WO2015164917A1 - A method of estimating a volume fraction of coal in a layered geological structure - Google Patents
A method of estimating a volume fraction of coal in a layered geological structure Download PDFInfo
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- WO2015164917A1 WO2015164917A1 PCT/AU2015/000259 AU2015000259W WO2015164917A1 WO 2015164917 A1 WO2015164917 A1 WO 2015164917A1 AU 2015000259 W AU2015000259 W AU 2015000259W WO 2015164917 A1 WO2015164917 A1 WO 2015164917A1
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- Prior art keywords
- coal
- volume fraction
- geological structure
- thomsen
- layered
- Prior art date
Links
- 239000003245 coal Substances 0.000 title claims abstract description 61
- 238000000034 method Methods 0.000 title claims abstract description 30
- 239000000463 material Substances 0.000 claims abstract description 8
- 238000012358 sourcing Methods 0.000 claims abstract description 5
- 230000006835 compression Effects 0.000 description 3
- 238000007906 compression Methods 0.000 description 3
- 239000011435 rock Substances 0.000 description 3
- 230000002596 correlated effect Effects 0.000 description 2
- 238000009795 derivation Methods 0.000 description 2
- 238000003384 imaging method Methods 0.000 description 2
- 238000001028 reflection method Methods 0.000 description 2
- 238000012935 Averaging Methods 0.000 description 1
- RHZUVFJBSILHOK-UHFFFAOYSA-N anthracen-1-ylmethanolate Chemical compound C1=CC=C2C=C3C(C[O-])=CC=CC3=CC2=C1 RHZUVFJBSILHOK-UHFFFAOYSA-N 0.000 description 1
- 239000003830 anthracite Substances 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 239000002802 bituminous coal Substances 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 238000005553 drilling Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 239000003077 lignite Substances 0.000 description 1
- 238000005065 mining Methods 0.000 description 1
- 239000003476 subbituminous coal Substances 0.000 description 1
- 230000035899 viability Effects 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
- G01V1/28—Processing seismic data, e.g. for interpretation or for event detection
- G01V1/30—Analysis
- G01V1/306—Analysis for determining physical properties of the subsurface, e.g. impedance, porosity or attenuation profiles
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
- G01V1/28—Processing seismic data, e.g. for interpretation or for event detection
- G01V1/30—Analysis
- G01V1/301—Analysis for determining seismic cross-sections or geostructures
- G01V1/302—Analysis for determining seismic cross-sections or geostructures in 3D data cubes
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V2210/00—Details of seismic processing or analysis
- G01V2210/60—Analysis
- G01V2210/62—Physical property of subsurface
- G01V2210/622—Velocity, density or impedance
- G01V2210/6222—Velocity; travel time
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V2210/00—Details of seismic processing or analysis
- G01V2210/60—Analysis
- G01V2210/62—Physical property of subsurface
- G01V2210/626—Physical property of subsurface with anisotropy
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V2210/00—Details of seismic processing or analysis
- G01V2210/60—Analysis
- G01V2210/64—Geostructures, e.g. in 3D data cubes
- G01V2210/641—Continuity of geobodies
Definitions
- a method for estimating a volume fraction of coal in a layered geological structure. The method utilises surface seismic data.
- the ability to estimate the relative volume of coal within a layer geological structure of host material and coal seams enables a determination to be made as to the economic viability of mining for the coal. It is possible using a core drill to drill multiple holes to relatively accurately determine the shape and configuration of coal seams and thus the volume fraction of coal within a geological structure. However core drilling is relatively expensive.
- coal seams are often thin compared to the vertical resolution achievable using surface seismic surveying techniques. Accordingly it is extremely difficult to estimate volume fraction of coal seams directly from standard surface seismic imaging.
- the method may be enhanced by also utilising vertical velocity sourced from surface seismic data. This may enable more accurate estimates of volume fraction and/or confine the properties of the coal seams.
- a method of estimating volume fraction (h) of coal in a layered geological structure having alternating layers of host material and coal comprising:
- the method comprises using the Thomsen parameter ⁇ as the estimate of volumetric fraction.
- the method comprises utilising a negative value of a Thomsen parameter ⁇ as the volume fraction.
- the method comprises sourcing vertical velocity from the surface seismic data and using the vertical velocity in addition to one or more of the Thomsen parameters to provide an indication of the properties of the coal in the geological structure.
- the method comprises using the sourced surface seismic data having offsets in the order of, or greater than, about 2 to 3 times the depth of the bottom of the coal stack.
