CN106295042A - A kind of coal seam top rock stability Quantitative Evaluation with Well Logging method - Google Patents

Abstract

A kind of coal seam top rock stability logging evaluation evaluation methodology, first calculate coal roof lithologic coefficient, calculate the porosity of roof again, then roof fracture development index is calculated, then roof moisture content is calculated, then calculate roof comprcssive strength, then build coal seam top rock stability Quantitative Evaluation with Well Logging model, last Appraisal of Stability of Coal Seam Roof Index for Calculation；The present invention is based on coal roof lithologic coefficient, porosity, fracture development index, the property of water-bearing and comprcssive strength parameter, construct Appraisal of Stability of Coal Seam Roof index well logging quantitative calculation, with this computation model, Appraisal of Stability of Coal Seam Roof index is calculated, borehole logging technical support will be provided for safety of coal mines exploitation.

Description

A kind of coal seam top rock stability Quantitative Evaluation with Well Logging method

Technical field

The invention belongs to the borehole logging assessment technique in process of coal mining, particularly to a kind of coal seam top rock stability Quantitative Evaluation with Well Logging method.

Background technology

In order to assess the stability of roof, it is an object of the invention to provide a kind of coal seam top rock stability well logging Method for quantitatively evaluating.Affect bigger lithologic character and comprcssive strength based on coal seam top rock stability, and fully take into account top The porosity of slate layer, moisture content and development degree of micro cracks in oil this objectively quality factor relatively big to stability influence, divides in system Analysis lithology factor, porosity, moisture content, internal relation between fracture development index and comprcssive strength and coal seam top rock stability it After, establish Appraisal of Stability of Coal Seam Roof index well logging computation model.This model has considered coal seam from many aspects Five indexs that roof stability impact is bigger, therefore, this evaluation methodology more can accurately characterize the stability of roof Can, and then can be that safety of coal mines exploitation provides logging technique support.

In actual production, for safe working colliery, it is necessary to the stability of assessment roof.It is said that in general, coal seam Directly top is for thick-layer tight sand, and during without crack, then comprcssive strength is big, good stability；If directly top is mud stone or hole The sandstone that gap is good, and during containing crack, then comprcssive strength is low, poor stability.

How existing Appraisal of Stability of Coal Seam Roof method, evaluate according to the comprcssive strength of rock stratum, some evaluation methodology Have also contemplated that the impact on stability of lithologic character and moisture content.It practice, the stability of roof is not only with anti- Compressive Strength, lithologic character are relevant with moisture content, and relevant with porosity and fracture development index.But, existing patent does not has Have in view of porosity, the impact of fracture development exponent pair coal seam top rock stability energy.Additionally, existing coal seam top rock stability is commented In valency, the most do not make full use of coalfield borehole logging data to calculate coal roof lithologic coefficient, porosity, fracture development refer to Number, moisture content and comprcssive strength, and then the stability of roof is carried out Quantitative Evaluation with Well Logging, this gives colliery safe working Detail design is made troubles.

Summary of the invention

In order to overcome above-mentioned existing methodical deficiency, it is an object of the invention to provide a kind of coal seam top rock stability well logging Evaluate evaluation methodology, based on coal roof lithologic coefficient, porosity, fracture development index, the property of water-bearing and comprcssive strength parameter, structure Build Appraisal of Stability of Coal Seam Roof index well logging quantitative calculation, with this computation model, Appraisal of Stability of Coal Seam Roof has been referred to Number calculates, and will provide borehole logging technical support for safety of coal mines exploitation.

