Sıra | DOSYA ADI | Format | Bağlantı |
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01. | Modified Function Infinitesimal Equation | pptx | Sunumu İndir |
Transkript
New technologies of TEM in ChinaGuoqiang Xue, Weiying Chen, Dongyang HouInstitute of Geology and Geophysics, Chinese Academy of SciencesJournal of Geophysics & Remote Sensing
OUTLINES• 1. Introduction• 2. new technology1-Infinitesimal point charge• 3. new technology2-Electric source short-offset TEM• 4. new technology3-Modified central loop TEM• 5. new technology4-EM pseudo-seismic imaging• 6. Reference
1. IntroductionTransient electromagnetic method ( TEM ( is a time domain method in electromagnetic exploration, which is sensitive to conductive targets and have been widely used in mineral source, coal, ground water, environment and engineering investigation(Nabighian,1991).1.1 TEM Introduction
1. Introduction continued1.2 Some vital issues in TEM exploration1) Understand and calculate the TEM response base on its physical mechanism.2) Greater investigation depth is needed to meet the need from deep mineral deposits and coal hydrogeology.3) Higher precision and faster detection for both shallow and deep investigation.4) Efficient processing method suitable to2D and3D data.
2. Infinitesimal Point Charge2.1 Traditional approach to calculate TEM responsedue to a finite source1). Regard the source as a dipole(Kaufman,1987) 2). Regard the source as a superposition of manydipoles(Nabighian,1991)The relative error drops with the decrease of dipole dimension. The smallest and intrinsic source should be point charge
2. Infinitesimal Point Charge continuedt xx 2 1 J x, x, Te 4t dxd 0 D 2.2 BasisAccording to Maxwell equations so long as an electric charge varies with time it willexcite electromagnetic wave .2.3 MathematicsBased on point charge hypothesis, TEM field analytical solution has been derived by introducing time-domain Green function. Integral formula has been used to transform electromagnetic field damping wave equation into Green function integral form. Auxiliary path has been constructed for solving singularity problem. Four heavy generalized integral formula of time-domain electromagnetic field response has been arrived by using Jordan's lemma, the residue theorem and generalized function method. Direct-time-domain exact solution of D’Alembert equations firstly has been derived(Zhou,2013;Xue,2014).E(x, t)
2.4 Comparison with dipole2. Infinitesimal Point Charge continuedSolid line represents infinitesimal point charge (left figure) and measured data( right figure), dashed represents dipole (both figures)It is shown that the field of the infinitesimal point charge in the near source zone is different from that of dipole, whereas the far-source zone fields of these two sources are identical. The comparison of real and simulated data shows that the infinitesimal point charge represents the real source better than dipole source.
3. Electric Source Short-offset TEM3.1 Background1) Loop source excites only horizontal induction current, while grounded wire source has both horizontal and vertical induction current. This leads to loop source TEM only sensitive to conductive targets.2) Detection depth of loop source TEM usually is shallower than 1km.3) Difficult to lay the transmitting loop at mountain areas.
3. Electric Source Short-offset TEM continued3.1 Background ContinuedLOTEM(Strack,1992)• Advantage: great detectiondepth (more than10km)• Disadvantages: great source- receiver distance (2~20Km), weak signal, volume effect, poor precision,MTEM(Ziolkowski,2007)Advantage: great power, pseudorandom transmitting source; multi-channel array, multi component, 3D detection; Pseudo- seismic imaging of dataDisadvantage: heavy, hard to conduct at mountain area; mainly used in marine; systemic and robust equipment have not been introduce to china
3. Electric Source Short-offset TEM continued3.2 DefinitionShort-offset TEM (abbreviated to SOTEM) means that the distance between transmitter and receiver is approximately equal to or less than the exploration depth(Xue,2013).Typical SOTEM layout diagram
3. Electric Source Short-offset TEM continued3.3 Observation area for each EM component5390o xy 35 90o 60o 60oy4 4 470o 70o70o 70o4 x x y 5 160o 160o 54 4 4x 470o 70o 70o 70o x55390o 60o 90o3 60oxy3 3 160 o Eyx 160o EyyEzHx Hy Hz
3.4 All-time apparent resistivity1E-005 0.0001 0.001 0.01 0.1 11E-0050.00010.0010.010.1110100100010000100000type Hall timeearly time late time t(s)r 1= 10 0 W.m h1=500mr 2 = 10 W.m h2=500mr 3 = 10 0 W.m3. Electric Source Short-offset TEM continued0.0001 0.001 0.01 0.1 1101001000p25025105Calculated by polynomial fitting methodCalculated by dichotomy method
3. Electric Source Short-offset TEM continued3.5 ImagingElectric field underneath the Tx2xuE (z,t)= Ilρ [erf( )- 1 +( 2 u- 1 )(1+ u2)e -u /2 ]πz3 2 π 2 22Time of maximum of Ex for a given depthz=zimagedEx (z,t) =0dtImage depthimagez2 (t) = 4tμ0σHz from a current filament located at image depthzHI y x L x L4 y2 z2 ((x 1)2 y2 z2 )1/ 2 ((x 1)2 y2 z2 )1/ 2slowness0d t = 1 zμ σd z 2Conductivity of the image02 d2 t dz2Source image for athree-layer model
3. Electric Source Short-offset TEM continued3.6 Case studyInvestigation of hydrous coal mine in Shandong ProvinceDiscovery of Dawangzhuang Iron Ore in Anhui Province
4. Modified Central Loop TEMRegular central loopTEM has only one survey point at once layout, which leads to energy waste and low work efficiency4.1 ReasonsThe vertical magneticresponse in the centralpart of loop is Approximately equal (Xue,2012)The modified deviceutilize the signal from a bigger central part which about 1/3 of loop area.
