Mfundo Zoyambira ndi Kugwiritsa Ntchito Njira ya TDEM mu Geophysics
Njira ya Time Domain Electromagnetic (TDEM) ndi njira yogwiritsidwa ntchito kwambiri yofufuzira kapangidwe ka zinthu za pansi pa nthaka kutengera kusiyana kwa mphamvu zamagetsi za zinthu, makamaka resistivity (kapena inverse, conductivity). TDEM ndi njira yosavulaza, yofulumira, komanso yothandiza pazinthu zosiyanasiyana kuyambira kufufuza pansi pa nthaka mpaka kufufuza mchere ndi mapu a kuipitsidwa. Nkhaniyi ikufotokoza mfundo zoyambira za TDEM, zigawo za dongosolo, momwe imagwirira ntchito, kutanthauzira deta, ubwino ndi zofooka, ndi ntchito zake zothandiza mu geophysics.
1. Mbiri ndi mfundo zoyambira
Mu geophysics, kukana kwa miyala kumakhudzidwa ndi zinthu zambiri, monga kuchuluka kwa madzi, kuchuluka kwa mchere, kuchuluka kwa ma porosity, mtundu wa mchere, kutentha, ndi kuchuluka kwa kusintha. Zipangizo zokhala ndi ma porosity odzazidwa ndi madzi amchere nthawi zambiri zimakhala ndi mphamvu yoyendetsa bwino (kukana kotsika), pomwe miyala youma imakonda kukhala yotsutsa kwambiri.
Njira ya TDEM imagwiritsa ntchito momwe Dziko Lapansi limayankhira ku gawo la ma electromagnetic losinthasintha nthawi. Mosiyana ndi njira ya frequency-domain electromagnetic (FDEM), yomwe imagwiritsa ntchito mafunde a sinusoidal pama frequency enaake, TDEM imagwiritsa ntchito gwero lamagetsi lomwe limayatsidwa ndi kuzimitsidwa (lomwe limayendetsedwa kapena kutsitsidwa). Mphamvu yamagetsi ikazimitsidwa, mphamvu yamagetsi yoyamba imagwa, ndikupanga mphamvu yamagetsi yomwe imayikidwa pansi pa pamwamba. Kuwonongeka kwa mphamvu yamagetsi iyi kumalembedwa nthawi zinazake, zomwe zimathandiza kuti chidziwitso chakuya chipezeke kuchokera momwe chizindikirocho chimasinthira pakapita nthawi.
2. Mfundo za fizikisi ya TDEM: mafunde oyambitsa ndi mafunde a eddy
Pamene magetsi akuyenda kudzera mu transmitter loop, mphamvu yaikulu ya maginito imapangidwa. Pamene mphamvu yamagetsi imayimitsidwa mofulumira (kutsika pang'onopang'ono), mphamvu ya maginito yosinthayi imapanga mphamvu yamagetsi yochokera ku mphamvu yamagetsi motsatira lamulo la Faraday. Zotsatira zake, mafunde a eddy amapanga pansi pa nthaka, omwe amafalikira kenako n’kuwola chifukwa cha kukana kwa njirayo.
Khalidwe lofunika la TDEM ndi ubale wa nthawi ndi nthawi:
– Nthawi yoyambirira: yankho limakhala losavuta kukhudza zigawo zosaya kwambiri chifukwa mafunde a eddy amakhalabe ozungulira pamwamba.
- Nthawi yochedwa: yankho limayimira kuzama kwakukulu chifukwa mafunde a eddy "afalikira" pansi ndipo afooka.
Mwachikhalidwe, cholumikizira chowongolera bwino chimapangitsa kuti chizindikiro chiwole pang'onopang'ono (kuwola kwa nthawi yayitali), pomwe chosinthira chotsutsa chimakonda kuwonetsa kuwola mwachangu.
3. Zigawo za dongosolo ndi kasinthidwe ka kafukufuku
Dongosolo la TDEM nthawi zambiri limakhala ndi:
1. Chotumizira: gwero lamagetsi lomwe limayenda ndi ma current pulses mu loop/coil.
2. Chingwe cholumikizira: chingwe chotambasulidwa pamwamba (chingakhale cha sikweya, chozungulira, kapena mawonekedwe ena).
3. Cholandirira: chipangizo chojambulira mphamvu yamagetsi yomwe yachitika pakapita nthawi.
4. Cholumikizira cholandirira: chitha kuyikidwa pakati pa lupu (lupu yapakati) kapena padera (lupu yochotsera).
5. Chida chowongolera ndi deta yolozera: chimasunga curve ya kuwonongeka kwa magetsi motsutsana ndi nthawi (yankho losakhalitsa).
Makonzedwe otchuka a kafukufuku:
– Chizunguliro chapakati: cholandirira chili pakati pa chizunguliro chotumizira uthenga; chabwino kwambiri pakumveka kwa 1D komanso kuyankha mokhazikika.
