Phát triển hệ chương trình xử lý, phân tích tài liệu phân cực kích thích ở việt nam

Cac phuang phap PCKT cho phep xac dinh su thay doi dien tra suat va do phan cue theo chi6u sau cua v6 trai dat, dugc sir dung rong rai d^ ve ban do dia chat, nghien ciiu cau true, tim ki

Trang MODAU 4 ChUOng 1: TONG QUAN VE CAC PHl/ONG PHAP PHAN ClTC KICH

THICH DONG MOT CHIEU 13 1.1 Vai net ve lich su phat trien ctia phuong phap ph^n cue kich

thich J 3

1.2 Coche ciia hien tucmg phan cue kich thich \j

1.3 Cac phuong phap phan cue kich thich thuong dung 21

1.3.1 Mot so he cue do cabdn 21

1.3.2 Mot vai phuangphap do sdu PCKT thong dung 24

1.4 Diem qua m6t vai phuofng phap do s^u dien tro vi phan da

duac de xuat cai tien 30

1.4.1 Phuofng phap do sdu dien chung 30

1.4.2 Phuang phap do sdu khdu trittrudng 33

1.4.3 Phuang phap do sdu dien doi xitng ludng cue hap nhdt 35

1.4.4 Mot so nhdn xet ve edc phuang phap do sdu dien tra vi phan

da duae de xudt edi tien 38

1.5 Cac ton tai chinh trong ap dung phuofng phap phan cue kich

thich dong mot chieu o Viet Nam 42

K ^ l u a n 45

Chuang 2: NHUNG DE XUAT U6\ TRONG PHUONG PHAP DO SAU

P H A N c u e KICH THICH 47 2.1 Dat va'nde 4-7

2.2 G\6\ thieu cac thong so PCKT mdi 48

2.3 Ca sof de xuat cac phuang phap do sau PCKT cai tien 50

2.4.1 He cue do sdu PCKT doi xicng edi tien

2.4.1.1 Mo td he cue do sdu PCKT doi xicng edi tien KM-01

2.4.1.2 Qui trinh do dgc ngodi thue dia

2.4.2 He cue do sdu PCKT luang cue edi tien

2.4.2.1 Mo td he cue do sdu PCKT ludng cue true edi tien KM-02

2.4.2.2 Mo td he cue do sdu PCKT ludng cue xieh dao edi tien

2.4.2.3 Qui trinh do dge ngodi thue dia

2.4.3 Mot so nhdn xet

Ket lutin

Chuofng 3: HUCiNG PHAT TRIEN MC*I VE X U L Y , PHAN TICH TAI

LIEU DO SAU PHAN c u e KICH THICH 3.1 Dat van de

3.2 Cac phep bien doi mdi - mot hudfng phat trien \t xu ly, phan

tieh tai litn do sau PCKT

3.2.1 Phuang phap do sdu PCKT doi xicng

3.2.2 Phuang phap do sdu PCKT luang cue

3.3 Tmh cac thong so PCKT mdi tren mo hinh ly thuyet

3.3.1 Tinh cac dudng cong do sdu dien tra va do sdu phdn cue tren

mdi trudng 3 lap

3.3.1.1 Casdly thuyet

3.3.1.2 Cac kit qud tinh todn

3.3.2 Kiem ehicng tinh dung dan vd tinh uu viet eua edc phep bien

doi mdi tren mdi trudng 3 Idp

3.3.2.1 Doi vdi phuang phap do sdu PCKT doi xicng

thong sdmdi trong khdo sat mdi trudng dia chat

3.4 Kiem chutig tinh dung d^n va tinh uu viet ciia cac phep bien

d6i mdi tren moi trucmg thuc td'

3.4.1 Doi vdi phuang phap do sdu doi xicng PCKT

3.4.2 Doi vdi phuang phap do sdu PCKT ludng cue

3.5 Cong thiic bien doi Petrovski cai tien

3.6 Gidi thieu ve he chuang trinh xir ly, phan tich

3.6.1 Ngon ngUMatlab

3.6.2 He chuang trinh xu ly, phdn tieh

Ket luan

Chuang 4: CAC KET QUA THlTNGHIEM

4.1 N6i dung ap dung thir nghiem thuc te eua cac d6 xuat mdi

4.2 Ket qua ap dung cac di xuat mdi de khai thac tai lieu do sau

PCKT doi xiing da c6

4.2.1 Dae diem dia chat vd tinh chat vat ly cua tuyen 20

4.2.2 Ket qud xu ly, phdn tich tai lieu do sdu PCKT doi xung

4.2.2.1 Ket qud theo tai lieu do sdu PCKT doi xicng thong thudng

4.2.2.2 Ket qud dp dung ede de xudt mdi dekhai thde tai lieu

4.3 Ket qua ap dung phuang phap do sau PCKT luang cue cai tien

4.3.1 Dae diem dia chat vd tinh chat vat ly cua tuyen Sll

4.3.2 Ket qud xic ly, phdn tich tai lieu

Ket luan

Ket luan va kien nghi

Tai lieu tham khao

Cac phuang phap Dja Vat ly la nhung cOng cu manh dung de nghien cun trai dat Chung lien tuc duge bo sung, hoan thien va phat trien Trong to hop phuang phap Dia Vat ly tham do, cac phuang phap Phan cue kich thich (PCKT) chiem mot vi tri quan trong va hien nay vSn la mot trong nhiing phuang phap Dia Vat ly tham do thong dung nhat

So vdi phan Ian phuang phap Dia Vat ly khac, phuang phap PCKT eo nhiJng uu diem nhu: chu tiinh ky thuat do dac tuang doi dan gian va khong

doi hoi may mdc thiet bi qua phiic tap, tinh vi; xit ly so lieu nhanh chong bang

tay hay tren may tinh vdi chi phi thap nhung kha nang giai quyet da dang, hieu qua kinh t6' cao Do do, phuang phap PCKT da dugc ap dung of nhieu nude tren the gidi va ngay ca a nude ta, thudng chiem mot ty le kha cao trong khoi lugng tham do dien ndi chung, no ngay cang dugc su dung pho bien trong cong tac tham do Dia Vat ly

Sau nhi6u nam lien tuc phat trien, ngay nay phuang phap PCKT da trdf thanh mot trong phuang phap chii dao de nghien euru dia chat c6 hieu qua kinh

te va khoa hoc cao Cac phuang phap PCKT cho phep xac dinh su thay doi dien tra suat va do phan cue theo chi6u sau cua v6 trai dat, dugc sir dung rong rai d^ ve ban do dia chat, nghien ciiu cau true, tim kiem cac khoang san c6 ich cQng nhu trong dia chat cong trinh va dia chat thuy van

Nhiem vu chii yen ciia phuang phap PCKT la chi ra dugc vi tri tuang

d6i cua cac doi tugng dia chat can tim Trong nhimg dieu kien thuan Igi cd the xac dinh b6 day cac I6p dat da cau thanh lat cat dia-dien, hinh dang, kich

thude, chieu sau the nam cua cac doi tugng nghien cuu trong pham vi sai so cho phep cua phuang phap

PCKT la do phan cue bieu kien % va dien trd sua't bieu kien A • Co nhieu

each khac nhau: tinh toan cac dudng cong 7^ va p^ d6'i vdi moi trudng phan

Idp, dong nhat, song phing ngang tren may vi tinh bang phuang phap lua

chon de xay dung cac ban chuan; tinh 7^ f(ABl2) true tiep tii dudng cong

p^ = f{ABI2)\ chuyen cac gia mat cat thanh cac mat cat ban dinh lugng; su

dung cac tham so thuc nghiem S, va Z^ (vdi 5,1a thdi gian ma tai do cd do

phan cue giam di mot nua, Z^ = 0,75 5^ % ) ; do phan cue bieu kien tuang

dd'i A^ va do phan cue bieu kien tong hgp Al, toe do suy giam the phan cue

Vpc

Tuy nhien, phai cong nhan rang vi th6ng tin con ngheo nan va phuang phap xir ly, phan tich cdn han ehe nen ket qua thu dugc con chua dap ling dugc ydu cau mong muon Cd the diem qua mot vai nguyen nhan ciia tinh trang tren la do:

+ Chi do true tiep dugc tiing loai dudng cong ling vdi m6t loai \\t cue

nen chi phan anh dugc mot dac trung nao do ciia moi trudng nghien ciiu

+ Cac cong thiic chuyen doi giua cac dudng cong nham thu dugc nhieu loai thong tin cho den nay vSn chua thuc su cd hieu qua, doi khi cdn lam cho

"meo" thong tin va khdng on dinh

+ Cac phuang phap s6 dung de xu ly, phan tich tuy da dugc nang cao khi ap dung nhung thanh tuu mdi hien dai cua Toan hoc va Tin hoc, nhung van cdn nhieu han che do tinh khong on dinh va da tri cua bai toan ngugc Doi khi vSn chi luan giai mot each dinh tinh va chi sir dung dau hieu diem gSy hoac diem udn ciia dudng cong de du bao hoac cdn sir dung qui luat bien doi ciia dudng cong dien trd de gan cho cac Idp dia - dien cac gia tri do phan cue bieu kien do dugc bang thiet bi do tuang duang vdi dudng cong dien trd

dieu kien md rong pham vi ap dung ciia phuang phap PCKT trong ditu kien

dia-di6n phiie tap? Do chinh la mot muc tieu kha hap dan da I6i cudn su dau

tu suy nghi ciia kha nhi6u nha khoa hoc trdn the gidi va trong nude trong nhieu nam qua