In order to achieve the above object, the technical scheme is that

A kind of coal seam top rock stability logging evaluation evaluation methodology, comprises the following steps:

Step one, calculating coal roof lithologic coefficient: use equation (1) to ask for relative natural gamma, and then utilize relatively The rock particle diameter that natural gamma and laboratory record carries out correlation analysis, asks for the particle diameter of roof rock, and then utilizes Rock particle diameter and shale content build coal roof lithologic coefficient calculations model, specific as follows:

$\mathrm{\Δ}GR=\frac{GR-{\mathrm{GR}}_{min}}{{\mathrm{GR}}_{max}-{\mathrm{GR}}_{\min }}---\left(1\right)$

M_d=-0.124 Δ GR+0.248 (2)

$I_l=\frac{M_d}{V_{sh}}---\left(3\right)$

$V_{sh}=\frac{2^{GCUR\·\mathrm{\Δ}GR}-1}{2^{GCUR}-1}---\left(4\right)$

In formula: Δ GR is relative natural gamma, dimensionless；GR、GR_max、GR_minIt is respectively computation layer point, pure shale, sharp sand The natural gamma value of rock, API；M_dFor rock particle diameter, mm；I_lFor coal roof lithologic coefficient, dimensionless；V_shFor shale content, Decimal；GCUR is regional experience parameter, and Tertiary Stratigraphy is taken 3.7, and old stratum is taken 2；

Step 2, the porosity of calculating roof: after porosity test data are playbacked, after extracting playback Density log data, and in view of the shale content impact on porosity, with density and shale content as independent variable, porosity is Dependent variable, carries out binary regression matching, just can get equation (5) shown pores porosity computation model,

φ=-1.392 ρ_b-0.028·V_sh+6.672 (5)

In formula: φ is the porosity of roof, %；ρ_bFor the density of roof, g/cm³；

Step 3, calculating roof fracture development index: the fracture development index shown in structure equation (8):

$R_f=\frac{E_{ma}-E}{E_{ma}}---\left(6\right)$

$E=\frac{{\mathrm{\ρ}}_b}{{{\mathrm{\Δt}}_s}^2}\·\frac{3{{\mathrm{\Δt}}_s}^2-4{{\mathrm{\Δt}}_c}^2}{{{\mathrm{\Δt}}_s}^2-{{\mathrm{\Δt}}_c}^2}---\left(7\right)$

$F_c=\frac{R_f}{K_v}---\left(8\right)$

$K_v={\left(\frac{{\mathrm{\Δt}}_m}{{\mathrm{\Δt}}_c}\right)}^2---\left(9\right)$

In formula: R_fThe fracture intensity index (FII) calculated for Young's modulus, dimensionless；E_maFor the dynamic modulus of elasticity of rock matrix, MPa, is tried to achieve by theoretical value；E is the Young's modulus in coal seam, MPa；Δt_c、Δt_sWhen being respectively compressional wave and the shear wave of roof Difference, μ s/m；Δt_mFor the compressional wave time difference of roof skeleton, μ s/m；F_cFor fracture development intensity index, dimensionless；K_νFor rock Integrity factor, dimensionless；

Step 4, calculating roof moisture content: build the moisture content computation model shown in equation (10),

$C_w=\frac{\mathrm{\φ}\·{\mathrm{\ρ}}_w}{\mathrm{\φ}\·{\mathrm{\ρ}}_w+(1-\mathrm{\φ})\·{\mathrm{\ρ}}_m}---\left(10\right)$

In formula: C_wFor roof moisture content, dimensionless；ρ_wThe density aqueous for roof, g/cm³；ρ_mFor coal seam The density of balkstone skeleton, g/cm³；Other parameter physical significances are ibid；

Step 5, calculating roof comprcssive strength: comprcssive strength is in close relations with Young's modulus and shale content, according to This, establish the computation model of comprcssive strength in equation (11) clastic rock section,

C_o=0.0045 E (1-V_sh)+0.008·E·V_sh (11)

In formula: C_oFor compressive strength of rock, MPa；

Step 6, structure coal seam top rock stability Quantitative Evaluation with Well Logging model: based on the scheme in step one～step 5 Understanding, the stability of rock is directly proportional to lithology factor, comprcssive strength, becomes anti-with porosity, fracture development index and moisture content Ratio, then the quantitative Analysis formula of definite equation (12) Appraisal of Stability of Coal Seam Roof index, it is steady that support equation (12) calculates Qualitative coefficient, and have 8 well logging sampled data points in view of 1m, the method using weighting to process constructs shown in equation (13) Appraisal of Stability of Coal Seam Roof Index for Calculation model:

