536 Trudng ung suSt hien tai va ap suit thanh he trong hi Ciiu Long va Nam Con Son,...
TRlTCJNG ITNG SUAT HIEN TAI VA AP SUAT THANH HE
TRONG BE CUtJ LONG VA NAM CON SOOV, THEM LUC DIA VIET NAM
Nguyin Thi Thanh Binh. Tomochika Tokunaga Trw&ng Dai hoc Tdng hgp Tokyo
Hoang Phuac Son, Mai Van Binh XNLD Vietsovpetro N126_V(40)
TOM TAT
Di thiit ki cdc giing khoan cd do lech l&n, md td dge diim tdng da chua, cung nhu nghien ciru dia ddng luc vd cdc dnh hu&ng ciia chiing din suphat triin ciia bi trdm tich thi hieu tru&ng img sudt tgi chd la diiu cdn thiet.
Su dung tdi lieu thu dugc trong cdng tdc thdm dd vd khai thde ddu khi, cdc tdc gid da tiin hdnh phdn tich trucmg img sudt tgi chd vd dp sudt thdnh hi ciia mdng tru&c Di tam vd cdc tdng phii trong bi Ciru Long vd Nam Cdn Son & thim luc dia Nam Viet Nam.
Hu&ng ciia ung sudt ngang cire tiiu vd cue dgi dugc xdc dinh theo hu&ng sap l& thdnh gieng khoan vd hu&ng cua khe nut sinh ra trong qud trinh khoan. O bi Cu'u Long, img sudt ngang cue dgi cd hucmg tir Bde Tdy Bde - Nam Ddng Nam din Bde - Nam &phdn phia Bde vd khdi ndng Trung tdm, tu Ddng Tdy din Tdy Bde - Ddng Nam phdn phia Nam. O bi Nam Cdn Son, irng sudt ngang cue dgi cd hu&ng theo Ddng Bde - Tdy Nam a phdn Bde vd Bde - Nam & phdn Trung tdm.
Cu&ng do cua img sudt thdng dung (hay img sudt doc) dugc xdc dinh tir tdi lieu
•:arota mat do. ung sudt ngang cue tiiu dugc xdc dinh tir tdi lieu thir va via cd chdt lucmg tdt. lfng sudt ngang cue dgi dugc tinh tu phucmg trinh nirt via thuy luc. Chi do ung sudt hiin tgi & be Ciru Long ed thi dugc xem la chi do tgo dirt gdy thudn, trong khi & bi Nam Cdn Son tdn tgi cd chi do tgo dut gdy thudn vd dirt gdy trugt ngang.
Anh hu&ng ciia su thay ddi dp sudt thdnh hi lin cuong do truong ung sudt tgi chd da dugc phdn tich dua tren tdi lieu tir cdc vung cd dp sudt thdnh he suy gidm vd dp sudt cao. Su- dung cdc phucmg trinh thuc nghiem thu duge, cdc tdc gid cd thi md td hgp ly trucmg irng sudt tgi chd vd dp sudt thdnh hi cua vung nghien ciru.
MO DAU
Viec nghien cim ung suat tai ch6 ciia Trai dat da thu hut dugc su quan tam ciia cac nha khoa hoc dia chat tren thi gioi. iTng suit hien tai dugc sir dung rong rai boi cac co so nghien cim va cac co so san xuit c6ng nghiep trong nhilu ITnh vuc ve khoa hoc trai dat nhu dia dong lire, khai thac dau khi va c6ng trinh.
Tuygn tap bao cao HQi nghj KHCN "30 nam Phu khi Viet Nam: Co' hoi mdi, thach thiic mdi" 537
6 Viet Nam, mgt s6 nha nghien cim vl kiln tao nhu Borisov (1996). Schmidt va n.n.k. (2003), Cao Dinh Trilu va Mai Xuan Bach (2004) da tiln hanh nghien cim c6 kiln tao va huong img suit c6. Tuy nhien, huong va cuong do truong img suit tai ch6 trong be trim tich cua Viet Nam van chua dugc hilu ro. Trong bai bao nay, cac tac gia phan tich huong va do Ion truang img suit tai ch6 tren co so tai lieu dia vat ly gieng khoan va ket qua thir via cac gilng tham do va khai thac a be Cim Long va Nam C6n Son. Cac tac gia cGng phan tich anh huong ciia di thuong ap suat len che do iing suat tren co so khai niem ciia ly thuyet do r6ng dan h6i.
DAC TRU^NG DIA CHAT CUA BE CUtJ LONG VA NAM CON SON L Dac diem chung cua be Ciru Long
Be Cim Long la be tram tich De tam nam o phia D6ng Nam them luc dia Nam Viet Nam (Hinh 1) CO dien tich khoang 250km x 100km. Day la vimg khai thac dau chinh ciia Viet Nam.