Cd the ndi rang cho den nay hau nhu tat ca cac tac gia deu tap trung sure lue cua minh theo hai hudng chinh sau:

• Cai tien cac he thiet bi do (may mdc, he cue do, phuang phap do ngoai thuc dia ) de cd the do true tiep dugc cac thong tin can thiet ngoai thuc dia

• Tim ra cac cong thiic de tinh chuyen doi giiia cac loai dudng cong nham tang lugng thong tin phuc vu cho cong tac xir ly, phan tich

Tuy vay, cac he thiet bi cdn phiic tap ca ve he cue do ISn cac phep do; c6ng thiic bi6n doi giua cac dudng cong cdn phai tinh qua phep dao ham khong on dinh Mac du cd nhi6u cd gang nhung cho den nay, dieu ba't hgp ly neu tren vSn chua dugc hoan toan giai quyet

Chung toi cho rang cd the giai quyet tirng phan hoac triet de nhiing van

di ca ban cdn ton tai neu tren m6t each thiet thuc (tuy theo muc dich va doi

tugng nghien ciiu) bang each ket hgp ca hudng de xuat cac thong sd PCKT mdi cd nhiing uu diem han (nhu do phan giai cao han, tong hgp thdng tin han ) vdi viec cai tien cac he thiet bi do, tim ra cac edng thiic bien doi thong tin chinh xac han Cd nhu vay mdi mong tang them nhieu thong tin khac loai thu dugc tuf moi trudng thuc te, nham lam phong phii han cac thong tin, tang

do chinh xac phuc vu cho cong tac xu ly, phan tich dat hieu qua nhat

De thuc hien dugc y tudng nay, trong pham vi de tai luan an, vdi mong mudn gdp phan khac phuc nhiing ton tai tren, chiing toi da nghien ciiu de xua't cac thong sd PCKT mdi (dac bi6t la thong sd PCKT Petrovski 7 ) de xir ly

dudng cong khac thong qua cac phep bien doi dai sd dan gian Tat ca cac thong tin nay da dugc khai thac triet de trong he chuang trinh tu dong xir ly, phan tich tong hgp, ma nd dugc viet bang ngon ngu cap cao MATLAB nhu

mot san pham phan mtm vdi cac chiic nang hoan toan tien ich, dd sir dung,

gan giii vdi thuc te Giai phap nay khong chi da dugc chiing minh bang mo hinh ly thuyet, ma cdn da dugc kiem nghiem tren moi trudng thuc te vdi cac

he cue do va cac phep do mdi ma tac gia da dt xuat, dac biet cdn dugc ap

dung de khai thac cac tai lieu thuc te cu ciia phuang phap do sau PCKT thong thudng, lam md rong va nang cao tinh hieu qua kha nang ap dung thuc te cua phuang phap Day la mot van d6 hap dan, hoan toan mdi can thiet phai lam,

dd Cling chinh la hudng suy nghi nghien ciiu va ket qua dat dugc cua tac gia trong thdi gian qua

2 Muc tieu va cac nhiem vu cua luan an:

• Muc tieu:

Hoan thien he chuang trinh xir ly, phan tich tai lieu PCKT tren ca sd

de xua't thong sd PCKT mdi 7^; thiet lap cac phep bien doi dai sd dan gian, ap dung de tinh toan khai thac, bo sung them cac thong tin cd ich doi vdi tai lieu PCKT da cd tCf trude den nay, cung nhu ap dung cho cac tai lieu mdi thu dugc bang cac phuang phap cai tien nham nang cao do chinh xac cua phuang phap

• Cac nhiem vu:

1 Tim hieu, phan tich tong hgp nhiing ket qua nghien ciiu cua cac tac gia trudc Dua ra va xay dung ca sd ly thuyet ciia thong sd PCKT Petrovski

2 Dua tren nguyen ly chong cha't dien trudng, dua ra cac cong thiic bi6'n d6i giiia cac dudng cong PCKT sao cho khac phuc dugc cac nhugc diem

ca ban ve tinh khong on dinh cdn tdn tai tii trudc den nay

3 Chiing minh tinh diing dan cua cac phep bien doi dd tren mo hinh ly thuyet va kiem nghiem tren moi trudng thuc te

4 xay dung cac thuat toan xir ly, phan tich qua cac phep bien doi dai

sd neu tren va thiet lap he chuang trinh tu dong tuang ling bang ngon ngii MATLAB

5 Cai tien cac he cue do va quy trinh do nham thu dugc thong tin dSu vao phu hgp de xir ly

6 Tien hanh thir nghiem ap dung phuang phap mdi trong thuc te, ciing

nhu khai thac cac tai lieu da cd de cd ket luan \t tinh hieu qua cua cac de xuat

theo hudng phat trien xir ly, phan tich mdi

3, Cac ket qua mdi:

1 Lan dau tien de xuat va sir dung thong sd PCKT Petrovski /j^ mdi ed

do phan giai cao, xay dung dugc ca sd ly thuyet va chiing minh dugc cac uu

diem cua chiing so vdi cac tham sd truyen thong p^, rj^ ,

2 Dua ra dugc cac phep bien doi mdi gifla cac dudng cong do sau PCKT Da chiing minh dugc tinh diing dan ciia cac phep bien doi dd tren mo hinh ly thuyet va moi trudng thuc te Day ciing chinh la mot phan thuat toan xir ly, phan tich tai lidu PCKT theo hudng mdi de xuat nay

3 Vdi thuat toan da thiet lap, xay dung dugc he chuang trinh tu dong bang ngon ngir MATLAB nhu mot san pham phSn mem vdi cac chiic nang hoan toan tien ich, d6 sir dung, giao dien va dd hoa tot, gan giii vdi thuc te

4 Cai tien cac he cue do va quy trinh do hgp ly nham giam thieu cac phep do, khdng lam phiic tap quy trinh thuc dia ma ta vSn cd dugc dii thong tin can thiet

phan giai cao, chieu sau nghien ciiu Idn da chiing minh hieu qua dia chat ciia

de xua't mdi ap dung trong thuc te

4, Y nghla khoa hoc va thiic te:

• Y nghia khoa hoc:

1 Thong sd PCKT Petrovski 7^ dugc xac lap va khai thac cd ca sd khoa hoc, lam tang dang ke lugng thong tin hiiu ich Chiing cd do phan giai cao nen phan anh sat thuc han hieu ling PCKT cua cac doi tugng nghien ciiu; tang do phan giai doi vdi cac di thudng yeu

2 Phep bien doi thong tin da dt xua't va sir dung chi qua cac phep tinh

dai sd dan gian, khdng phai thuc hien qua cac phep tinh dao ham cd tinh khong on dinh, nen chiing da khac phuc dugc cac nhugc diem cdn ton tai trudc day Cac phep bien doi nay cd do tin cay va khoa hoc cao Phat trien he thong chuang trinh xir ly, phan tich tai lieu PCKT tren ca sd cd lua chon thong tin dang tin cay nhung mang tinh tong hgp han

3 De xua't cai tien he cue do va qui trinh do hgp ly, thuan tien, cd tinh kha thi trong thuc te

• Y nghla thuc te:

\ Hudng xir ly, phan tich tai lieu PCKT mdi thong qua cac phep bien

d6i da de xua't lam ro han va tang dd tin cay ciia cac ket qua du bao dia chat vi lam phong phii them nhieu thong tin bo ich Trong trudng hgp thuan Igi cd the dung kd't qua du bao de theo doi, phat hien cac ddi tugng can tim

2 Md rong va nang cao kha nang ap dung ciia phuang phap PCKT, chang nhiing ddi vdi cac phuang an do mdi, ma cdn khai thac bo sung them dugc cac thong tin cd ich khac giiip cho cong tac xir ly, phan tich tai lieu

PCKT eua cac phuang phap cii da cd trudc day Trong trudng hgp cd the cdn giiip cho viec kiem tra, phat hien cac ddi tugng can tim ddi vdi cac phuang an cii da dugc thuc hien

3 Kha nang thir nghiem va ap dung vao san xuat la hien thuc

5 Cac luan diem mdi chii yeu cua luan an

1 Tir cac ket qua do thu dugc bang m6t loai he cue thong thudng nao

dd ta vSn cd dugc thong tin tin cay cua cac loai dudng cong tuang ling vdi cac

he cue khac thong qua cac phep bien doi dai sd dan gian khong phai tinh dao ham, nen da md rdng va nang cao cd hieu qua kha nang ap dung thuc te cua phuang phap

2 Y nghia cua viec de xuat thong sd PCKT mdi Petrovski 7^, ed do phan giai cao va mang tinh tong hgp Phat trien he chuang trinh tu dong xir ly, phan tich tai lieu PCKT bang ngon ngii MATLAB, theo hudng khai thac thong

sd PCKT Petrovski ^^va cac phep bien ddi da de xuat, nham xir ly, phan tich tai lieu PCKT hieu qua han

6 Bd cue cua luan an

Ngoai phan md dau, phan ket luan va kien nghi, danh muc cac tai lieu tham khao, ngi dung luan an dugc trinh bay trong 4 chuang

Chuorng 1: Tong quan ve phuang phap do sdu phdn cue kich thich ddng mot chieu,

Trong chuang nay chiing tdi trinh bay vai net ve lich sir phat trien ciia phuang phap phan cue kich thich (PCKT); ca che cua hien tugng PCKT; nhiing net tong quan hien trang eua cac phuang phap do sau dien vi phan tren the gidi va trong nude cd lien quan den de tai, danh gia uu diem va nhugc

diem ciia cac phuang phap nay; cac tdn tai chinh trong ap dung phuang phap phan cue kich thich ddng mot chieu d Viet Nam

