Hpi nghj KHCN 2000 "Nganh Dau khi Viet Nam trifdc them theky 21'
QUY TRiNH P H A N TICH D A N H G I A LAI TRANG T H A I
KY THUAT CAC KET CAU CONG TRJNH DAU KHI BI^N
Od' San Vien Ccf hgc Lam Quang Chien Hoang Le Ngoc Vinh, Vu Xuan Lai
XNLD Vietsovpetro
TOM TAT
De danh gia trang thai ky thuat cae cdng trinh dau khi bien, tac gia de xuat nhung phuang phap va quy trinh theo tieu chuan quy pham qudc te phu hgp vdi dieu kien thuc te eua Viet Nam. Ket qua thir nghiem danh gia lai ket cau gian khoan IVISP -1 a XNLD Vietsovpetro cho thay quy trinh cd tinh kha thi neu khdng bi cac tac ddng ngau nhien ngoai du kien.
M6OAU
Cac cdng trinh d i u khi bien nhu gian khoan, dudng dng, v.v.. do phai chju tac ddng khic nghiet ciia tai trgng va mdi trudng bien, thugng bj xudng c i p nhanh han so vdi dy tinh, dae biet la sy suy giam nhanh chdng cac ket c i u thep ciia chung. Oe dam bao an toan khai thac va duy tri hoae keo dai tudi thg edng trinh, mdt trong cae khau quan trgng dugc quy dinh theo eae tieu chuan quy pham (TCQP) hien hanh (xem Hinhl) la phai thudng xuyen phan tich danh gia lai trang thai ky thuat eiia eae ket cau nay de kip thdi de ra phuang an duytu, bao dudng.
6 nhieu nude tren the gidi viec phan tich danh gia lai ket c i u cdng trinh khai thac d i u khi tren bien da trd thanh nhiem vu thudng ky ciia cac ky su xay dyng edng trinh va phuang phap phan tich danh gia lai da dugc quy trinh hoa. Xuit phat tU cac dieu kien khaeh quan ciia mdi nude (khf tugng thuy van, dja chit edng trinh, cdng nghiep vat lieu, v.v...) ma ndi dung eiia cac quy trinh cd nhUng diem khae nhau. 6 nude ta, day la cdng viec hoan toan mdi me. Odng thdi, dieu kien khi tugng thuy van bien lai khic nghiet. Vi vay, de phan tich danh gia lai trang thai ky thuat eiia cae ket cau cdng trinh khai thae dau khi tren bien, chung ta cin cd phuang phap va quy trinh rieng ciia minh, dya tren cac tieu chuan quy pham qudc te [2,3,4,5] ket hgp vdi cac dieu kien eu the ciia Viet Nam.
QUY TRiNH P H A N TICH D A N H G I A LAI KET CAU CONG TRJNH OAU KHI BIEN 1. Cdsdxay dung quy trinh phan tich danh gia lai
Cae cdng trinh khai thac dau khi bien d Viet Nam hien nay chii yeu la cdng trinh bien cd djnh, viec phan tich danh gia lai chiing ed the bao gdm hai phan: phan tich hien trang tdng the va phan tieh hu hdng cue bd. Ca sd ciia viec phan tich danh gia lai v i n dya tren phuang trinh chuyen ddng ciia he ket cau dugc viet dudi dang ma tran nhu sau:
Mu -)- Cu -I- Ku = P ( u , L i , t ) (1.1)
Trong dd: M la ma tran khdi lugng; C - ma tran can; K - ma tran do eirng; u , u , u lin lugt la cac vee ta gia tdc, van tdc, chuyen vi va F(t) la vee ta tai trgng.
Trong trugng hgp ket eiu d trang thai tinh, phuang trinh can bang (1.1) dugc dua ve dang:
Ku = P (1.2)
Cdn trong trudng hgp cin xac djnh cac dae trung dao ddng rieng eiia ket ciu khi tai trgng va thanh phin can bing 0, ta ed phuang trinh:
Mu + Ku = 0 (1.3)
Nhu vay, bai toan phan tich danh gia lai ket eau cung chinh la bai toan phan tieh ket ciu. Chung chi khae nhau d cac yeu td "diu vao" va d cac ket qua" diu ra" (Hinh 2). Cac yeu td "diu vao", ngoai cac du lieu thiet ke edn dugc bd sung them cac sd lieu khao sat va bao tri. Sy tac ddng eiia cac sd lieu khao sat va bao tri, lam thay ddi eae yeu td "diu vao" eua bai toan phan tich danh gia lai ket eiu, duge eho tren Hinh 3.
Cdng viec phan tich duge tien hanh theo cac bude sau day:
• Tinh toan eae yeu td tai trgng, trugc het la tai trgng sdng, va cac td hgp tai trgng;
• Tinh toan tuang tac ket ciu - cgc - nen;
• Phan tich kiem tra cac trang thai ky thuat eiia ket cau.
