CN106295042B - A kind of coal seam top rock stability Quantitative Evaluation with Well Logging method - Google Patents
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Abstract
A kind of coal seam top rock stability logging evaluation evaluation method, first calculate coal roof lithologic coefficient, the porosity of roof is calculated again, then roof fracture development index is calculated, then roof moisture content is calculated, then roof compression strength is calculated, then builds coal seam top rock stability Quantitative Evaluation with Well Logging model, last Appraisal of Stability of Coal Seam Roof index calculates；The present invention is based on coal roof lithologic coefficient, porosity, fracture development index, the property of water-bearing and compression strength parameter, construct Appraisal of Stability of Coal Seam Roof index well logging quantitative calculation, Appraisal of Stability of Coal Seam Roof index is calculated with this computation model, will be exploited for safety of coal mines and borehole logging technical support is provided.
Description
Technical Field
The invention belongs to a borehole logging evaluation technology in a coal mining process, and particularly relates to a coal seam roof stability logging quantitative evaluation method.
Background
In order to evaluate the stability of the coal seam roof, the invention aims to provide a coal seam roof stability logging quantitative evaluation method. Based on lithology characteristics and compressive strength which have large influence on the stability of the coal seam roof and the objective geological factors that the porosity, the water content and the crack development degree of the roof rock stratum have large influence on the stability are fully considered, after the internal relation between the lithology coefficient, the porosity, the water content, the crack development index and the compressive strength and the stability of the coal seam roof is systematically analyzed, a coal seam roof stability evaluation index logging calculation model is established. Five indexes which have large influence on the stability of the coal seam roof are comprehensively considered by the model from multiple aspects, so that the stability of the coal seam roof can be more accurately characterized by the evaluation method, and further, a logging technical support can be provided for coal mine safety mining.
In actual production, the stability of the coal seam roof must be evaluated in order to safely mine the coal. Generally, the coal seam is directly topped by thick-layer compact sandstone, and when no crack is contained, the compressive strength is high, and the stability is good; if the steel is directly propped against mudstone or sandstone with good porosity and contains cracks, the steel has low compressive strength and poor stability.
In the existing coal seam roof stability evaluation method, a plurality of coal seam roof stability evaluation methods are evaluated according to the compressive strength of a rock stratum, and some evaluation methods also consider the influence of lithological characteristics and water content on the stability performance. In fact, the stability of coal seam roof is not only related to compressive strength, lithology characteristics and water content, but also porosity and fracture development index. However, the prior patent does not consider the influence of porosity and crack development index on the stability performance of the coal seam roof. In addition, in the existing evaluation of the stability of the coal seam roof, the lithology coefficient, porosity, crack development index, water content and compressive strength of the coal seam roof are not calculated by fully utilizing drilling and logging data of the coal field, so that the stability of the coal seam roof is quantitatively evaluated by logging, and the inconvenience is brought to the safe mining construction design of coal mines.
Disclosure of Invention
In order to overcome the defects of the existing method, the invention aims to provide a coal seam roof stability logging evaluation method, which constructs a coal seam roof stability evaluation index logging quantitative calculation model based on the coal seam roof lithology coefficient, porosity, crack development index, water content and compressive strength parameters, calculates the coal seam roof stability evaluation index by using the calculation model, and provides a drilling logging technical support for coal mine safety mining.