Chuang 2: Nhiing de xudt moi trong phuang phap do sdu PCKT

Trong chuang nay chiing tdi trinh bay wt cac tham sd PCKT truyen thong; gidi thieu cac thong sd PCKT mdi; ca sd dt xuat va gidi thieu ve cac

ht cue, qui trinh do sau PCKT cai tien

Chuang 3: Hu&ng phat trien m&i ve xvt ly, phdn tich tdi lieu do sdu phdn cue kich thich

Trong chuang nay chung toi trinh bay v6 ca sd ly thuyet cua cac phep

bien doi mdi - mot hudng phat trien ve xii ly, phan tich tai lieu PCKT; tinh toan va kiem chiing tinh diing dan, tinh uu viet ciia cac phep bien doi mdi tren

md hinh ly thuyet 3 Idp va moi trudng thuc te, tii dd cd mot sd nhan xet \t

tinh cha't ca ban va kha nang eua cac thong sd mdi trong khao sat moi trudng

dia cha't; gidi thieu cong thiic bien ddi Petrovski cai tien; gidi thieu \t he

chuang trinh xir ly, phan tich lap bang ngon ngii MATLAB

Chuang 4: Mot so ket qud thu: nghiem

Trong chuang nay chung toi trinh bay mot sd net chinh ve dac diem eua viing nghien eiiu thir nghiem; cac ket qua xir ly, phan tich tai lieu theo hudng mdi ddi vdi cac tai lieu thuc te, tii dd nit ra ket luan ve hieu qua ap dung thuc

te ciia cac de xuat mdi

7 Ldi cam on

Ban luan an nay dugc hoan thanh tai Bg mon Dia Vat ly, Khoa Vat ly, Trudng Dai hoc Khoa hoc Tu nhien - Dai hoc Qudc gia Ha Noi, dudi su hudng dan khoa hoc cua PGS.TSKH Tang Mudi, PGS.TS Le Viet Du Khuang

Trudc het, tdi xin bay td Idng biet an sau sac ddi vdi cac thay true tiep hudng dan khoa hoc - PGS.TSKH Tang Mudi va PGS.TS Le Viet Du Khuang

- vl su tan tinh chi bao, giiip dd tdi trong qua trinh thuc hien va hoan thanh luan an

Trong thdi gian hoe tap va nghien ciiu, de hoan thanh ban luan an nay, tdi cdn nhan dugc su giiip da ciia Bd mdn Dia Vat ly, Khoa Vat ly Tac gia da nhan dugc nhCrng y kien ddng gdp quy bau va sau sac ciia: GS.TSKH Ngd Van Buu, GS.TSKH Lam Quang Thiep, GS.TSKH Pham Nang Vu, GS.TS Bui Cong Que', PGS.TSKH Mai Thanh Tan, GS.TS Nguyen Trong Nga, PGS.TS Nguyen Nggc Thiiy, TS Nguyen Tai Thinh, TS Nguyen Nggc Loan,

TS Doan Van Tuyen va nhieu nha khoa hoc khac Ngoai ra, tac gia cdn nhan dugc su giup da nhiet tinh, cd hieu qua ciia TS Nguyen Tai Thinh va cac can bg Doan Dia Vat ly mat dat thudc Lien doan Vat ly-Dia chat trong qua trinh thu thap tai lieu va do dac thir nghiem tren thuc te Tac gia xin chan thanh cam an sau sdc de'n cac dan vi va ca nhan ndi tren

Nhan dip nay, tdi xin cam an su quan tam, dong vien, iing ho va tao dieu kien thuan Igi eua GS.TSKH Nguyen Van Mau cung tap th^ lanh dao trudng Dai hoc Khoa hoc Tu nhien - DHQGHN; xin cam on GS.TS Mai Trong Nhuan ve su giiip dd chan thanh ddi vdi tdi trong qua trinh thuc hien, hoan thanh luan an va thu dugc ke't qua tot dep

• 0 Lien X6 (cQ) viec nghien ciiu hien tugng phan cue kich thich cua da't

da va quang ciing nhu nghien ciiu phuang phap va che' tao thiet bi ghi chinh xac the' phan cue kich thich dugc nhieu nha khoa hoc va to chiic Dia Vat ly quan tam, thu dugc nhiing ket qua dang ke ca ve ly thuye't va thuc nghiem

Trudc khi ra ddi tram do phan cue kich thich kieu VP-59, phuang phap

do sau PCKT duge ddng dao cac nha Dia Vat ly, Dia chat ap dung va thir nghiem bang cac may do dien the thong thudng nhu EP-1, ESK-1 cd lap them

bg phan phu de dieu chinh thdi gian phat ddng qua dat va thdi gian ghi cac tin hieu tren nhieu viing khac nhau da khang dinh tinh uu viet cua phuang phap ddi vdi quang xam tan ma cac phuang phap Dia Vat ly khac it cd hieu qua

Tijr khi ra ddi tram tham dd dien VP-59 do VITR, VNHIGEOPHYSIKA va MPZ nghien ciiu che tao, tiep sau la cac tram hoan thien han nhu: VP.62, VP-0.62 va VPP-67 , phuang phap do sau PCKT da dugc ap dung pho bien trong

cong tac tim kie'm va tham dd khoang san d Lien Xd Cung vdi su ra ddi cac tram do PCKT tren mat dat, VITR va MPZ da nghien ciiu che tao cac tram do phan cue trong 16 khoan kieu VPS-63 va san xuat hang loat vao nam 1964 Den nay da md rong kha nang ap dung cua phuang phap d ca tren mat dat va dudi mat dat Dd la cac may do PCKT bang ddng mot chieu

Vao nam 1972, Lien Xd da che tao tram do PCKT bang ddng xoay chieu INFA2-VP de do pha phan cue trong gidi han tan sd tii 0,3 den 78 HZ Tiep sau dd la che tao tram VP-F vao nam 1975 Tii dd da tao ra dieu kien ap dung rdng rai phuang phap phan cue xoay chieu trong tim kiem va tham dd khoang san

Su ra ddi va phat tri^n eua cac thiet bi do PCKT ndi tren da tao dieu kien di sau nghien ciiu ban cha't cua hien tugng phan cue kich thich, xay dung

ca sd ly thuyet cua phuang phap tren ca sd tong hgp cac thanh qua nghien ciiu

ap dung cua nhieu nha Dia Vat ly d Lien Xd va nude ngoai, cac phuang phap

do PCKT d thuc dia va phuang phap tinh toan xir ly ke't qua Mot trong sd cac cong trinh tong hgp neu tren phai ke de'n la cdng trinh cua Comarov V.A [70], [71]

Tii dd del nay, ciing vdi su ap dung ky thuat dien tir va tin hoc, phuang phap do sau PCKT khong ngiing dugc md rdng pham vi ling dung, do cd su cai tien ve may do va phuang phap tinh toan Trong sd cac phuang phap tham

dd, phuang phap do sau PCKT dugc coi la phuang phap chii yeu de phat hien

va theo ddi cac than quang xam tan Dang chii y la ngoai cac tham sd do phan

cue bieu kien 7^ va dien trd suat bieu kien p^ da sir dung them tham so td'c

dd suy giam he sd phan cue kieh thich theo thdi gian tinh bang [%/ms] do ddi tugng sulfur - vang gay ra [66] cd gia tri han han so vdi da vay quanh

• 6 cac nude XHCN Ddng Au (cu) nhu Hungary, Tiep Khac, CHDC Diic, Nam Tu, Ba Lan , phuang phap do sau PCKT dugc ap dung pho bien

va cd hieu qua trong dieu tra dia chat, tim kiem va tham dd khoang san cua

•

tiing nude Viec ap dung phuang phap do sau PCKT d cac nude nay di theo hudng thuc dung han nen cd su hgp tac vdi cac nude tu ban nhu Canada, My nham che tao may do gon nhe, ghi sd va tu ddng tinh toan ke't qua ngay tii nhiing nam 1980 Rieng d Hunggary, Vien Dia Vat ly ELLGI (Budapet) luc

dd da che' tao may do phan cue cd kha nang do 11 gia tri he so phan cue sau khi ngat ddng phat tao thuan Igi cho cac nghien ciiu dac trung suy giam ciia the PCKT theo thdi gian Cac nghien ciiu ciia cac nha Dia Vat ly Hunggary nham phan biet quang va da vay quanh dua tren cac tinh toan hang sd thdi

gian r^ = f{t) va ty sd bien do 2 thanh phan chinh gay nen the phan cue kieh

thich la Wi va W2 Chiing da dat dugc nhiing ket qua nhat dinh va dugc cdng

bd trong cac tuyen tap cdng trinh nghien ciiu hang nam eua Vien

Cac may do phan cue do cac nude XHCN Ddng Au (cii) dugc xem nhu

la mot tien bg ky thuat trong he thong XHCN liic ba'y gid nhu may DIAPIR E+T cua Hunggary, may IPOR cua Tiep Khac Dd la cac may do true tiep

cac ket qua 7^ va p^ bang dong ho chi thi kim hoac hien sd

• O Trung Qudc, phuang phap do sau PCKT ciing duge phat trien gan nhu dong thdi vdi qua trinh phat trien d Lien Xd (cii) Do cd su cai tien may

do dien the' kieu UJ-18 thanh may do kieu DDJ-I, nen phuang phap do sau PCKT duge ap dung rdng rai va pho bien trong tim kiem va tham dd khoang san d Trung Qudc May do DDJ-I la may xach tay, ed do ben ca hoc cao, nen

da tao thuan Igi cho viec md rdng pham vi ap dung cua phuang phap do sau PCKT Hien nay Trung Qudc da che tao cac thiet bi do phan cue cd vi xir ly nhu DFJ-5 dat trinh do trung binh tien tien