– Chizunguliro chogwirizana: cholandirira ndi chotumizira ndi chimodzimodzi; chothandiza, koma chimafuna kuthana ndi zotsatira zolumikizira ndi yankho loyambirira.
– Chizunguliro cha offset: cholandirira chimayikidwa patali pang'ono ndi chizungulirocho; chimathandiza ndi kulimba kwa mbali ndi zolinga zinazake.
Kusankha kukula kwa lupu ndi mphamvu ya mafunde kumakhudza kuzama kwa kulowa: ma lupu akuluakulu ndi mafunde apamwamba nthawi zambiri amawonjezera luso "lowona" mozama, koma amafunikira zinthu zambiri.
4. Kupeza deta : nthawi ndi kuchepetsa phokoso
Deta ya TDEM imalembedwa mu mawindo a nthawi osiyana, mwachitsanzo, kuyambira ma microseconds mpaka ma milliseconds (kapena kupitirira apo) magetsi atazimitsidwa. Mawindo oyambirira amajambula mayankho osaya, pomwe mawindo ochedwa amajambula kuzama kwakukulu.
Zovuta zofala pakuyezetsa kwa TEM ndizo:
- Phokoso lachikhalidwe: zingwe zamagetsi, mipanda, magalimoto, ndi zomangamanga zachitsulo.
– Kulumikiza kwa maginito: kuchokera ku zinthu zachitsulo pafupi ndi cholandirira kapena chotumizira.
- IP (Induced Polarization) imakhudza zinthu zina zomwe zingasinthe mawonekedwe a kuwonongeka.
- Kusinthasintha kwa zida ndi mphamvu yamagetsi: kulinganiza ndi kuyika zinthu m'makoma kumafunika.
Kuti deta ipitirire bwino, kuyika zinthu pamodzi (kubwerezabwereza kwa kugunda kwa mtima ndi kusalala kwa chizindikiro) kumagwiritsidwa ntchito kuchepetsa phokoso mwachisawawa. Kuphatikiza apo, kusankha malo oyezera ndi malo ozungulira nthawi zambiri zimakhala zinthu zofunika kwambiri kuti kafukufuku apite patsogolo.
5. Kutanthauzira deta ndi kusintha kwake
Kutulutsa kwa TDEM nthawi zambiri kumakhala kusinthasintha kwa kupsinjika komwe kumachitika poyerekeza ndi nthawi. Kuti kumveke ngati chitsanzo cha pansi pa nthaka, deta imakonzedwa ndikusinthidwa kukhala mbiri yotsutsa.
Njira zodziwika bwino zotanthauzira:
– Chitsanzo cha 1D (kumveka): chimagwiritsa ntchito zigawo zopingasa; zoyenera kufufuza kosavuta kwa stratigraphic, ma sedimentary basin, kapena madzi a m'madzi.
- Ma model a 2D: amagwiritsidwa ntchito pa nyumba zazitali monga zolakwika, malire a lithological, kapena kulowerera.
- Ma model a 3D: ofunikira pa malo ovuta, mwachitsanzo miyala ya sulfide, makina otentha a nthaka, kapena malo osiyanasiyana okhala m'mizinda.
Kusinthasintha kwa TDEM kumayesa kupeza chitsanzo cha resistivity chomwe chimapanga yankho la chiphunzitso lomwe likugwirizana bwino ndi deta. Chifukwa vutoli silili lapadera, kukhazikika (kuletsa kusalala kwa chitsanzocho) ndi kuphatikiza ndi zidziwitso zina za geological kapena geophysical nthawi zambiri zimagwiritsidwa ntchito.
6. Ubwino ndi zofooka za njira ya TDEM
Kuposa
– Yosavuta kukhudza ma conductor: yothandiza kwambiri pozindikira madera oyendetsera mpweya monga dongo, madzi amchere, ma sulfide ambiri, kapena zinthu zodetsa.
- Kuzama kolowera bwino: makamaka m'malo otetezedwa komanso okhala ndi zingwe zazikulu.
- Kutha kokwanira koyima: kuthekera kolekanitsa zigawo kutengera kusintha kwa resistivity.
- Mwachangu: kafukufuku wa m'munda ukhoza kuchitika bwino pa mfundo zambiri zomveka bwino.
Zolepheretsa
- Phokoso la chikhalidwe likhoza kukhala lovuta: madera a m'mizinda kapena pafupi ndi mawaya amagetsi.
- Kusamveka bwino kwa tanthauzo: kukana kwa nthaka kumakhudzidwa ndi zinthu zambiri; kuwongolera kwa nthaka ndikofunikira.
- Zolepheretsa za kulimba kwa mbali ya mawu a 1D: ngati kapangidwe kake kali ndi 3D kwambiri, mitundu ya 1D ikhoza kukhala yosokeretsa.
