CN105332685A - Propping agent multistage paving method for improving coal bed complicated crack supporting effect - Google Patents

Abstract

The invention discloses a propping agent multistage paving method for improving coal bed complicated crack supporting effect. The propping agent multistage paving method comprises the following steps: A, calculating a coal bed complicated crack type grade mark M1 affected by the content W of a brittle component; B, calculating a coal bed complicated crack type grade mark M2 affected by a uniaxial strength ratio R; C, calculating a coal bed complicated crack type grade mark M3 affected by a horizontal stress diversity factor theta; D, calculating a coal bed complicated crack type grade mark M4 affected by average cleat density as shown in the specification; E, calculating a coal bed complicated crack type grade mark M5 affected by a cleat approaching angle beta; F, calculating a coal bed complicated crack type grade mark M affected by the above five factors so as to calibrate a coal bed complicated crack type; and G, designing multi-grain-size propping agent combined multistage paving for different crack types. The propping agent multistage paving method is reliable in principle and easy and convenient to operate, and provides guidance for propping agent optimized paving in a coal bed reservoir hydrofracture scheme design, and a supporting effect which is matched with the reservoir and a hydraulic fracture system further is achieved.

Description

A kind of multistage spread method of proppant improving coal seam complex fracture support effect

Technical field

Spread method optimized by the proppant that the present invention relates in oil field bed gas reservoir fracturing design, to ensure that proppant can effectively support coal seam complex fracture, improves fracturing yield increasing effect.

Background technology

China's coal bed gas resource is very abundant, and buried depth 2000m reaches 36.8 trillion sides with shallow total resources.China's coal seam output keeps good volume increase situation at present, but total output is still not high, drilling well in 2014 exploitation output only 3,600,000,000 sides.In general, China's cbm development has a high potential, and is still badly in need of research of technique and improves development effectiveness.

The occurrence status of coal bed gas comprises ADSORPTION STATE, free state and solubilised state, and wherein 75-90% composes with ADSORPTION STATE and is stored in coal seam.High degree of water in coal seam simultaneously, the extraction of coal bed gas need through draining, desorb, diffusion, seepage flow, the several process of output.Therefore how to maximize and improve stratum filtration condition, promote that drainage and step-down desorb is the core of cbm development design.In addition, China's coalbed methane reservoir has " three is low " feature of low gas content saturation ratio, low-permeability, low-pressure.

For reservoir characteristic more than coal bed gas, fracturing, by highly pressurised liquid is injected coal seam, forms man-made fracture and links up extension coal seam hugger in reservoir; In dynamic crack, inject the liquid carrying proppant, through the row of returning, rear support agent stays in complex fracture thereupon, forms the high speed seepage channel that coal seam has certain flow conductivity; Final expansion seepage flow and step-down area, thus promote draining, step-down, desorb, diffusion, the whole process of seepage flow, make the quick output of coal bed gas.Thus, fracturing become coal bed gas can one of the key technology of economical and effective exploitation.

The laid mode of proppant is the importance of coal bed gas fracturing design, be referred from the mentality of designing that a long crack of high flow conductivity is made in conventional reservoir fracturing, current coalbed methane reservoir fracturing still adds sand based on single particle size, effectively supports with the single-stage realizing major fracture.

Be controlled by coal seam component and cement structure, coal seam mechanical property is more crisp, thus causes coal petrography frangible; The buried depth more shallow relative to conventional reservoir, coal seam geostatic stress is relatively lower, is conducive to fracture extension; A large amount of hugger (the orthogonal fracture system combined by end hugger and face cleat) is grown in coal seam simultaneously; And current coal bed fracturing technique is based on lower-cost riverfrac treatment; Under low sticky fracturing fluid (clear water) effect, hugger is easily linked up and is extended to form Fracture System.Therefore, the actual hydraulic fracture in coal seam form is comparatively complicated.The trunk crack that in coal seam, complex fracture has aperture larger, the secondary crack also having aperture less and the small microcrack of aperture.Thus, evenly laid being difficult to effectively supports complex fracture single particle size single-stage, needs according to multiple particle diameter, based on crack, coal seam complicated type, appropriate design many particle diameters multistage-combination is laid, makes master-secondary-microcrack in complex fracture all have enough flow conductivities and efficient combination coupling.