$R_s=\frac{I_l\·C_o}{\mathrm{\φ}\·F_c\·C_w}---\left(12\right)$

$I_s=\frac{\underset{i=1}{\overset{8H}{\Σ}}\frac{R_s}{i}}{ln\left(8H\right)}---\left(13\right)$

In formula: R_sFor coal seam top rock stability coefficient, dimensionless；I_sFor Appraisal of Stability of Coal Seam Roof index, dimensionless；H For roof thickness, m, this value can be taken as 10m；The log data that i is to be calculated is counted, dimensionless；

Step 7, Appraisal of Stability of Coal Seam Roof Index for Calculation: each evaluation that will calculate in above-mentioned steps one～step 5 Index substitutes in the equation (12) in step 6, equation (13), just can realize the calculating of roof index of stability, roof Estimation of stability index I_sChange in value is bigger, in order to according to I_sValue divides the type of top board closed performance, to R_sValue is also carried out Normalized, through normalized good, I_sMaximum be 1, minima is 0, and its value is the biggest, the stability of roof The strongest, according to its result of calculation, in system contrasts actual process of coal mining on the basis of roof stability monitoring materials, Give the Appraisal of Stability of Coal Seam Roof grading standard shown in table 1:

Table 1 Appraisal of Stability of Coal Seam Roof grade classification table

Roof stability type	Estimation of stability index Is
		I class	>0.7
II class	0.4<Is<0.7
		III class	<0.4

As shown in Table 1, the stability of roof is divided into three classes by the present invention, and I class represents good stability；II class represents Stability is medium；III class represents poor stability.

The present invention is first for coal seam top rock stability, it is proposed that a kind of coal seam top rock stability Quantitative Evaluation with Well Logging side Method, it is possible to effectively utilize well-log information and carry out roof index of stability calculating, to providing boring for safety of coal mines exploitation Logging technique is supported, had both taken into full account the impact on stability of coal roof lithologic feature, comprcssive strength and moisture content, and had held concurrently again Having turned round and look at the impact of roof porosity, characteristics of fracture development, the coal seam top rock stability evaluated is with colliery practical situation relatively It is identical.

Accompanying drawing explanation

Fig. 1 is the coal seam top rock stability Quantitative Evaluation with Well Logging method flow diagram in the present invention.

Fig. 2 is the roof natural gamma in the present invention and particle diameter graph of a relation.

Fig. 3 is the roof density in the present invention and porosity graph of a relation.

Fig. 4 is the roof shale content in the present invention and porosity graph of a relation.

Fig. 5 is the coal seam top rock stability Quantitative Evaluation with Well Logging result map in the present invention.

Detailed description of the invention

Below in conjunction with the accompanying drawings technical scheme is done narration in detail.

With reference to Fig. 1, a kind of Quantitative Evaluation with Well Logging method of coal seam top rock stability, comprise the following steps:

Step one, calculating coal roof lithologic coefficient: in clastic rock section, the granule of rock is the thickest, and comprcssive strength is the strongest, Then stability is the best.The rock that granule is the thinnest, the radioactive substance entrained by rock particles surface is the most, gamma ray log It is worth the biggest.Then, gamma ray log can characterize the size of rock effectively.With reference to Fig. 2, fully take into account samely Layer, multiple wells natural gamma amplitude of variation relatively big, use equation (1) to ask for relative natural gamma, so utilize relatively from The rock particle diameter that so gamma and laboratory record carries out correlation analysis, asks for the particle diameter of roof rock, and then utilizes Rock particle diameter and shale content build coal roof lithologic coefficient calculations model, specific as follows:

$\mathrm{\Δ}GR=\frac{GR-{\mathrm{GR}}_{min}}{{\mathrm{GR}}_{max}-{\mathrm{GR}}_{min}}---\left(1\right)$

M_d=-0.124 Δ GR+0.248 (2)

$I_l=\frac{M_d}{V_{sh}}---\left(3\right)$

$V_{sh}=\frac{2^{GCUR\·\mathrm{\Δ}GR}-1}{2^{GCUR}-1}---\left(4\right)$

In formula: Δ GR is relative natural gamma, dimensionless；GR、GR_max、GR_minIt is respectively computation layer point, pure shale, sharp sand The natural gamma value of rock, API；M_dFor rock particles diameter, mm；I_lFor coal roof lithologic coefficient, dimensionless；V_shContain for shale Amount, decimal；GCUR is regional experience parameter, and Tertiary Stratigraphy is taken 3.7, and old stratum is taken 2.

When coal roof lithologic coefficient increases, showing that contained chiltern proportion increases, top board more tends towards stability.Otherwise, work as coal When layer Roof rock feature coefficient reduces, showing that contained shale proportion increases, top board is the most unstable.

Step 2, the porosity of calculating roof: with reference to Fig. 3, Fig. 4, density log can reflect stratum effectively Porosity, and density log be coalfield produce in must survey project.Accordingly, after porosity test data are playbacked, carry Take the density log data after playback, and in view of the shale content impact on porosity, become for oneself with density and shale content Amount, porosity is dependent variable, carries out binary regression matching, just can get equation (5) shown pores porosity computation model,

φ=-1.392 ρ_b-0.028·V_sh+6.672 (5)

In formula: φ is the porosity of roof, %；ρ_bFor the density of roof, g/cm³。

Step 3, calculating roof fracture development index: Young's modulus can reflect the development degree of micro cracks in oil of its rock. Owing to the elastic modelling quantity of rock and the development degree of micro cracks in oil of rock are relevant, crack is more grown, and Young's modulus is the least, and rock matrix Elastic modelling quantity be a constant for same rock, the most just can be carried out table by the fracture intensity index (FII) shown in equation (6) Levy whether top board grows crack.Sound wave runs into generation diffraction when rupturing in rock, when impact is walked；The zone of fracture is more grown, i.e. rock Stone complete the poorest, velocity of longitudinal wave is the least.Therefore, utilize rock integrity factor to characterize whether roof grows broken Band.Obviously, it is the biggest that intensity index is sent out in crack, and crack is more grown；Integrity factor is the biggest, and rock more grows crushed zone.Accordingly, may be used Build the fracture development index shown in equation (8).

$R_f=\frac{E_{ma}-E}{E_{ma}}---\left(6\right)$

$E=\frac{{\mathrm{\ρ}}_b}{{{\mathrm{\Δt}}_s}^2}\·\frac{3{{\mathrm{\Δt}}_s}^2-4{{\mathrm{\Δt}}_c}^2}{{{\mathrm{\Δt}}_s}^2-{{\mathrm{\Δt}}_c}^2}---\left(7\right)$

$F_c=\frac{R_f}{K_v}---\left(8\right)$

$K_v={\left(\frac{{\mathrm{\Δt}}_m}{{\mathrm{\Δt}}_c}\right)}^2---\left(9\right)$

In formula: R_fThe fracture intensity index (FII) calculated for Young's modulus, dimensionless；E_maFor the dynamic modulus of elasticity of rock matrix, MPa, is tried to achieve by theoretical value；E is the Young's modulus in coal seam, MPa；Δt_c、Δt_sWhen being respectively compressional wave and the shear wave of roof Difference, μ s/m；Δt_mFor the compressional wave time difference of roof skeleton, μ s/m；F_cFor fracture development intensity index, dimensionless；K_νFor rock Integrity factor, dimensionless；Other parameter physical significances are the same.