In order to achieve the purpose, the technical scheme of the invention is as follows:
a coal seam roof stability logging evaluation method comprises the following steps:
step one, calculating a coal seam roof lithology coefficient: the method comprises the following steps of (1) solving a relative natural gamma by adopting an equation, further carrying out correlation analysis on the relative natural gamma and the rock particle size measured by a laboratory, solving the particle size of the rock of the coal seam roof, and further constructing a coal seam roof lithology coefficient calculation model by utilizing the rock particle size and the shale content, wherein the method specifically comprises the following steps:
M d ＝-0.124·△GR+0.248 (2)
in the formula: delta GR is a relatively natural gamma, and is dimensionless; GR, GR max 、GR min Respectively calculating natural gamma values, API, of the bed points, the pure mudstone and the pure sandstone; m d Is the rock grain size, mm; i is l The lithology coefficient of the coal seam roof is dimensionless; v sh Is the mud content, decimal; GCUR is a regional experience parameter, 3.7 is taken for the tertiary stratum, and 2 is taken for the old stratum;
step two, calculating the porosity of the coal seam roof: after the porosity test data is subjected to homing, extracting the density logging data after homing, taking the influence of the shale content on the porosity into consideration, carrying out binary regression fitting by taking the density and the shale content as independent variables and the porosity as a dependent variable to obtain a porosity calculation model shown in equation (5),
φ＝-1.392·ρ b -0.028·V sh +6.672 (5)
in the formula: phi is the porosity,%, of the coal seam roof; rho b Is the density of the coal seam roof, g/cm 3 ；
Step three, calculating the coal seam roof crack development index: constructing a fracture development index shown in equation (8):
in the formula: r is f The crack strength index calculated for young's modulus, dimensionless; e ma The dynamic elasticity modulus, MPa, of the rock skeleton is obtained from a theoretical value; e is the Young modulus of the coal bed, MPa; delta t c 、△t s Time difference of longitudinal wave and transverse wave of the coal seam roof is respectively, mu s/m; delta t m The longitudinal wave time difference is the longitudinal wave time difference of the framework of the coal seam roof, and is microsecond/m; f c Is crack development strength index, and has no dimension; k ν Is a rock integrity coefficient without dimension;
step four, calculating the water content of the coal seam roof: constructing a water cut calculation model shown in equation (10),
in the formula: c w The water content of the coal seam roof is dimensionless; rho w Density of water contained in coal seam roof in g/cm 3 ；ρ m Is the density of the rock skeleton of the coal seam roof in g/cm 3 (ii) a The physical meaning of other parameters is the same as above;
step five, calculating the compressive strength of the coal seam roof: the compressive strength is closely related to the Young modulus and the shale content, so that a calculation model of the compressive strength in the clastic rock section of equation (11) is established,
C o ＝0.0045·E·(1-V sh )+0.008·E·V sh (11)
in the formula: c o The compressive strength of rock is MPa;
step six, constructing a coal seam roof stability well logging quantitative evaluation model: based on the schemes in the first step to the fifth step, the stability of the rock is in direct proportion to the lithology coefficient and the compressive strength and in inverse proportion to the porosity, the crack development index and the water content, so that a quantitative calculation formula of the coal seam roof stability evaluation index of the equation (12) is defined, a coal seam roof stability evaluation index calculation model shown in the equation (13) is constructed by taking 8 logging sampling data points in 1m into consideration and adopting a weighting processing method according to the stability coefficient calculated by the equation (12):
in the formula: r s The stability coefficient of the coal seam roof is dimensionless; i is s The evaluation index is a coal seam roof stability evaluation index without dimension; h is the thickness of the coal seam roof, m, which may be 10m; i is the number of the well logging data points to be calculated, and is dimensionless;
step seven, calculating the evaluation index of the stability of the coal seam roof: substituting the evaluation indexes calculated in the first step to the fifth step into the equation (12) and the equation (13) in the sixth step to realize the calculation of the stability index of the coal seam roof, namely the stability evaluation index I of the coal seam roof s The numerical variation is large, in order to be based on I s Value-divide the type of roof seal performance, for R s The values are also normalized, I s The maximum value of (1) and the minimum value of (0), the larger the value is, the stronger the stability of the coal seam roof is, and according to the calculation result, on the basis of the comparison of the system with the monitoring data of the roof stability in the actual coal mining process, the classification standard of the stability evaluation grade of the coal seam roof shown in the table 1 is given:
TABLE 1 evaluation grade division table for stability of coal seam roof
| Roof stability type | Stability evaluation index I s |
| Class I | >0.7 |
| Class II | 0.4<I s <0.7 |
| Class III | <0.4 |
As can be seen from the table 1, the stability of the coal seam roof is divided into three types, wherein the type I shows that the stability is good; class II indicates moderate stability; class III indicates poor stability.