Summary of the invention

The object of the present invention is to provide a kind of multistage spread method of proppant improving coal seam complex fracture support effect, the method principle is reliable, easy and simple to handle, can provide guidance for proppant optimization is laid in bed gas reservoir fracturing schematic design.

For reaching above technical purpose, the invention provides following technical scheme.

The present invention approaches angle according to coal seam fragility constituent content, uniaxial strengeth ratio, flatly stress difference coefficient, average hugger density and hugger, coal seam complex fracture type is divided into four kinds of groups, for different coal seam complex fracture types, design different proppants respectively and combine multistage support, obtain with this support effect more mated with reservoir and hydraulic fracture system.

Improve the multistage spread method of proppant of coal seam complex fracture support effect, comprise the following steps successively:

A, height according to the fragility constituent content W in coal seam, calculate the coal seam complex fracture type classification scoring M of fragility constituent content W impact ₁, standards of grading are as follows:

As W<10%, M ₁=0;

As 10%≤W<20%, M ₁=1;

As 20%≤W<30%, M ₁=2;

As 30%≤W<40%, M ₁=3;

When W>=40%, M ₁=4;

B, according to the uniaxial strengeth in the coal seam size than R, calculate uniaxial strengeth and to mark M than the coal seam complex fracture type classification that R affect ₂, standards of grading are as follows:

As R<10, M ₂=0;

As 10≤R<15, M ₂=1;

As 15≤R<20, M ₂=2;

As 20≤R<25, M ₂=3;

When R>=25, M ₂=4;

C, size according to the horizontal stress diversity factor δ in coal seam, the coal seam complex fracture type classification scoring M that calculated level stress difference coefficient δ affects ₃, standards of grading are as follows:

When δ>=0.48, M ₃=0;

As 0.36≤δ <0.48, M ₃=1;

As 0.24≤δ <0.36, M ₃=2;

As 0.12≤δ <0.24, M ₃=3;

As δ <0.12, M ₃=4;

D, average hugger density according to coal seam calculate average hugger density the coal seam complex fracture type classification scoring M of impact ₄, standards of grading are as follows:

When time, M ₄=0;

When time, M ₄=1;

When time, M ₄=2;

When time, M ₄=3;

When time, M ₄=4;

E, approach angle β according to the hugger in coal seam, calculate hugger and approach the coal seam complex fracture type classification scoring M that angle β affects ₅, standards of grading are as follows:

As 72 °≤β <90 °, M ₅=0;

As 54 °≤β <72 °, M ₅=1;

As 36 °≤β <54 °, M ₅=2;

As 18 °≤β <36 °, M ₅=3;

As 0 °≤β <18 °, M ₅=4;

F, the coal seam complex fracture type classification scoring M affected according to each factor calculated respectively in steps A ~ E ₁, M ₂, M ₃, M ₄, M ₅, adopt following formula to calculate the coal seam complex fracture type classification scoring M of comprehensive above five factors impact:

$M=\underset{i=1}{\overset{5}{\&Sigma;}}(b_i\&CenterDot;M_i)/\underset{i=1}{\overset{5}{\&Sigma;}}{b}_i$

In formula: M _irefer to M respectively ₁, M ₂, M ₃, M ₄, M ₅; b _ifor M ₁, M ₂, M ₃, M ₄, M ₅shared weight, is respectively 0.15,0.15,0.25,0.25,0.2.

Adopt following standard, demarcate coal seam complex fracture type according to M value:

When 0≤M≤1, coal seam complex fracture type is A type (double-vane seam type);

When 1<M≤2, coal seam complex fracture type is Type B (multiple cracking type);

When 2<M≤3, coal seam complex fracture type is C type (dendritic);

When 3<M≤4, coal seam complex fracture type is D type (network-type);

G, according to the coal seam complex fracture type of demarcating in step F, design for often kind of types of fractures many particle diameters proppant combination multistage laid:

1. for A type (double-vane seam type) crack, design 20/40 order, 30/50 order, 40/70 order proppant volume ratio be 7:2:1;

2. for B (multiple cracking type) type crack, design 20/40 order, 30/50 order, 40/70 order proppant volume ratio be 3:2:1;

3. for C type (dendritic) crack, design 20/40 order, 30/50 order, 40/70 order proppant volume ratio be 4:3:2;

4. for D type (network-type) crack, design 20/40 order, 30/50 order, 40/70 order proppant volume ratio be 1:1:1.