106°E 108**E
10'^N
8°U
10**N
8°M
lOe^E 108°'E
Hinh 1: Ban do vi tri be Ciru Long va Nam Con Son
B I Ciru Long la be tach gian theo huong D6ng BIC - Tay Nam, dugc tao thanh boi qua trinh tao rift vao Oligocen som (Nguyin Du Hung va Le Van Hung, 2003). Trong bl co thi
538 Tru-6-ng irng suat hifn tai va dp suat th^nh hf trong bg Ciru Long v^ Nam Cdn jojiy
dugc chia thanh ba khu vuc lang dgng tram tich va nhilu clu tao. Cac khu vuc ling dgng trim tich nim 6 phan Bae, Tay va Dong cua be.
Cac lofp phii tram tich co tuoi thay doi tir Eoxen (?) din De tii va chilu day Ion nhat khoang 8km (Vo Nang Lac va n.n.k., 1997, Phan Truong Thi va n.n.k., 2003). Trong giai doan dau ciia pha tach gian, cac dia hao hep dugc tao ra va mgt qua trinh oIn vong tao nen mot be liin chim n6ng. True cua be lai bi liin chim nhanh vao Oligocen mugn. Vao cuoi Miocen som bien tien phu rong toan dien tich be, cac tang set day Rotalia dugc tich tu, chiing la tang chan khu vuc. Cac tang tram tich Miocen giiia - Miocen tren va Pliocen - De tii dugc lang dgng trong cac chu ky bien tien, bien thoai cua chau th6 Cim Long hien dai.
Cac chu ky bien tien, thoai hi anh huong boi sir thay d6i ciia mirc nuoc bien. Cot dia ting tong hgp cua be Cim Long dugc trinh bay trong Hinh 2.
UthoK^y t^positlonal Env
Sandstones interbsdeted with minor Smestone Ato^omiles
RotaUte shale.
Sandstones irtefiieskieti vtiXh Oaystones.
Minor coals
SarHJstones snd ciaystanes
•; Barh Ho shale
Coaslal (rfairt sanetetones ctaystones inteftiEidded Lacustrine shale Sdluviat sandstones
A^ose sandstones/
claystor»s hTtert»eddeel volcanlc^ntrusive dyke
Grante^^nodiorite
Shadow marine
Deftaic- ShaHoM marine
Lacusirlne- Ruvial Delt»c Ffesh water UacusltirtB/
AHuviat fan
f
1
1
S e
I
Pre-ntt Faulting vtiic antes
Hinh 2: Cot dia tang bi Cu-u Long (theo Nguyin Du Hung vd Le Vdn Hiing, 2003)
Tuygn tap Mo cao Hoi nghj KHCN "30 n^m Dau khi Vift Nam: Cff hoi mdi, thach thuc mdi" 539
2. Dac diem chung cua bi Nam Con Son
Be Nam Con Son ciing la mgt be tram tich De tam nam 6 phia D6ng Nam thim luc dia Nam va nim gin kl bl Cim Long (Hinh 1). B I CO dien tich khoang 90.000 km^ cung la mot viing khai thac diu va khi chinh cua Viet Nam.
Be nam or noi giao nhau cua hai he th6ng kiln tao chinh gin voi sir tach ra ciia mang D6ng Duong va tach gian day Biin D6ng. B l co huong D6ng BIC - Tay Nam 6 phin phia Bae va Nam - D6ng Nam a phin phia Nam ciia bl. Trong bl co hai triing lun noi ling dgng tram tich chinh va nhilu clu tao. Cac trung liin ling dgng trim tich nim 6 phia BIC va Trung tam cua be.
Cac lop phu trim tich co tu6i tir Oligocen din De tir va c6 chilu day Ion nhit khoang 10km (Hoang Ngge Dang, 2002). Trong giai doan Eoxen - Oligocen, tach gian gin vai hinh thanh Biin D6ng tao ra cac ban dia hao co huong D6ng BIC - Tay Nam va cac thanh tao tram tich hinh thanh do boat dgng tao rift, lip diy cac ban dia hao. Khi qua trinh liin chim tilp tuc, cac ban dia hao rieng biet da dugc lip diy, trim tich tra nen mang tinh khu vuc ban, tram tich tuong s6ng tich tu rong khIp tir huong Tay cua bl chung co ty le chilu day hieu dung so voi chilu day chung Ion. Cac tap hgp trim tich o khu vuc sut lun co tuong thay d6i tir luc dja den biin tir duoi len tren, tuong biin kha ph6 biin tir Tay sang D6ng do qua trinh biin tiln va thu hep d6ng bing chau th6 vao Miocen som. Vao cuoi Miocen giira, su mo rong theo huong Tay B I C - Dong Nam gin vdi sir thay doi huong tach gian cua day Biin Dong lam thay doi dia hinh 0 Trung tam b6n trung chung anh huong din clu tnic ciia cac tuong tram tich, trong do trim tich carbonat phat triln ban chi a phin thim va chan thim trong khi phin thim sau tudng suon d6c dugc tich tu trong cac dia hao. Vao Miocen mugn, bl dugc tai boat dgng kiln tao bori sir nghich dao nhe, tilp theo sir lun chim, din din thanh tao cac clu triic ldn da v6i am tieu va cat tudng dong chay roi. Qua trinh nay hi gian doan vao Pliocen sdm do qua trinh biin tiln. Cot dia ting tdng hgp cua bl Nam C6n Son dugc trinh bay trong Hinh 3.
