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P B T R O V I B T N A M Su dung bien do dia ehan trong phuong phap phan tieh AVO TS Nguyen Dire Khanh DH Tong hap Faroe, Dan Mach TS Nguyen Thu Huyen Vien Diu khi Viet Nam Tom tat Phwang phap phan tfe[.]
PBTROVIBTNAM Su dung b i e n dia ehan phuong phap phan tieh AVO TS Nguyen Dire Khanh DH Tong hap Faroe, Dan Mach TS Nguyen Thu Huyen Vien Diu Viet Nam Tom tat Phwang phap phan tfeh AVO (Amplitude Variations with Offset) la phwo'ng phap tim kiem trwc tiep eae biy chira dau dwa tren ky thuat phan tfch bien cua tai lieu dja chan trw&c eong AVO tr& nen rat bien eong tae tim kiem tham nh& kha nang lien ket bien dja ehan v&i dae tfnh eua da chira Cae dj thw&ng bien (phan xa dja chan co bien cao tren mat eat dja chin song dge) co the dwg'C nghien eiru trw&c eong de xem lieu chiing co dj thw&ng AVO hay khong? Dieu giiip chiing ta phan biet eae dieu kien dja chat (eat ket chira khf, than da hay da nui Iwa) da gay dj thw&ng bien AVO da dwg'C ap dung eong tai mot so mo tren the gi&i, nhwng cung eo nhieu trw&ng hg'p that bai Phwo'ng phap chju anh hw&ng rat l&n tir eae hieu irng thach hgc, day cua da chira cung nhw dac tinh eua cac l&p phia tren Cong tae thu no va xu' ly tai lieu dja ehan cung eo the gay eae dj thw&ng AVO gia Tuy nhien, rat nhieu trw&ng hg'p ap dung khong eong eo nguyen nhan tir viee sir dung bien dja ehan khong ehinh xae chir hoan toan khong phai ban chat eua phwang phap Trong bai bao nay, trw&e tien ehung toi chia ky thuat phan tich AVO hai loai: Phan tich dinh tinh va phan tfeh dinh twg'ng Ca s& ly thuyet va kha nang ap dung eua tirng phwang phap dwg'C khai quit & phan tiep theo Cuoi eiing, sir dung ea s& toan hge eua AVO, ehiing toi thao luan viee sir dung bien dja chan va anh hw&ng cua no t&i phan tieh AVO cung nhw phwang phap sir dung bien dja chan chfnh xae phan tieh AVO ngwg-c fJ^^ ^ | y Sir dung tai lieu dia chan song dpc khong cho phep chung ta phan biet duge cac Phuang phap tim kiem cac bay chira dau sir dung dj thuang bien dp tren tai nguyen nhan gay dj thuang bien dp lieu dia chan tra nen bien tu nam Trong song ngang lai it chju anh ^ 1972 Tuy nhien, co rIt nhiiu cac d i i u kien huang eua eae via chira do rat huu dja chat khac (via than, da carbonate hoae hieu viee phan biet eae dj thuang da nui lira) cung gay dj thuang bien dp bien dp bai vi dj thuang bien dp khong gay DAU KHi-S6 12/2010 27 T H A M DO - KHAI THAC D A U KHi ciia via cat k i t ehu'a Mpt nam sau Shuey [2] chu'ng minh b i n g toan hpe thong qua viee sir dung cae phuang trinh g i n dung eiia he phuang trinh Zoeppritz r i n g ty so Poisson chinh la hang s i dan hoi tryc tiep nhat lien quan d i n s y phu thupc ciia he so phan xa dja c h i n (co goc tai len den 30°) vao khoang each thu no bai se the hien tren ca mat cat song dpc va song ngang Tuy nhien, viee thu no song ngang phu'c tap han rIt nhiiu so vai song dpc Do phuang phap phan tieh AVO la mpt giai phap co the cung d p mat d t song ngang tir s i lieu song dpc Phuang phap phan tich AVO dai vao nam 1984 bai bao ciia Ostrander [1] dugc dang tren tap chi "Geophysics" ong chi sy t i n tai cua t i n g cat k i t dugc phii bai tang set se gay hien tugng thay doi bien dp dja chan theo khoang each thu no (AVO) Ostrander cOng phat hien sy thay doi bien dp lien quan den sy suy giam ciia ty s i Poisson gay bai sy hien dien Phuang phap phan tich AVO dugc tien hanh sau tai lieu dja chan da dugc xir ly theo chu trinh bao toan bien dp V l ca ban, phan tich AVO dugc chia loai chinh (Hinh 1): Phan tich AVO djnh tinh (qualitative AVO analysis) va phan tich AVO djnh lugng (quantitative AVO analysis) RAW SEISMIC DATA (PP, PS) i AVO - PR SERVED PROCESSING QUALITATIVE QUANTITATIVE WELL LOG DATA AVO ANALYSIS AVO ANALYSIS (Vp, Vs, p) CMP, Partial Intercept, Stacks Analysis Sradient Analysi; 1 1 L » - AVO Inversion AVO Forward Modeling 1 J Amplitude Calibration _ _.' LambdaRtio, AVO iZoeppritzl MuRho Analysi! Cross-Plotting 'Modelingi jiviodelingi f-k i •/ PP Inversion •' Joint PP, PS Inversion Hinh Sa phan loai cac phwang phap phan tich AVO Phan tich AVO djnh tinh Phuang phap phan tich AVO djnh tinh bao gom cae phuang phap phan tich su' dung bang diem giO'a ehung (CMP gathers) va mat e l t cpng vai khoang each thu no khac (partial stacks), cung nhu eae thupc tinh AVO khac (intercept, gradient ) d l tim di thuang AVO lien quan d i n eae via cat k i t ehu'a 1.1 Phan tieh AVO sir dung bang diem ehung (CMP) va mat eat eong v&i eae each thu - no khac (partial giira khoang stacks) Quan sat tai lieu dja c h i n tren bang CMP va 28 DAU KH|-S(!) 12/2010 mat d t cpng vai khoang each thu no khac cho phep chung ta xac djnh sy thay doi ciia bien dp dja chan theo khoang each thu no O i l u rIt quan trpng bai vi no cho phep chiing ta kiem chu'ng cac dj thuang AVO quan sat thay tren cac mat d t thupc tinh khac (intercept, gradient ) Trong rat nhiiu truang hgp eae di thuang khong lien quan d i n sy thay doi eua bien dp dja c h i n theo khoang each thu no Ngoai ra, chung ta cung co the tao rat nhieu thupc tinh AVO khac tif eae mat cat cong vai khoang each thu no khac Vi du: Thupc tinh FN (duge tao l l y mat cat cipng vai khoang PETROVIETNAM each thu no xa - far stack (F) tru' di mat d t cpng vai khoang each thu no g i n - near stack (N)) co tinh chit gan gilng vai thupc tinh AVO gradient (phIn 1.2) viec phat hien dj thuang AVO loai II (phan 1.3) Thupc tinh FNxF (F trir di N roi nhan vai F) cho phep phat hien tot han dj thuang AVO loai II vai N eo gia trj am nho va F co gia trj am lan Thupc tinh FNxN (F tru di N roi nhan vai N) cho phep phat hien t i t han dj thuang AVO loai III 1.2 Phan tieh AVO sir dung he so ehan (intercept) va gradient (gradient) eua ham so tuyen tinh Nhu da noi phIn tom t i t , ky thuat phan tich AVO eho phep chiing ta xac djnh dugc cac thong so cua da chira thong qua viee phan tieh sy thay doi bien dp dja chan theo khoang each thu no He so phan xa cua song dan hIi dugc mo ta bing he phuang trinh phirc tap Zoeppritz [3] Su' dung phuang phap b i l n doi t u y l n tinh gan dung va chi giO' lai phIn bae 2, Shuey [2] dua phuang trinh sau: R(Q)=Rp + Gsm"Q (1) Trong do: R(9) la he so phan xa ciia song dpc CO goc tai AV, Ap la he so phan xa eiia song dpc CO goc tai 90° G- V, V' Ap ^AK, + 2- ^ p V, t h i hien sy thay doi tai cac khoang each thu no trung gian Phuang trinh (1) la t u y l n tinh bieu d i i n R(6) dual dang ham so eua b i l n sin2 Khi chiing ta eo the tien hanh phan tich bien dp dja chin dual dang hIi qui tuyln tinh de xac djnh he so chan Rp va gradient G ciia ham tuyln tinh T i i n hanh phan tich cho tat ca cac mach dja chan se cho k i t qua la mat d t thupc tinh AVO: Thupc tinh he so ehan Rp ehinh la mat e l t cpng eiia song phan xa dpc Kp vai goc tai 90°, thupc tinh gradient G chira dyng thong tin v l song phan xa dpc Kp va ngang Vs Gia thilt rang ty s i Fp/Fs = thi cong thu'c tinh G = R,-1R, (2) gradient G se tra thanh: Trong do: ih Al-', Ap' la he so phan xa eua song ngang co goe tai 90° Phuang trinh (2) eo the viet dual dang: Rs = iRp - G)/2 Ro rang la hieu s i ciia thupc tinh he s i ehan va gradient sau hieu chinh bien dp se la thupc tinh t h i hien g i n dung mat e l t song phan xa ngang Dieu eho phep