Below 1. ~ 4. infusion order is first infusion 40/70 order proppant in situation fracturing process, then infusion 30/50 order proppant, last infusion 20/40 order proppant.

In the present invention, in described steps A, fragility constituent content W is the summation (%) of inertinite content and non-clay inorganic mineral content in coal seam.In coal seam, fragility constituent content is the internal factor determining coal petrography mechanical characteristics, thus also affects crack, coal seam complex characteristic.Fragility constituent content is higher, and crack, coal seam is more complicated, M ₁higher.

In described step B, uniaxial strengeth is coal seam uniaxial compressive strength σ than R _cwith uniaxial tension test σ _tratio (zero dimension).Coal petrography single shaft Compressive Strength σ _cwith tensile strength sigma _tdifference reflection coal petrography mechanics fragility, difference is larger, and fragility is stronger, and coal petrography is more easily cracked, and crack, coal seam is more complicated, M ₂higher.

In described step C, horizontal stress diversity factor δ is the maximum horizontal principal stress σ in coal seam _hwith minimum horizontal principal stress σ _hdifference divided by minimum horizontal principal stress σ _hincome value (zero dimension).Coal seam flatly stress difference is under formation conditions less, and namely horizontal stress diversity factor δ is less, and experience coal seam, crack hugger more easily turns to and prolongs hugger and extends, and thus crack, coal seam is more complicated, M ₃higher.

In described step D, the average hugger density in coal seam for end hugger density ω _swith face cleat density ω _faverage.Hugger density is that number (bar/m) grown by the hugger under unit length, and coal seam hugger is divided into the end hugger and face cleat that move towards mutually orthogonal, and coal seam hugger is educated all the more, hugger density is higher, hydraulic fracture more easily links up cleat system, and crack, coal seam is more complicated, M ₄higher.

In described step e, hugger is approached angle β and is calculated by following formula:

β＝|θ _f-θ _s|＝|(90-θ _s)-θ _s|＝|90-2θ _s|

In formula: θ _ffor face cleat trend and orientation of principal stress angle, °,

θ _sfor end hugger trend and orientation of principal stress angle, °.

The angle moved towards when major fracture bearing of trend (horizontal biggest principal stress direction) and hugger (holding hugger and face cleat) extends close to 0 ° of time delay hugger; When major fracture bearing of trend and hugger move towards vertical in 90 ° time directly extend through hugger; When major fracture bearing of trend and hugger move towards at about 45 °, the easiest major fracture and hugger extend to form fracture network simultaneously, and coal seam fracture pattern is the most complicated.Move towards mutually orthogonal due to end hugger and face cleat, therefore to approach angle β less for hugger, and major fracture bearing of trend and hugger move towards more close to 45 °, and crack, coal seam is more complicated, M ₅higher.

In described step G, A type (double-vane seam type) crack, crack is based on single major fracture, and secondary-microcrack is few, thus laid based on 20/40 order proppant, and 30/50 order, 40/70 order proppant use less.From A type ~ D type crack, fracture pattern complicates gradually, the trunk crack proportion that aperture is larger reduces gradually, and the less secondary crack of aperture and the small microcrack proportion of aperture increase gradually, and thus 30/50 order, 40/70 order usage ratio increase gradually.Finally make multistage effective support of major fracture, secondary crack, microcrack in the multistage laid coupling complex fracture of the combination of proppant, thus raising is supported with efficiency, and then improves fracturing effect.

