260 Nang cao hieu qua phuong phap dja chan trong digu kien chu true dja chSt phiic tap d mien vdng NANG CAO HIEU QUA P H U O T V G PHAP DIA CHAN TRONG DIEU KIEN CAU TRUC DIA CHAT PHlTC TAP 6 MIEN VONG[.]
260 Nang cao hieu qua phuong phap dja chan digu kien chu true dja chSt phiic tap d mien vdng NANG CAO HIEU QUA P H U O T V G PHAP DIA C H A N T R O N G DIEU KIEN CAU T R U C DIA CHAT PHlTC TAP MIEN V O N G HA N Q I Phan Tien Vien, Ha Qu6c Quan, Le Due Cong Nguyen Thu Huyin, Nguyen Trung Hieu Viin Diiu Khi Nu Tat Thang Cdng ty Ddu tw vd Phdt triin Ddu TOM TAT Mien vdng Hd Ndi (MVHN) v&i mirc khdo sdt dia chdn vd nghien cim chua chi tiit vdy chung ta chua cd dii sd lieu cd tin cdy cao di ddnh gid chinh xdc tiim ndng ddu ciia vimg, ddc biet la ria Tdy Nam Vimg nghiin ciru lgi ndm & noi ddn cu ddng diic, nhiiu hi thdng sdng l&n nen dnh hu&ng rdt ldn din qud trinh thu nd dia chdn vd chdt lugng tdi lieu Ddc diim dia chdn - dia chdt cua vimg cung rdt phirc tgp, ranh gi&i bdt chinh hgp Paleogen - Neogen ndm rdt ndng vd cd tuong phdn dm hoc l&n tgo cdc mat phdn xg la cdc mat khiic xg mgnh, su thay ddi l&n cua tdc khdng nhung theo chieu sdu md cdn cd theo chiiu ngang, phdn du&i cua Idt cdt c& dge trung phdn dl yiu Cdc yeu td tren ngdn cdn ndng lugng dia chdn xuyen sdu xudng du&i, ddng th&i tgo nen nhiiu logi sdng phdn xg nhieu ldn vd sdng khuc xg Vi vdy, chting ta cdn phdi ndng cao hiiu qud phuo'ng phdp dia chdn Di gidi quyit nhung vdn di trin chung tdi da tiin hdnh md hinh hod thu nd dia chdn, dua tren tdi lieu gieng khoan PV-XT-IX vd tuyen dia chdn A94-36 Chiing tdi da phdn tieh, ddnh gid kit qud md hinh hod thu nd dja chdn vd chon cdc tham sd thu nd, chu trinh xir ly phii hgp v&i vung nghien ciru Ldn ddu tien & MVHN cdc cdng cu md hinh hod dia chdn da duoc sir dung vd dem lgi kit qud dinh lugng cd tin cdy cao giiip cho viec lua chon ede tham sd thu nd vd xir ly & thue dia cd co s& khoa hoc Tren ca s& kit qud nghien ciru chimg tdi da lira chgn cdc tham sd thu nd vd di xudt chu trinh xir ly dieu kiin cdu triic dia chat phuc tgp & ria Tdy Nam vd MVHN Chu trinh xir ly di xudt da dugc dp dung cd hieu qud qud trinh xu ly lgi tdi lieu dia chdn MVHN MO DAU Den thai diem hien nay, vai muc khao sat va nghien cuu ria Tay Nam MVHN noi rieng va MVHN noi chung, chua co du so lieu de danh gia vai tin cay can thilt vl tilm nang dau cua ca khu vuc Nguyen nhan la vi dieu kien khao sat kho khan a vung dan cu dong due, he thong song ngoi qua day, dong thai MVHN co cau true dia ch4t rk phuc tap Do kit qua minh giai tuyin dia chhn A94-36 truac khoan GK PV-XTIX noc tang mong truac Kainozoi dugc du doan nhm rat nong (cy vao khoang sau 700 800m tuang duong vai 600 - 650ms tren mat ck thai gian), song tren thuc te GK da khoan qua sau 1870m van chua gap da mong [2] Vi the can thiet phai nghien cuu danh gia lai tilm nang dAu o ria Tay Nam, dac biet la tim cac biy chua dau Mgt cau hoi Tuygn tap bao cao Hoi nghj KHCN "30 nam DSu Viet Nam: Co- hdi mdi, thach thuc mdi" 26 dat la lat cat dia chit a ria T^y Nam co phan di ve mat dia chan hay khong? Chat lugng tai lieu dia chan a ria Tay Nam co the cai thien duge bang viee ap dung cac cong nghe xu ly va thu no thich hgp khong? Va vai tham so thu no va xu ly nhu the nao? De gop phan giai quyet nhijng van de tren, bao cao cac tac gia da tiln hanh nghien cuu tong hgp so lieu dia chat - dia vat ly, phan tich danh gia lai cac tham s6 thu nd - xu ly da ap dung a MVITN, xu ly lai tuyen A94-36 vai quy trinh va tham s6 xu ly mai de so sanh vai cac quy trinh va tham so xu ly da ap dung truac do, tien hanh cac buac mo hinh hoa thu no dia chan bang cac chuang trinh ung dung ph§n mim