Kunzwisisa kwekutanga kwe anisotropy ye seismic
Kupararira kwepasi (Seismic anisotropy) ipfungwa huru mu geophysics inotsanangura kuti sei mafungu epasi (seismic waves) achigona kufamba nekumhanya kwakasiyana kuburikidza nedombo, zvichienderana nekwaanoenda uye/kana polarization. Mumamodeli mazhinji ekutanga, Nyika yaiwanzofungidzirwa kuti isotropic - zvichireva kuti hunhu hwayo hwe elastic hwakafanana munzira dzese. Zvisinei, muchokwadi, goko repasi ne mantle zvinowanzoratidza hunhu hwe anisotropic nekuda kwechimiro chemukati chematombo, kurongeka kwemaminerari, kupwanyika, uye kushushikana kwakashandiswa. Kunzwisisa kupararira kwepasi kunobatsira mukududzira data re seismic, kunovandudza kururama kwemifananidzo yepasi, uye kunopa zviratidzo zvemaitiro e geological akadai se deformation, mantle flow, kana fracture systems muma reservoirs.
1. Pfungwa huru: isotropy vs anisotropy
Munzvimbo ine isotropic medium, kumhanya kwemafungu e seismic kunoenderana chete nerudzi rwemafungu (P kana S) uye ma elastic parameters enzvimbo (semuenzaniso, bulk modulus, shear modulus, uye density), kwete padivi rekupararira. Kusiyana neizvi, mune nzvimbo ine anisotropic medium, elastic properties dzinosiyana zvichienderana negwara. Nekuda kweizvozvo, mafungu eP neS anogona kuona kuchinja kwespeed ne azimuth (horizontal direction) kana ne angle of incidence maererano ne rock layer/structure.
Kuchinja kwepasi hakurevi kuti dombo "rakasiyana" kubva kune rimwe divi kuenda kune rimwe, asi kazhinji zvinoreva kuti dombo rine marongerwo aro madiki nemakuru, semuenzaniso lamination, foiation, mineral grain orientation, kana fracture network inotonga mune rimwe divi.
2. Zvikonzero zvikuru zvekudengenyeka kwenyika
Kune nzira dzakasiyana-siyana dze geological dzinokonzera anisotropy:
1. Kuisa zvikamu zvakatsetseka
Pazviyero zvidiki pane denderedzwa remvura repasi pemvura, zvikamu zvitete zvine hunhu hwakasiyana hwe elastic zvinogona "kuonekwa" nemafungu senzira inoshanda ye anisotropic. Izvi zvinowanzoitika mumadhaka akaturikidzana.
2. Kurongeka kwezvicherwa (kurongeka kunodiwa ne crystalgraphic / CPO)
Mukati meganda, zvicherwa zvakaita semuorivine zvinogona kuenderana nemafambiro azvo nekuda kwekushanduka uye kuyerera. CPO iyi inogadzira anisotropy yakasimba, inowanzoonekwa kuburikidza nekupatsanurwa kweS-wave.
3. Kutsemuka kweganda ne pores zvinoenda kudivi (anisotropy inokonzerwa nekutsemuka kweganda)
Munzvimbo dzine mahydrocarbon, geothermal, kana crystalline reservoirs, ma "oriented fracture sets" anogona kugadzira shanduko dzenzira mumafambiro emafungu. Rudzi urwu rwe "anisotropy" rwakakosha zvikuru pakuongorora kutyoka kwe "fracture" uye kufanotaura kwe "directional permeability".
4. Kushushikana uri panzvimbo imwe chete (anisotropy inokonzerwa nekushushikana)
Kunyangwe pasina kutsemuka kuri pachena, kushushikana kunogona kukanganisa kuvhurika kwe microcrack uye kubatana pakati pe granular, zvichikonzera anisotropic response. Chiitiko ichi chakakosha mu geomechanics uye kutarisa kugadzirwa kwe reservoir.
3. Zviratidzo uye kuratidzwa kweanisotropy mu data rekudengenyeka kwenyika
Anisotropy inogona kuonekwa mumhando dzakasiyana dzekuongorora:
- Kuchinja kwekumhanya maererano nekwakananga (directional velocity)
Semuenzaniso, mafungu eP anofamba nekukurumidza akaenzana nemubhedha kupfuura akamira akatarisana nemubhedha uri mumatombo e sedimentary akarongwa.