Compared with existing single-stage spread method, the present invention has following beneficial effect: existing single-stage spread method only effectively can support A type (double-vane seam type) crack, for the comparatively complicated Type B (multiple cracking type) of fracture pattern, C type (dendritic), D type (network-type) crack, be supported with efficiency not high.The present invention can according to the difference of coal seam complex fracture type, design different multistage laid modes, thus meet effective support in crack, dissimilar coal seam, make the laid design of the proppant in Fracturing Project more targeted, meet the pressure break demand in coal seam under different geologic feature.

Detailed description of the invention

Embodiments of the present invention are described in detail below in conjunction with embodiment.For south, Yanchuan coal bed gas field coal bed gas well YX well, this well vertical depth 1420m, reservoir thickness is 4.6m.

A, the fragility constituent content W obtaining coal seam according to core test are 30.8% (inertinite content 23.6%, non-clay inorganic mineral content 7.2%), calculate the coal seam complex fracture type classification scoring M of fragility constituent content W impact ₁=3;

B, obtain coal seam uniaxial compressive strength σ according to core test _cfor 17.5MPa, uniaxial tension test σ _tfor 0.93MPa, calculating uniaxial strengeth is 18.8 than R, calculates the coal seam complex fracture type classification scoring M that uniaxial strengeth affects than R ₂=2;

C, reservoir maximum horizontal geostatic stress σ _hfor 28.4MPa, minimum horizontal principal stress σ _hfor 21.3MPa, calculated level stress difference coefficient δ is 0.33, the coal seam complex fracture type classification scoring M that calculated level stress difference coefficient δ affects ₃=2;

D, by rock core statistics obtain coal seam end hugger density ω _sbe 70/m, face cleat density ω _farticle 120 ,/m, calculates average hugger density be 95/m, calculate average hugger density the coal seam complex fracture type classification scoring M of impact ₄=3;

E, horizontal major principal stress orientation, this area are NE95 °, and end hugger moves towards NE62 °, and face cleat moves towards NE152 °, θ _fbe 57 °, θ _sit is 33 °.Utilizing formula (1) calculating hugger to approach angle β is 24 °, calculates the coal seam complex fracture type classification scoring M that hugger approaches angle β impact ₅=3;

F, according to calculate M ₁, M ₂, M ₃, M ₄, M ₅, adopt formula (2), calculate coal seam complex fracture type classification scoring M=2.6 (2<M≤3) of comprehensive above five factors impact, demarcating coal seam complex fracture type is C type (dendritic);

G, be C type crack (dendritic) according to coal seam complex fracture type calibration result, select 20/40 order, 30/50 order, 40/70 order proppant ratio is that 4:3:2 carries out multistage support, in fracturing process, infusion order is first infusion 40/70 order proppant, infusion 30/50 order proppant again, last infusion 20/40 order proppant.

Current the method expands the secondary field conduct application of more than 30 wells at south, Yanchuan coal bed gas field, achieves good result.Compared with the coal bed gas well not adopting the method adjacent with block, after adopting this method, the initial stage on average produces tolerance daily increases 185.3m ³/ d, gas breakthrough time on average shifts to an earlier date 108d.

Claims (6)

1. improve the multistage spread method of proppant of coal seam complex fracture support effect, comprise the following steps successively:

A, height according to the fragility constituent content W in coal seam, calculate the coal seam complex fracture type classification scoring M of fragility constituent content W impact ₁, standards of grading are as follows:

As W<10%, M ₁=0;

As 10%≤W<20%, M ₁=1;

As 20%≤W<30%, M ₁=2;

As 30%≤W<40%, M ₁=3;

When W>=40%, M ₁=4;

B, according to the uniaxial strengeth in the coal seam size than R, calculate uniaxial strengeth and to mark M than the coal seam complex fracture type classification that R affect ₂, standards of grading are as follows:

As R<10, M ₂=0;

As 10≤R<15, M ₂=1;

As 15≤R<20, M ₂=2;

As 20≤R<25, M ₂=3;

When R>=25, M ₂=4;

C, size according to the horizontal stress diversity factor δ in coal seam, the coal seam complex fracture type classification scoring M that calculated level stress difference coefficient δ affects ₃, standards of grading are as follows:

When δ>=0.48, M ₃=0;