540 Tnrdng irng suat hien tai va ap suat thanh he trong bi CUTI Long va Nam Cdnjg}^:
Hinh 3: Cot dia ting bi Nam Con Son (theo Hodng Ngoc Dang 2003)
Tuygn tap bao cao HQi nghj KHCN "30 nam Phu khi Viet Nam: Cff hoi mdi, thach thiic mdi" 54]^
HUONG ITNG SUAT TAI CHO TRONG BE ClTU LONG VA NAM CON SON 1. Tai lieu sir dung xac djnh trircmg u'ng suat tai cho
Cac tac gia tiln hanh phan tich trudng ung suat tai ch6 va ap suat thanh he trong vimg nghien cim dua tren tai lieu dia vat ly gieng khoan, thir via, nirt via thiiy luc va phan lich mau loi. Mgt so tai lieu dugc T6ng cong ty Dau khi Viet Nam va Vien Dau Khi cho phep tham khao. Mgt phan khae dugc thu thap tir cac ngu6n khae nhau nhu cac bao cao va tai lieu da xuat ban (Martyntsiv va n.n.k., 1996; Sirin-dade va Duong Danh Lam, 1996; Pham Hong Que, 1996, Korolev va n.n.k., 1997, Schmidt va n.n.k., 2003, Hoang Ngoc Dang va Mai Thanh Tan, 2000, Hoang Ngge Dang, 2002, Nguyen Dinh Ha, 2003, Mai Van Binh va nn..k., 2004) va cac luan an tien sT (Hoang Ngge Dang, 2002 va Nguyen Dinh Ha, 2004).
2. Hu'dng irng suat tai cho
Hudng sap Id thanh gieng khoan va hudng nirt ne sinh ra trong qua trinh khoan d thanh gieng khoan cho hinh anh ro net ve hudng cua iing suat (Brudy va Zoback, 1999).
Trong gieng khoan thang dung, true sap Id cho biet hudng ciia img suat ngang cue tieu trong khi khe niit tao ra trong khi khoan c6 hudng triing vdi hudng cua iing suat ngang cue dai.
De tranh anh hudng bao mon thanh gieng khoan dugc sinh ra do choong khoan d cac gieng khoan nghieng, cac tac gia chi sir dung tai lieu tir cac gieng khoan goc nghieng nh6 ban 20 do. Hudng sap Id thanh gieng khoan cd the xac dinh bang tai lieu chup anh thanh gieng khoan nhu: BHTV, CAST-V (Hinh 4) hoae FMI va cac s6 do dudng kinh gieng khoan. Chat lugng tai lieu dimg de phan tich dat chat lugng A va B theo tieu chuan chat lugng ciia du an nghien ciiu trudng img suat hien tai cua the gidi (Zoback, 1992). D6i vdi loai CO chat lugng hang A, trong mgt gieng co do lech nho hon 12 do phai quan sat ro mudi hay hon mudi khoang sap Id thanh gieng klioan vdi t6ng chieu dai sap Id hon 300m. D6i vdi loai CO chat lugng hang B, trong mot gieng khoan co do lech nh6 hon 20 do phai quan sat dugc ro rang it nhat 6 khoang sap Id vdi t6ng chieu dai hon 100m.
542 TruoTig ling suat hien tai va ap suat thanh he trong bg Ciiu Long v^ Nam Con Son,
a)
360
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; ^ ^ i I :
kl: I n , , ,
( t . i - ' 1
b)
Nut ne tao thanh trong qua trinh khoan theo huong Dong Bae - Tay Nam
'jflSjja^KMKftSB-*^ ••jff&Jft
Hinh 4: Vi du ve xac djnh hirang sap 16" thanh gieng khoan (a) va hu-otig nut ne tao thanh trong qua trinh khoan theo tai lieu CAST-V (b)
O be Cim Long, sap Id va khe niit sinh ra trong qua trinh khoan quan sat dugc trong Miocen dudi (he tang Bach H6) va trong mong niit ne d 4 gilng khoan. d be Nam C6n Son, sap Id va khe nurt sinh ra trong qua trinh khoan dugc quan sat d 5 gilng khoan thuge cac tang
Tuygn tap bao cao Hoi nghj KHCN "30 nam Phu khi Viet Nam: Cff hoi moi, thach thuc mdi^ 543
Miocen giua, Miocen dudi, Oligocen va mong nirt ne. Du: lieu dia vat ly gieng khoan CAST-V va FMI tir gilng khoan trong viing nghien cim cho thiy kh6ng co thay d6i mot each he thong hudng iing suat theo do sau.