Viec phan tich kiem tra ket eau theo phuang phap irng suit cho phep hoae theo phuang phap he sd rieng phan dugc thyc hien trong eae trang thai gidi han sau day [6]:
• Trang thai gidi han cifc dalfULS/. Tien hanh kiem tra do ben, do dn dinh, kha nang chju lye cit, ap lye thuy tinh ciia eae phin tir ket ciu va cgc trong ca dieu kien thiet ke thi cdng lan dieu kien thiet ke khai thae.
• Trang thai gidi han moifFLS/. Tien hanh kiem tra cac ket eiu chju cae ung suit thay ddi, trong dd sy tang sd lugng chu trinh ung suit la nguyen nhan gay ra pha huy mdi.
Cd the tinh toan tudi thg mdi dya tren gia thiet tdn thuang tinh luy tuyen tinh [3]. Theo gia thiet nay, phan phdi dai han eiia sd gia irng suit duge bieu didn bing tap hgp eiia mdt sd thich hgp cac khd'i sd gia irng suit ed bien do khdng ddi, mdi khdi cd mdt ehu trinh irng suit tuang irng. Viee kiem tra mdi duge dya vao cdng thirc:
t^<-.. n,4,
Trong dd: k la sd khd'i irng suit; n; la sd ehu trinh irng suit trong khd'i thir i; N^ la sd chu trinh tdi pha huy d sd gia irng suit khdng ddi dugc suy tU dudng eong mdi S-N thich hgp; r| la ty le tdn thuang tieh luy eho phep.
Trong cac tieu chuan [4,6] can quy djnh tinh toan mdi theo ly thuyet ea hgc pha huy. Cdng thyc kiem tra mdi d day dugc bieu dien bing:
N
^ ^ < T i , (1.5)
N
k
Trong dd: N^, la tdng sd chu trinh yng suat (N,„, = ^ n , ) ; Ng la sd chu trinh ifng suit can thiet lam khLiyet tat (vet nirt) phat trien tU kich thudc ban dau den kich thudc tdi han.
• Trang thai gidi han phuc vy (hay khi nang lam viec, SLS). 6 trang thai nay chi' tieu danh gia chu yeu la chuyen vj eiia ket ciu khdng dugc vugt qua gjgi han eho phep.
. Trang thai gidi han pha huy luy tien (PLS). Trang thai nay quy djnh viec kiem tra mdi ndi (nut va cac phin tir) ket eiu bj hu hdng, dugc phat hien trong qua trinh khao sat, hoae chju irng suit Idn theo cac
Hpi nghi KHCN 2000 "Nganh Dau khi Viet Nam trifdc them theky 21'
trang thai ULS va SLS, nhim tranh xay ra eae hien tuang pha huy do chay deo, mit dn djnh, pha huy cit dot va mdi khi ket ciu phai chiu cac tac dgng sy ed hay bit thudng.
Khao sat
Bao tri
^ 1 i i a i i Li^ii u a i i i i y i a tai
Hinh 1. So dd dam bao an toan ket ciu Phan tich danh gia lai (PTOGL)
DO" lieu vao cua PTDGL Phan tich Ket qua cua PTDGL
Sudung Oat
Bao tri Khdng dat
Hinh 2. Sa dd phan tich danh gia lai ket cau
Hinh 3. Sa dd tac ddng cua cac yeu td khao sat, bao tri den di/ lieu vao ciia PTDGL
TU viee phan tieh mdi tren ca sd ca hgc pha huy cd the rut ra khoang thai gian khao sat djnh ky nhim phat hien cae vet nut mdi tiem an trudc khi xay ra pha huy mdi cudi cung.
Trong truang hgp nay cin phai tien hanh phan tich phan tir huu han phi tuyen (ma tran do cirng ciia phuang phap phin tir huu han phu thudc vao hinh dang va kich thudc ciia cae hu hdng) hoae phai nhan do ben dac trung ciia cac md'i ndi nhan dugc tU cac cdng thire tham sd vdi he sd Q, sau day (khi mdi ndi ehi chju lye dge true):
Q,= 1.0-a7A' (1.6)
Trong dd: y = R/t, R la ban kinh ngoai va t la do day thanh ciia dng chii (dng chinh); a la he sd xet tren dng giang (dng nhanh): a = 0.030 ddi vdi luc dge true, a = 0.045 - ud'n trong mat phang va a = 0.021 - ud'n ngoai mat phang;
^ 2 ^ ^.;i + ^M + ^IM
(1.7)
Vdi cac gia trj thiet ke d'ng chu: ag^ la yng suit dge true; QJ^ la urng suat ud'n trong mat phang d'ng chii, a^ud la irng suit ud'n ngoai mat phang d'ng chii va cr ^^ la gidi han chay cua d'ng chii.