• O cac nude tu ban phuang Tay, phuang phap PCKT dugc nghien ciiu, thir nghiem va ap dung rat sdm Tu" nhiing nam 1950, cac cdng ty tu nhan nhu Newmont Mining Co., Me Phar Geophysics Ltd., Sharp Instrument da ap dung cd ke't qua phuang phap do sau PCKT trong tim kiem khoang san Cac may do phan cue bang ddng xung va xung doi chieu cd chu ky da dugc che

tao d My va Canada (Cdng ty Scintrex, Mc Phar Intrument, Phoenix Geophysics, Huntec, Crone Geophysics) Cac tap doan md Idn nhat da hoan thanh cac xir ly khoa hgc va ap dung rdng rai phuang phap do sau PCKT d nhieu nude tren the gidi 6 Canada, My, Irland, Perue, Ao, Nam Tu, Phan lan, Iran, Tho Nhi Ky va cac nude khac, nhd phuang phap do sau PCKT da phat hien md da kim, ddng, kim loai quy hiem cd quy md Idn

Ngay nay cac may do PCKT da dugc cac nude phuang Tay hoan thien

va che' tao cd do chinh xac cao va ed nhieu tinh nang khac nhau nhu IPR-12 cua Canada, GPR-12 cua My, SYSCAL-R2 ciia Phap Nhd dd da nang cao hieu qua va pham vi ap dung ciia phuang phap do sau PCKT

• 6 Viet Nam, tii nhiing nam 1970 phuang phap do sau PCKT dugc dua vao thir nghiem tren ddi tugng Pyrit d viing md Giap Lai (VTnh Phu) va ddng Sinh Quyen (Lao Cai) khi ta nhap dugc tram VP-62 cua Lien Xd Sau dd phuang phap dugc trien khai thir nghiem tren cac ddi tugng khac nhu ddng Ta Khoa (San La), chi kem Chg Dien (Bae Thai), mangan (Bac Thai) va mot sd viing md khac Ke't qua cho tha'y phuang phap da td ra cd nhieu hieu qua trong viec tim kie'm, phat hien cac than quang ndi tren, dac biet la quang xam tan

ma trude dd rat khd phat hien nd bang phuang phap dien trd va dien trudng tu nhien Viec phat hien di thudng phan cue ma sau dd dugc cdng trinh khoan sau tim ra than quang pyrit so 12 d Giap Lai da khang dinh vai trd chii yeu cua phuang phap do sau PCKT trong tim kiem quang pyrit d Viet Nam

Trong khoang 10 nam trd lai day, phuang phap do sau PCKT dugc md rdng cho nhieu loai khoang san, dac biet la khoang san cd ty le khoang vat dan dien dien tir thap nhu molipden (Sapa - Lao Cai), thiec (Quy Hgp - Nghe An), apatit (Lao Cai), thach anh - sulfur chiia vang d Cao Ram (Hoa Binh), d

Na Pac (Lang San), d Cam Tam (Thanh Hoa) , vang-antimon d Ta Sdi ( Nghe An), Nam San - Na Pac (Hoa Binh), antimoan d Khe Chim - Ddng Md (Quang

Ninh) Phuang phap do sau PCKT da duge md rdng ap dung de xac dinh do tong khoang hoa cua nude dudi dat viing ddng bang Nam Bd

Cac may do PCKT pho bie'n d nude ta hien nay van la cac tram VP - 62

va VP - 062, DDJ-I, DIAPIR E+T, DGJ-1 cai tien cua Trung Qudc Nam 1989

ta nhap dugc tram do phan cue xoay chieu VP-O eua Lien Xd (cii) Gan day ta

da nhap duge may do phan cue SYSCAL-R2 eua Phap Vdi tinh hinh thiet bi nhu vay, d Viet Nam cho de'n nay mdi chi ap dung do PCKT bang ddng mot chieu hoac xung doi chieu la chii yeu

Cd the ndi rang phuang phap do sau PCKT d nude ta dugc ap dung mudn han nhieu so vdi cac nude phat trien tren the' gidi, song lai dugc phat trien manh me trong cdng tac dieu tra, tim kiem va tham dd khoang san Trong tim kiem phat hien hau he't cac khoang san ma to hgp khoang vat tao quang cd khoang vat dan dien dien tir thi phuang phap do sau PCKT deu cd mat va dugc ap dung de tim kiem phat hien chiing Ciing do hieu qua cua phuang phap ma ty trong dau tu cho phuang phap nay kha Idn, khong nhiing d Viet Nam ma cdn tren the' gidi Theo cac tai lieu thd'ng ke ty le chi phi cho cdng tac Dia Vat ly tim kiem va tham dd khoang san tren the' gidi tii nam

1958 de'n 1970 cho thay ty le chi phi cho phuang phap do sau PCKT chiem tdi han 50% vao nam 1970 da chiing td vai trd chii dao cua phuang phap nay trong td hgp cac phuang phap tim kie'm tham dd khoang san [71]

1.2 CO CHE CUA HIEN Tl/ONG PHAN Cl/C KICH THICH

Cho de'n nay, chua cd cdng trinh nao nghien ciiu hoan chinh ve hien tugng PCKT, cac ket qua nghien ciiu [71], [80], [81], [82] chii yeu bang thuc

nghiem d6u cho rang ca che hien tugng PCKT la cac qua trinh ly hoa phiic tap

xay ra d ranh gidi tiep xiic giiia khoang vat ran vdi dung dich dien phan choan trong Id hong cua da khi cd ddng dien chay qua Hien tugng PCKT cd the khai quat gdm 3 dang chinh sau:

- Do su bie'n dang dien kep d ranh gidi 2 pha ran va Idng cua dat da lien

ke't d trang thai chuyen ddng nhiet Khi dd trudng dien nguyen sinh lam dinh

hudng md men Idp dien kep, Idp dien kep bi bien dang khdi vi tri can bang,

tao thanh trudng dien thii cap Epc^^*(t) Trudng thii ca'p nay hinh thanh tiic thdi

va ciing tat di nhanh va chi ton tai tdi 2-3 giay say khi ngat ddng phat

- Do dien phan va phan ling oxy hoa khir xay ra d be mat khoang vat

dan dien dien tir va mdi trudng dan dien ion Khi cd ddng dien chay qua quang

dan dien dien tii, theo hudng ddng dien chay tdi thi hien tugng dien phan tao

thanh khi H^, hudng ngugc lai thi tao thanh khi CL", O", tir dd tao nen cac pin

yeu td Ddng thdi do san pham dien phan d hai phia vat quang ciing xay ra

phan ling dxy hda khir lam xuat hien cac dien tich trai dau Ket qua tao thanh

trudng dien phan cue thii cap Epc*-*(t) So vdi trudng Idp kep, trudng do dxy

hoa khir xay ra eham han va tdn tai ciing lau han, thudng keo dai tdi 7-8 giay

sau khi ngat ddng phat

- Do phan cue ndng do: Trong Id h6ng eua dat da, cd dung dich dien

phan, do su ha'p thu ciia set tao nen cac vimg cd ndng do khac nhau Khi cd

trudng dien ben ngoai lam cac ion chuyen ddng, lam mat can bamg trang thai

ban dau tao nen trudng thii ca'p Epe*^*(t) Trudng dien nay xay ra cham va tdn

tai tdi vai chuc giay sau khi ngat ddng phat

Nhu vay, the' PCKT chi tdn tai chii yeu trong mot khoang thdi gian nha't

dinh sau khi ngat ddng phat Ne'u dung thiet bi do the PCKT trong khoang thdi

gian thich hgp ay, ta se nhan dugc the PCKT

Do phan cue bieu kien la ty sd hieu dien the' phan cue AUpc{t) do d thdi

die'm t sau khi ngat ddng phat va hieu dien the AL'' do duge d thdi diem chua

ngat ddng phat (tinh theo ty le %) khi cting dieu kien thu phat:

Af/pc(t)

^ ^ — ° (1.1)

% = Bil^lOO%

7^(0 la ham ciia thdi gian, cd quy luat suy giam tuang tu nhu the' phan cue

AUpc(t), Ham //^(t) dugc ggi la ham dd phan cue bieu kien cua mdi trudng

• D6 thi bi^u dien dd phan cue bieu kie'n 7^ (/) theo kich thudc he cue r dugc ggi

la dudng cong do sau phan cue [15]

Bai toan phan bd the' eua ngudn dien ddng khong ddi cudng do I tren mat nira mdi trudng phan Idp, ddng nha't, song phang ngang da dugc nhieu tac gia quan tam va giai hoan chinh Theo Vanhian [68J khi phat ddng khong ddi

I bdi ngudn diem dat tren mat mdi trudng nira khdng gian ddng nhat vd han, dien trd suat p, dien the' tai diem each ngudn mot khoang r dugc tinh theo cdng thiic:

U(r)