- Kupatsanurana kwemafungu maviri kana kuti mafungu maviri
S-wave inopinda mu anisotropic medium inogona kupatsanurana kuita maS-wave maviri anotenderera (anowanzonzi fast-S uye slow-S), nenguva dzakasiyana dzekusvika (kunonoka kwenguva). Nzira ye fast-S polarization inowanzoenderana nekwakatsemuka kana nzira inotonga ye strain.
- Kufamba kweAnisotropic padata rekufungisisa
Mukufungidzira kwekudengenyeka kwenyika, anisotropy inokanganisa hukama huripo pakati penguva yekufamba uye offset (daro renzvimbo inobva kune source-receiver). Kana ikasateererwa, kugadzirisa kwakadai sekugadzirisa NMO, kurongedza, uye kutama kunogona kugadzira mifananidzo yakakanganisika kana isina kujeka.
- AVO/AVA (kuchinja kweamplitude ne offset/angle) shanduko
Anisotropy inogonawo kugadzirisa amplitude response ku angle of incidence, kuitira kuti dudziro ye lithology ne fluids igone kutorwa seyakasiyana kana uchishandisa isotropic assumes.
4. Mhando dzeanisotropy dzinowanzoshandiswa mu geophysics
Nekuti anisotropy muzvisikwa inogona kuva yakaoma zvikuru, nyanzvi dze geophysicists dzinowanzo shandisa modhi inorerutsa:
1. VTI (Vertical Transverse Isotropy)
Inonziwo TI ine vertical axis of symmetry. Iyi modhi yakakodzera kune sediments dzakatwasuka: hunhu hwemedium hwakasiyana-siyana muhombe, asi hwakasiyana-siyana muhombe. VTI yakajairika mukutsvaga kwe seismic.
2. HTI (Horizontal Transverse Isotropy)
TI ine axis yakatambanudzwa yekuenzanisa inowanzoshandiswa kumiririra mitsetse ine makumbo akatsemuka akatarisana negwara rakati. Iyi modhi inoshandiswa zvakanyanya pakuongorora makumbo akatsemuka.
3. TTI (Tilted Transverse Isotropy)
Zvakafanana neTI, asi ine axis yakamanikana yekuenzanisa. TTI inoshanda muzvikamu zvakapetwa kana maumbirwo akaomarara akadai semapapiro ekudzivirira, zvikanganiso, uye nzvimbo dzekuputira.
4. Orthorhombic anisotropy
Zvakanyanya kuoma, ine maaxe matatu ane maitiro akasiyana. Inogona kumiririra musanganiswa wezvikamu zvakatenderedzwa uye kuputsika. Iyi modhi iri kushandiswa zvakanyanya muzvidzidzo zvemazuva ano nekuda kwehunhu hwayo hwechokwadi, kunyangwe parameterization yayo uye inversion zvichinetsa zvakanyanya.
5. Zviyero zveAnisotropy: pfungwa huru
Mukudzidzira kwekutsvaga, TI anisotropy inowanzo patsanurwa neThomsen parameters (ε, δ, γ) yeanisotropy isina simba. Pasina kupinda mumasvomhu akadzama, pfungwa huru ndeiyi:
– ε ine chekuita nemusiyano wekumhanya kweP-wave munzvimbo yakatwasuka zvichienzaniswa negwara rakatwasuka (muVTI).
– δ inokanganisa maitiro emafungu eP pamakona ari pakati (pedyo neakatwasuka kusvika pakati), zvakakosha pakufamba.
– γ ine chekuita neanisotropy yemafungu eS (kunyanya muchikamu cheSH) uye inokanganisa mafungu eshear.
Izvi zvinobatsira kugadzirisa kufamba, kunatsiridza kutama, uye zvine chekuita nekuita kwekudengenyeka kwenyika kune zvimiro zvepasi zvakaita sema laminations kana kupwanyika.
6. Nzira dzekuyera nekududzira anisotropy
Kupararira kwepasi kwepasi (seismic anisotropy) kunogona kuverengerwa kubva pamhando dzakasiyana dzedata:
1. Kupatsanurana kwemafungu ekucheka
Inoyera divi rekukurumidza-S uye kunonoka kwenguva. Inoshandiswa zvakanyanya mu kudengenyeka kwenyika seismology kudzidza kuyerera kwe mantle uye divi re crustal stress, pamwe ne mu multicomponent 3D surveys dze reservoirs.