Step 4, calculating roof moisture content: when roof exists a large amount of moveable water, may directly influence The exploitation in colliery.Being defined from moisture content, moisture content is the mass ratio of the aqueous quality of rock and whole rock.Based on This thought, just can build the moisture content computation model shown in equation (10) based on rock physics volume-based model.

$C_w=\frac{\mathrm{\φ}\·{\mathrm{\ρ}}_w}{\mathrm{\φ}\·{\mathrm{\ρ}}_w+(1-\mathrm{\φ})\·{\mathrm{\ρ}}_m}---\left(10\right)$

In formula: C_wFor roof moisture content, dimensionless；ρ_wThe density aqueous for roof, g/cm³；ρ_mFor coal seam The density of balkstone skeleton, g/cm³；Other parameter physical significances are ibid.

Step 5, calculating roof comprcssive strength: the comprcssive strength of rock is that rock sample is issued at uniaxial tension The ultimate value destroyed, it is numerically equal to maximum crushing stress when destroying.The rock of different minerals composition, has different resisting Compressive Strength.Then, comprcssive strength reflects the stability of roof largely.Learnt by forefathers' research, pressure resistance Spend in close relations with Young's modulus and shale content, accordingly, establish the calculating of comprcssive strength in equation (11) clastic rock section Model.

C_o=0.0045 E (1-V_sh)+0.008·E·V_sh (11)

In formula: C_oFor compressive strength of rock, MPa；Other parameter physical significances are ibid.

Step 6, structure coal seam top rock stability Quantitative Evaluation with Well Logging model: for stablizing of quantitatively characterizing roof Property, introduce Appraisal of Stability of Coal Seam Roof index, as the parameter of quantitative assessment coal seam top rock stability energy, i.e. with this exponent pair The stability of roof carries out quantitative assessment.Understand based on the scheme in step one～step 5, the stability of rock and rock Property coefficient, comprcssive strength are directly proportional, and are inversely proportional to porosity, fracture development index and moisture content.Then definite equation (11) coal The quantitative Analysis formula of layer Evaluation on Roof Stability index.According to production practices, when evaluating coal seam top rock stability, it is contemplated that away from Rock stratum in the range of the 10m of top, coal seam, the top board that top, distance coal seam is the nearest, the biggest to stability influence, i.e. weight coefficient is the biggest.Based on This thought, the coefficient of stability calculated based on equation (12), and have 8 well logging sampled data points in view of 1m, use at weighting The method of reason constructs the Appraisal of Stability of Coal Seam Roof Index for Calculation model shown in equation (13).

$R_s=\frac{I_l\·C_o}{\mathrm{\φ}\·F_c\·C_w}---\left(12\right)$

$I_s=\frac{\underset{i=1}{\overset{8H}{\Σ}}\frac{R_s}{i}}{\ln \left(8H\right)}---\left(13\right)$

In formula: R_sFor coal seam top rock stability coefficient, dimensionless；I_sFor Appraisal of Stability of Coal Seam Roof index, dimensionless；H For roof thickness, m, this value can be taken as 10m；The log data that i is to be calculated is counted, dimensionless；Other parameter physics is anticipated Justice is the same.

Step 7, Appraisal of Stability of Coal Seam Roof Index for Calculation: each evaluation that will calculate in above-mentioned steps one～step 5 Index substitutes in the equation (12) in step 6, equation (13), just can realize the calculating of roof index of stability.Roof Estimation of stability index I_sChange in value is bigger, in order to according to I_sValue divides the type of top board closed performance, to R_sValue is also carried out Normalized.Good through normalized, I_sMaximum be 1, minima is 0, and its value is the biggest, the stability of roof The strongest.According to its result of calculation, in system contrasts actual process of coal mining on the basis of roof stability monitoring materials, Give the Appraisal of Stability of Coal Seam Roof grading standard shown in table 1.

Table 1 Appraisal of Stability of Coal Seam Roof grade classification table

Roof stability type	Coefficient of stability Is
		I class	>0.7
II class	0.4<Is<0.7
		III class	<0.4

As shown in Table 1, the stability of roof is divided into three classes by the present invention, and I class represents good stability；II class represents Stability is medium；III class represents poor stability.