4. Modified Central Loop TEM continued4.2 Modified theory1zI0k2a3H () [3 (3 3k a k2a2 )ek1a ]1 132at5t B z (t )4t 2I a 2 L (t ) 0 ( 0 0 )2 2 00 1 2 1 312 31zIk ak1a H () [Z (r) (Z (r) Z (r)k a Z (r)k a )e]0 1 0 023L za60tu Z (r) I (B (t)) [ t B(t) ]ttCentral loop Modified Central loop
4. Modified Central Loop TEM continued4.3 Modified instrumentsAir coil:heavyand with smallreceivearea(100m2)Magnetic probe: portable and with great receive area(10000m2, 20000m2)Probe 1coilProbe 20.01 0.1 101t/ ms1000010001001010.10.01Significantlyincrease the signal strength
5. TEM Pseudo-seismic Imaging5.1 Basic theory(Xue,2013)Background1). The precision in TEM prospecting is relative low compare with seismic method 2). Interpretation and judgment always be made based on experience of interpreter 3). 2D and 3D TEM inversion are time-consuming and expensive.For the aim to improve the precision, can we interpret TEM data similar to seismicmethod?Basic equation constructionDiffusion equations for TEM 2 2 U (r , ) (r )U (r , ) 0012 t3 2Hm (t) e 4tU ( )d H(r, p2 ) U(r, p) Hm (r,t) (r) t Hm (r,t) 0Diffusion equations for seismicInverse Laplace transform1 22113n2ji 4ti4titin1j 2 q q qH 2 1 1 j( n n1 )Um )j 1 j 1 )U j ne(( )U 2 e( e2 tDiscrete
5. TEM Pseudo-seismic Imaging continued5.2 Key techniquesWavelet extractionKirchhoff integral function 1 u(x, y, z,t) [u] (1) 1 [ u ] 1 r [ u ]dQ F4 Q n r r n vr n t r0----main idea of calculation1). normalize method has been adopted,2). optimizing normalizing parameter havebeen selected by deviation theory 3).Newton iterative form to be used to makethe transformed wave field stable andreliable.Migration imaging
5. TEM Pseudo-seismic Imaging continued5.3 Models simulation1 5 m,h1 80m2 500 m1 1 m,h1 60m2 10 m, h2 60m3 100 m1 10 m2 300 mh 70m
5. TEM Pseudo-seismic Imaging continued5.4 Case studyRecognizing electrical interfacein Shanxi provinceDetecting deep electric structure and distribution in Guangdong province
6. ReferenceG.Q. Xue, Gelius, L.Xiu 3-D Pseudo-seismic Imaging of TEM data– a Feasibility Study. GeophysicalProspecting, 2013, 61(S1), : 561–571doi:10.1111/j.1365-2478.2012 . 01109.Guo-Qiang X, Wei-Ying C, Nan-Nan Z, Hai L, Hua-Sen Z (2013) Understanding of Grounded-Wire TEM Sounding with Near-Source Configuration. J Geophys Remote Sensing 2:113. doi: 10.4172/2169 0049.1000113Kaufman, A.A., and Keller, G.V., 1983, Frequency and transient sounding: Methods in geochemistry andgeophysics: Elsevier Publ. Co, 1–32.Nabighian, M.N., and Macnae, J.C., 1991, Time-domain electromagnetic prospecting methods: in Nabighian,M.N. (ed.), Electromagnetic methods in applied geophysics–Theory volume II, Part A, Society of Exploratio Geophysicists, Tulsa,Strack K M.Exploration with deep transient electromagnetic method[M], Elsevier,1992Xue, G.Q., Bai, C.Y., and Yan, Y., 2012, Deep sounding TEM investigation method based on a modified fixed central-loop system: Journal of Applied Geophysics, 76(2012) 23–32.Xue, G.Q., Wang, H.Y., Yan S., Zhou N.N. 2014, Time-domain Green function solution for transientelectromagnetic field. Chinese Journal geophysics,57(2:671-678)Zhou Nan-nan, Xue Guo-qiang, Wang He-yuan. Comparison of the time-domain electromagneticfield from an infinitesimal point charge and dipole source. Applied Geophysics, 2013,10(3):349-356Ziolkowski A, Hobbs B. A, Wright D (2007) Multi-transient electromagnetic demonstration survey in France.Geophysics 72: 197-209.
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