Nheyo huru dzenzira yeCSAMT mu geophysics
Nzira yeCSAMT (Controlled-Source Audio-frequency Magnetotellurics) inzira yemagetsi inoshandiswa pakuongorora kusiyana kwe resistivity pasi pevhu. CSAMT inoshandiswa zvakanyanya mukutsvaga geothermal, mineralization, hydrogeology, uye kuferefeta zvivakwa zve geological zvakaita sezvikanganiso nenzvimbo dzekuchinja. Chinhu chikuru chakanakira kugona kwayo kupa mifananidzo yakadzika ye resistivity ine resolution yakanaka, uku ichiramba "ichidzorwa" kupfuura nzira yechisikigo yeMT nekuti simba rinogadzirwa nemaoko (rinodzorwa).
Chinyorwa chino chinokurukura misimboti yekutanga yeCSAMT, kubva papfungwa yefizikisi, gadziriro yekuwana, kusvika pakupfupikiswa kwetsananguro yayo.
1. Nhoroondo uye pfungwa yekudzivirira
Nzira zhinji dze geophysical dzinovavarira kufungidzira ma physical parameters ematombo. MuCSAMT, chinhu chikuru chinoshandiswa ndechekudzivirira magetsi (ρ) kana kuti conductivity yayo (σ). Kudzivirira kunokonzerwa nerudzi rwematombo, porosity, fluid content, salinity, tembiricha, uye kuvapo kwema minerals anofambisa mvura (semuenzaniso, sulfides kana ivhu).
Semuenzaniso, munzvimbo dzine mvura inopisa, nzvimbo dzevhu dzakachinjwa nemhepo dzinowanzoratidza simba shoma rekudzivirira, nepo matombo makuru uye akaoma anowanzo dzivirira simba. Mapatani aya ekudzivirira simba anobva ashandiswa kududzira hurongwa hwemvura inopisa: chivharo chevhu, dziva, uye zvivakwa zvinodzora.
2. Musiyano uripo pakati peCSAMT neMT yechisikigo
Nzira dzeClassical Magnetotellurics (MT) dzinoshandisa kusiyana kwechisikigo mumunda wemagetsi wePasi (unobva muionospheric uye magnetospheric activity) senzvimbo. MT inobudirira pakuferefeta kwakadzama, asi kunaka kwedata kunoenderana nesimba rechiratidzo chechisikigo uye ruzha rwetsika.
CSAMT inouya semhando inoshandisa chinhu chekugadzira—kazhinji kacho chiri chinhu chinochinja-chinja ruzha rwemagetsi—chinotumirwa kuburikidza ne long current dipole. Nekuti chinhu chacho chinodzorwa, CSAMT ine zvakanakira zvakawanda:
– Chiratidzo chakasimba uye chakagadzikana mune frequency range inodiwa.
- Chiyero chechiratidzo-kune-ruzha chinowanzova nani, kunyanya munzvimbo dzine ruzha.
- Yakakodzera zvinangwa zvisina kudzika kusvika pakati nepakati (kazhinji mazana emamita kusvika makiromita akati wandei, zvichienderana nekusimba uye mamiriro ekufamba kwenguva).
Zvisinei, CSAMT ine miganhu: zvimwe zvinhu zvinofungidzirwa (semuenzaniso mamiriro ezvinhu ari kure) zvinofanira kuzadzikiswa kuti data rigadziriswe seMT.
3. Nheyo dzefizikisi: kubva pamagetsi ekugadzira kusvika kumhinduro dzepasi pevhu
MuCSAMT, AC current ye specific frequency inopfuudzwa muvhu kuburikidza nema emit electrodes maviri (achigadzira current dipole). Iyi current inogadzira primary electromagnetic field, iyo inobva yabatana nevhu. Kusiyana kwe resistivity ye subsurface kunokanganisa kuti munda unopararira sei uye unonyoroveswa, zvichigadzira second field.