The invention provides a coal seam roof stability well logging quantitative evaluation method for the first time aiming at the coal seam roof stability, which can effectively utilize well logging information to calculate the coal seam roof stability index so as to provide a drilling well logging technical support for coal mine safety mining, fully considers the influence of the lithologic characteristics, compressive strength and water content of the coal seam roof on the stability, and also considers the influence of the porosity and crack development characteristics of the coal seam roof, and the evaluated coal seam roof stability is more consistent with the actual situation of a coal mine.
Drawings
FIG. 1 is a flow chart of a coal seam roof stability logging quantitative evaluation method in the invention.
FIG. 2 is a graph showing the relationship between natural gamma and particle size of the coal seam roof in the present invention.
FIG. 3 is a graph of the relationship between the density and porosity of a coal seam roof in accordance with the present invention.
FIG. 4 is a graph showing the relationship between the shale content and the porosity of the coal seam roof in the present invention.
FIG. 5 is a diagram of the result of the well logging quantitative evaluation of the stability of the coal seam roof in the present invention.
Detailed Description
The technical scheme of the invention is described in detail in the following with reference to the accompanying drawings.
Referring to fig. 1, a logging quantitative evaluation method for coal seam roof stability includes the following steps:
step one, calculating a coal seam roof lithology coefficient: in a clastic rock profile, the coarser the rock particles, the stronger the compressive strength and thus the better the stability. The finer the rock, the more radioactive material carried by the rock particle surface, and the greater the natural gamma log. Thus, natural gamma logging can effectively characterize the size of the rock particles. Referring to fig. 2, considering that the natural gamma variation amplitude of the same stratum and multiple wells is large, equation (1) is adopted to obtain the relative natural gamma, correlation analysis is performed on the relative natural gamma and the rock particle size measured in a laboratory to obtain the particle size of the coal seam roof rock, and then the rock particle size and the shale content are used to construct a coal seam roof lithology coefficient calculation model, which is specifically as follows:
M d ＝-0.124·△GR+0.248 (2)
in the formula: delta GR is a relatively natural gamma, and is dimensionless; GR and GR max 、GR min Respectively calculating natural gamma values, API, of the bed points, the pure mudstone and the pure sandstone; m d Is the diameter of rock particles, mm; i is l The lithology coefficient of the coal seam roof is dimensionless; v sh Is made of mudMass content, decimal; GCUR is a regional experience parameter, 3.7 for the tertiary stratum and 2 for the old stratum.
When the lithological coefficient of the coal seam roof is increased, the specific gravity of the contained sand is increased, and the roof tends to be more stable. Conversely, when the lithology coefficient of the coal seam roof is reduced, the specific gravity of the contained shale is increased, and the roof is more unstable.
Step two, calculating the porosity of the coal seam roof: referring to fig. 3 and 4, the density log can effectively reflect the porosity of the formation, and is a necessary item in the production of the coal field. Accordingly, after the porosity test data is reset, the reset density logging data is extracted, the influence of the shale content on the porosity is considered, the density and the shale content are used as independent variables, the porosity is used as a dependent variable, binary regression fitting is carried out, and a porosity calculation model shown in an equation (5) can be obtained,
φ＝-1.392·ρ b -0.028·V sh +6.672 (5)
in the formula: phi is the porosity,%, of the coal seam roof; rho b Is the density of the coal seam roof, g/cm 3 。
Step three, calculating the coal seam roof crack development index: the young's modulus may reflect the extent of crack development in its rock. Since the elastic modulus of the rock is related to the development degree of the cracks of the rock, the more the cracks develop, the lower the Young's modulus, and the elastic modulus of the rock skeleton is a constant for the same rock, whether the roof develops cracks can be characterized by the crack strength index shown in equation (6). Diffraction occurs when the sound waves encounter the cracks in the rock, and the travel time is influenced; the more developed the fractured zone, i.e., the poorer the integrity of the rock, the smaller the velocity of the longitudinal wave. Therefore, the rock integrity coefficient is used for characterizing whether the coal seam roof develops a fracture zone. Obviously, the larger the crack initiation strength index is, the more developed the crack develops; the greater the integrity factor, the more developed the fracture zone the rock. From this, the fracture growth index shown in equation (8) can be constructed.