- Figure 1 is a representation of a layered geological structure containing a number of coal seams
- Figure 2a is a graphical representation of anisotropy parameter delta in comparison with the inverse of the coal fraction derived from density and velocity logs;
- Figure 2b is a graphical representation of anisotropy parameter epsilon in comparison with coal fraction derived from density and velocity logs;
- Figure 2c is the coal fraction derived from density and velocity logs.
- FIG. 1 is a representation of a layered geological structure 10 having a plurality of layers of host material 12 and coal.
- the layers of coal are known as coal seams 14.
- the coal seams 14 may range in thickness from several centimetres to several tens of metres.
- One well known surface seismic measuring technique is the seismic reflection method. This utilises one or more seismic sources placed on the ground and a plurality of geophones with known offset from the source and from each other. A source emits a wave (i.e. vibration) into the ground. The reflection of the wave occurring at interfaces between different materials is picked up by the geophones.
- the seismic reflection method utilises measuring the travel time of the waves from the source(s) to the geophones.
- An embodiment of the present method proposes using anisotropy parameters for an estimation of the volume fraction of coal in a layered geological structure.
- the anisotropy parameters can be determined relatively easily from reflection surface seismic data.
- One example of the method for deriving this information and determining the various anisotropic parameters, in particular the Thomsen parameters ⁇ , ⁇ and ⁇ is set out below.
- the volume fraction of the coal matches very well with the Thomsen anisotropy parameter ⁇ . This match can be explained by a simple derivation shown below.
- the negative value of Thomsen's 5 is also
- the choice of the appropriate formula can be given by any of the supporting information: prior geological knowledge, vertical velocity estimates, or estimates of different anisotropy parameter. If the coefficient C is approximately equal to 1 , as is the case of the following two examples, then we can see that for small anisotropy the coal volume fraction is approximately equal to the Thomsen anisotropy parameter ⁇ , in other words, h ⁇ s . Similar to using the Thomsen anisotropy parameter ⁇ , other Thomsen anisotropy parameters can be used to better constrain the volume fraction.
- Thomsen parameter delta S can be related to volume fraction h as a function of both shear and compression wave modulus as follows:
- Figures 2a-2c we show the effective anisotropic parameters ⁇ and S together with the computed volumetric fraction of the coal respectively. Both anisotropic parameters are well correlated to the volumetric fraction; the match with parameter ⁇ is explained above. Specifically Figure 2a shows effective anisotropy parameter S 20 overlaid with the negative or inverse coal fraction 22' derived from a density log. Figure 2b shows effective anisotropy parameter 8 24 overlaid with the coal fraction 22 derived from the density log. While Figure 2c shows the coal fraction derived from the density log. If the vertical velocity is known it is possible to better constrain the properties of the coal.
- the Thomsen anisotropy parameters of ⁇ , ⁇ , and ⁇ of layered geological structures containing coal seams can be related to the volume fraction of coal. In particular for typical properties of the host rock and the coal with small volumetric fraction, the volume fraction is approximately equal to the Thomsen anisotropy parameter ⁇ .
- the P-wave and shear moduli of the coal and the host rock are known, then it is possible to use a simple exact relation between the Thomsen anisotropy parameter ⁇ and the volume fraction of the coal in the formation. This means that by measuring this parameter by reflection seismic methods, one can directly estimate the resource quantities. To produce an accurate estimate of ⁇ it is preferable to use long offsets for the seismic methods. For example the offsets may be in the order of, or greater than, about 2 to 3 times the depth of the bottom of the coal stack.
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- Engineering & Computer Science (AREA)
- Remote Sensing (AREA)
- Physics & Mathematics (AREA)
- Life Sciences & Earth Sciences (AREA)
- Acoustics & Sound (AREA)
- Environmental & Geological Engineering (AREA)
- Geology (AREA)
- General Life Sciences & Earth Sciences (AREA)
- General Physics & Mathematics (AREA)
- Geophysics (AREA)
- Geophysics And Detection Of Objects (AREA)
Abstract
A method of estimating volume fraction of coal (h) in a layered geological structure having alternating layers of host material and coal. The method includes the steps of (a) sourcing surface seismic data pertaining to the layered geological structure; (b) determining at least one of the Thomsen parameters ε, δ and γ from the surface seismic data; and, (c) utilising one or a combination of two or more of the Thomsen parameters ε, δ and γ as an estimate of the volume fraction (h) of coal in the layered geological structure.
Description
A METHOD OF ESTIMATING A VOLUME FRACTION OF COAL IN A LAYERED
GEOLOGICAL STRUCTURE
Technical Field
A method is disclosed for estimating a volume fraction of coal in a layered geological structure. The method utilises surface seismic data.
Background Art
The ability to estimate the relative volume of coal within a layer geological structure of host material and coal seams enables a determination to be made as to the economic viability of mining for the coal. It is possible using a core drill to drill multiple holes to relatively accurately determine the shape and configuration of coal seams and thus the volume fraction of coal within a geological structure. However core drilling is relatively expensive.