H I U hit khe nirt sinh ra trong qua trinh khoan co hudng song song vdi true gieng khoan, dilu nay chiing t6 ring img suit thang dimg la mgt trong nhir ng iing suat chinh. Ci bl Cim Long, img suit ngang cue dai, ve co ban c6 hudng Bae Tay Bae - Nam D6ng Nam din BIC - Nam trong phin phia Bae va ddi nang trung tam va tir D6ng - Tay den Tay Bae - D6ng Nam trong phan phia Nam (Hinh 5). O be Nam C6n Son, img suat ngang cue dai c6 hudng D6ng Bae - Tay Nam d phia Bae va Bae - Nam d phan Trung tam ciia be (Hinh 6).
Mgt bang chiing ve hudng img suat ngang cue dai D6ng Bae - Tay Nam d phan phia Nam cda be Nam C6n Son la hien tugng khi phun d mo Lan Tay nam 1993. Khao sat do sau muc nude bien phia tren md cho thay cac noi khi phun tim thay gan nhu nam tren cac dudng thang CO hudng D6ng Bae - Tay Nam (Jakopsson v^ n.n.k., 1995). Cac vi tri khi phun d m6 Lan Tay co the hieu nhu la niit vd thiiy luc ty le ldn. Hudng ciia khe nut bi gay ra do khi phun phii hgp vdi hudng img suat ngang cue dai hien tai D6ng Bae - Tay Nam.
107°E 107°30'E 108°E 108°30'E
10°30't
10°N
9"30' N
10"30' N
10"N
9°30'N
107°E 107°30'E 108°E 108°30'E
Hinh 5: Hu'OTig iing suat ngang cue dai be Ciru Long
544 Trudng ung suht hien tai v^ dp suat thanh he trong bl Ciru Long va Nam Con Sffn,
IO7OE IO8OE IO9OE
90N
8ON
'70N
Xac djnh tir hudng sap la thanh gieng khoan
Xac djnh tir huang nut ne sinh ra trong qua trinh khoan Xac dmh tu huong noi cac diem pht
90N
80N
70N
IO70E IO8OE IO90E
Hinh 6: Hvong irng suit ngang eve dai be Nam Cqn Sorn
Tuygn tap bao cao H^i nghj KHCN "30 nSm Dau khi Viet Nam: Cff hoi mdi, thach thiic mdi' 545 AP SUAT T H A N H H E T R O N G BE CUtJ L O N G VA N A M C O N SON
Ap suat thanh he thu dugc xac dinh tir tai lieu thir via RFT va DST d cac gilng tham do va khai thac. De tranh anh hudng cua sir suy giam ap suat via trong qua trinh khai thac, cac tac gia kh6ng sir dung tai lieu do ap suat ciia cac gieng khai thac. Ap suit thanh he trong be Cim Long gan bang ap suat thiiy tinh trir tang Oligocen tren (Hinh 7).
4500 0
500
1000
3
hieu sa
" 2000
2500
3000
3500
4000
V-i
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thu-fl
I
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Ap suat thanh h?
Ap sui IJngsu
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20 40
Hinh 7:
60 80
Ap suat (MPa)
100
Trong be Nam Con Son, ap suit thanh he co gia tri thay d6i tir tuong duong vdi ap suat thuy tinh den ap suit cao va tham chi rit cao trong mgt s6 gilng. Phin ap suit cao dugc quan sat tir do sau tren 1100m d phin Nam va 2500m d phin BIC ciia bl (Hinh 8 va 9).
546 Tru-oTig ung suat hien tai va ap suat thanh he trong bg Ciiu Long va Nam Con Soiy^
3 3
x: U
4000 0
500
1000
1500
2000
2500
3000
3500
w
\i
i ' 1
I \ i
\ • X
\ • • \
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V 20 40
Gieng khoan A2 Gieng khoan A3 Gieng khoan A2-1
60 80 100
Ap suit (MPa)
Gieng khoan Al Ap suat thuy tTnh ifng suat thang diing
Hinh 8: Di thircmg ap suat 6" phan nong quan sat diro'c
i. .A.
trong mot so gieng khoan be Nam Con Son
Tuygn tap bao cao Hpi nghj KHCN "30 nam DSu khi Viet Nam: Cff hoi mdi, thach thiic moi' 547
1000
B 2000
«0 3
(/>
3
'sz.
o 3000
4000
5000
20
a Gi4ng khoan B2
% Gi^ng khoan B6 X Gi4ng khoan B I I
• Gi^ng khoan B13
40 60 80 100 120 140
Ap suit (MPa) Gi6ng khoan B3 x Gilng khoan B5
• Gilng khoan B7 Ap suit thuy tinh U'ng suit thing dipng • Gilng khoan B14 D Gilng khoan Bl5
Hinh 9: Di thiro'ng ap suat ff phan sau quan sat duffc trong mot so gieng khoan be Nam Con Son
CU^OfNG DO I T N G S U A T TAI CHO 6 CAC BE CUtJ LONG VA NAM CON SON De don gian hda, cac tac gia chi xac dinh ba thanh phan iing suat chinh trong hai be tram tich. Neu img suat thang dung dugc chgn la mgt trong cac img suat chinh cua vimg nghien ciiu, thi hai iing suat chinh con lai la cac iing suat ngang cue dai va iing suat ngang cue tieu.
