole
Degree；
6) according to maximum tensional stress criterion, the fracture pressure model on hard brittle shale stratum is obtained：
P in formulaFFor formation fracture pressure, Mpa；α, β are geological structure stress coefficient；
S is overlying stress, Mpa；StFor the tensile strength of rock, Mpa.
The results are shown in Table 2.
Table 2
Curve of the fracture pressure with change in depth is drawn according to table 2, as shown in Figure 2.
In order to which the accuracy of prediction result is better described, by the method for the present invention with according to model, anderson model,
Exlog models and Huang Shi models are compared, as shown in Fig. 2, the results show：Prediction result of the present invention is ruptured with actual formation
The accordance of barometric gradient is very high, and the equivalent drilling fluid density being calculated more meets reality, and the prediction result of other methods
It is then relatively relatively low.Statistics is drawn, is 39.49% according to the error of model, and the error of anderson model is 15.89%, exlog
The error that the error of model then reaches about 12.88%, Huang Shi models is 4.95%, and the error of model of the present invention is about 3.65%.
This is because when carrying out hydraulic fracturing to mud shale stratum, drilling fluid or fracturing fluid enter mud shale stratum with causing mud shale
Layer occurs aquation and generates Hydrogeochemical anomaly, causes the increase of Sidewall Surrounding Rock stress, fracture pressure is caused to increase.
Claims (4)
- A kind of 1. hard brittle shale Fracturing Pressure Prediction method, which is characterized in that comprise the following steps:1) rock parameter of hard brittle shale is obtained by indoor aquation triaxial tests, compression strength, elasticity including rock Modulus and Poisson's ratio；2) the detecting earth stress data for obtaining mud shale stratum are tested by live formation breakdown, including maximum horizontal effective stress σ1, minimum level effective stress σ2, overlying stress σv, tensile strength of rock StWith the compression strength of rock；3) collect calculate needed for other routine datas, including geological structure stress coefficient, Hydrogeochemical anomaly, poroelasticity constant, Permeable membrane efficiency, gas constant, pure water partial molar volume, into the activity of water in stratum liquid activity, mud shale and mud shale hole Porosity；4) based on plastoelasticity and rock mechanics theory, the stress for calculating the vertical well 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<mo>-</mo> <mi>&mu;</mi> <mo>)</mo> </mrow> </mrow> </mfrac> <mrow> <mo>(</mo> <mn>1</mn> <mo>+</mo> <mfrac> <msup> <mi>R</mi> <mn>2</mn> </msup> <msup> <mi>r</mi> <mn>2</mn> </msup> </mfrac> <mo>)</mo> </mrow> <mo>-</mo> <mi>&phi;</mi> <mo>&rsqb;</mo> <mrow> <mo>(</mo> <msub> <mi>p</mi> <mi>i</mi> </msub> <mo>-</mo> <msub> <mi>p</mi> <mi>p</mi> </msub> <mo>)</mo> </mrow> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <msub> <mi>&sigma;</mi> <mrow> <mi>r</mi> <mi>&theta;</mi> </mrow> </msub> <mo>=</mo> <mo>-</mo> <mfrac> <mrow> <mo>(</mo> <msub> <mi>&sigma;</mi> <mn>1</mn> </msub> <mo>-</mo> <msub> <mi>&sigma;</mi> <mn>2</mn> </msub> <mo>)</mo> </mrow> <mn>2</mn> </mfrac> <mrow> <mo>(</mo> <mn>1</mn> <mo>-</mo> <mfrac> <mrow> <mn>3</mn> <msup> <mi>R</mi> <mn>4</mn> </msup> </mrow> <msup> <mi>r</mi> <mn>4</mn> </msup> </mfrac> <mo>+</mo> <mfrac> <mrow> <mn>2</mn> <msup> <mi>R</mi> <mn>2</mn> </msup> </mrow> <msup> <mi>r</mi> <mn>2</mn> </msup> </mfrac> <mo>)</mo> </mrow> <mi>sin</mi> <mn>2</mn> <mi>&theta;</mi> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <msub> <mi>&sigma;</mi> <mi>z</mi> </msub> <mo>=</mo> <msub> <mi>&sigma;</mi> <mi>v</mi> </msub> <mo>-</mo> <mi>&mu;</mi> <mo>&lsqb;</mo> <mn>2</mn> <mrow> <mo>(</mo> <msub> <mi>&sigma;</mi> <mn>1</mn> </msub> <mo>-</mo> <msub> <mi>&sigma;</mi> <mn>2</mn> </msub> <mo>)</mo> </mrow> <msup> <mrow> <mo>(</mo> <mfrac> <mi>R</mi> <mi>r</mi> </mfrac> <mo>)</mo> </mrow> <mn>2</mn> </msup> <mi>cos</mi> <mn>2</mn> <mi>&theta;</mi> <mo>&rsqb;</mo> <mo>+</mo> <mi>&delta;</mi> <mo>&lsqb;</mo> <mfrac> <mrow> <mover> <mi>&alpha;</mi> <mo>&CenterDot;</mo> </mover> <mrow> <mo>(</mo> <mn>1</mn> <mo>-</mo> <mn>2</mn> <mi>&mu;</mi> <mo>)</mo> </mrow> </mrow> <mrow> <mn>2</mn> <mrow> <mo>(</mo> <mn>1</mn> <mo>-</mo> <mi>&mu;</mi> <mo>)</mo> </mrow> </mrow> </mfrac> <mrow> <mo>(</mo> <mn>1</mn> <mo>+</mo> <mfrac> <msup> <mi>R</mi> <mn>2</mn> </msup> <msup> <mi>r</mi> <mn>2</mn> </msup> </mfrac> <mo>)</mo> </mrow> <mo>-</mo> <mi>&phi;</mi> <mo>&rsqb;</mo> <mrow> <mo>(</mo> <msub> <mi>p</mi> <mi>i</mi> </msub> <mo>-</mo> <msub> <mi>p</mi> <mi>p</mi> </msub> <mo>)</mo> </mrow> </mrow> </mtd> </mtr> </mtable> </mfenced>Wherein：σrFor radial stress, Mpa；σθFor tangential stress, Mpa；σrθFor shear stress, Mpa；σzFor vertical stress, Mpa；σv For overburden pressure, Mpa；piFor drilling well liquid columnpressure, Mpa；ppFor prime stratum pore pressure, Mpa；To there is effect Force coefficient；μ is Poisson's ratio；σ1Horizontal maximum crustal stress, Mpa；σ2For horizontal minimum crustal stress, Mpa；R is maximum wellbore radius, m；R be wellbore radius, m；δ is infiltration coefficient；φ is mud shale porosity；5) the effective tangential stress considered under the action of aquation is calculated：<mrow> <msubsup> <mi>&sigma;</mi> <mi>&theta;</mi> <mo>&prime;</mo> </msubsup> <mo>=</mo> <mn>3</mn> <msub> <mi>&sigma;</mi> <mn>2</mn> </msub> <mo>-</mo> <msub> <mi>&sigma;</mi> <mn>1</mn> </msub> <mo>-</mo> <msub> <mi>p</mi> <mi>i</mi> </msub> <mo>+</mo> <mo>&lsqb;</mo> <mfrac> <mrow> <mover> <mi>&alpha;</mi> <mo>&CenterDot;</mo> </mover> <mrow> <mo>(</mo> <mn>1</mn> <mo>-</mo> <mn>2</mn> <mi>&mu;</mi> <mo>)</mo> </mrow> </mrow> <mrow> <mn>2</mn> <mrow> <mo>(</mo> <mn>1</mn> <mo>-</mo> <mi>&mu;</mi> <mo>)</mo> </mrow> </mrow> </mfrac> <mo>-</mo> <mi>&phi;</mi> <mo>&rsqb;</mo> <mrow> <mo>(</mo> <msub> <mi>p</mi> <mi>i</mi> </msub> <mo>-</mo> <msub> <mi>p</mi> <mi>p</mi> </msub> <mo>)</mo> </mrow> <mo>-</mo> <msub> <mi>p</mi> <mi>p</mi> </msub> <mo>-</mo> <msub> <mi>I</mi> <mi>m</mi> </msub> <mfrac> <mrow> <msup> <mi>R</mi> <mo>&prime;</mo> </msup> <mi>T</mi> </mrow> <mover> <mi>V</mi> <mo>&OverBar;</mo> </mover> </mfrac> <mi>ln</mi> <mfrac> <msub> <mrow> <mo>(</mo> <msub> <mi>A</mi> <mi>w</mi> </msub> <mo>)</mo> </mrow> <mi>m</mi> </msub> <msub> <mrow> <mo>(</mo> <msub> <mi>A</mi> <mi>w</mi> </msub> <mo>)</mo> </mrow> <mrow> <mi>s</mi> <mi>h</mi> </mrow> </msub> </mfrac> <mo>&times;</mo> <msup> <mn>10</mn> <mrow> <mo>-</mo> <mn>6</mn> </mrow> </msup> </mrow>Wherein：σ'θFor effective tangential stress, Mpa；ImFor permeable membrane efficiency；R ' is gas constant；T is absolute temperature；It is inclined for pure water Molal volume；(Aw)mTo enter stratum liquid activity；(Aw)shFor the activity of water in mud shale；φ is mud shale porosity；6) according to maximum tensional stress criterion, the fracture pressure model on hard brittle shale stratum is obtained：<mrow> <msub> <mi>p</mi> <mi>F</mi> </msub> <mo>=</mo> <mfrac> <mn>1</mn> <mrow> <mn>1</mn> <mo>-</mo> <mrow> <mo>(</mo> <mfrac> <mrow> <mover> <mi>&alpha;</mi> <mo>&CenterDot;</mo> </mover> <mrow> <mo>(</mo> <mn>1</mn> <mo>-</mo> <mn>2</mn> <mi>&mu;</mi> <mo>)</mo> </mrow> </mrow> <mrow> <mn>2</mn> <mrow> <mo>(</mo> <mn>1</mn> <mo>-</mo> <mi>&mu;</mi> <mo>)</mo> </mrow> </mrow> </mfrac> <mo>-</mo> <mi>&phi;</mi> <mo>)</mo> </mrow> </mrow> </mfrac> <mrow> <mo>(</mo> <msub> <mi>S</mi> <mi>t</mi> </msub> <mo>-</mo> <msub> <mi>I</mi> <mi>m</mi> </msub> <mfrac> <mrow> <msup> <mi>R</