chiing ta sir dung phan tich AVO d l danh gia dj thuang bien dp: Neu dj thuang bien dp x u l t hien tren thupc tinh he s i chan Vp (mat e l t song phan xa doe) ma khong x u l t hien tren mat d t gia song ngang Ks (lly thupc tinh he s i chan tru di gradient) thi dj thuang bien dp eo the lien quan tai via eat k i t chira Phuang trinh (1) dugc Verm va Hilterman [4] biln doi thanh: R{e)=Rp Trong do: PR = cos'e+PRsm'e Aa (3) a he s i phan xa Poisson Aa la sy thay doi eua ty so Poisson Og^.g la ty so Poisson trung binh Gia thilt ring a^,^^ = V^ ta co PR = % AO va phuang trinh (3) tra thanh: R{Q)=R^+i'^ &a~RAsm'd (4) So sanh phuang trinh (1) va (4) ta eo G = % Aa - Rp hay: Aa = {Rp+ G)*% (5) Phuang trinh (5) cho thIy n l u lay thupc tinh he so ehan cpng vai gradient se cho k i t qua la sy thay doi ty s i Poisson ACT Ty so Poisson a lai lien quan d i n (Vp/Vs)2, do sy thay doi ty so Poisson CO gia trj am se lien quan den noe ciia via eat k i t chira sy thay doi ty so Poisson CO gia trj duang se lien quan den day ciia via cat k i t chira DAU K H i - S 12/2010 29 T H A M DO - KHAI THAC D A U KHi Ngoai ra, n l u l l y tich s i ciia thupc tinh he so ehan va gradient (Rp * G) ehung ta se duge thupc tinh mai rIt huu hieu viee phat hien cac via eat k i t chira co dp ring cao (gay dj thuang AVO loai III) Cac via cat k i t dang co ca thupc tinh he s i chan va gradient vai gia trj am lan do tich so ciia chung se co gia trj duang rIt lan cae via cat khong chira se eo bien dp y l u va tich s i (Rp * G) co gia trj am Thupc tinh cung cho phep phan biet eae dj thuang bien dp lien quan d i n vai cac dj thuang bien dp khac 1.3 Phan tfeh AVO su' dung thj Phan tich AVO sir dung thj la mpt phuang phap hO'u hieu d l minh giai eae thupc tinh AVO He so ehan Rp dugc bieu dien cung vai gradient G tren thj la mpt eong eu tryc quan bieu d i l n cac dj thuang AVO giup chung ta xae djnh ro han cac dac tinh ciia da chira Rutherford and Williams [5] dua mpt he thong phan loai cac dj thuang AVO tuang irng vai eae via ehu'a khac (Hinh 2) loai dj thuang AVO dugc djnh nghla dya tren viee xae djnh vj tri eiia t i n g noc va t i n g day eua via chira tren d l thj Sau nay, Castagna and Smith [6] djnh nghTa them dj thuang AVO thir nhu sau: - Dj thuang AVO loai I dugc ve a goc phan tu thir vai he s i chan duang va gradient am Loai dj thuang lien quan d i n cac ranh giai co tra khang am hpe lan va ty so V/Vs nho han so vai t i n g chan - Dj thuang AVO loai II lien quan den cac via eat k i t vai he so chan nho nhung lai CO gradient co gia trj am lan Loai dj thuang rIt kho co the phat hien tren mat d t dja c h i n vi chung thuang la cac dj thuang bien dp y l u - Di thuang AVO loai III la dj thuang lien quan den cac dj thuang bien dp lan va n I m 30 DAU KHi -S6 12/2010 0.20 0.16 ''"x 0.12 m o.oa t- 004 [Class IV| \ ^ •o 000 m O -0.04 > < 0.08 -0.12 |aass l| Class II jClass lll| \ -0.16 ^IV III -0.20 -0 20 -0 16 -0 12 -0 08 -0.04 0.00 0.04 08 12 0.16 0.20 AVO Intercept (A) Hinh Phan loai di thwang AVO theo Rutherford va Williams (loai I, II va III) cung vai loai IV ciia Cagtana va Smith Hinh ve dwac sira tw [7] vai cac sd La Ma tai goc thi hien sd thir tw cac goc phin tw tren dd thi a goc phIn tu thu" Dj thuang the hien cac via cat k i t chira co dp rong lan - Dj thuang AVO loai IV n I m a goc phan tu thu' Loai h i l m gap nhung x u l t hien cac via eat k i t ehu'a CO dp rong eao bj chan bai cac t i n g set cirng co ty s i K/FJ cao han chut it so vai da chira 1.4 Phan tfeh AVO sir dung eae tham so LambdaRho va MuRho Goodway [8] giai thieu mpt phuang phap phan tich AVO sir dung cac tham so