L Cu'o-ng do irng suat thang dirng (hay irng suat de nang Sy)
ling suat thang diing tai bat ky do sau z nao ciing dugc gay ra bdi trgng lugng cua cot nude bien va dat da nam phia tren diem do. U'ng suit nay la tich phan mat do nude biin va mat do kh6i ciia da theo do sau dugc xac dinh bing phuong trinh sau:
548 Tru-Q-ng u-ng suat hien tai va ap suSt thanh he trong bl Cihi Long va Nam Con Son^^-^
( Z Z '
^V =A\^^ Pseadz + |^ p^dz (1) Trong do:
Sy la ling suat dge, ZB la do sau day bien, Pb la mat do kh6i cua da theo carota mat do, Psea la ty trgng nude bien, va g la gia t6c trgng trudng.
Tai lieu carota mat do thudng do d phan sau cua gieng khoan. Ci cac gieng khoan kh6ng CO tai lieu carota mat do d phan n6ng, cac tac gia sir dung gia tri mat do do dugc tir cac gieng khoan lan can.
T6ng hgp tai lieu tir cac gieng khoan trong be, cac tac gia xay dung mat cat iing suit da phu theo do sau va phuong trinh thuc nghiem (2) de tinh img suat da phii cho cac gilng khoan kh6ng co tai lieu mat do. Hinh 10 the hien mat cat img suat thang dimg theo do sau d be Nam C6n Son.
1.1066
S = 0.00093* (z)' (2)
40 3
O
500
1000
1500
2000
2500
3000
3500
4000
\ Sv =0.0093'
! i _ ; 1 • ••
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*De pth'^1.1066
= 0.999
1
1 1 1 1 1
1
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20 40 60 80 100
Ap suit (MPa)
Hinh 10: iTng suat thing dirng o" be Nam Con Son
Tuygn tap b^o cao Hgi nghj KHCN "30 n2m Phu khi Vi^t Nam: Cff hoi mdi, thach thuc mdi" 549 2. CiroTig do irng suat ngang
Cudng do img suit ngang cue tiiu (Sh) dugc do bing cac ky thuat nirt via thiiy lire nhu thir vd via trong cac ldp cat ket.
Lfng suit ngang cue tiiu (Sh) dugc xem la bang ap suat khep kin khe mit (Pc) (Gjonnes va n.n.k., 1998).
Sh=Pc (3)
Trong qua trinh thir, ap suat cot dung dich dugc nang dan len bang each bom dung dich vao gieng khoan va vao khoang thir. Khi thanh gieng khoan bat dau nirt co hien tugng mat dung dich thi dimg bom va theo doi sir suy giam ap suat.
Ap suat tai diem thay doi do d6c tren dudng cong suy giam ap suat chinh la ap suat khep kin khe nirt. Ap dung phuong phap ciia Lee va Haimson (1989), cac tac gia xay dung do thi quan he gitra dao ham ap suat theo thdi gian (dP/dt) vdi ap suat sau khi ngimg bom dung dich (P). Tren do thi nay, sir suy giam ap suat trudc va sau khi ddng khe nirt thay d6i theo hai ham tuyen tinh khae nhau. Ap suat khep kin khe niit nam tren diem giao nhau ciia hai dudng tuyen tinh dd (Hinh 11 va 12).
(PSI)
O)
c
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7000 6900 6800 6700 6600 6500 6400
6300
c
- - -• - - ~ - " •
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X
..._.. .. ^ - - X X
V
. _ X ^
- - - - —
- -
X
0 1 2 3 4 5 6 7
Thai gian sau khi ngu-ng bam (phut)
Hinh 11: Su- thay doi ap suat day gieng sau khi ngirng bom trong thu* v& via tai gieng khoan Al be Nam Con Son
550 Tru-6-ng ung su^t hien tai va ap suit thajihJi|n;ong bg Ciiu Long va Nam Con Son,..^
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CD
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300
250
200
150
Ap suat dong khe niit
6200 6300 6400 6500 6600 6700 6800 6900 7000
A p suit (psi)
Hinh 12: Vi du ve each xac dinh ap suat dong khe nirt sir dung tai lieu ap suat suy giam sau khi ngimg bom (Hinh 11)
U'ng suat ngang cue dai (SH) kh6ng thi xac dinh true tilp tir mgt phuong nirt via thuy lire nao. Gia thilt rang vat lieu co do r6ng va thim dii dk chk lun thim vao thanh he trudc khi bat dau nirt, SH CO the dugc tinh bing each sir dung quan he (Detoumay va n.n.k., 1988):
% = 3^^/, - a-\-2v
Py -a l - 2 v
1 - v •Pr (4) Trong d6:
Pr la ap suat cin thilt md lai khe nirt, Pp la ap suit thanh he trudc khi bom, v la he s6 din luu Poisson, va a la he s6 img suit hieu dung.