Landmark hien CO tai Vien Dau Khi Nham nang cao hieu qua phuang phap dia ch4n, cac phuang phap mo hinh hoa dia chan, xu ly dia chan va minh giai dugc thuc hien kit hgp mot ehudi cac chu irinh khep kin Hinh 1: So" khoi phu-ong phap nghien ciiu PHAN TICH DANH GIA CAC THAM SO THU NO/ XlT LY SO LIEU DIA CHAN MIEN VONG HA NOI Cac tham so thu no chu yeu cua phuang phap dia chan phan xa duge tom tat a Bang So sanh cac mat cat thai gian bang phuang phap dia chan phan xa diem sau chung giai doan 1975 - 1988 va 1988 - 2002 chung ta thay co su khae biet ve chat lugng, muc chi tiet ve hinh thai cau true, tinh chat moi truang vat ly Trong ITnh vuc xu ly so lieu dia chan ky thuat may tinh quyet dinh nang suat xu ly Vi vay, co nhiang chuang trinh xu ly dugc hoan thien tu lau nhung ap dung dai tra xu ly can phai eo cac may tinh co toe xu ly Ion MVHN noi co chu true rk phuc tap, van t6e thay d6i theo ehilu ngang rht lan va nhanh, phong phan xa nhilu \hn rk manh, phan di am hgc a phhn duoi lat ck rht ylu, mong chim sau (3,7 - 4,2s) va phan di am hgc a mat mong truac Kainozoi khong dang kl thi quy trinh xu ly da ap dung chua phai la '"nang" 262 Nang cao hieu qua phuong phap dja chhn dilu kien c^u triic dja chat phiic tap d niigivvongi:: Bang 1: So sanh cac tham so thu no chinh yeu giai doan truoc va sau nam 1988 g MVHN Cdc tham sd thu nd Nguon no bang 1994-1997 Tnr&c ndm 1988 (Petro Vietnam) (Anzoil) Ghep nhom x 5,2kg hoae X 7.8kg No don kg Chieu sau dat min, m 18-30m 29m Khoang each giiia diem no, m 100 hoae 50m 50m 1150m (ghi tuang tu) 2387,5(1994- 1995) 2350m (ghi s6) 3587,5(1997) Cira so (offset), m 100,200,400m 12,5m So no (he quan sat thu no) No canh, no giiia No giira Loai may thu CP-30 SM4-10HZ So may thu nhom 11 12 Chieu dai nhom may thu, m 50 25m Khoang each giiia may thu hoae 10m 2,27m Khoang each giiia tam nhom may thu 50m 25m MOB (ghi tuang tu) Chieu dai cap dia chan Loai tram may 24 kenh hoae SN 338B (ghi s6) 48 kenh SN 386 (ghi ?6 192 kenh) - 178Hz hoae I/O system one (ghi so 288 kenh) - 180Hz Buoc mau hoa, ms 2ms 2ms Thofi gian ghi song, s hoae 4s 6s Boi quan sat 6,12 hoae 24 48 va 72 Dua mgt vai nhan xet vl quy trinh, tham s6 xu ly loat tai lieu dia ch4n thu n6 giai doan 1994 - 1997 va truac 1988 a MVHN nhu tren dl thhy rhng mu6n cai thien ban niia ket qua xu ly, dap ung tdt ban niia cac bai toan vl hinh thai chu true, tinh chk moi truang va du bao ph§n vat chat cua lat cat dugc khao sat chn phai xu ly lai bSng cac qui trinh xu ly phue tap ban va chgn tham s6 xu ly hgp ly ban MO HINH HOA THU NO DIA CHAN Mo hinh hoa dia chan la mgt nhiing phuang phap dugc nhieu cong ty su dung de thiet ke chuang trinh va lua chgn tham s6 thu n6 dia chhn tren dat liln cung nhu tren bien Trong bao cao de dap ung duge cac yeu cau thuc te thi mo hinh boa truang song dia chan dugc thuc hien vai cac muc dich sau: - Xac dinh moi truang dia ch4t a ria Tay Nam - MVHN co phan di vl dia chhn va co the thu dugc song phan xa tu cac ting duai sau hay khong? Tuygn tap bao cao Hdi nghj KHCN "30 nam D^u Viet Nam: Co' hoi mdi, thach thiic mdi" 263 - Lua chgn cac tham so thu no va XLT ly phu hgp vai dae diem mo hinh dia chan dia chat ria Tay Nam MVHN Qua trinh mo hinh boa dia chan dugc thuc hien theo cae buac sau: • Xdy dung md hinh dia chdn - Mo hinh hinh hgc - Mo hinh tra khang am hgc: mo hinh van toe va mo hinh mat • Md hinh hod thu nd - Mo hinh boa truang song dia chan - Thu song dia chan theo cac he quan sat thii nghiem - Ghi so lieu dia chan mo hinh bang tu Kit qua cua qua trinh mo hinh hoa dia chhn la cac bang dilm n6 chung tuang tu nhu so lieu thu duge a thuc dia Cac s6 lieu mo hinh duge xii ly theo chuoi xu