In the formula: r f The crack strength index calculated for young's modulus, dimensionless; e ma The dynamic elasticity modulus, MPa, of the rock skeleton is obtained from a theoretical value; e is the Young modulus of the coal bed, MPa; delta t c 、△t s Time difference of longitudinal wave and transverse wave of the coal seam roof is respectively, mu s/m; delta t m The longitudinal wave time difference is the longitudinal wave time difference of the framework of the coal seam roof, and is mu s/m; f c Is crack development strength index, and has no dimension; k is ν Is a rock integrity coefficient without dimension; the other parameters have the same physical meaning as before.
Step four, calculating the water content of the coal seam roof: when a large amount of movable water exists on the coal seam roof, the mining of the coal mine can be directly influenced. The water cut is defined as the ratio of the mass of water contained in the rock to the mass of the entire rock. Based on the thought, a water content calculation model shown in equation (10) can be constructed based on the rock physical volume model.
In the formula: c w The water content of the coal seam roof is dimensionless; ρ is a unit of a gradient w Density of water contained in coal seam roof in g/cm 3 ；ρ m Is the density of the rock skeleton of the coal seam roof in g/cm 3 (ii) a The other parameters have the same physical meaning as above.
Step five, calculating the compressive strength of the coal seam roof: the compressive strength of a rock is the limit at which a rock specimen will fail under uniaxial pressure and is numerically equal to the maximum compressive stress at failure. Rocks composed of different minerals have different compressive strengths. Thus, the compressive strength reflects to a large extent the stability of the coal seam roof. According to previous researches, the relation between the compressive strength and the Young modulus and the shale content is close, and accordingly, a calculation model of the compressive strength in the section of the clastic rock in the equation (11) is established.
C o ＝0.0045·E·(1-V sh )+0.008·E·V sh (11)
In the formula: c o Compressive strength of rock, MPa; the other parameters have the same physical meaning as above.
Step six, constructing a coal seam roof stability well logging quantitative evaluation model: in order to quantitatively represent the stability of the coal seam roof, introducing a coal seam roof stability evaluation index as a parameter for quantitatively evaluating the stability performance of the coal seam roof, namely quantitatively evaluating the stability of the coal seam roof by using the index. Based on the schemes in the first step and the fifth step, the stability of the rock is in direct proportion to the lithology coefficient and the compressive strength and in inverse proportion to the porosity, the crack development index and the water content. And then defining a quantitative calculation formula of the evaluation index of the stability of the coal seam roof of the equation (12). According to production practice, when the stability of the coal seam roof is evaluated, rock strata within 10m from the top of the coal seam can be considered, and the roof closer to the top of the coal seam has larger influence on the stability, namely the weight coefficient is larger. Based on the idea, a coal seam roof stability evaluation index calculation model shown in equation (13) is constructed by adopting a weighting processing method based on the stability coefficient calculated by equation (12) and considering that 1m has 8 logging sampling data points.
In the formula:R s the stability coefficient of the coal seam roof is dimensionless; I.C. A s The evaluation index is a coal seam roof stability evaluation index without dimension; h is the thickness of the coal seam roof, m, which may be 10m; i is the number of the well logging data points to be calculated, and is dimensionless; the other parameters have the same physical meaning as before.