mi> <mo>&prime;</mo> </msup> <mi>T</mi> </mrow> <mover> <mi>V</mi> <mo>&OverBar;</mo> </mover> </mfrac> <mi>l</mi> <mi>n</mi> <mfrac> <msub> <mrow> <mo>(</mo> <msub> <mi>A</mi> <mi>w</mi> </msub> <mo>)</mo> </mrow> <mi>m</mi> </msub> <msub> <mrow> <mo>(</mo> <msub> <mi>A</mi> <mi>w</mi> </msub> <mo>)</mo> </mrow> <mrow> <mi>s</mi> <mi>h</mi> </mrow> </msub> </mfrac> <mo>&times;</mo> <msup> <mn>10</mn> <mrow> <mo>-</mo> <mn>6</mn> </mrow> </msup> <mo>)</mo> </mrow> <mo>+</mo> <msub> <mi>p</mi> <mi>p</mi> </msub> <mo>+</mo> <mfrac> <mn>1</mn> <mrow> <mn>1</mn> <mo>-</mo> <mrow> <mo>(</mo> <mfrac> <mrow> <mover> <mi>&alpha;</mi> <mo>&CenterDot;</mo> </mover> <mrow> <mo>(</mo> <mn>1</mn> <mo>-</mo> <mn>2</mn> <mi>&mu;</mi> <mo>)</mo> </mrow> </mrow> <mrow> <mn>2</mn> <mrow> <mo>(</mo> <mn>1</mn> <mo>-</mo> <mi>&mu;</mi> <mo>)</mo> </mrow> </mrow> </mfrac> <mo>-</mo> <mi>&phi;</mi> <mo>)</mo> </mrow> </mrow> </mfrac> <mrow> <mo>(</mo> <mfrac> <mrow> <mn>2</mn> <mi>&mu;</mi> </mrow> <mrow> <mn>1</mn> <mo>-</mo> <mi>&mu;</mi> </mrow> </mfrac> <mo>+</mo> <mn>3</mn> <mi>&beta;</mi> <mo>-</mo> <mi>&alpha;</mi> <mo>)</mo> </mrow> <mrow> <mo>(</mo> <mi>S</mi> <mo>-</mo> <msub> <mi>p</mi> <mi>p</mi> </msub> <mo>)</mo> </mrow> </mrow>P in formulaFFor formation fracture pressure, Mpa；α, β are geological structure stress coefficient；S is overlying stress, Mpa；StFor the tensile strength of rock, Mpa.
- 2. a kind of hard brittle shale Fracturing Pressure Prediction method according to claim 1, it is characterised in that：The step 1) compression strength, elasticity modulus, the Poisson's ratio of test rock, comprise the following steps in：1.1) standard cylinder rock sample is prepared：It is prepared, will be taken out according to International Society of Rock Mechanics (ISRM) proposed standard The mud shale rock core come is processed into the cylindrical standard sample of diameter 25.4mm, a height of 50mm, and the flatness of end face is 0.1mm；1.2) standard cylinder rock sample prepared by 3 groups of steps 1.1) is immersed in distilled water, impregnates 1d, 3d and 5d respectively, so After weigh and calculate corresponding moisture content；Moisture content calculation formula is ωc=(mω- m)/m, wherein, m is the quality after impregnating；mωFor the quality before immersion；1.3) confining pressure is carried out respectively again as the triaxial compression test under 15MPa, 20MPa and 25MPa：1. starting MTS Wikis control electro-hydraulic servo rock triaxial pressure experimental machine, the parameter setting of control program is carried out；2. sample is wrapped up with thermal shrinkable sleeve, pressure chamber base is fixed on, extensometer is installed；3. balancing gate pit's cover is loaded onto, oiling discharge gas；After oil is full of, to triaxial chamber plus confining pressure, with the speed of 1MPa per minute or so Rate is loaded into predetermined confining pressure value, then with axial strain rate 10-6The rate of/s carries out loading experiment；4. being loaded into sample to destroy suddenly, system is automatically stopped.
- 3. a kind of hard brittle shale Fracturing Pressure Prediction method according to claim 1, it is characterised in that：The step 2) the tensile strength S of disrupted beds rock intIt is estimated on the basis of live burst test graph is obtained.
- 4. a kind of hard brittle shale Fracturing Pressure Prediction method according to claim 1, it is characterised in that：The step 3) the other basic parameters collected in are considered as constant value in oilfield internal these coefficients.
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| CN111927446A (en) * | 2020-09-11 | 2020-11-13 | 西南石油大学 | Method for predicting collapse instability of well wall of hydrated shale stratum |
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