ly dich chuyin truac cgng, cae tham s6 thu n6 duge lira chgn tren co sa danh gia chk lugng cac lat cat da xu ly Do vay, mo hinh boa thu n6 dia chhn dugc tiln hanh tren mo hinh Mo hinh CO van toe, mat chi biin doi theo chilu sau va mo hinh eo van toe mat biin d6i theo chieu sau va chieu ngang (a) (b) Hinh 2: Mo hinh dja chan (a) duffc xay dyng theo mo hinh van toe GK PV-XT-IX (b) Cac phan di am hoc du-ffc thay ro lat cat Paleogen tii chieu sau 500m den day gieng khoan Mo hinh dia chSn theo so lieu giing khoan PV-XT-IX De xac dinh moi truang dia ch§t a MVHN co phan di vl dia chan hay khong, mo hinh dia chan - dia chat don gian dugc xay dung dua tren tai lieu sieu am GK PV-XTIX Trong mo hinh van t6e va mat chi biin doi theo sau (Hinh 2) Tren Hinh 3,4 1a bang dia chhn tdng hgp cua GK PV-XT-1X va bang dja chhn dilm no chung (DNC) Tren cac hinh cae phan xa lat ck Oligocen dugc nhan thhy ro den day gieng khoan 1,10s Kit qua mo hinh hoa cho ta thhy moi truang dia chk a ria Tay Nam MVHN co dae tinh phan dj theo dia chan va eo thi thu song dia ch4n tu cac ranh giai dia chat, a day loai song nhilu manh tren bang DNC xuat hien sau song true tilp song 264 Nang cao hieu qua phuong phap dja chan digu kien cau triic dja chat phiic tap mign vong lien quan vai song khuc xa tu lap co van toe cao cua tang Oligocen (250m) Day la mgt nhiing nguyen nhan anh huong den chat lugng tai lieu dia chan xu ly nam 1995 Trong xu ly sau can loai bo loai song Mo hinh dia chan theo tuyen dia chan A94-36 va so lieu GK PV-XT-IX a Xdy dwng md hinh dia chdn Mo hinh dugc xay dung tren co so so lieu GK PV-XT-IX, mat cat tuyen dia chan A94-36 va ket qua tong hgp so lieu dia chat MVHN Trong mo hinh gia tri van toe va mat bien doi theo chieu sau va chieu ngang Mo hinh hinh hgc xay dung theo ket qua xu ly, minh giai tuyen dia chan A94-36 De CO dugc mat cat dia chan vai ty so tin hieu/nhieu dap ung dugc cac yeu eau, tuyen dia chan A94-36 da dugc xu ly lai a day mo hinh boa - xu ly va minh giai tai lieu dia chan la mgt chuoi chu trinh khep kin ho trg va bo sung lan Xii ly nghich dao dia chan dugc tien hanh theo cac buac sau: - Lira chgn wavelet tu mat cat dia chan - Tinh bang dia chan tong hgp cua GK PV- XT-IX: so lieu sieu am, so lieu mat - Lien ket tuyen dia chan vai bang dia chan tong hgp - Xu ly tinh he so phan xa - Lien ket vai so lieu gieng khoan - Tinh mo hinh van toe hoae mo hinh tra khang am hgc itttfitttr r" Iiiiiii Mm : \fmmv- Hinh : Bang dia chan tong hop gieng khoan PV- XT-IX ThSy duffc cac phan xa tu cac ranh gioi lat c5t lo khoan da mo Hinh 4: Bang DNC tren ca so mo hinh dia chan (a) Hinh Thay ro cac phan xa tir cac ranh gioi am hoc lat cat GK PV-XTIX tu 200ms -1100ms (day GK), cuffng song khtic xa Ion Hinh la mo hinh van toe sau xu ly nghich dao dia ch4n, van t6c thay d6i tu 1500m/s-5500m/s Cac ranh giai phan xa co goc d6c lan, dai nang ctia chu tao Xuan Truang co truang van toe rat cao Ranh giai van t6e thay d6i nhanh tu 1500 -1700m/s din 3500 - 4000m/s nam a sau nho han 250m, su thay d6i gay song nhieu khuc xa CO bien eao anh huong den ty so tin hieu nhieu cua lat cat sau duai 500ms Tuygn tap bao cao Hdi nghj KHCN "30 nam Phu Viet Nam: Co' hdi mdi, thach thiic mdi' 265 Hinh : Mo hinh van toe theo sau xay du-ng tren cff so" tuyen dia chan A94-36 va gieng khoan PV-XT-IX Ta thay duffc cac doan co ranh gioi the nSm rat doc b Mo hinh hod thu no Viec thu no dia chan dugc thuc hien tren mo hinh dia ch^n a Hinh Thu n6 dia chan tren mo hinh da dugc thuc hien vai t6 hgp cac thong s6 khae nhau: nhom may thu, cua so, s6 may thu, chieu dai cap, bgi cgng diem sau chung (DSC) Lua chgn cac tham s6 thuc dia khong chi dua vao