It would be preferable if possible to obtain data relating to the volume of fraction of coal using data derived from surface seismic surveying. However coal seams are often thin compared to the vertical resolution achievable using surface seismic surveying techniques. Accordingly it is extremely difficult to estimate volume fraction of coal seams directly from standard surface seismic imaging.
The above described background art is not intended to limit the scope and application of the disclosed method of estimating a volumetric fraction of coal in a layered geological structure.
Summary of the Disclosure In broad terms there is disclosed a method of estimating the volume fraction of coal in a layered geological structure utilising the anisotropy of the layered structure. In various embodiments the Thomsen parameters epsilon ε, delta δ and gamma γ may be used as appropriate anisotropy values either by themselves or in various combinations as estimates of the volume fraction of coal.
The method may be enhanced by also utilising vertical velocity sourced from surface seismic data. This may enable more accurate estimates of volume fraction and/or
confine the properties of the coal seams.
In one aspect there is disclosed a method of estimating volume fraction (h) of coal in a layered geological structure having alternating layers of host material and coal, the method comprising:
sourcing surface seismic data pertaining to the layered geological structure; determining at least one of the Thomsen parameters ε, δ and γ from the surface seismic data; and,
utilising one or a combination of two or more of the Thomsen parameters ε, δ and γ as an estimate of the volume fraction (h) of coal in the layered geological structure.
In one embodiment the method comprises using the Thomsen parameter ε as the estimate of volumetric fraction.
In an alternative embodiment the method comprises utilising a negative value of a Thomsen parameter δ as the volume fraction.
In one embodiment the method comprises sourcing vertical velocity from the surface seismic data and using the vertical velocity in addition to one or more of the Thomsen parameters to provide an indication of the properties of the coal in the geological structure.
In one embodiment the method comprises using the sourced surface seismic data having offsets in the order of, or greater than, about 2 to 3 times the depth of the bottom of the coal stack.
Brief Description of the Drawings Notwithstanding any other forms which may fall within the scope of the method as set forth in the Summary, specific embodiments will now be described, by way of example only, with reference to the accompanying drawings in which:
Figure 1 is a representation of a layered geological structure containing a number of coal seams;
Figure 2a is a graphical representation of anisotropy parameter delta in comparison
with the inverse of the coal fraction derived from density and velocity logs;
Figure 2b is a graphical representation of anisotropy parameter epsilon in comparison with coal fraction derived from density and velocity logs; and
Figure 2c is the coal fraction derived from density and velocity logs.
Detailed Description of Specific Embodiments Figure 1 is a representation of a layered geological structure 10 having a plurality of layers of host material 12 and coal. The layers of coal are known as coal seams 14. The coal seams 14 may range in thickness from several centimetres to several tens of metres. One well known surface seismic measuring technique is the seismic reflection method. This utilises one or more seismic sources placed on the ground and a plurality of geophones with known offset from the source and from each other. A source emits a wave (i.e. vibration) into the ground. The reflection of the wave occurring at interfaces between different materials is picked up by the geophones. The seismic reflection method utilises measuring the travel time of the waves from the source(s) to the geophones. The velocity of the waves is dependent upon the elasticity and density of the ground. Further, travel time will be different for compression waves and shear waves. Generally speaking, compression waves are much faster than shear waves. As mentioned above, as coal seams are often thin in comparison to the vertical resolution of seismic data it is difficult to estimate with any reasonable degree of confidence the volume fraction of coal seams from standard reflection seismic methods/imaging. It is nonetheless known that layered geological structures can cause seismic anisotropy. Usually this effect is relatively weak due to the low contrast in elastic properties of the layers. However for materials where the elastic properties are very different the contrast can be sufficiently significant to enable the derivation of useful information. Indeed this is often the case in relation to coal which has elastic properties that are usually very different to that of its surrounding host rock. An embodiment of the present method proposes using anisotropy parameters for an estimation of the volume fraction of coal in a layered geological structure. The anisotropy parameters can be determined relatively easily from reflection surface
seismic data. One example of the method for deriving this information and determining the various anisotropic parameters, in particular the Thomsen parameters ε, δ and γ is set out below. As can be seen from the following example, the volume fraction of the coal matches very well with the Thomsen anisotropy parameter^ . This match can be explained by a simple derivation shown below. The negative value of Thomsen's 5 is also
remarkably well correlated with the coal volumetric fraction. For horizontally layered medium consisting of the host material with P-wave velocity v density px , shear modulus μ, and coal seams with relative volume fraction h and with P-wave velocity v2 , density p2 , shear modulus μ2 , the Thomsen anisotropy parameter ε is given by s = h(\ - h)C, where
(Μ - Μ2) -(μ - μ2)
C = 2(//, -//2 )
Μ Μ2 and Mj = ptv is the P-wave modulus. For volume fraction h < 0.5 it can be expressed in terms of ε as
whereas for h > 0.5 the expression is
The choice of the appropriate formula can be given by any of the supporting information: prior geological knowledge, vertical velocity estimates, or estimates of different anisotropy parameter.