Step seven, calculating the evaluation index of the stability of the coal seam roof: and substituting each evaluation index calculated in the first step to the fifth step into the equation (12) and the equation (13) in the sixth step to realize the calculation of the stability index of the coal seam roof. Evaluation index I of stability of coal seam roof s The numerical variation is large, in order to be based on I s Value-divide the type of roof seal performance, for R s The values were also normalized. Normalized, I s Has a maximum value of 1 and a minimum value of 0, and the greater the value of (a), the stronger the stability of the coal seam roof. According to the calculation result, on the basis that the system compares the monitoring data of the roof stability in the actual coal mining process, the classification standard of the coal seam roof stability evaluation grade shown in the table 1 is given.
TABLE 1 evaluation grade division table for stability of coal seam roof
| Roof stability type | Coefficient of stability I s |
| Class I | >0.7 |
| Class II | 0.4<I s <0.7 |
| Class III | <0.4 |
As can be seen from the table 1, the stability of the coal seam roof is divided into three types, wherein the type I shows that the stability is good; class II indicates moderate stability; class III indicates poor stability.
The invention is tried in an actual coal field. In the application of quantitative evaluation of the stability of the coal bed roof of the X well, referring to FIG. 5, a 550.1-552.5 meter well section is a coal bed, the lithology of the immediate roof of the well section is argillaceous sandstone, the thickness is 4m, the lithology of the old roof is argillaceous rock, and the thickness is 6m, the distribution range of the stability coefficient calculated by the method is 0.21-0.56, and the stability evaluation index of the coal bed roof subjected to weighting treatment is 0.48, which indicates that the stability of the roof is moderate; the mining area where the well belongs is mined in coal mines in recent years, and safety accidents such as collapse of a coal seam roof and the like do not happen, so that the evaluation result of the method can completely meet the design requirement of a coal mine safety mining scheme.
The method not only fully considers the influence of the lithologic characteristics, the compressive strength and the water content of the coal seam roof on the stability, but also considers the influence of the porosity and the crack development characteristics of the coal seam roof, and the evaluated stability of the coal seam roof is more consistent with the actual situation of a coal mine. Each evaluation index in the method can be obtained from coal field borehole logging data, and almost all coal fields have a large amount of borehole logging data. Therefore, the coal seam roof stability well logging quantitative evaluation method has good popularization and application prospects and value.
As will be understood by those skilled in the art, since well logging data is susceptible to borehole environment such as hole enlargement, in order to evaluate the stability of the coal seam roof more accurately, it is necessary to correct the environmental impact of the well logging data, and the compressive rock strength calculated by well logging must be scaled through dynamic and static conversion.
Claims (1)
1. A logging evaluation method for coal seam roof stability is characterized by comprising the following steps:
step one, calculating a coal seam roof lithology coefficient: the method comprises the following steps of (1) solving a relative natural gamma by adopting an equation, further carrying out correlation analysis on the relative natural gamma and the rock particle size measured by a laboratory, solving the particle size of the rock of the coal seam roof, and further constructing a coal seam roof lithology coefficient calculation model by utilizing the rock particle size and the shale content, wherein the method specifically comprises the following steps:
M d ＝-0.124·ΔGR+0.248 (2)
in the formula: Δ GR is a relatively natural gamma, dimensionless; GR and GR max 、GR min Respectively calculating natural gamma values of the bed points, the pure mudstone and the pure sandstone, wherein the unit is API; m d Is the rock particle size in mm; i is l The lithology coefficient of the coal seam roof is dimensionless; v sh Is the mud content; GCUR is a regional experience parameter, 3.7 is taken for the tertiary stratum, and 2 is taken for the old stratum;
step two, calculating the porosity of the coal seam roof: after the porosity test data is reset, extracting the reset density logging data, considering the influence of the shale content on the porosity, performing binary regression fitting by taking the density and the shale content as independent variables and the porosity as dependent variables to obtain a porosity calculation model shown in an equation (5),