chat lugng cua cac bang DNC nhu truae day ma tren ca sa kit hgp chat lugng mat cat cuoi cung sau xu ly Cac kit qua thu n6 theo mo hinh dugc xuly, minh giai va doi sanh vai mo hinh- dia chan ban dau de lira chgn t6 hgp cae tham s6 thu no phu hgp vai dac diem dia chan dia chat MVHN Lira chgn nhom may thu: Chung toi da mo hinh boa vai viec ghep nhom 3, 5, va 10 may tren day thu 25m va dugc cac bang diem no chung (DNC) Dl so sanh chat lugng tai lieu dia chan thu dugc, tai lieu dia chan mo hinh dugc xu ly cgng DSC D I nang cao ty so tin hieu nhieu cac chuang trinh lge tan so, Igc Radon phan giai cao dugc ap dung truac cgng DSC Ket qua xir ly cac mat cat cgng DSC ta thhy viec ap dung nhom 10 din 12 may vai chieu dai nhom thu 25m la phu hgp vai dieu kien dia chat a MVHN Lira chgn khoang each thu no xa nhat (Xmax): Ket qua xir ly, minh giai mat cat cgng DSC, doi tugng quan tam a sau 2s (3500m) thi Xmax = 2500m la phu hgp Bgi quan sat: De co ca sa lira chgn so bgi tich luy toi thieu can thiet, cac he quan sat vai bgi 24, 48, 96 da dugc mo hinh hoa Tai lieu mo hinh boa dugc xu ly, ap dung chu trinh dich chuyin truac cgng theo sau (PSDM) ban chi anh huang d6i vai chat lugng mat cat va lira chgn tham so thu no chinh xac ban Vay dl khao sat dugc doi tugng nam sau lat cat Oligocen chung ta can ap dung bgi quan sat tu 48 din 96 Kit qua minh giai cac mat cat xu ly theo chu trinh PSDM va ddi sanh vai mo hinh dia chan dia chat (Hinh 5) cho thay viee ap dung cae thong so thu n6 sau day co thi nang cao chat lugng tai lieu dia chhn a ria Tay Nam MVHN (Hinh 6, 7) - Nhom may 10 - 12 may thu x 2,25 - 2,5m - Chilu dai cap 2500 - 3000m 266 Nang cao hieu qua phuong phap dja chin digu kien cau triic dja chat phiic tap d niign_v6iig;^ Khoang each giira tam cac may thu: 25m Khoi lugng thuoc no: 1kg Khoang each giiia cae diem no: 25m va 50m Bgi - Do sau dat min: 25 - 29m Thai gian ghi: giay Hinh 6: Bang dia chan mo hinh "thu no" Hinh 7: Bang dja chan diem no chung (DNC) tuyen A94-36 6' SP 1151 (gan GK PV-XT-IX) va SP 1500 (Gan GK 101) Song nhieu khuc xa CO bien manh chi xuat hien o' diem no dau LU'A CHON THAM SO XIJ^ LY TUYEN DIA CHAN A94 - 36 Tham so thu no va xii' ly nam 1995 Tuyen dia chan A94-36 la tuyen dia chan nhat di qua vung cau tao Xuan Truang noi rieng va ria Tay Nam noi chung Vi vay, tuyen dia chan A94-36 dugc chgn xu ly dl chgn tham so Muc dich la de nghien cuu ap dung va lira chgn cong nghe xu ly phu hgp nham nang cao chat lugng tai lieu dia chan Cae tham s6 thu no duge thuc hien vai he quan sat trung tam va s6 may thu la 12, bgi 48 la kha phu hgp vai dilu kien a MVHN song dai cap ban chi, thai gian ghi song ngan Chu trinh xu ly da ap dung duge cac chuang trinh hien co va da dap ung dugc cac dieu kien doi vai tai lieu dat liln, song ban cbl bai mgt s6 chuang trinh chua phu hgp (Mute, dich chuyen, lge song phan xa nhilu ian Radon, can bang bien scaling, phan tich van tdc, v.v.) hoae chua c6 (tap hgp mach mat phan xa chung, lge F-X, v.v.) lam anh buong den chat lugng mat cat xu ly Phan tich ky cac thilu sot chung toi da dua dugc tham so thu n6, xu ly phu hgp co chat lugng tot ban Lua chon tham so xu- ly lai tuyin A94-36 theo cong nghe dich chuyin tru-oc cong theo thoi gian (PSTM) Hinh la mat cat dia chan tuyin A94-36 Cong ty Anzoil xu ly nam 1995 Day la tuyen dia chan dugc sir dung nhu mgt co so dl chgn vj tri giing khoan PV-XT-IX Truoc khoan mong truoc De tam dugc du bao la a sau 700 - 800m Thue tl GK da khoan sau hon 1800m nhung van chua gap da mong Theo tai lieu VSP tang mong co thi sau Tuygn tap bao cao Hdi nghj KHCN "30 nam Dau Viet Nam: Co' hdi mdi, thach thiic mdi" 267 hon 3000m Mgt nhiem