De xac dinh P^, cac tac gia sir dung phuong phap thir timg bude sau khi thir vao khoang thir. Trudc khi thir timg bude, khe nirt dugc tao bdi khoang thir. Trong thir timg bude, luu lugng bom ep dugc gia tang timg h6i (Hinh 13). Gia tri ciia P^ dugc chgn tir d6 thi quan he giua ap suat day d cuoi ciia m6i giai doan bom ep va luu lugng bom ep (Charlez, 1997) (Hinh 14). Bieu d6 dugc dac tnmg bdi hai dudng thing, dudng thing thir nhit d6c hon phan anh giai doan bom ep vao khung da va dudng thing thii hai it d6c hon phan anh giai doan md rong khe nirt. Ap suit ngoai suy khi luu lugng bom bang kh6ng tren dudng thang thii hai xap xi bing vdi ap suit md lai khe mit (Charlez, 1997).
Tuygn tap b^o c^o Hoi nghj KHCN "30 nam Phu khi Viet Nam: Co hoi mdi, thach thuc mdi" 551
10000
oooo
6000
^ 4000
2000
— A p suit (£ty gi4ng - ThA tich bom 6p
a
20
S500
8000
7500
^ E c b
= QL 7000 .o
15 e .
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E 10
a>
40
Q.
25 30 35 40 45 Th(f\ gian bam thir via (phut)
50
6500
6000
5500
5000
4500,
4000
• • ' ^ • - - 4 ^ ^ - -
f
I -y'T''
! : Ap suit b t^i
khe nirt
L 1
1 t
; 1
1 i 5 10 T h i tich bom 6p (thiing/phut)
15
Hinh 13: Sy thay doi ap suat day gieng trong qua trinh thir via tirng buffc
Hinh 14: Xac djnh ap suat mo' lai khe nirt dira tren so lieu 6' Hinh 13
De sir dung phuong trinh (3), can tinh cac gia tri a va v. He s6 img suat hieu dung (a) lien he vdi m6dun kh6i dan luu (K) va m6dun kh6i kh6ng bgc (Kg) theo Wang, 2000:
Ks (5)
Tir phan tich do nen cua da, m6dun kh6i 16 r6ng dan luu (Kp) dugc do ciing vdi do r6ng (([)). M6dun kh6i 16 r6ng dan luru co the lien he vdi a, (|) va K bdi phuang trinh sau day (Wang, 2000):
1 K.
Tir phuong trinh (5) va (6) co:
a = l a (fK
K,
(6)
^K,^K,
(7)Gia thilt ring Ks bing vdi 37GPa, gia tri diln hinh cho thach anh (Gary va n.n.k., 1998), va sir dung Kp va (j) do dugc, co thi tinh a nhu la mgt ham cua (j). Ap dung phudng trinh thuc nghiem cua Fabre va Gustkiewicz (1997), thu dugc quan he giira he s6 img suit hieu dung (a) va do r6ng (cj)) (Hinh 15) nhu sau:
552 Tru-6-ng irng suat hien tai va ^p su^t th^nh hf trong bg Ciru Long v^ Nam Con Son,...
a = l-exp(7.5*tan-^ )
+ Theo tdi li#u phan tich cua b l Ci>u Long
—Theo tinh todn m6 hinh + Theo tdi li§u phdn tich cua b l
Nam C6n San
0.1 0.2 0.3 0.4
Dp r5ng
0.5 0.6
Hinh 15: Do thj bieu dien quan he giira he so nen ep hieu dung va do rong
Bdi vi kh6ng cd s6 lieu he so Poisson tir miu loi, do vay phai tinh bing tai lieu carota sieu am va do nen cua da. He s6 Poisson kh6ng din luu (v,) co thi tinh bing phuang trinh sau:
Vu
2-M1 IMI
2{\-MIIMI)
(9)Trong do:
^t, va Ate la thai gian truyen s6ng ngang va song dge tuong img. He so Poisson din luu CO the tinh theo he s6 Poisson kh6ng din luu th6ng qua he s6 Skemton (B) (Wang, 2000) theo phuong trinh sau:
3 - 2aB{\ + v^) (10)
Tu^yln tap b^o c^o HQi nghj KHCN "30 nam Dau khi Vift Nam: Cff hpi mdi, thach thirc mdi" 553
B = \IK-\IK,
\IK -\IKs+<K^IK^-\IKs) (11) Trong do:
Kf la modun kh6i ciia chit lim trong 16 rong. Cac tac gia gia thiet mddun khoi ciia chat lim 16 r6ng bing 2,3GPa, img vdi gia tri cua nude. Sir dung cac thong s6 thu dugc bang phuang phap tren va tai lieu ap suat cd dugc tir thir timg bude, cd the tinh iing suat ngang cue dai.
Hinh 16 cho thay iing suat thang dimg, iing suat ngang cue tieu va cue dai tinh dugc trong be Cim Long. Ta thay rang Sv > SH > Sh va nhu vay trudng umg suat hien tai trong viing nghien cim la trudng img suat cua dirt gay thuan (Anderson, 1951).
3
500
1000
1500
2000
H(0
6 2500
3000
3500
4000
4500
<ix\
— ^ !