2. Kuongororwa kwe azimuthal kwekufungisisa kwepasi
Data iri rakakamurwa neazimuth (semuenzaniso, zvikamu zvakasiyana-siyana zveazimuth), uye rozoongororwa kuti rione musiyano uripo pakumhanya/kufamba/kukwira. HTI ne orthorhombic zvinowanzo ongororwa kubva mukusiyana uku.
3. Mufananidzo wekutarisa/VSP negwaro retsime
Data retsime rinopa kudzora kudzika uye rinogona kuyera kumhanya kwakamira nemazvo. Mune zvimwe zviitiko, kuyerwa kwesonic dipole logging kunogona kuona zviratidzo zveS-wave anisotropy uye zviratidzo zvekutyoka.
4. Rabhoritari yefizikisi yematombo
Mienzaniso mikuru yakaedzwa kuti ione ma elastic constants uye anisotropic response, zvichibatsira kubatanidza data re seismic ne physical properties.
7. Sei anisotropy ichikosha mukugadzirisa nekutora mifananidzo yekudengenyeka kwenyika?
Kusateerera anisotropy kunogona kukonzera matambudziko akawanda anoshanda:
- Chikanganiso chekuona modhi yekukurumidza chinokonzera kudzika kusina kururama kwe reflector.
- Mifananidzo yekufamba haina kunyanya kutarisisa zvakanyanya kunyanya munzvimbo dzine machira akarerekera kana zvivakwa zvakaoma.
– Kududzirwa zvisizvo kweAVO nekuti kuchinja kwehukuru hweamplitude kunogona kukanganiswa nemhedzisiro yefluid/lithology asi kutaura chokwadi zvinokanganiswa neanisotropy.
- Kukundikana kuongorora kuputsika kwemapfupa kana kusiyana kweazimuthal kusina kuongororwa nemazvo.
Nekushandisa anisotropy, mamodheru ekukurumidza uye ekufamba (semuenzaniso, TTI migration) anogona kugadzira mifananidzo yakajeka uye nzvimbo dzakarurama dzekuratidzira, zvichivandudza kuvimbika kwedudziro dzezve geology.
8. Matambudziko nemiganhu
Kunyange zvazvo zvichibatsira, kudengenyeka kwenyika kunokonzera matambudziko:
– Zvisiri zvakasiyana (kusanzwisisika): kusanganiswa kwema parameter akawanda kunogona kuburitsa mhinduro dzakafanana dzedata.
– Hunhu hweAzimuthal uye kufukidza: ongororo yeazimuthal anisotropy inoda hunyanzvi hwakakwana hwekuwana.
– Chikero: anisotropy inoonekwa mukudengenyeka kwenyika ndiyo anisotropy inoshanda pachikero chewavelength, kwete hazvo micro anisotropy.
– Kuomarara kwenzvimbo: munzvimbo dzakaoma, modhi yeTI yakapusa kazhinji haikwani.
Saka, dudziro ye anisotropy inofanira kugara yakabatana neruzivo rwe geology, data retsime, uye kunzwisisa fizikisi yedombo.
9. Mhedziso
Kunzwisisa kwakakosha nezve seismic anisotropy kunobva pakuti Nyika haisi nguva dzose iri isotropic. Kuisa zvidimbu, kupwanyika, kurongeka kwemineral, uye kushushikana zvinogona kukonzera kuti mafungu e seismic apararire zvakasiyana munzira dzakasiyana, zvichikonzera zviitiko zvakaita sekusiyana kwespeed, anisotropic moveout, uye shear-wave splitting. Mukutsvaga uye seismology, anisotropy haisi kungo "kugadzirisa tekinoroji," asiwo hwindo rekuita geological: deformation direction, fracture systems, uye kunyange mantle dynamics. Nemuenzaniso wakakodzera (VTI, HTI, TTI, kana orthorhombic) uye kubatanidzwa kwakanaka kwedata, seismic anisotropy inogona kuvandudza kururama kwe subsurface imaging uku ichivandudza kududzirwa kwechimiro chedombo uye hunhu hwaro.
Kana muchida, ndinogona kuwedzera chikamu chipfupi chine mienzaniso yezviitiko (semuenzaniso, VTI anisotropy mu layered shale kana HTI mu breakage reservoirs) kana kusanganisira mufananidzo we shear-wave splitting concept uye Thomsen parameters mu tableular form.