vu dat la vai tai lieu dia chan co the cai thien dugc chat lugng tai lieu bang viec nghien cuu ap dung cong nghe xu ly tien tien khong Hinh 8: Trich doan mat cat dja chan tuyen A94-36, Cong ty Anzoil xii' ly nam 1995 Tham so thu no - xu* ly chua thich hop nen kho theo doi cac phan xa cau tao Xuan Truong r a Ddnh gid chdt lwffng tdi lieu nguyin thuy Cac bang diem no chung (DNC) da dugc nghien cuu ti mi, sir thay doi ty so tin hieu nhieu dugc dae biet chu y (Hinh 7), diem no 1151 qua dinh cua cau tao Xuan Truang Qua cac bang DNC ta thay ty so tin hieu nhieu a vung cau tao Xuan Truang rat thap, a day bat gap cac song nhieu tuyen tinh co bien manh Ket qua mo hinh boa cho thay loai song nhieu manh tren bang DNC co lien quan voi song khuc xa o GK PV-XT-IX ranh gioi tang van toe cao nam rat nong (250m) so voi GK 101 nam sau 650m (Hinh 9) Do lap van toe cao cua tang Oligocen rat nong (250m) nen song khuc xa c6 bien cao xuat hien nhiing mach gan Trong ian xu ly truoc ehuang trinh Mute ap dung khong doi tren toan tuyen Do co sir xuat hien eua lop van toe cao o cau tao nen chuang trinh Mute thay doi dge theo tuyen da duge nghien cuu ap dung .j.j.^4j**j.~.M.* ^**w^.iWR (a) i.i-Y. *ij-^ (b) Hinh 9: Mo hinh van toe GK PV-XT-IX (a) va GK 101 (b) theo karrta sieu am GK PV-XT-IX ranh gioi tang van toe cao nam rat nong (250m) so voi d GK 101 (KX-A) (650m) 268 Nang cao hieu qua phuong phap dja chan digu kien chu triic dja chSt phiic tap d nuerrvong^jj^ b Lwa chon chu trinh xw ly tru&c cong diim sdu chung D I cho ket qua xii ly tot hon so voi nam 1995 chung toi da dac biet quan tam den cac chu trinh chinh sau: • Loc nhieu lien kit F-K Kit qua nghien cuu bien cho thay loai nhieu tan thap co goc nghieng Ion hon +/- 24 ms/mach thu.Thu nghiem voi eae tham so cua bg lge F-K ta thay voi bg lge F-K ap dung chi "'qua" +/- 16ms/mach cho hieu qua tot nhat • Phdn tich van tdc Phan tich t6c dugc tiln hanh voi nhieu giai doan khae Trong ian phan tieh t6c thu nhat cac dilm phan tieh toe each 1000m mgt diem dge theo tuyen o ian phan tieh t6c dich chuyin cae dilm phan tich toe each 500m Sau buoc dich chuyen buac phan tich toe cuoi cung voi khoang each 500m dge theo tuyen Bg lge radon phan giai cao dugc ap dung tinh van toe vi vay tang tin cay cua van toe • Tdng ty sd tin hiiu nhiiu d MVHN he thong song ngoi va lang mac nen nhieu diem no khong thuc hien dugc Vi vay, so bgi cgng DSC giam, mat khae khoang each thu no mach DSC khong deu De giam thieu su khong dong nhat eae mach DSC, truoc xu ly dich chuyen truoc cgng chung toi tien hanh noi suy tao nhiing mach thieu, viec noi suy dugc thuc hien tap hgp cac mach eo cung khoang each thu no • Loc sdng phdn xg nhieu ldn Radon Trong lan xu ly nam 1995 da khong su dung bg lge lge song phan xa nhieu ian Radon Trong lat cat dieh chuyen song lap phan xa nhieu lan co bien kha ldn anh huong den ty so tin hieu/nhieu dac biet phan duoi cua lat eat Bg lge Radon phan dai cao da duge ap dung de ban che song phan xa nhieu lan De tang cao hieu qua lge song phan xa nhieu lan bg Igc Radon da dugc ap dung theo buoc Bg lge Radon nhe ap dung truoc dich chuyen PSTM - Gioi ban gia tri phan di NMO: -1000ms, 2000ms - Buoc mau boa: 10 ms - cac gia tri bg Igc: Phan di NMO (ms) 2000, 1500, 1000,500,200, 120, 100,85,80 - Tau (ms): 300, 310, 339, 678, 1020, 1357, 2000, 2500, 5000 Sau dieh chuyin bd loc Radon mgnh hon dd dugc dp dung: - Gioi ban gia tri phan di NMO: - 800ms - 1500ms - Buac mau hoa: 10 ms - Cac gia tn bg lge: Phan di NMO (ms): 1500,1000,500, 190, 110, 80, 75, 60 - Tau (ms): 310, 339, 678, 1020, 1357, 2000, 2500, 5000 • Tap hgp mgch mat phdn xg chung (CRS - common refection surface) Buoc