• V X A
• V X A
' X U'ng Ap s A O-ng
U'ng
• A p s
suat ngang ci/c tiiu ult thuy tmh
suit ngang circ dai suat thing dipng ult thanh h$
20 40 60 80 100 120
Ap suat (MPa)
Hinh 16: Cuo^ng do ba irng suat co ban be Cuu Long
Trong be Nam C6n Son, img suat ngang cue tiiu tir thir vd via trong 4 gilng (Hinh 17) dugc xac dinh trong cac thanh he co ap suat bang ap suit thiiy tinh va co di thudng ap suit.
554 Truong ung suat hien tai v^ Ap suht th^nh he trong bg Ciru Long v^ Nam Conjcrn^
3
(/>
O
500
1000
1500
2000
2500
3000
3500
4000
4500
sj Tir cac thanh he co ap suat bang ap suat thuy tmh
A Sh-giing khoan Bl Ap sulit thuy tTnh
• Sh-giIng khoan B2 + Sh-giIng khoan 84
+ Ap suit thdnh h$ gilng khoan 84 o
80 100
Apsult (MPa) Ap suit thdnh h$ gilng khoan Bl
•Ap suit thing dirng Sh-giIng khoan 63
Ap suit thdnh h$ gilng khoan B2
Hinh 17: Cucmg do hai irng suat cff ban bl Nam Con Sffn
3. Anh hu-dng ciia thay ddi ap suat via len cycmg do irng suat d be Cihi Long
Theo ly thuyit do r6ng dan h6i, sir thay d6i ap suit via (APp) tao ra thay d6i cac img suit ngang (ASh va ASH) (Wang, 2000). Trong dilu kien biin dang don true, m6i lien he bieu dien nhu sau (Wang, 2000):
AShiASH) = a^-^AP,
1-v ^ (12)
Trong do: APp la do lech cua ap suit so vdi ap suit thuy tinh binh thudng va ASh (ASH)
la do lech cua iing suit tuong iing.
Tuygn tap bao c^o HQi nghj KHCN "30 nSm Dau khi Viet Nam: Cff hoi mdi, thach thuc mdi" 555
Sir dung gia tri ap suit thanh he suy giam do dugc va cac he s6 do rong dan h6i (a va v) tinh dugc nhu tren, tinh ASh cr hai do sau trong bl Cim Long noi cd ap suit thanh he bi suy giam trong khai thac diu khi. Sau do tir gia tri ASh(ASH) tinh dugc kit hgp vdi s6 lieu ling suit ngang do dugc, tinh cac iing suit ngang d dieu kien ap suat thanh he bang ap suat thuy tinh (Bang 1).
Bang 1: Ket qua tinh irng suat ngang cyc tieu trong dieu kien ap suat thanh he bang ap suat thuy tinh
GK
A B
V
0,08 0,126
a
0,785 0,7
\-2v a
\-v
0,72 0,6
AP (MPa)
-3,61 -4,4
Sh tgi nai
cd dp sudtsuy gidm (MPa)
44,83 50,12
Sh tgi noi cd
dp sudt bdng dp sudt thiiy
tinh (MPa)
47,42 52,76
SH
tgi nai cd dp sudt suy gidm
(MPa)
53,6 56,19
SH
tgi noi cd dp sudt bdng dp sudt thiiy tinh
(MPa)
56,22 58,82 Ket hgp so lieu do irng suat ngang trong dieu kien thiiy tTnh vdi gia tri img suat ngang xac dinh dugc tir cac khoang suy giam ap suat, ta thay rang iing suat ngang cue tieu gia tang tuyen tinh theo do sau d dieu kien ap suat thanh he thiiy tinh (Hinh 18).
Tir cac nhan dinh neu tren va cac s6 lieu dan ra trong Hinh 18, cac tac gia da xay dung phuong trinh thuc nghiem bieu dien quan he giiia iing suat ngang, do sau va ap suat thanh he cho be Cim Long nhu sau:
'^/7=^5^-P5ea + 0-0135*z + a
\-2v
\-v {Pp-Ph)
(13)1-v ^ (14)
vdi Ph la ap suat thiiy tinh. Trong phuong trinh (13) va (14) don vi cua cac img suat ngang va ap suit la MPa va do sau la met.
556
Tru-Q-ng iJ-ng suat hifn tai va ap suat thanh hf trong bg Cihi Long va Nam Con Son,<ro 3 w 3
'sz O
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
Sh trongd ieu kien ap suat thanh hf bang ap suat thuy tinh
Sh trong dieu kien ap suat thuy tTnh
-Ap suat thuy tTnh
• Sh tgi nai cip suat da bj suy giam
• Ap suatth^nh he X Ap suit v& via
10 20 30 40 50 60
Pressure (MPa)
Hinh 18: Do thj bieu dien su thay doi irng suat ngang cyc tieu theo chieu sau ff be Cxnx Long
4. Anh hirdng ciia thay doi ap suat via len cirdng do img suat d bi Nam Con Son
Sir dung cimg cac phuong phap nhu d be Cim Long, ta cd phuong trinh thuc nghiem tinh cudng do iing suat ngang cue tieu theo do sau va ap suit via cho bl Nam Con Son nhu sau:
'^/j = ^^^P^ea + 0-0136* z + a l - 2 v
1-v
iPp-Ph)(15)
Neu phuong trinh nay phan anh dung iing suit trong bl, co the tinh iing suit ngang cue tieu d bat ky do sau nao khi bilt ap suit thanh he, he s6 iing suat hieu dung va he s6 Poisson. Phuong trinh nay da dugc kilm tra bing cac s6 lieu trong viing ap suit cao.