Khi phat ddng khdng ddi / bdi hai dien cue AB dat tren mat mdi trudng

nira khdng gian ddng nha't vd han, dien trd suat p, hieu dien the' giiia hai dien

cue thu MN dugc tinh theo cdng thiic:

va diem do, dugc tinh theo (1.3), cd thii nguyen dien trd suat phan anh thong

tin chung ve cau tnic va tinh cha't dien cua mdi trudng, ddng thdi phu thudc

vao each bd tri he cue do Ham p^ (r) dugc ggi la ham dien trd suat bieu kien

ciia mdi trudng Do thi bieu dien dien trd suat bieu kien Pi^{r) theo kich thudc

he cue r dugc ggi la dudng cong do sau dien trd [15], [75]

Do phan cue bieu kie'n cd mdi quan he vdi dien trd sua't bieu kien cua

mdi trudng phan cue va khdng phan cue That vay, khi mdi trudng phan cue,

trudng dien ciia chiing bieu dien bang bieu thiic:

E = E,+E^^ (1.5)

do dd hieu dien the' do dugc la:

At/ = A [ / o + A t / ^ , (1.6)

d day EQ , AUQ va Ep^, AC/^^ tuong ling la dien trudng va hieu dien the' do dugc

khi mdi trudng khdng phan cue va mdi trudng cd phan cue

Tii bieu thiic tinh do phan cue bieu kie'n (1.1), ta cd:

d day PI va p^ la dien trd suat bieu kie'n ciia mdi trudng khi d trang thai phan

cue va khdng phan cue, tuang ling vdi cac tham sd dien trd suat la p] va p cd

quan he:

vdi / la chi so cua md hinh mdi trudng

Cdng thiic (1.8) cho phep tinh dudng cong J]^ ly thuyet khi cd cac tham

• sd cua md hinh mdi trudng

Hai tham so p^, rj^ la cac tham sd truyen thd'ng da va dang dugc sir

dung pho bie'n trong phuang phap do sau PCKT de dieu tra dia chat, tim kiem khoang san d Viet Nam tii trudc tdi nay

1.3 CAC PHl/ONG PHAP PHAN ClTC KICH THICH THl/C)NG DUNG

Khi phat ddng khdng doi tii cac dien cue dat tren mat mdi trudng, thong tin ve mdi trudng dia dien se phan anh qua phan bd trudng dien tai moi diem eua mdi trudng De thu nhan cac thong tin ed ich nay, trong phuang phap do sau PCKT, ngudi ta phai bd tri cac dien cue phat va dien cue thu mot each thich hgp tren mat mdi trudng, mdi each bd tri dd tao nen mot he cue do Phuang phap do sau PCKT bang ddng khdng ddi la phuang phap the hien nguyen ly do sau hinh hgc: cang tang kieh thudc giiia cac dien cue phat va cac dien cue thu thi do sau nghien ciiu cang tang Phu thudc ddi tugng va nhiem

vu khao sat ma ngudi ta sir dung each bd tri he cue thich hgp de' thu nhan dugc

sd lieu tot nha't ve mdi trudng, do dd cac phuang phap do sau PCKT cd the duge phan loai theo he cue do

1.3.1 Mot sd he cue do ca ban:

Ngudi ta phan loai he cue do dua vao each bd tri cac dien cue va kich thudc giiia cac dien cue phat va thu (ggi la kieh thudc he cue) Cac loai he cue

do khac nhau dugc sir dung phu thudc vao dac diem mdi trudng va dieu kien

do dac, trong dd hai nhdm he cue do ca ban thudng dimg nhat la he cue do 4 cue ddi xiing va he cue do ludng cue

13.1.1 He cue do bdn cue doi xitng:

He cue do 4 cue ddi xiing gdm bdn dien cue tie'p da't phan bd ddi xiing

vdi nhau qua tam do sau, trong dd ddng dien / duge phat qua hai dien cue phat

A, B d ngoai, hieu dien the AU dugc do giiia hai dien cue thu M, N d trong

Cac dien cue phat va thu dugc bd tri thang hang, ddi xiing vdi nhau qua tam

O, tam nay dugc qui udc la diem do eua he cue (Hinh 1.1)

+1 -I

Hinh 1.1: He cue do 4 cue ddi xiing

He so ciia he cue do dugc tinh theo cdng thiic:

^^ TTAM.AN

MN

AB trong dd: ^s ~ ^ la kich thudc he cue

- Trong trudng hgp khoang each MN « AB, he cue do 4 cue ddi xiing

dugc ggi la he cue Schlumberger, duge sir dung pho bien trong thue te tham

dd dien d nude ta He sd he cue Schlumberger duge tinh bdi cdng thiic:

^^^'^ = ^ (1-11)

MN ^ ^

Khi mot cue phat dat ra't xa cac cue thu ( 5 -^ oo), he cue do trd thanh he

cue nira Schlumberger

- Trong trudng hgp khoang each AM=MN=L/3, vdi L = Z s thi he cue

do 4 cue ddi xiing trd thanh he cue Wenner He so he cue Wenner dugc tinh

bdi cdng thiic:

K(r) = -;rAB

1.3.1.2 He cue do luang cue:

He cue do luang cue gdm hai dien cue phat AB va hai dien cue thu MN,

vdi khoang each AB va MN deu rat nhd so vdi kieh thudc he cue r = 0 0 ,

trong dd hai diem O, O tuang ling la tam hai dien cue phat va hai dien cue thu

(Hinh 1.2) Ddng dien / dugc phat qua hai dien cue AB, hieu dien the' AU dugc

do giixa hai dien cue MN

M

N

Hinh 1.2: He cue do ludng cue,

He cue nay thudng duge sir dung hiru hieu trong phuang phap do mat cat dien de nghien ciiu sau, nham khac phuc khd khan trong viec bd tri he cue phat ddng AB vdi kich thudc he cue Idn ciia he cue do 4 cue dd'i xiing; hoac dugc sir dung trong trudng hgp tim kiem phat hien bat ddng nhat ngang, trong tim kie'm quang md

- Khi MN l O O ta ggi la he ludng cue phuang vi He sd he cue do nay dugc tinh theo cdng thiic:

'~^MN,sm0 ^^'^^^

Khi 6 = 90^, he cue do nay duge ggi la he ludng cue xieh dao

- Khi MN // 0 0 ' ta ggi la he ludng cue xuyen tam He sd he cue do nay

dugc tinh theo cdng thiic:

Khi 0 = 0^, he cue do nay dugc ggi la he ludng cue true

1.3.2 Mot vai phuang phap do sau PCKT thong dung

1.3.2.1 Phuang phap do sdu doi xAngphdn cue kich thich

• He cue do 4 cue dd'i xiing Schlumberger chinh la he cue do ciia phuang

phap do sau PCKT dd'i xiing Phuang phap do sau PCKT ddi xiing td ra thich

hgp de phat hien va du bao hinh dang cac ddi khoang hoa va than quang thau

kinh cd xu hudng nam ngang va dia hinh tren mat khdng qua phiic tap [64]

Tuy thudc vao dieu kien dia cha't - khoang san cu the cua viing va dac diem

ciia ddi tugng nghien ciiu ma lua chon cac bang he sd he cue do sau thich hgp

da quy dinh trong quy pham ky thuat tham dd dien PCKT bang ddng khdng

ddi Trong trudng hgp can thiet ed the dan day them cac kich thudc he cue

nham phan anh rd han dd'i tugng nghien ciiu [7]

Ket qua do dac ngoai thuc dia la cac dudng cong p^ = f{AB/2)Yk

7]^ = f(AB/2) de phan tich dinh lugng va lap mat cat dia - dien eua lat cat

• Giai thich dinh lugng tai lieu do sau PCKT ddi xiing cd nghia la phan

tich dinh lugng ddng thdi cac dudng cong 7^, A •

Viec phan tich dinh lugng cac dudng cong do sau PCKT ciing da dugc

nhieu nha Dia vat ly nghien ciiu va xay dung ban chuan (palet) de phan tich

cac dudng cong do sau 77^ cd dang 2 hoac 3 Idp

Ddi vdi mdi trudng nhieu Idp, cac nha Dia vat ly Lien Xd (cii) gdm

Vanhian L.L, Morozova E.M va Logienxuna L.V [69] da de nghi phuang

phap tinh toan cac dudng cong rj^ tren may tinh dien tir theo each tinh toan

dudng cong p^ cua Vanhian L.L tii nam 1961

Hien nay, d Nga va My , ngudi ta da de nghi tinh toan cac dudng cong

7^ va p^ dd'i vdi mdi trudng phan Idp, ddng nha't, song phang ngang tren

may vi tinh bang phuang phap lua chon Ket qua tinh toan se dugc chinh xac

han bang each sir dung cac thong tin tien nghiem cd dugc tii mat cat thuc te'

va ddng thdi han che' dugc anh hudng eua nguyen ly tuang duang

Viec xir ly cac dudng cong rj^ cd the tien hanh theo cac each sau:

> Cach thii nha't:

Cd th^ tinh rj^ =f{ABI2) true tiep tir dudng cong p^ =f{AB/2) theo

cdng thiic (1.8)

Vdi each tinh toan nay, ta cd the xir ly dinh lugng cac dudng cong do

sau PCKT dd'i xiing va lap duge mat cat dia-dien theo hai tham so chinh la do

phan cue 7^ va dien trd sua't p^ Lien ket cac Idp cd dac trung ciia di thudng

quang, cho phep ta du bao duge hinh dang ciia than quang cd trong lat cat dia

chat [2]

> Cach thii hai:

Dudng cong 7^ =f(AB/2) dugc xa'p xi theo cdng thiic cua Pispareva

N.A khi mdi trudng phan Idp, ddng nhat song phang ngang, it phan di ve dien

trd suat [71]:

N N

- % =T.uX<Pi - ^ M ) = ^1 + X(7, - 7 M ) - ^ / (1.15)

/=i 1=1

dday: (p, ={\ + H./if ^{l + Z.f vdi Z- =H./L

trong dd: H- la chieu sau de'n mai Idp thii /; L = OA = AB/2

Nam 1992, khi tie'n hanh do sau PCKT ddi xiing [2] di tim kiem

molipden d 6 Quy Ho va Bang Khoang (Sa Pa - Lao Cai), sulfur ehiia vang Dich Qua (Thanh San - VTnh Phu), chi-kem Na Turn (Chg Don -Bac Thai) , cac tac gia da xay dung chuang trinh tinh toan tu ddng tren may vi tinh theo phuang phap lua chon va cd nhiing ket qua tin cay

Ket qua xir ly dinh lugng cac dudng cong 7^ = f{AB/2) va

p^ =f(AB/2) diem so 17 Ld Than tren ddi quang thach anh sulfur cd chiia

vang d viing sudi Linh (Ddng Nai) [3] khdng sai khac nhieu so vdi ket qua dao cdng trinh kiem tra

1.3.2.2 Phuang phap do sdu PCKT luang cue true lien tuc deu

Ddi vdi cac than quang cd dang via, thau kinh va dia hinh tren mat phiic tap, khdng the tie'n hanh phuang phap do sau PCKT dd'i xiing ma phai ap dung phuang phap do sau PCKT ludng cue Trong dd, phuang phap do sau PCKT ludng cue true lien tuc deu dugc ap dung pho bien d cac nude phuang Tay tii lau, hien nay d nude ta ciing dang duge ap dung mot each rdng rai [1], [33], [40], [41], [42], [43]

•t* He cue do luang cue true lien tuc deu la he cue do luang cue true, nhung ed khoang each luang cue phat AB, khoang each ludng cue thu MN va

bude dich chuyen ludng cue thu tren tuyen la bang nhau va bang mot sd a nao

dd Vdi mdi vi tri ciia luang cue phat AB, ta lan lugt do va dich chuyen ludng cue thu tren tuyen n lan Khi n=l thi kich thudc he cue r = 2a, n = 2 thi r = 3 a

, cd nghia la r = (n+1) a Tuy theo cdng suat ciia ngudn phat va dieu kien thi

cdng thuc te' ma ngudi ta tien hanh do vdi n bang bao nhieu Hien nay, trong dieu kien d nude ta thudng phuang phap nay dugc thue hien vdi n = 6 -^ 8 Diem ghi eua phuang phap dugc quy dinh trong quy pham ky thuat cua phuang phap, va dugc quy udc la giao diem eua mang ludi tia nghieng 45° tai

tam luang cue Ke't qua do dugc ghi va ve thanh mat cat dang gia tri p^, 7^

va ggi la cac gia mat cat (pseudoseetion)

Khi do phuang phap nay, dien trd suat bieu kien dugc tinh theo cdng

thiie (1.3) vdi he sd he cue la

K = n{n + l).(w + 7),7Ui (1.16)

cdn do phan cue bieu kie'n 7^ dugc tinh theo cdng thiic (1.7)

Nhu vay d cac kich thudc dau n=l va n=2 khdng thoa man dieu kien

luang cue a « r, chi cd cac kich thudc sau n > 3 mdi thoa man dieu kien

ludng cue

Phuang phap do sau luang cue true lien tuc deu mang sac thai eua do

sau ludng cue true, nen phat huy duge uu diem la tang do phan giai, phat hien

tot cac ddi tugng ba't ddng nha't dudi Idp phu, dac biet la cac ddi tugng cd the

nam ddc phu hgp vdi nhieu md hinh vat ly-dia cha't ciia cac than quang

• Phuang phap xir ly tai lieu do sau luang cue true lien tuc deu thuc hien

theo each phan tich mat eat ban dinh lugng [33], [50]:

Trong qua trinh nghien ciiu trien khai de tai cap nha nude KT-01-13

[14], cac tac gia da de nghi phuang phap xir ly de chuyen cac gia mat cat neu

tren thanh cac mat eat thuc

Theo nguyen ly tuang hd mot vat the ba't ddng nha't duge phan anh bang

hai di thudng d hai ben vat the, nen de nghi cdng thiic xir ly dua ve chieu sau

thang diing nhu sau:

PXZ„) = y2[P,_„^,,(Z„)-P,,„^„(Zj] (1.17)

trong dd: / la thii tu diem do sau tren tuyen

n la thii tu diem dich chuyen do sau

Z„ = 1 / 2(/2 + \)a la chieu sau

P.(Z^) la tham sd p^, 7^ e^n tinh toan

Ciing cd the bang each chuyen gia mat cat (ghi d giiia) thanh hai mat

cat cd diem ghi d tam luang cue phat (ghi trai) va tam ludng cue thu (ghi

phai) Chong chap hai mat cat ghi trai va ghi phai len nhau va tinh gia tri

Pi(Z„) theo chieu sau thang diing:

P,(ZJ=ll2[PaX,,^P.(ZXH,J (1.18)

trong dd: / la thii tu diem do sau tren tuyen ling vdi cac chieu sau Z„ khac

nhau

Pi(ZJ^^^i la gia tri tham sd d mat cat ghi trai

Pi(ZJ^fj^i la gia tri tham sd d mat cat ghi phai

Vdi each xir ly nay, coi nhu diem ghi ciia do sau ludng cue true lien tuc

diu da dugc xac dinh va tren mat cat xir ly nay vi tri hinh dang ciia ddi tugng

nghien ciiu dugc the hien sat thue han vdi lat eat thuc te va cd the xem nhu lat

eat dia-dien ban dinh lugng

Ket qua phan tich mat cat ban dinh lugng tuyen 34a viing Cao Ram

(Luang San - Hoa Binh) cho thay di thudng dien trd suat va do phan cue tren

cac mat eat da xir ly phan anh kha triing hgp vdi vi tri than quang va su phat

trien ciia nd dudi sau [14]

1.3.2.3 Viec phdn tich theo mo hinh hai vd ba chieu:

Viec phan tich dinh lugng cac dudng cong do sau dien trd p^ = f{AB/2)

da dugc nghien ciiu tii lau va da cd nhieu ban chuan (palet) de phan tich bang

tay cGng nhu nhieu chuang trinh phan tieh tu ddng tren may vi tinh [6], [11],

[12], [13], [16], [19], [25], [26], [37], [38], [47], [65], [74], [75] Viec tinh

toan se ed do tin cay cao, neu cd cac thdng tin tien nghiem ve sd Idp dia dien,

chieu day va dien trd suat cua cac Idp giiia Cac thdng tin nay cd the cd dugc

tir cac ke't qua khoan va do cardta dien trd d giai doan trude

Cho den nay cung da ed nhieu ngudi dua ra cac phuang phap tinh toan

ddi vdi mdi trudng phiic tap hai va ba chieu dugc thue hien bang cac phuang

phap sd gan diing Cd the neu ra hai hudng giai chinh la phuang phap phuang trinh tich phan va phuang phap phuang trinh vi phan:

> Phuang phap phuang trinh tich phan dua tren md phong tinh chat cua khdi ba't ddng nhat bang mot tap hgp ngudn dien thii cap tao ra d mat tiep xuc cua khdi ba't ddng nha't Phuang trinh tieh phan thiet lap trong trudng hgp nay ggi la phuang trinh tich phan be mat Neu khdi ba't ddng nhat dugc md phdng bang tap hgp cac dien tieh dan gian hay bang cac thanh ludng cue thi ket qua tuang ling duge ggi la phuang trinh tich phan khdi Phuang trinh tich phan cd

the thie't lap cho ham the U, cudng do dien trudng E hay cudng do ngudn thii

cap /, bao gdm phan hieu ling di thudng do bat ddng nha't gay ra va phan binh thudng dac trung cho mdi trudng (ddng nhat hay phan Idp xac dinh) Cac phuang trinh nay ed dang tich phan Fredholm loai II da dugc de cap day du trong cac cdng trinh [30], [31], [39], [41], [44], [45], [53], [79] v.v

> Phuang phap phuang trinh vi phan dua tren su dien giai true tiep cac phep tinh sai phan trong phuang trinh cho tirng phan tir ciia mdi trudng ed the

tich Vj va do dan a vdi dac trung dien the' Uj do ngudn diem I phan bd trong

mdi trudng gay ra Cac phep tinh tich phan va vi phan se dugc thuc hien theo

sa dd sai phan thay the' thdng qua mdi quan he eua phan tii V^ (vdi tinh chat cT-, Uj) va cac phan tir V; d lan can Nhu vay, neu md phdng mdi trudng bang mot tap hiiu han cac p h & tir Vj (ddng nha't ve tinh dSn dien cr, va ed kich thudc xac dinh), va viet phuang trinh theo sa dd sai phan cho mdi phan tir Vj vdi cac dieu kien can thiet de dam bao su tdn tai ciia ham the' U trong mdi trudng bat ddng nhat do mdt ngudn diem I gay ra ta se nhan dugc mdt he phuang trinh dai sd tuyen tinh vdi Uj la ^n sd dac trung cho trudng the Vj

Viec xir ly dinh lugng cac mat cat sau theo phuang phap nay da dugc nghien ciiu nhieu d cac phuang Tay theo each lua chgn md hinh hoa lat eat dia