Khi mdi ndi chju ddng thdi lye dge va md men ud'n, cd the diing edng thirc tuang tae sau day thay cho cac sd lieu thir md hinh hay phan tieh phan tir huu han phi tuyen:
l.R.= H—arcsin.
71
M.
V - ^ R J J^h
H- M.
M (1.8)
R'l / o h
Trong dd: Chi sd sd la ehi sd cac gia trj thiet ke eiia hieu Ung tai trgng; ehi sd Rd la ehi sd cae gia trj sire ben thiet ke; Cac chi sd lb va ob la ehi sd ud'n trong va ngoai mat phang dng chii. Gia trj arcsin duge tinh bing Radian.
Oieu kien de danh gia la Q, < 1.0 va I.R < 1.0.
Odi vdi cac phin tir bj cac hu hdng dien hinh nhu mop, nirt v9, eong, v.v... lam thay ddi eae dae trung hinh hgc ciia tiet dien nhu dien tieh F, md men chdng ud'n W, do lenh tam y, v.v..., viec danh gia ed the dugc tien hanh nhd cac he sd suy giam tuang Ung Kp, Kw^ K^" [7].
2. Quy trinh phan tich danh gia lai
Dya vao cac ca sd neu tren, quy trinh phan tich danh gia lai ket eau cdng trinh d i u khi bien (vi du, MSP) ed the bao gdm cac bude ehii yeu sau day:
• Mo ta cong trinh: Vj tri, do sau nude nai dat edng trinh va cac vat lieu sir dung lam ket ciu edng trinh.
• Md hinh hoa ket cau: Md hinh chan de (chan de, lien ket d'ng cd tram vua, hieu irng eiia an mdn, eae hu hdng); khung chiu lye; san cap tau va cac phan ket ciu khae; mdng.
• • Xac dinh tai trong: Tai trgng ban than eiia ket c i u chan de, ciia khung chju lye va cae phin phi ket eiu khae; cac tai trgng thuy dgng lye (md hinh thuy dgng lye, lye day ndi, ha bien, cae he sd ca ban ciia phuang trinh Morison va cudi ciing la tai trgng sdng tinh va tai trgng sdng mdi); eae tai trgng eiia phin thugng ting (tai trgng ban than ciia cac ket c i u thugng tang, trgng lugng thiet bj, tai trgng tam thgi va tai trgng khai thae); tai trgng gid. Ket qua ta ed cac tardng hgp tai trgng va eae td hgp tai trgng.
• Phan tich tinh: Kiem tra dieu kien chay, dieu kien thuy tinh, dieu kien dn dinh, dieu kien eat dot va dieu
Hpi nghi KHCN 2000 "Nganh Dau khi Viet Nam trifdc them theky 21'
kien chuyen vj.
• Phan tich dgng luc hgc: Kiem tra t i n sd hay ehu ky dao ddng rieng eiia ket c i u va xac djnh sd gia yng suit do eae tai trgng chu ky gay ra.
• Phan tich moi: Md ta lien ket cgc - dit, phan tieh mdi theo md hinh dgng lye hgc tien djnh hay theo phuang phap phd va hieu ung do day thanh dng.
• Tinh toan mong: Xem xet cae thdng sd ve dit, c i u tao md hinh mdng, tinh toan va kiem tra chuyen vj diu cgc, Ung suit va kha nang chju lye ciia ege.
• Kiem tra cac hu hong cue bg: Kiem tra theo cac hu hdng dien hinh va kiem tra an mdn.
• Ket luan ve tinh trang ky thuat cua ket cau.
• Cac kien nghi: Bao tri ngin han va bao tri dai han.
Cin ndi them ring quy trinh da dugc ca quan Phan cap Qudc te ve edng trinh bien ed djnh DNV (Nauy) xem xet, gdp y kien va kien nghj cho sir dung.
PHAN TI'CH O A N H G I A LAI KET CAU G I A N KHOAN BIEN CO OjNH MSP-1
Oe minh hoa cho phuang phap va quy trinh phan tich danh gia lai ket cau cdng trinh bien ed djnh ta xet mot gian khoan, MSP-1. Day la cdng trinh bien ed djnh d i u tien d Viet Nam, ed du cac sd lieu khao sat va bao tri. Phin Idn cac sd lieu vao va ket qua phan tich ddi vdi gian khoan MSP-1 da duge trinh bay trong [7]. 6 day ehi neu mdt sd ket qua chinh nhu sau:
1. Chuyen vj
Gia trj chuyen vi Idn nhat nhan duge tai dinh ket eau chan de la 24,2cm. Khi ke den sy thay ddi ciia cac yeu td an mdn va ha bien thi gia trj nay tang len la 24,4cm. Nghla la, sau han 10 nam gia tri nay tang len gin 1%, sy gia tang la khdng Idn.