Sir dung ap suit thanh he do dugc trong cac ting ap suit cao va cac th6ng s6 do rong
dan h6i (a va v) tinh dugc, tinh ASh cho 5 khoang co ap suat cao.
Tuygn tap bao cao HQi nghj KHCN "30 nam Phu khi Viet Nam: Cff hoi mdi, thach thiic mdi" 557
Dieu dang luu y la cac ung suit ngang cue tieu dugc tinh tir phuong trinh (15) hau nhu tat ca deu trimg vdi sd lieu dugc xac dinh trong khi thir vd via (Hinh 19). Dieu nay chimg t6 rang phuang trinh (15) thich hgp dl tinh img suat ngang cue tieu (Sh) trong bl Nam C6n Son. Bdi vi md hinh tinh iing suat ngang cue tieu cho be Nam C6n Son tuong tu nhu trong be Cim Long, do do co thi tinh iing suat ngang cue dai (SH) cho bl Nam C6n Son bing phuong trinh (14).
<ro 3
CO 3 .<Q)
x: O
500 1000
1500
2000
B 2500
3000
3500
4000
4500
A Sh-gleng khoan 81
• Ap suat thuy tTnh Sh-gieng khoan 82 Sh - gieng khoan 84
Ap suat thanh he gilng khoan 84
80 100 Ap suat (MPa)
A Ap suat thanh he gieng khoan 81 U'ng suat thing (3i>ng
® Sh-gieng khoan 83
o Ap suat thanh he gieng khoan 82
• U'ng suat ngang theo tinh toan Sh
Hinh 19: iTng suat ngang cyc tiiu tinh duoc theo phu-ffng trinh thyc nghiem (phuo'ng trinh 15) (hinh thoi mau xanh) va irng suat ngang eye tiiu duffc minh giai tir tai lieu thu' vo via be Nam Con Son (hinh tam giac mau do va hinh vuong mau tim)
Cin chu y rang, gia tri img suit ngang cue tiiu rit gin vdi img suit thing dimg d cac ting ap suat cao (Hinh 19), che do img suit co thi thay d6i tir chi do img suit ciia dirt gly thuan sang che do img suat cua dirt gly trugt bing d phin sau ciia bl Nam Con Son.
558 Trudng ung suat hien tai va ap su5t thanh he trong bl Cuu Long va Nam Cdn^ffnv^
KET LUAN
Tir kit qua thu dugc co the c6 mgt s6 nhan dinh sau:
• Trong bl Cim Long, iing suat ngang cue dai chii yeu co hudng BIC Tay Bae - Nam D6ng Nam din BIC - Nam d phan Bae va phan giiia, va tir D6ng - Tay den Tay Bae - D6ng Nam d phan Nam. d be Nam C6n Son, img suat ngang cue dai chii yeu co hudng D6ng BIC - Tay Nam d phan Bae va Bae - Nam phan Trung tam ciia be.
• d cac b l Cim Long va Nam C6n Son, iing suat ngang tang tuyen tinh theo do sau trong dilu kien ap suit thuy tinh, va chiing thay d6i khi co di thudng ap suat.
• Bdi vi umg suat ngang tang theo ap suat via (phuong trinh 13 va 14), che do iing suat CO the thay d6i tir che do dirt gay thuan sang che do diit gay trugt ngang trong vimg co di thudng ap suat ldn.
• Hudng va cudng do ciia SH va Sh ciia cac kh6i kien tao nho dugc chia cat bdi he th6ng diit gay tiiy thuoc vao cac yeu t6 chinh nhu vi tri cua kh6i kien tao, phan b6 va tai boat dong cua he th6ng diit gay c6 va cu6i ciing la tinh chat co hgc ciia da.
• Hieu ro ve trudng irng suat hien tai giiip ta danh gia tinh dgng ciia he th6ng diit gay, mil ne va kha nang chan ciia chung. Tir do, co the danh gia viing da mong mil ne trien vong nhat ciing nhu du doan kha nang ngap nude va he s6 quel trong qua trinh thu h6i dau tang cudng.
• D6i vdi cac gieng khoan tham do va khai thac, hieu ro ve iing suat hien tai se giup t6i uu hoa c6ng tac thiet ke hudng ciia gieng khoan, kiem soat tinh 6n dinh ciia gieng khoan ciing nhu hoan thien gieng, kiem soat viec tao cat va nut vd thuy lire.
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