- dien 2 va 3 chieu [27], [29], [32], [34], [36], [54], [61] 6 Viet nam

phuang phap hieu hiru han mdi dugc ap dung [14], [24] Cac ke't qua da

cdng bd cho tha'y cac mat cat lua chgn da phan anh duge hinh dang quy v6

chinh tac ciia ddi tugng gay di thudng dien trd, ddng thdi cac tac gia ciing da thir nghiem, tinh toan cho tham sd phan cue 7^ va da cd nhiing ket qua budc dau [23] Ngoai ra nd cdn dugc tien hanh bdi cac cdng ty nude ngoai dang lam viec d Viet Nam nhu cdng ty CRA-E d md ddng Diic Bd (Tam Ky), cdng ty Leader Resources d ngoai vi md Chg Don (Bac Thai) va cdng ty KMPC (Han Qudc) d viing md Nam An Khe (Binh Dinh) Ket qua ap dung thir nghiem da cho cac ket qua budc dau kha tot

Ciing can phai nhae de'n mot sd cdng trinh khac sir dung tham so mat do dien phiic [58], [59], [60], ky thuat nghich dao [52], [55], [57]

L4 DIEM QUA M O T VAI PHl/ONG PHAP DO SAU DIEN TRCJ VI PHAN DA

DUOC DE XUAT CAI TIEN

De khac phuc cac nhugc diem eua phuang phap do sau dien trd, cac nha Dia Vat ly da de xuat nhieu phuang phap khac nhau Sau day chiing tdi chi diem qua mot vai phuang phap do sau dien trd vi phan da duge de xua't cai

tie'n cd lien quan true tiep den hudng suy nghi ciia chiing tdi khi thuc hien d6

tai nay

1.4.1 Phuang phap do sau dien chung

• Phuang phdp do sdu nhdm danh gid do meo cua du&ng cong do sdu

dien (DSD)

Cd hai loai he cue do va each do nhu sau [12]:

> Tii he cue do 4 cue ddi xiing AMNB, ta bd tri them 1 dien cue thu dat tai tam O cua he cue de bien nd thanh he vi phan 5 cue ddi xiing thang hang

AMONB Vdi he cue nay ta se thu dugc hieu A p^ (0) ciia dien trd suat bieu

kie'n bae 2 [8] ciia rieng ngudn phat tai A va ngudn phat tai B qua he thiic [9]:

M(c\\ ^ # # / m ^ ^ # / m ^##m^ ^^%

AA'^(0)=A!I(0)-/^S(0)=AA'^(0) (1.19)

AB

Ve ban chat vat ly, hieu nay hoan toan triing vdi hieu dien trd suat bieu

kien 2 canh cua he cue do ludng cue true

- Ne'u A/?f (0)= 0 thi cd nhieu kha nang dudng cong p^ khong bi meo

va phan anh moi trudng phan Idp, ddng nhat, song song

- Neu A/?f^ ( 0 ) ^ 0 thi dudng cong p^ bi meo, miic do meo tuy thudc

vao gia tri dai sd ciia dai lugng nay

> Taeh rieng p^^ va p^^ tir so lieu duy nha't p^^^ do dugc bang he cue do 4

cue dd'i xiing Schlunberger Viec taeh nay [10] dugc thue hien nhu sau: Tien

hanh 2 phep do bang hai he 4 cue thang hang AjMNBj ddi xiing va Aj^jMNB;

khdng dd'i xiing Ggi At/^'V/*'* va A^*-V/*^* tuang ling la sd lieu thu duge

bang he cue ddi xiing va he cue khdng ddi xiing Van dung nguyen ly chong

cha't tuyen tinh cac trang thai dien, ta de dang thu dugc quan he sau:

'•- /<^> /'" -KM.) KM)

Ve trai la cac dai luong do diroc, con ve phai c6 cac he so he cue deu da

bi6t Vi vay, neu biet p^^ {r.) ta c6 the tinh duofc p^^ {r.^^) ciia kich thu6c he

cue tiep theo bang cong thiic truy h6i sau:

va khang dinh rang:

- Ne'u PsA = PsB thi cd nhieu kha nang dudng cong P^AB khdng bi

meo

- Neu PsA ^ PsB thi dudng cong P^AB bi meo

Bang mot trong hai each neu tren, ta cd the danh gia dugc mdi trudng thuc te' khac vdi md hinh ly thuyet nhu the' nao, tii dd xac dinh miic do sir dung cac ke't qua phan tich tai lieu do sau dien trong viec giai thich tong hgp tai lieu dia eha't-dia vat ly ciia khu vuc khao sat

• Phuang phdp do sdu dien chung

Vdi muc dich khdng chi dirng lai d viec danh gia mot each dinh tinh ve

su sai khac giiia mdi trudng thue te' va md hinh ly thuyet phan Idp, ddng nhat, song phang ngang, tac gia Tang Mudi da de xua't phuang phap do sau dien chung (DSDC) [56] nham danh gia dinh lugng su sai khac giiia mdi trudng

thue te' va md hinh ly thuyet, tii dudng cong pf do dugc theo hudng ^ bat ky

cd the taeh dugc dudng cong do sau dien binh thudng /?fo phan anh mdi trudng phan Idp, ddng nhat, song phang ngang tai mdi diem khao sat va hieu

ling di thudng pf^r (phan di thudng theo khoang each r), pf^^ (phan di thudng

theo phuang vi ^ ) Thuc cha't eua phuang phap DSDC la de xuat bien phap tang lugng thdng tin tai mdi diem khao sat bang each "quet" ngudn phat dien vdi ban kinh r = AB/2 quanh diem giiia eua AB, ket hgp vdi viec "quet" cac cue thu vdi ban kinh l=MN/2 quanh diem khao sat Nhu vay, ngoai viec thu

dugc dudng cong pi phan anh mat do ddng theo cac phuang khac nhau trong khu vuc cac dien cue thu, cdn thu dugc dudng cong p" [8] phan anh gradient

mat do ddng theo cac phuang khac nhau trong khu vuc cac dien cue thu dd Nhu vay, chang nhiing cho phep xem xet mdi trudng mot each chi tiet han, ma cdn tao dieu kien danh gia dugc miic do bie'n dang ciia dudng cong [9] va taeh dien trd suat ndi d tren [10]

1.4.2 Phuang phap do sau khau triir trudng

• Nhu da biet, Petrovski ed de nghi mdt phuang phap bien d6i dudng

cong do sau dien trd ddi xiing p^ (do bang he Schlumbeegie - 4 cue ddi xiing)

thanh mot dudng cong khac cho do nghien ciiu Idn han va kha nang phan giai

cao han - ggi la dudng cong Petrovski Phep bien ddi dugc thuc hien theo cdng

thirc [4], [67]:

^ dr ^ p^

^' ~ dirlpy [\-{rlpMdPsldr)\ ^^'^^^

trong dd r=AB/2 ggi la kich thudc he cue do (nira khoang each giiia hai dien

cue phat AB)

Dudng cong Petrovski ed nhieu uu diem [5] Tuy nhien, can luu y rang

du sao phep bie'n doi nay cd chiia thanh phan dao ham ^' la mdt phep tinh

dr

khdng on dinh (toan tir vi phan thudng dSn tdi bai toan khdng chinh) [17] nen

can phai nghien ciiu cai tien khac phuc nhugc diem nay

•J* Nam 1965 nha Dia Vat ly Lien Xd (cii) Rabinovich [76] da de nghi mot

phuang phap mdi ggi la phuang phap khau trir trudng Phuang phap nay cd

the thuc hien do true tiep tir thuc dia nhiing dai lugng can thiet de tinh dudng

cong Petrovski nham khac phuc tinh khdng on dinh ndi tren

Rabinovich da them vao mdt cap cue phat A2B2 dat ben ngoai he cue do

bdn cue ddi xiing AjMNBi thdng thudng, d mdi vi tri eua he cue lan lugt phat

hai ddng dien Ij va I2 de do hai hieu the AUj (khi phat AjB^, he sd he cue AT^,)

va AU2 (khi phat A2B2, he sd he eUc K^^) giiia cap cue thu MN Sau dd phat

ddng thdi hai ddng Ii va I2 ngugc chieu nhau de do hieu the A(AU) (Hinh 1.3)

Mdt yeu cau quan trgng ciia phuang phap khau trii trudng la phai dam

bao sao cho do Idn cua hai ddng phat tuan theo mot he thiic xac dinh

'-2 ^ 2

Al M N B, B

Hinh 1.3: Sa do he cue do sau khau triir trucmg cua Rabinovich

Vdfi he cue do tren, dien trd suat bieu kien p duoc tinh theo c6ng thiJc

(1.24) ( ' ' 2 / A 2 ) - ( n / A , ) ^' ^2 A(A^)

<• Phat trien y tudng eua Rabinovich, nha Dia Vat Ly My Zohdy [63] da

de nghi sir dung chinh he cue do cua Rabinovich de do mdt dai lugng dien trd sua't bieu kien vi phan khac theo cdng thiic:

Zohdy ggi p la dien trd sua't vi phan dge, p^ la dien trd suat vi phan ngang Quy trinh thue dia de thu dugc p^ tuang tu nhu quy trinh de thu p^

nhung do Idn ciia hai ddng phat phai tuan theo mdt he thiic khac:

Cac dai lugng p , p deu dugc bieu diln phu thugc vao kich thudc

trung binh:

r « (rj + r2) / 2

Hien nhien, ngoai cac dudng cong p^, /?, cac phuang phap do sau khau

trir trudng tai mdi vi tri ciia he cue cdn cho phep ddng thdi thu dugc mot gia tri

p,^ir^) va mdt gia tri p,2(^2) tuang ling vdi hai he cue do 4 cue ddi xiing AiMNBi va A2MNB2, tii dd ta thu duge cac dudng cong p^^ (r^) va p^^ {r^)