The present invention is tried out in actual coalfield.In the coal seam top rock stability Quantitative Evaluation with Well Logging of X well is applied, reference Fig. 5,550.1～552.5 meters of well sections are coal seam, and this direct rimrock of well section is argillaceous sandstone, and thickness is 4m, and old rimrock is mud Rock, thickness is 6m, and the coefficient of stability distribution utilizing the inventive method to calculate is 0.21～0.56, the coal seam that weighting processes Evaluation on Roof Stability index 0.48, illustrates that the stability of top board is medium；Mining area belonging to this well, carried out coal mining in recent years, There is not the security incidents such as roof collapses, showed that the result of the method for the invention evaluation was fully able to meet colliery peace The requirement of conceptual design adopted by standard-sized sheet.

The method had both taken into full account the impact on stability of coal roof lithologic feature, comprcssive strength and moisture content, again Take into account the impact of roof porosity, characteristics of fracture development, the coal seam top rock stability evaluated and colliery practical situation The most identical.Each evaluation index in this method can be asked for from coalfield borehole logging data, and almost all of coalfield It is respectively provided with substantial amounts of borehole logging data.Therefore, coal seam top rock stability Quantitative Evaluation with Well Logging method of the present invention has good Good popularizing application prospect and value.

It will be understood by those of skill in the art that owing to well-log information is easily waited borehole environment to be affected, in order to more by expanding Evaluating the stability of roof accurately, its well-log information is carried out the correction method of surroundings effecting is the most necessary, and well logging meter The compressive strength of rock calculated has to pass through dynamic static conversion scale.

Claims (1)

1. a coal seam top rock stability logging evaluation evaluation methodology, it is characterised in that comprise the following steps:

Step one, calculating coal roof lithologic coefficient: use equation (1) to ask for relative natural gamma, and then utilize the most natural The rock particle diameter that gamma and laboratory record carries out correlation analysis, asks for the particle diameter of roof rock, and then utilizes rock Particle diameter and shale content build coal roof lithologic coefficient calculations model, specific as follows:

$\mathrm{\Δ}GR=\frac{GR-{\mathrm{GR}}_{min}}{{\mathrm{GR}}_{max}-{\mathrm{GR}}_{min}}---\left(1\right)$

M_d=-0.124 Δ GR+0.248 (2)

$I_l=\frac{M_d}{V_{sh}}---\left(3\right)$

$V_{sh}=\frac{2^{GCUR\·\mathrm{\Δ}GR}-1}{2^{GCUR}-1}---\left(4\right)$

In formula: Δ GR is relative natural gamma, dimensionless；GR、GR_max、GR_minIt is respectively computation layer point, pure shale, clean sandstone Natural gamma value, API；M_dFor rock particle diameter, mm；I_lFor coal roof lithologic coefficient, dimensionless；V_shFor shale content, decimal； GCUR is regional experience parameter, and Tertiary Stratigraphy is taken 3.7, and old stratum is taken 2；

Step 2, the porosity of calculating roof: after porosity test data are playbacked, extract the density after playback Log data, and in view of the shale content impact on porosity, with density and shale content as independent variable, porosity be because of change Amount, carries out binary regression matching, just can get equation (5) shown pores porosity computation model,

φ=-1.392 ρ_b-0.028·V_sh+6.672 (5)

In formula: φ is the porosity of roof, %；ρ_bFor the density of roof, g/cm³；

Step 3, calculating roof fracture development index: the fracture development index shown in structure equation (8):

$R_f=\frac{E_{ma}-E}{E_{ma}}---\left(6\right)$

$E=\frac{{\mathrm{\ρ}}_b}{{{\mathrm{\Δt}}_s}^2}\·\frac{3{{\mathrm{\Δt}}_s}^2-4{{\mathrm{\Δt}}_c}^2}{{{\mathrm{\Δt}}_s}^2-{{\mathrm{\Δt}}_c}^2}---\left(7\right)$