noi suy a tren da lam giam thilu mgt each dang ke cac mach thieu hut khong tien hanh thu hoae n6 duge Tuy nhien voi ty so tin hieu/nhieu thap nhu ddi voi Tuygn tap bao cao Hdi nghj KHCN "30 nam DSu Viet Nam: Co hdi mdi, thach thuc mdi" 269 tuyin dia chan A94-36 chn phai lam tang s6 bgi cgng DSC Mgt nhiing phuong phap la ap dung cong nghe mat phan xa chung, eong nghe xu ly dua tren nguyen tac la phan giai dia chan gioi ban boi ban kinh Fresnel Ban kinh zone Fresnel dugc tinh theo cong thuc sau: R = (V/2) (t/f) x 1/2 Voi dac dilm dia chan dia chat ria Tay Nam MVHN a sau 2000 - 3000m V = 3000m/s, f = 40Hz, t = 2s ban kinh Fresnel co gia tri: R = 335m Nhu vay phan giai khong vugt qua ban kinh 335m Phuang phap CRS chi moi phat trien gan day va dugc Vien Dau Khi nghien cuu ap dung va da eho ket qua tot tren tuyen A94-36 va toan MVHN c Lua chgn phuffng phdp vd tham so dich chuyin Viee ap dung dich chuyen truoc cgng theo thoi gian PSTM hoae DMO dugc thue hien tap hgp cae mach dia chan co cung khoang each thu no Do dac diem dia hinh nen nhieu diem no va thu khong thuc hien duge nen hieu qua cua DMO hoae PSTM se giam anh buong cua nhieu bien Truoc thuc hien buoc xu ly PSTM cac phuong phap CRS va noi suy da dugc ap dung Voi dae diem mo hinh van toe dia chan bien doi nhanh theo dien va theo thai gian cua lat cat dia chat a MVHN phuong phap dich chuyen dia chan truoc cgng F-K la khong phu hgp, phuang phap dich chuyen Kirchhoff dugc sir dung Ban kinh djch chuyen la thong so quan trgng quyet dinh den chat lugng mat cat dja chan Ket qua thu nghiem chuong trinh dich chuyen Kirchhoff voi ban kinh dich chuyen 3000m da dugc lira chgn va ap dung cho toan tuyen A94-36 Mo hinh van toe dich chuyen xay dung tren co so phan tich toe dich chuyen truoc cgng, ket hgp voi mo hinh van toe GK PV-XT-IX Sau thu nghiem, mo hinh van toe dugc trung binh boa voi ban kinh 500m voi he so sau: 0ms - 98%, 2000ms - 95%, 4000ms - 90%) van toe cgng DSC d Lwa chpn chwffng trinh xw ly sau cgng DSC Cac chuong trinh xu ly sau cgng DSC c6 y nghla dae biet quan trgng doi voi chat lugng mat cat cuoi cung Do dac diem dia chat MVFIN, song dia chan bj hap thu manh va bien giam nhanh theo sau dac biet la phan tan so eao va trung binh Vi vay, chu trinh xu ly cac phuong phap can bang tan so da dugc nghien cuu ap dung Ket qua xii- ly tuyen dja chan 6' MVHN Tuyen dia chan A94-36 da dugc xu ly lai (Hinh 11) theo chu trinh o Bang So vai mat cat xu ly nam 1995, mat cat tai xu ly lai c6 chat lugng dugc cai thien ro ret Voi tai lieu xu ly nam 1995 (Hinh 10) khong the theo doi dugc cac phan xa sau hon 0.6 - 0.7s tuong duong voi sau (700 - 800m) o phan dinh c^u tao ti s6 tin hieu nhieu thap Cung chinh vi vay, tang mong da dugc du bao rat nong so vai thuc te Nguge lai, voi mat cat tai xu ly (Hinh 11) ta co the lien kit dugc eae phan xa sau din 1,8 - 2,0s tuong duong \ sau 3000 - 3400m Nhu vay voi chat lugng tai lieu dia chan sau tai xu ly viee lien kit tin tuong hon, du bao lat cat gieng khoan se tranh duge nhiing sai lech Ion 270 Nang cao hieu qua phuong phap dja ch5n digu kien chu triic dja ch§t phiic tap d mi^n_v6ng^ zic:rni Xiir-i:z -] I Hinh 10: Mat cat tuyen A94-36 Anzoil xu ly nam 1995 Do ty so tin hieu/nhieu kem nen khong theo doi dutfc cac phan xa sau hon 0,7s (tuong du-otig 700 - 800m) 6" phan dinh ciia cau tao Hinh 11: Mat cat tuyen A94-36 tai xir ly theo chu trinh o" Bang So voi mat cat Hinh 10 thay chat lu'ong du-ffc cai thien ro ret Co the theo doi du-ffc cac phan xa toi 1,8s (3000m) o" phan dinh cau tao Bang 2: Chu trinh xu ly lai cho tuyen A94-36 va toan MVHN Chuyen khuon ghi Loai nhieu spike va hieu dinh Doi buoc mau boa tu 2ms