So vdi cac quy djnh hien hanh [2] thi gia trj chuyen vi gia tang van nam trong gidi han cho phep, 0,244 + 0,018 = 0,262m < 0,005 X 67,5 = 0,338m.
2. NoilLTc
Cac gia trj ndi lye dugc sir dung de tinh toan Ung suit nham muc dich danh gia do ben va do dn djnh CLia cac phan tir ket ciu. Ha bien da lam tang tai trgng sdng tac ddng len ket eau va do dd lam eho ndi lye ciia eae phin tir ket eau tang len dang ke. Vi du, gia trj lye dge Idn nhit trong cgc (chan de OBI) la - 466/+110 (T). Ket qua phan tich danh gia lai theo phuang an khao sat thi gia trj nay la - 515/+ 135, tire la tang len 13,1%/33% (dau"-" irng vdi "nen", cdn d i u " + " ung vdi "keo").
3. Sure chiu tai cua coc
Sire chiu tai cua cgc duge danh gia theo tieu chuan API RP 2A. Ket qua tinh toan eho thay, he sd an toan ddi vdi sire chiu tai eiia ege la 4,08 > 1,5. (1,5 la gia trj quy djnh trong API RP 2A).
4. Do ben va do dn djnh cua cac phan tu"
Od ben va do dn djnh eiia eae phin tir ket cau duge kiem tra theo tieu chuan TCVN 6170 - 4/1998.
Ket qua tinh toan eho thiy, t i t ca cac phin tir ket eau deu thoa man. Phan tir giang ed he sd khdng an toan lan nhit (phin tir 344), ^ = 0,632, tire la he sd an toan cdn lai SF = Vr\ = 1/ 0,632 = 1,58.
5. Do ben cua phan tCf co hif hdng
Hu hdng eiia cac phin tir ket ciu khao sat dugc phin Idn la mop va nirt va vai sd lugng kha nhieu va kich CO rit khae nhau. Og ben ciia cac phin tir nay dugc danh gia dya tren eae duang cong suy giam cae dae trung hinh hgc ciia tiet dien [7]. Ket qua tinh toan cho thiy, irng vdi eae vet mop, nirt/va lan nhat he sd an toan tien g i n den gia trj cho phep (r| = 1,25).
6. Tuoi tho mdi cua ket cau
Tudi thg mdi ciia ket ciu dugc danh gia theo TCVN 6170 - 4/1998 [6] ket hgp vgi API-RP-2A, tuc la dya vao gia thiet tdn thuang tieh luy tuyen tinh (1.4) va dudng cong mdi S-N [3]. Ung vdi diem nim trong viing dao ddng nude, duge coi la bit Igi nhat ve kha nang chju mdi, [Dj = 0,33, tudi thg mdi eiia MSP-1 la
16.7 nam, tire tudi thg cdn lai ciia cdng trinh la 8,35 nam.
KET LUAN
1. Phan tich danh gia lai trang thai ky thuat ciia eae ket eiu edng trinh bien cd djnh, trong dd cd cac cdng trinh khai thac diu khi la viec lam cin thiet va thudng xuyen, nhim dam bao an toan khai thac va keo dai tudi thg cdng trinh.
2. Quy trinh phan tieh danh gia lai ket cau cdng trinh dau khi bien dugc soan thao dya tren phuang phap phan tich ket eau cd ke den cac yeu td thyc trang ciia ket eiu nhu cac hu hdng, an mdn, ha bam, v.v...
dap irng dugc cac yeu cau cip thiet ciia viec khai thae diu khi bien nude ta va thoa man d i y du eae quy djnh ciia tieu chuan quy pham hien hanh.
3. Ket qua phan tich danh gia lai ket cau chan de gian khoan bien ed djnh (MSP - 1) da khang djnh tinh kha thi eiia quy trinh ddng thdi eho phep danh gia ve trang thai ky thuat eiia gian khoan nay la ed the lam viee an toan khdng bj pha hu;y' mdi trong thai gian tren 8 nam, neu khdng bj cac tae ddng ngiu nhien chua tinh den.
TAI LIEU THAM KHAO
1. Quy trinh phan tich danh gia lai ket cau gian khoan bien co dinh (MSP). XNLD Vietsovpetro, 1, 2000.
2. BCH. 11.3.85.
3. API R P 2 A - 1 9 " edition.
4. DNV. Rules for classification of fixed offshore installations, 1933.
5. LLoyd's Register. Rules and regulations of fixed offshore inatallations and pipelines, 1988 6. TCVN 6170 - 4/1988. Cong thnh bien cddinh - Thiet ke ket cau thep.
7. Od San. Phan tich danh gia lai trang thai ky thuat va kien nghi giai phap stra chira ket cau chan de gian khoan bien codmh. (MSP) Ha Ndi, 1998.