1.4.3 Phuomg phap do sau dien ddi xirng luang cue hgp nhat

Cac tac gia Lam Quang Thiep va Le Viet Du Khuang [16], [17], [20] da

de nghi quy trinh do sau dien trd mdi vdi y tudng la ed gang tang mot each hgp ly so lugng tin hieu dien trudng do d thuc dia de qua su tong hgp cac tin hieu dd thu dugc cac dudng cong ed mat do thong tin Idn han, phan anh lat eat

chinh xac han Cac dien trd sua't bieu kien vi phan p^ va /?, thu dugc bang

each thiic dan gian han so vdi phuang phap kha'u trir trudng Dd la phuang phap do sau dien dd'i xiing luang cue hgp nha't (CSDES - Combined Symmetrical Dipole Electric Sounding)

Sa dd he cue do sau dien dd'i xufng luong cue hgp nhat dugc md ta tren Hinh 1.4, trong dd hai dien cue phat AB dugc bd tri ben trong 4 dien cue thu

Ml, Nj, M2 , N2 dd'i xiing qua tam hai dien cue phat AB (ta cd he cue lan lugt

la M2M1ABN1N2)

<v>

A a

-• AU3I

•-/ •-/ •-/ \ \ \ •-/ •-/ •-/ \ \ \ M2 Ml A

/// \ \ \ / / / \ V \

B N, N

Hinh 1.4: Sa do he cue do sau dien dd'i xiing va luang cue hgp nhat

Trude het can nhac lai, da cd nhieu ngudi dua ra cac cdng thiie tinh chuyen giiia cac dudng cong do sau dien trd [49], tuy nhien cdng thiic vSn

thudng dugc sir dung tuf trudc den nay bieu dien mdi quan he giiia gia tri p^ va

Pr [5], [15] nhu sau:

r dp(r) pM) = Psi^)

6 mdi vi tri, he cvtc chi phat m6t dong I va do 4 hieu dien the AU31

(giOaMiN,), AU,2 (giiia M2N2), AU.p (gifla N.N^), AU,T (gifla MiM.) Tit do

tinh duoc gia tri cac dudng cong dien tro suat bieu kien p^, va p^^ (tuong umg

vdi do sau doi xflng), p,, va p^^ (tuong flng v6i do sau luong cue true canh

phai va canh trai) theo cong thflc (1.3) va cac gia tri trung binh:

Ngoai ra, de hoan thien phuong phap, cac tac gia da de nghi tinh gia tri

dien trd suat bieu kien vi phan Petrovski suy rong p\ [18], [21] thay cho p^:

• p^ : trung binh cdng ciia dien trd sua't bieu kien ling vdi he luang cue

true trai va phai

• a = [0,1]: he sd dieu chinh phep bien doi phu thugc ty sd pj p,

• Cac dai lugng Prj.PrF^Pr^Pp^Pz^Pp ^^^ dugc bieu dien phu thugc vao

kich thudc trung binh ciia he cue do duge quy udc ddi vdi he cue ddi

xiing va ludng cue:

r = iJAN,.AN^,BN,.BN^ (1.35)

1.4.4 Mot sd nhan xet ve cac phuang phap do sau dien tra vi phan da

dugc de xuat cai tien

• Trudc he't \i mat ly thuyet:

Muc dich cua cac phuang phap do sau dien trd neu tren la mudn thu dugc tir cac sd lieu thuc dia cac ham bieu dien su bien doi ciia dien trd suat bieu kie'n /7^^(r) theo kich thudc he cue do sao cho cac ham dd gan nha't so vdi

ham bi^u dien su bie'n doi ciia dien trd suat that theo do sau p{h) Tuy nhien,

muc dich dd khdng phai la trong mgi trudng hgp deu dat dugc Trong cdng trinh [4] da chiing minh dieu nay

That vay, chiing ta xet cac dudng cong p,,Pp, va p, dugc tinh ling vdi

cac lat cat dien hai Idp Mgi dudng cong ndi de'n trong nay deu dugc bieu dien tren ty xieh logarit kep

Ddi vdi lat cat dien cd /?, </?,: cac dudng cong p^ va p ed dang dieu khac nhau nhung p^ vao tiem can phai ling vdi r cd bang niia so vdi p^, tiic la

do sau nghien ciiu ciia p, Idn gap hai Mn p^; cdn cac dudng p bam gan vdi

lat cat dien that han nhieu tuy chiing cd di qua mot cue dai yeu trudc khi vao tiem can phai

Ddi vdi cac lat cat dien cd p, <p^: phan dau ciia cac dudng cong p^ va /7, bam sat lat cat dien that han p^, Tuy nhien cac dudng p^ cd nhugc diem

la trudc khi di vao tiem can phai cd di qua mot cue tieu, cue tieu nay cang rd

khi p, cang be han /?,; cdn cac dudng cong /?, pham nhugc diem nghiem

trgng han la chung nhan gia tri am trudc khi di vao tiem can phai Cd the hieu

rd kha nang xuat hien cac gia tri am ciia p^ va p^ neu viet cac cdng thiic

(1.22) va (1.25) dudi dang khac:

trong dd t la he sd gdc ciia dudng cong p^ tai diem (/7^,r) Tir (1.36) va (1.37)

ta cd the thay rd: p^ se am neu t >1, tiic la khi dudng cong p^ tuang ling di

len vdi do ddc Idn han 45^, dieu dd xay ra khi md hinh mdi trudng phan Idp

ngang bi vi phan manh; cdn p^ se am neu t<-l, tiic la khi dudng cong p^

tuang ling di xud'ng vdi dd ddc nhd han - 45^, dieu nay xay ra vdi mdi trudng phan Idp ngang cd dien trd sua't ciia Idp ke' tiep ben dudi be han nhi^u so vdi

ciia Idp ben tren Chinh cac gia tri am ciia p.^ gay nhieu phien phirc khi phan

tich ke't qua nen tac dung ciia chiing trong thuc te he't siic han che Ciing vi ly

do dd khi cac tac gia de xuat phuang phap do sau dien ddi xiing va luang cue

hgp nha't chi luu y sir dung cac dudng cong p^

Theo cdng thiic (1.34) cho phep nit ra nhan xet: p^ va p^ chang qua la

cac trudng hgp rieng ciia /?* khi sd mii a lay tuang ling bang 1 va 0 Cd the chgn gia tri cua a thich hgp sao cho ling vdi cac phan dien trd sua't that ciia lat cat dien tang theo chieu sau thi dudng cong /?* cd dang gan gidng dudng cong

Pp nhung giam bdt do Idn cue dai; ling vdi cac phan dien trd suat that giam theo chieu sau thi dudng cong /?* cd dang bam sat lat cat dien that han p^

nhung tranh dugc cac cue tieu gia Nhu vay, cac gia tri cua a cd the chgn tuy thugc vao do ddc eua dudng cong /7^(r) tuang ling, hoac ndi each khac tuy

thudc vao gia tri ty sd pj p^ tinh duge true tiep tir sd lieu thuc dia Bang

phuang phap thir nghiem sd tren may tinh dien tir ed the chgn ham

a=a(/7,1 p^) thich hgp cho cac dudng cong p^ ddi vdi ca trudng hgp lat cat

dien hai Idp va nhieu Idp

Rd rang cac dudng cong p\{r) duy tri dugc nhiing uu die'm cua cac dudng cong p nhung khac phuc duge nhiing nhugc diem cua nd

Nhu vay, cac phuang phap do sau dien ddi xiing va ludng cue hgp nhat

dam bao thu dugc day dii cac dudng cong p,,{r;)^Psii^i\Pp^^\Pzir) ^ ^ hai

phuang phap do sau khau trir trudng ciia Robinovich va Zohdy cd the dem lai,

ngoai ra cdn cho phep thu cac dudng cong PrFi^^PrT^rXPpir)

• VI dieu kien thi cdng thuc dia:

Chinh Zohdy [63] da phan tich rat rd cac uu nhugc dilm cua cac phuang phap do sau khau trir trudng, trong dd cd thd luu y de'n cac nhugc diem chinh sau day:

1 Cac gia tri am cd the cd ciia p^(r) va Pp(r) ddi hoi phai theo ddi rat

can than gia tri ciia hieu dien the" A(AU), dieu dd gay phiic tap cho cdng tac thuc dia

2 Gia tri A(AU) thudng rat be, ddi hdi phai cd cac ngudn phat ddng Idn mdi do chinh xac

3 Viec dung hai mach phat ddng lam tang kha nang rd dien

4 Ddi hdi ty sd ddng tuan theo he thiic (/, / / J ; ^ (r, Ir^y se lam cho p^

va p^ mac sai so Idn ngay khi r,, r, pham sai sd khdng Idn lam

Rd rang phuang phap do sau ddi xiing va luang cue hgp nhat tranh dugc ta't ca cac nhugc diem quan trgng vira neu ciia cac phuang phap khau trir trudng

He cue do vdi cap cue phat ben trong (Hinh 1.4) cd nhiing uu diem quan trgng ve mat ky thuat nhu sau:

1 He cue do nay da sir dung nguyen ly tuang hd trong tham dd dien Su diing dan ciia nguyen ly nay dd'i vdi mdi trudng dia chat bat ddng nhat bat ky

da dugc chiing minh trong cdng trinh [72]