If the coefficient C is approximately equal to 1 , as is the case of the following two examples, then we can see that for small anisotropy the coal volume fraction is approximately equal to the Thomsen anisotropy parameter ε , in other words, h ~ s . Similar to using the Thomsen anisotropy parameter ε, other Thomsen anisotropy parameters can be used to better constrain the volume fraction.
For example the Thomsen parameter γ is related to the volumetric fraction as a function of the shear moduli by the following formula: r = h(\ - hy-
2μχμτ
Further the Thomsen parameter delta S can be related to volume fraction h as a function of both shear and compression wave modulus as follows:
The strong impedance contrast between the layers in coal seam environments may cause significant seismic attenuation that could impede the anisotropy estimation from seismic data. However, only the high frequencies are expected to attenuate significantly, while the low frequencies that are relevant to the Backus averaging would not suffer from such scattering attenuation. In the claims which follow, and in the preceding description, except where the context requires otherwise due to express language or necessary implication, the word
"comprise" and variations such as "comprises" or "comprising" are used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence of addition of further features in various embodiments of the method as disclosed herein.
Claims
1. A method of estimating volume fraction of coal (h) in a layered geological structure having alternating layers of host material and coal, the method comprising: sourcing surface seismic data pertaining to the layered geological structure; determining at least one of the Thomsen parameters ε, δ and γ from the surface seismic data; and,
utilising one or a combination of two or more of the Thomsen parameters ε, δ and γ as an estimate of the volume fraction (h) of coal in the layered geological structure.
2. The method according to claim 1 comprising using the Thomsen parameter ε as the estimate of volume fraction of coal in the geological structure.
3. The method according to claim 1 comprising utilising a negative value of a Thomsen parameter δ as the volume fraction of coal in the geological structure.
4. The method according to any one of claims 1 to 3 comprising sourcing vertical velocity from the surface seismic data and using the vertical velocity in addition to the Thomsen parameters to provide an indication of the properties of the coal in the geological structure.
5. The method according to any one of claims 1 to 4 comprising using the sourced surface seismic data having offsets in the order of, or greater than, about 2 to 3 times the depth of the bottom of the coal stack.
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| AU2014901587 | 2014-05-01 | ||
| AU2014901587A AU2014901587A0 (en) | 2014-05-01 | A Method of Estimating a Volume Fraction of Coal in a Layered Geological Structure |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN108761531A (en) * | 2018-04-12 | 2018-11-06 | 中国矿业大学 | A kind of Coal Pore Structure intelligent Forecasting based on SVM theories |
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|---|---|---|---|---|
| US5835452A (en) * | 1995-10-06 | 1998-11-10 | Amoco Corporation | Reflected shear wave seismic processes |
| US20100135115A1 (en) * | 2008-12-03 | 2010-06-03 | Chevron U.S.A. Inc. | Multiple anisotropic parameter inversion for a tti earth model |
| US20130013209A1 (en) * | 2010-03-11 | 2013-01-10 | Yaping Zhu | Predicting anisotropic source rock properties from well data |
-
2015
- 2015-05-01 WO PCT/AU2015/000259 patent/WO2015164917A1/en active Application Filing
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5835452A (en) * | 1995-10-06 | 1998-11-10 | Amoco Corporation | Reflected shear wave seismic processes |
| US20100135115A1 (en) * | 2008-12-03 | 2010-06-03 | Chevron U.S.A. Inc. | Multiple anisotropic parameter inversion for a tti earth model |
| US20130013209A1 (en) * | 2010-03-11 | 2013-01-10 | Yaping Zhu | Predicting anisotropic source rock properties from well data |
Non-Patent Citations (1)
| Title |
|---|
| THOMSEN: "Weak Elastic Anisotropy", GEOPHYSICS, vol. 51, no. 10, 1986, pages 1954 - 1966, XP002082613 * |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN108761531A (en) * | 2018-04-12 | 2018-11-06 | 中国矿业大学 | A kind of Coal Pore Structure intelligent Forecasting based on SVM theories |
| CN108761531B (en) * | 2018-04-12 | 2019-06-21 | 中国矿业大学 | A kind of Coal Pore Structure intelligent Forecasting based on SVM theory |
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