Chinogamuchira chinoyera simba remagetsi (E) uye simba remagineti (H). Hukama huripo pakati peE neH pahuwandu hwakatarwa hunoratidzwa kuburikidza ne impedance:
\[
Z(\omega) = \frac{E(\omega)}{H(\omega)}
\]
Kubva pakusapindirana uku, maparamita anowanzoshandiswa mukududzira anoverengwa, kureva kuti resistivity inooneka uye phase. Muchimiro chakareruka che1D MT/CSAMT case:
\[
\rho_a(\omega) = \frac{1}{\mu_0 \omega} |Z(\omega)|^2
\]
apo \(\mu_0\) iri magnetic permeability ye vacuum uye \(\omega = 2\pi f\). Chikamu chinotsanangura kuchinja pakati peE neH, izvo zvinowanzobatsira kusiyanisa mhedzisiro ye layer uye mhando yedata.
Chinhu chakakosha pakunzwisisa: mafrequency akakwirira anonyanya kunzwa kudzika kusina kudzika (kudzika kweganda kudiki), nepo mafrequency akaderera achiongorora zvakadzama.
4. Pfungwa yekudzika kweganda uye kudzika kwekuongorora
Kudzika kunobudirira kwekupinda kwemafungu eEM munzvimbo inofambisa mvura kunowanzo fungidzirwa nehukuru hweganda:
\[
\delta \approx 503 \sqrt{\frac{\rho}{f}}
\]
(ne δ mumamita, ρ muma ohm-meters, uye f muHz). Equation iyi inoratidza:
– Dombo rinoramba richirwisa (ρ yakakura), mafungu anopinda zvakanyanya.
– Kana frequency yakaderera (f diki), ndipo panopinda zvakanyanya.
Nekuti CSAMT inoshanda muhuwandu hwema audio-frequency (semuenzaniso ~0,1 Hz kusvika ku kHz dzinoverengeka zvichienderana nesystem), nzira iyi inoshanda zvikuru pakadzika kwe shallow-medium, kunyanya kana chinangwa chiri chimiro che resistivity chakasiyana.
5. Kugadziriswa kwekutenga: chinotumira uye chinogamuchira
a) Chitubu (chinotumira)
Zvikamu zvikuru zvemuchina wekutumira weCSAMT ndeizvi:
- Chigadzirwa chejenareta/Tx chinogadzira magetsi eAC anodzorwa.
– Current dipole: maerekitirodhi maviri akaiswa kure kure (kureba kwedipole kunogona kuva mazana emamita kusvika makiromita akati wandei).
- Tambo yekutumira inobatanidza chikamu chekutumira uye maerekitirodhi.
Kusarudzwa kwehurefu hwe dipole nehukuru hwezvino kunokanganisa simba rechiratidzo uye huwandu hwekuyera.
b) Mugamuchiri
Pakuyera, mugamuchiri anowanzo nyora:
– Nzvimbo yemagetsi: kushandisa maerekitirodhi maviri anogona kuwanikwa kuti uwane chikamu cheEx kana Ey.
– Simba remagineti: kushandisa magnetic coil yeHx kana Hy.
Kuyerwa kunoitwa pamafrequencies akasiyana-siyana (kutsvaira) kuti pave ne resistivity inooneka uye phase curves inopesana nemafrequencies.
c) Kutungamira uye zvikamu zve tensor
Mukuita, zviyero zvinogona kuitwa nenzira mbiri dzinoenderana (x na y) kuti pave nemhinduro yakakwana, kunyanya mumamiriro e2D/3D geological. MuMT, izvi zvinozivikanwa se impedance tensor. Nheyo yacho yakafanana muCSAMT kana kuyerwa kwezvinhu zvakawanda kuchiitwa.
6. Zvinodiwa zvemunda uri kure uye nyaya dzemunda uri pedyo
Imwe yenheyo dzakakosha dzeCSAMT ndeyekuti pane mamiriro ekunze ari kure, kureva kuti daro riri pakati pechinhu chinotumira nepanogashira rinofanira kunge rakakwana kuitira kuti nzvimbo yakayerwa isvike pamaitiro emhepo yakaita seye plane wave sezvakaita muMT.