sang 4ms Xac dinh vi tri cac mach thu Hieu chinh tTnh Phuc hoi bien He so = VT/2 Thai gian (ms)200 500 1000 1500 2000 4500 Vant6c(m/s) 1650 1950 2485 2937 3363 4000 Vung loc : +/-16ms/mach Loc F-K FILTER Loc nguge tien doan Do dai toan tu : 200MS Khoang tien doan :24MS Nhieu trang :0,1 : 400 3500MS Cira so Mach gan : 1950 3900MS Mach xa Phan tich van toe Khoang each 1000m mgt dilm phan tich Tinh chinh hieu chinh tinh Phan tich van toe Khoang each 500m mgt dilm phan tich Tinh chinh hieu chinh tinh Hieu chinh dong Loc nhieu PXNL Radon Hieu chinh dgng nguge Phan tich van toe dich chuyen truoc cgng, khoang each 500m mgt diem Dich chuyin KIRCHHOFF truac cong theo thoi gian Hieu chinh dong nguge Phan tich van toe cuoi cung Hieu chinh dong Tuygn tap bao cao Hdi nghj KHCN "30 nam Phu Viet Nam: Co" hdi mdi, thach thiic mdi" Loc nhieu PXNL Radon cat mach gan Cua so (m) 40 100 1000 2200 Thoi gian (ms)0 50 762 1590 1950 Cgng diem sau chung bgi 48 Phuc hoi tan so Loc tang lien ket FX LoctansoTVF 15/18-70/72 400ms 10/18- 60/72 2000 ms 6/18 - 40/48 3500ms can bang bien gian TVS, Cua so 800ms goi 50%) Ghi bang tu SEGY In mat cat cuoi cung 271 2500 Tren cae Hinh 12, 13 ta thay rang hai mat cat duge xu ly lai theo chu trinh de xuat c6 chat lugng tot hon so vai xu ly nam 1995 Cac song lap da dugc loai bo, lien tuc cua cac ranh gioi phan xa tot hon, chung ta co the quan sat duge cac ranh gioi phan xa sau ban khoang din 2,2s Su phan tap dugc nhin thay ro hon, va mat cat xu ly lai co tin cay tot ban so voi mat cat xu ly nam 1995 Tren Hinh 12b, chung ta da nhin thay dugc sir phan lop a phan nong, eae tap xac dinh de dang hon, lien tuc pha tot ban so voi Hinh 12a Tren Hinh 13b ta khong thay cae phan xa lap, cac ranh gioi ro rang va lien tuc, tinh phan di tot hon va lien tuc cua pha ttot ban ban so vai Hinh 13a 5g|i5'j5;CiC2^ a) b) Hinh 12: Tuyen 83-07 xu- ly nam 1995 (a) va xu ly lai theo chu trinh (b) dua ff Bang 2: ta thay lien ket pha tot hon va thay du-ffc cac phan xa sau khoang 2,2s m^^^^m^^^^ a) b) Hmh 13 ; Trich doan tuyen 80-44 xir ly nam 1995 (a) va xu- ly lai theo chu trinh dua raffBang (b): Cac phan xa nhieu lan da duffc loai bo, su phan di tot hon va cac ranh gioi ro hon 272 Nang cao hieu qua phuong phap dja chhn digu kien c5u triic dja chdt phiic tap d mign vong^^ Dat dugc chat lugng xu ly tot nhu tren day truoc hit nho ap dung quy trinh xu ly dich chuyen diem phan xa ve vj tri thuc truong thoi gian truoc cgng diem sau chung (PSTM) va phan tich toe cho chuang trinh hieu chinh dgng (NMO) sau PSTM (tranh dugc anh huong eua goc nghieng doi voi kit qua phan tich van toe) Ngoai ra, dieu kien thu no a dat lien, cac chuong trinh hieu chinh tmh du va loc nguge truoc cgng (DBS) ciang cai thien rat nhieu lien ket pha va phan giai cua lat cat dia chan Lan dau tien Viet Nam ap dung phuong phap CRS (Common Reflection Surface) nghia la tap hgp mach mach phan xa chung xu ly lai tuyen A94-36 da cai thien rat nhieu chat lugng mat cat dia chan nhat la o nhung doan bgi thap (do dieu kien dia hinh) hoae nhiing doan ty so tin hieu/nhieu thap Hon nira, a MVHN, cac ranh gioi phan xa rat manh tap trung chu yeu o phan tren lai cat (Miocen va tre ban) thudng tao nhieu phan xa nhieu lan c6 cuong manh a thoi gian Ion tuong ung voi lat cat Paleogen von c6 cac ranh gioi phan xa rat yeu den trung binh va lien tuc khong dai Vi vay, bat bugc phai co chuong trinh tru phan xa nhieu ian (RADON) ma viec chgn cac tham so xu ly cua ehuang trinh khong phai lan la xong, nhung nho vao ma lat cat o phan thoi gian Ion dugc cai thien rat nhieu Them vao doi voi tai lieu tren dat lien, noi co mat dan cu rat cao la dong bang Song Hong thi