$F_c=\frac{R_f}{K_v}---\left(8\right)$

$K_v={\left(\frac{{\mathrm{\Δt}}_m}{{\mathrm{\Δt}}_c}\right)}^2---\left(9\right)$

In formula: R_fThe fracture intensity index (FII) calculated for Young's modulus, dimensionless；E_maFor the dynamic modulus of elasticity of rock matrix, MPa, Tried to achieve by theoretical value；E is the Young's modulus in coal seam, MPa；Δt_c、Δt_sIt is respectively compressional wave and shear wave slowness, the μ s/ of roof m；Δt_mFor the compressional wave time difference of roof skeleton, μ s/m；F_cFor fracture development intensity index, dimensionless；K_νFor rock integrity Coefficient, dimensionless；

Step 4, calculating roof moisture content: build the moisture content computation model shown in equation (10),

$C_w=\frac{\mathrm{\φ}\·{\mathrm{\ρ}}_w}{\mathrm{\φ}\·{\mathrm{\ρ}}_w+(1-\mathrm{\φ})\·{\mathrm{\ρ}}_m}---\left(10\right)$

In formula: C_wFor roof moisture content, dimensionless；ρ_wThe density aqueous for roof, g/cm³；ρ_mFor roof The density of rock matrix, g/cm³；

Step 5, calculating roof comprcssive strength: comprcssive strength is in close relations with Young's modulus and shale content, accordingly, builds Found the computation model of comprcssive strength in equation (11) clastic rock section,

C_o=0.0045 E (1-V_sh)+0.008·E·V_sh (11)

In formula: C_oFor compressive strength of rock, MPa；

Step 6, structure coal seam top rock stability Quantitative Evaluation with Well Logging model: understand based on the scheme in step one～step 5, The stability of rock is directly proportional to lithology factor, comprcssive strength, is inversely proportional to porosity, fracture development index and moisture content, in It is the quantitative Analysis formula of definite equation (12) Appraisal of Stability of Coal Seam Roof index, relies on the stability system that equation (12) calculates Number, and have 8 well logging sampled data points in view of 1m, the method using weighting to process constructs the top, coal seam shown in equation (13) Plate estimation of stability Index for Calculation model:

$R_s=\frac{I_l\·C_o}{\mathrm{\φ}\·F_c\·C_w}---\left(12\right)$

$I_s=\frac{\underset{i=1}{\overset{8H}{\Σ}}\frac{R_s}{i}}{ln\left(8H\right)}---\left(13\right)$

In formula: R_sFor coal seam top rock stability coefficient, dimensionless；I_sFor Appraisal of Stability of Coal Seam Roof index, dimensionless；H is coal Layer top plate thickness, m, this value can be taken as 10m；The log data that i is to be calculated is counted, dimensionless；

Step 7, Appraisal of Stability of Coal Seam Roof Index for Calculation: each evaluation index that will calculate in above-mentioned steps one～step 5 Substituting in the equation (12) in step 6, equation (13), just can realize the calculating of roof index of stability, roof is stable Property evaluation number I_sChange in value is bigger, in order to according to I_sValue divides the type of top board closed performance, to R_sValue is also returned One change processes, good through normalized, I_sMaximum be 1, minima is 0, and its value is the biggest, and the stability of roof is more By force, according to its result of calculation, in system contrasts actual process of coal mining on the basis of roof stability monitoring materials, be given Appraisal of Stability of Coal Seam Roof grading standard shown in table 1:

Table 1 Appraisal of Stability of Coal Seam Roof grade classification table

Roof stability type Estimation of stability index I_s I class >0.7 II class 0.4<I_s<0.7 III class <0.4

As shown in Table 1, the stability of roof is divided into three classes by the present invention, and I class represents good stability；II class represents stable Property is medium；III class represents poor stability.