As 0.36≤δ <0.48, M ₃=1;

As 0.24≤δ <0.36, M ₃=2;

As 0.12≤δ <0.24, M ₃=3;

As δ <0.12, M ₃=4;

D, average hugger density according to coal seam calculate average hugger density the coal seam complex fracture type classification scoring M of impact ₄, standards of grading are as follows:

When time, M ₄=0;

When $25\&le;\stackrel{\&OverBar;}{\mathrm{\&omega;}}<50$ Time, M ₄=1;

When $50\&le;\stackrel{\&OverBar;}{\mathrm{\&omega;}}<75$ Time, M ₄=2;

When $75\&le;\stackrel{\&OverBar;}{\mathrm{\&omega;}}<100$ Time, M ₄=3;

When time, M ₄=4;

E, approach angle β according to the hugger in coal seam, calculate hugger and approach the coal seam complex fracture type classification scoring M that angle β affects ₅, standards of grading are as follows:

As 72 °≤β <90 °, M ₅=0;

As 54 °≤β <72 °, M ₅=1;

As 36 °≤β <54 °, M ₅=2;

As 18 °≤β <36 °, M ₅=3;

As 0 °≤β <18 °, M ₅=4;

F, the coal seam complex fracture type classification scoring M adopting comprehensive above five factors of following formula calculating to affect:

$M=\underset{i=1}{\overset{5}{\&Sigma;}}(b_i\&CenterDot;M_i)/\underset{i=1}{\overset{5}{\&Sigma;}}{b}_i$

In formula: b _ifor M ₁, M ₂, M ₃, M ₄, M ₅shared weight, is respectively 0.15,0.15,0.25,0.25,0.2,

Thus demarcate coal seam complex fracture type according to M value:

When 0≤M≤1, coal seam complex fracture type is A type, i.e. double-vane seam type;

When 1<M≤2, coal seam complex fracture type is Type B, i.e. multiple cracking type;

When 2<M≤3, coal seam complex fracture type is C type, i.e. dendritic;

When 3<M≤4, coal seam complex fracture type is D type, i.e. network-type;

G, according to coal seam complex fracture type, design for often kind of types of fractures many particle diameters proppant combination multistage laid:

For A type crack, design 20/40 order, 30/50 order, 40/70 order proppant volume ratio be 7:2:1;

For Type B crack, design 20/40 order, 30/50 order, 40/70 order proppant volume ratio be 3:2:1;

For C type crack, design 20/40 order, 30/50 order, 40/70 order proppant volume ratio be 4:3:2;

For D type crack, design 20/40 order, 30/50 order, 40/70 order proppant volume ratio be 1:1:1.

2. the multistage spread method of proppant improving coal seam complex fracture support effect as claimed in claim 1, it is characterized in that, in described steps A, fragility constituent content W is the summation of inertinite content and non-clay inorganic mineral content in coal seam.

3. the multistage spread method of proppant improving coal seam complex fracture support effect as claimed in claim 1, it is characterized in that, in described step B, uniaxial strengeth is coal seam uniaxial compressive strength σ than R _cwith uniaxial tension test σ _tratio.

4. the multistage spread method of proppant improving coal seam complex fracture support effect as claimed in claim 1, it is characterized in that, in described step C, horizontal stress diversity factor δ is the maximum horizontal principal stress σ in coal seam _hwith minimum horizontal principal stress σ _hdifference divided by minimum horizontal principal stress σ _hincome value.

5. the multistage spread method of proppant improving coal seam complex fracture support effect as claimed in claim 1, is characterized in that, in described step D, and the average hugger density in coal seam for end hugger density ω _swith face cleat density ω _faverage.

6. the multistage spread method of proppant improving coal seam complex fracture support effect as claimed in claim 1, it is characterized in that, in described step e, hugger is approached angle β and is calculated by following formula:

β＝|θ _f-θ _s|＝|(90-θ _s)-θ _s|＝|90-2θ _s|

In formula: θ _ffor face cleat trend and orientation of principal stress angle, °,

θ _sfor end hugger trend and orientation of principal stress angle, °.