Kana mugamuchiri ari pedyo zvakanyanya netransmitter, data racho richakanganiswa nemhedzisiro yepedyo (zvikamu zvemunda zvisati "zvakura" kuita mafungu endege). Nekuda kweizvozvo, resistivity inoonekwa yakaverengerwa uchishandisa fomura yeMT inogona kunge yakarerekera. Nokudaro, ongororo dzeCSAMT dzinowanzo:
– kuisa chinotumira mashoko kure nenzira yemugamuchiri,
- sarudza nguva yakakodzera kuitira kuti zvinodiwa zvemunda uri kure zvigone kuzadzikiswa,
- kana kushandisa zvigadziriso/modeling yakakosha kana nzvimbo dziri pedyo dzisingadzivisiki.
7. Zvigadzirwa zvedata: zvinooneka kuti hazvigoneki, chikamu, uye chikamu chekuchinja
Mhedzisiro yekutanga yeCSAMT inowanzo kuve:
– ρa vs frequency curve yepoindi imwe neimwe.
- Phase vs frequency curve yepoinzi yega yega.
Zvisinei, chinangwa chikuru cheongororo iyi ndechekuratidza resistivity iri pasi pevhu. Pachinangwa ichi, inversion (1D, 2D, kana 3D) inoshandiswa. Inversion inotsvaga resistivity model iyo, kana yaitevedzera, inogadzira mhinduro dzeE neH dzinoenderana zvakanyanya nedata rakaonekwa. Mukutsvaga kwegeothermal, mhedzisiro ye inversion ye2D kana 3D inowanzo kuratidzwa se:
- chikamu chekudzivirira simba,
- mepu chaiyo yehudzamu (chidimbu chehudzamu),
- kududzirwa kwenzvimbo dzinofambisa mhepo/dzinodzivirira dzine chekuita nekuchinja, mvura, kana maumbirwo.
8. Zvakanakira nemiganhu yeCSAMT
Keunggulan
– Nzvimbo yakasimba uye yakagadzikana, yakanaka kunzvimbo dzine ruzha.
- Kugadziriswa kwakanaka kwemvura yakadzika kusvika pakati nepakati.
- Gadzirisa musiyano wekudzivirira hunhu hwezvinhu zvine chekuita nezvikanganiso, nzvimbo dzevhu, nzvimbo dzemvura, kana mineralization.
Miganhu
- Inoda zvinhu zvinotumira: kupinda kwepasi, tambo refu, maerekitirodhi, simba.
– Inonzwa zviri pedyo nemunda kana daro remuchina wekutumira-kugamuchira risina kukwana.
- Dudziro inogona kunge isiri yakasiyana; inoda kubatanidzwa nedata re geological, geochemical, gravity, seismic, kana drilling.
9. Mhedziso
Nheyo huru yeCSAMT yakavakirwa pakuyera hukama huripo pakati pemagetsi nemagineti anokonzerwa nezvinhu zvakagadzirwa pamagetsi. Kubva kuE/H impedance, zvinoonekwa kuti zvinodzivirira uye phase zvinowanikwa, izvo zvinozoshandurwa kuita subsurface resistivity model. Pfungwa yefrequency-depth (ganda depth) inobvumira CSAMT kuti iongorore zvivakwa zvisina kudzika kusvika pakati nepakati zvine hunhu hwakanaka hwechiratidzo, chero bedzi dhizaini yekuongorora ichitarisa zvinodiwa nefar-field uye kuderedza ruzha.
Mukuita, CSAMT chishandiso chinobatsira zvikuru mukutsvaga geology uye kugadzira mapu nekuti resistivity iparameter inonzwa mvura, shanduko, uye chimiro—zvinhu zvitatu zvakakosha muhurongwa hwakawanda hwe geology hwakadai segeothermal uye mineralization.
Kana muchida, ndinogona kubatsira kuwedzera chinyorwa chino nemienzaniso yemagadzirirwo eongororo (nzvimbo yekutumira, frequency ranges), processing flows, kana zvidzidzo zveCSAMT dudziro mumasystem egeothermal.