nhieu ngau nhien co bien rat lan, vugt trgi truang song eo ich nhieu lan can phai eat bo het Day la cong viec mat nhieu cong sue va thai gian khong the khong tinh den xay dung gia xu ly so lieu Hien tugng bo mat mach thu no tren dat lien ciang rat bien neu khong kiem tra ky eae bang diem sau chung thi cac chuang trinh xu ly sau (nhu Migration chang ban) se tao cae nhieu nhan tao khae pha buy ca doan mat cat thofi gian Cong viec "hieu dinh" cung ton nhieu cong sue cua nguai xu ly Nhiing van de thuong eho la nho, nhung neu bo qua thi chat lugng xu ly khong the cao dugc nhu mong muon KET LUAN • Lan dau tien o MVHN cac phuong phap mo hinh boa, xu ly va minh giai dia chan da dugc nghien cuu ung dung ket hgp mgt chu trinh khep kin va da dem lai nhiing ket qua dinh lugng eo tin cay eao giup eho viee chgn lira eae tham so thu no va xu ly tai lieu dia chan dat hieu qua • Dae diem dia chat ria Tay Nam MVHN co tinh phan di vl dia chan va co the thu duge song dia chan tu cae tang phan xa o duoi sau bang phuong phap tham dia chan • Ap dung cac tham so thu no va chu trinh xu ly nhu trinh bay o tren co thi nang cao chat lugng tai lieu dia chan ria Tay Nam MVFTN • Chu trinh xu ly de xuat da dugc ap dung c6 hieu qua qua trinh tai xu ly lai tai lieu dia chan MVHN • De danh gia tiem nang dau va xac dinh cae bay chua dau ria Tay Nam MVHN can thiet phai tien hanh khao sat dia chan 2D Tuygn tap bao cao Hdi nghj KHCN "30 nam DSu Viet Nam: Co' hdi mdi, thach thiic mdi" 273 TAI LIEU THAM KHAO Arkhipov, Tran Due Thu, 1975 Tdng kit cdng tdc thi nghiem tdng chiiu sdu nghien CU'U bdng phuong phdp dia chdn phdn xg phdn Ddng Nam ddi Khoai Chdu - Tiin Hdi, ty le 1/25.000 ndm 1972 - 1975 Hung Yen, Luu trii Vien Dau Khi Bdo cdo ddnh gid dia chdt giing khoan PV-XT-IX cdu tgo Xudn Tru&ng Ha Noi, 52002 Luu tru PIDC Do van Luu, Ha Quoc Quan, 1982 Tdng kit cdng tdc thi nghiem phuong phdp dia chdn diem sdu chung nhdm ndng cao chieu sdu nghiin cim & miin vong Hd Ndi Hung Yen Luu trtr Vien Dau Khi Golovenok, Le Van Chan, 1970 Thgch hoc trdm tich Neogen - Di tu miin vdng Hd Ndi Hung Yen Luu trii Vien Dau Khi Ho Dac Hoai, 1974 Tdng kit cdng tdc dja chdn phdn xg & miin vong Hd Ndi, ty li 1/100.000, 1965 - 1969 Hung Yen Luu trii Vien Dau Khi Phan Tiln Viln va n.n.k., 2005 Bdo cdo Tdi xu ly tdi lieu dia chdn MVHN Ha Noi Luu tru PIDC Kruehennhuc L.A., Murzin lu.M., 1978 Cdng tdc thdm dd dia chdn bdng phuong phdp diim sdu chung phdn Ddng Nam miin vong Hd Ndi 1975 - 1978 Hung Yen Luu trii Vien Dau Khi Maexuytova V.V., Ho Dac Hoai, 1965 Tdng kit cdng tdc dia chdn phdn xg & miin vdngHd Ndi 1962 - 1965 Hung Yen Luu tru Vien D^u Khi edo6an Yilmaz, 1987 Seismic data processing 10 W.D Powell, 1994 Review of Hanoi basin seismic acquisition parameters (based on experimental and production recording In 1979 - 1983) August 11 W.D Powell, 1994 Review of the 1993 - 1994 reprocessing of onshore and offshore seismic lines in the Hanoi basin August Tai lieu Anzoil 12 W.D Powell, 1996 Analysis of onshore seismic acquisition parameters Hanoi basin, Vietnam August ... tang van toe cao nam rat nong (250m) so voi GK 101 nam sau 650m (Hinh 9) Do lap van toe cao cua tang Oligocen rat nong (250m) nen song khuc xa c6 bien cao xuat hien nhiing mach gan Trong ian xu... sau song true tilp song 264 Nang cao hieu qua phuong phap dja chan digu kien cau triic dja chat phiic tap mign vong lien quan vai song khuc xa tu lap co van toe cao cua tang Oligocen (250m) Day... dugc, tai lieu dia chan mo hinh dugc xu ly cgng DSC D I nang cao ty so tin hieu nhieu cac chuang trinh lge tan so, Igc Radon phan giai cao dugc ap dung truac cgng DSC Ket qua xir ly cac mat cat