φ＝-1.392·ρ b -0.028·V sh +6.672 (5)
in the formula: phi is the porosity of the coal seam roof; rho b Is the density of the coal seam roof, and the unit is g/cm 3 ；
Step three, calculating the coal seam roof crack development index: constructing a fracture development index shown in equation (8):
in the formula: r f The crack strength index calculated for young's modulus, dimensionless; e ma The dynamic elasticity modulus of the rock skeleton is calculated according to a theoretical value, wherein the unit of the dynamic elasticity modulus is MPa; e is the Young modulus of the coal bed and has a unit of MPa; Δ t c 、Δt s Time differences of longitudinal waves and transverse waves of a coal seam roof are respectively, and the unit is microsecond/m; Δ t m The unit of longitudinal wave time difference of the coal seam roof framework is mus/m; f c Is crack development strength index, and has no dimension; k ν Is a rock integrity coefficient without dimension;
step four, calculating the water content of the coal seam roof: constructing a water cut calculation model shown in equation (10),
in the formula: c w The water content of the coal seam roof is dimensionless; rho w Is the density of water contained in the coal seam roof and has the unit of g/cm 3 ；ρ m Is the density of the rock skeleton of the coal seam roof, and the unit is g/cm 3 ；
Step five, calculating the compressive strength of the coal seam roof: the compressive strength is closely related to the Young modulus and the shale content, so that a calculation model of the compressive strength in the clastic rock section of equation (11) is established,
C o ＝0.0045·E·(1-V sh )+0.008·E·V sh (11)
in the formula: c o The compressive strength of rock is in MPa;
step six, constructing a coal seam roof stability well logging quantitative evaluation model: based on the schemes in the first step to the fifth step, the stability of the rock is in direct proportion to the lithological coefficient and the compressive strength, and is in inverse proportion to the porosity, the crack development index and the water content, so that a quantitative calculation formula of the coal bed roof stability evaluation index of the equation (12) is defined, the stability coefficient calculated by the equation (12) is relied on, and in consideration of 8 logging sampling data points at 1m, a coal bed roof stability evaluation index calculation model shown in the equation (13) is constructed by adopting a weighting processing method:
in the formula: r is s The stability coefficient of the coal seam roof is dimensionless; I.C. A s The evaluation index is a coal seam roof stability evaluation index without dimension; h is the thickness of the coal seam roof in m, and the value can be 10m; i is the number of the well logging data points to be calculated, and is dimensionless;
step seven, calculating the evaluation index of the stability of the coal seam roof: substituting the evaluation indexes calculated in the first step to the fifth step into the equation (12) and the equation (13) in the sixth step to realize the calculation of the stability index of the coal seam roof, namely the stability evaluation index I of the coal seam roof s The numerical variation is large, in order to be based on I s Value-divide the type of top plate seal Performance, for R s The values are also normalized, I s Has a maximum value of 1 and a minimum value of 0, whichThe larger the value is, the stronger the stability of the coal bed roof is, and according to the calculation result, on the basis of roof stability monitoring data in the system comparison actual coal mining process, the coal bed roof stability evaluation grade division standard is given: stability evaluation index I s &Class I at 0.7, showing good stability; stability evaluation index I s Class II at 0.4-0.7, indicating moderate stability; stability evaluation index I s &And (iii) at 0.4, indicating poor stability.
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| CN108804849B (en) * | 2018-06-22 | 2022-04-26 | 西南石油大学 | Rock mechanical parameter evaluation method based on structural complexity |
| CN114418365B (en) * | 2022-01-05 | 2024-05-03 | 华北电力科学研究院有限责任公司 | Fly ash applicability evaluation method, system, device and storage medium |
| CN116757557B (en) * | 2023-08-15 | 2023-11-07 | 山东新巨龙能源有限责任公司 | Raw gangue filling mining quality assessment method based on data analysis |
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| CN102865078A (en) * | 2012-04-28 | 2013-01-09 | 中国神华能源股份有限公司 | Method of determining water-preserved mining geological conditions under loose water bearing layer |
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| 利用测井资料评价煤层顶底板的裂缝发育程度;王剑，王珺，候淞译;《西安石油大学学报（自然科学版）》;20150531;第30卷(第3期);第7页-第11页 * |
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