- Zotsatira za pafupi ndi pamwamba: zigawo zosaya kwambiri zoyendetsa mpweya zimatha "kubisa" yankho kuchokera pansi.
7. Kugwiritsa ntchito kwakukulu kwa TDEM mu geophysics
7.1 Kufufuza madzi apansi pa nthaka (hydrogeophysics)
TDEM ndi yotchuka kwambiri pakupanga mapu:
- makulidwe a matope ndi miyala,
– malire a aquifer ndi aquitard (monga dongo loyendetsa madzi),
- kulowa kwa madzi a m'nyanja m'mphepete mwa nyanja (malo operekera mpweya chifukwa cha mchere wambiri),
- kudziwa komwe kuli zitsime zopangira zinthu ndikuwunika momwe madzi a m'madzi angayendere.
Mu maphunziro ambiri, TDEM imagwiritsidwa ntchito limodzi ndi zobowola ndi deta ya geology kuti achepetse kusamveka bwino.
7.2 Kufufuza za mchere ndi zolinga zoyendetsera
Ma sulfide ambiri kapena madera ena okhala ndi mchere nthawi zambiri amakhala ndi mphamvu, zomwe zimapangitsa kuti TDEM ikhale yothandiza pa:
- kuzindikira ma conductor osiyana (zolinga za ore),
- kuzindikira kusintha kwina kwa kutentha kwa madzi,
- zimathandiza kudziwa zinthu zofunika kwambiri pakubowola.
Pa zolinga zoyendetsa bwino komanso zazing'ono, makonzedwe a offset kapena kafukufuku wa TDEM wokwanira (kuphatikizapo machitidwe oyenda pandege m'malo ena) ndi oyenera kwambiri.
7.3 Kutentha kwa Dziko
Mu makina otentha a dziko lapansi, chivundikiro cha dongo nthawi zambiri chimakhala ndi mphamvu yotsika, pomwe chosungiramo madzi chimakhala cholimba kwambiri. TDEM imagwiritsidwa ntchito ku:
- chivundikiro cha dongo chojambula mapu,
- kupanga mapu a malire a makina ndi kapangidwe ka olamulira,
- thandizani kusankha malo ofufuzira zinthu.
TDEM nthawi zambiri imaphatikizidwa ndi MT (magnetotelluric) kuti iphimbe kuzama kwakukulu.
7.4 Malo ndi kuipitsidwa
Zinthu zodetsa zomwe zasungunuka (monga madzi otayira zinyalala kapena madzi amchere) zimatha kuwonjezera mphamvu ya nthaka. TDEM imagwiritsidwa ntchito ku:
- kujambula kufalikira kwa ma plums oipitsidwa,
- yang'anirani kusintha kwa kayendedwe ka magetsi pakapita nthawi,
- kufufuza za zinyalala zamafakitale kapena malo otayira madzi.
7.5 Geotechnics ndi uinjiniya
Pazofunikira pa zomangamanga, TDEM ingathandize:
- mapu a kuya kwa thanthwe,
- kuzindikira madera ofooka kapena zigawo zokhuthala za dongo,
- maphunziro oyambirira a njira za mapaipi, misewu kapena madamu pamlingo winawake.
Komabe, pakakhala kusaya kwambiri, njira zina monga GPR kapena resistivity (ERT) zitha kukhala zowonjezera mwatsatanetsatane.
8. Mapeto
Njira ya TDEM ndi njira yamphamvu yamagetsi yofotokozera pansi pa nthaka kutengera kusintha kwa resistivity. Pogwiritsa ntchito kuwonongeka kwa yankho lamagetsi pambuyo poti transmitter current yazimitsidwa, TDEM imapereka chidziwitso chothandiza chakuya pa ntchito zosiyanasiyana: madzi apansi panthaka, mchere, kutentha kwa nthaka, zachilengedwe, ndi geotechnical. Kupambana kwa kafukufuku wa TDEM kumadalira kapangidwe ka kupeza (lup, current, nthawi), kuwongolera phokoso, ndi kutanthauzira ndi kusinthasintha komwe kumaganizira mikhalidwe ya malo am'deralo. M'machitidwe amakono, TDEM imagwira ntchito bwino kwambiri ikaphatikizidwa ndi deta yobowola ndi njira zina za geophysical, zomwe zimapangitsa zotsatira zake kukhala zolimba komanso zodalirika popanga zisankho.
Ngati mukufuna, nditha kusintha nkhaniyi kuti igwirizane ndi kalembedwe ka ophunzira (kokhala ndi mawu ofotokozera), kuwonjezera zithunzi za momwe kafukufuku amachitikira, kapena kupanga chitsanzo cha kafukufuku wa TDEM cha madzi apansi panthaka/geothermal/minerals.