LambdaRho(Ap) va MuRhoijup) (phuang trinh 6) eho phep phan biet tot han cae dac tinh vat ly ciia da chira) so vai phuang phap phan tich AVO thong thuang sir dung ty s i F/Ks (phuang trinh 7): ^pp(e) = - [ l + t a n ' e ] ^pp(e)= A(X + 2[i) -4^sin F„- X + 2ii F„- • ^ + i r i - tan-e l ' ^ ( ) u _AF, 2cos'e F„ 4L F„- F (7) Trong do: ? va n la eae tham s i Lame va p la mat dp Cac thupc tinh cho phep chung ta hieu biet sau sac han da chira vi chung chia tach cac dae tinh cua da chira nhu dung djch va thach hpe theo eae tham s6 Lame dya tren phan xa dja c h i n PBTROVIBTNAM Phan tich AVO djnh lu'O'ng Trong dja c h i n phan xa, nhu d u tinh toan cac tham s i : Van toe song dpc va song ngang cOng nhu mat dp cua cac lap dat da dual sau su' dung s i lieu dja chan thu no tren mat d I t la moi quan tam nghien ciru tu' lau Viee tinh toan dugc eae thong tin each djnh lugng cho phep chung ta tien hanh phan tich thach hoc chinh xae gop phan vao viee tham d i u tryc t i i p sir dung tai lieu dja chan Phan tieh AVO djnh tinh dya tren cac thupc tinh he so chan va gradient nhan dugc tir phuang trinh gan dung ciia Shuey khong cho phep chung ta tinh toan each djnh lugng eae tham so dja chan Buac t i i p theo phan tich AVO se la phan tich djnh lugng de xac djnh eae tham s i noi tren sir dung bien dp cua tai lieu dja chan truae cpng (phan tieh AVO ngugc) Phan tieh AVO djnh lugng g I m buac chinh: Mo phong AVO thuan va phan tich AVO ngugc Buac thif nhlt dugc t i i n hanh bing each xay dyng mo hinh van t i e va mat dp sau mo phong tai lieu sir dung phuang trinh Zoeppritz hoae phuang trinh song (xem phIn 3) Buac thir hai bao g I m viec cap nhat mo hinh d l tao sy phu hgp han giira s i lieu mo phong va s i lieu thyc dja (Hinh 3) SLP dung bien dja chan phan tich AVO Ca sa toan hpe eua phuang phap phan tieh AVO tren thyc te dugc xay dyng sir dung bien dp tuang d i i dual dang he s i phan xa hoae bien dp phan xa da duge hieu chinh theo bien dp cua song tai Tuy nhien, viec ap dung phan tich AVO lai dugc tien hanh tren tai lieu dia c h i n thu no sir dung bien dp ciia mach dja c h i n (bien dp tuyet doi) O i l u dan den cau hoi kha quan trpng: Lam ehung ta CO t h i nhan duge bien dp tuang d i i phan tich AVO chung ta chi c6 tai lieu dja chan vai bien dp tuyet d i i ? Vi du bai bao [9] ciia minh Smith & Gidlow v i l t : a (8) (3 Trong 66 a = Vp va /5 = Fv -'-^sm^e,+-tan-e 2a' va fi == - - ! ^ sin a' (9) Ca hai phuang trinh (8) va (9) deu khong co thir nguyen; chung bao g I m bien dp tuang d i i Tuy nhien, Smith & Gidlow t i i p tuc va viet " n l u bien dp that ciia tu'ng mach dia c h i n la a,, thi sai so binh phuang trung binh " se la: Aa -i^: Ap (10) Tiep theo ong dua k i t qua phan tich h I i qui binh phuang nho nhlt cho a va b: Hinh Sir dung phan tich AVO dinh iwang di tinh toan van tdc sdng doc, sdng ngang va mat Cac dwang cong mau den la md hinh trwac phan tich AVO ngwac Mau dd la md hinh sau da cap nhat sir dung phan tich AVO ngwac Mach dia chin md phdng (mau xanh) sau phan tich AVO ngwac phii hap kha tot vai vai mach dia chin thwc dia AV V I«,c, (11) Trong V dai dien cho a va DAU KHi-so 12/2010 31 T H A M DO - KHAI THAC D A U KHi p C, la cac trpng s i khong co thu' nguyen bai vl ehiing chi bao gom tong va tich so ciia cac b i l n khong thu' nguyen A va B Do cac gia tri a- hien nhien cung la cac dai lugng khong co thir nguyen, hoae da dugc hieu ehinh theo bien dp song tai Cae gia trj bien dp tuyet doi ciia mach dja chan CO the duge viet dual dang Ka^, K la hang s i hieu ehinh dugc gia thilt la khong bilt Do phuang trinh (11) se thanh: ^';r=i(^«.)c, (12) Trong Ka- la cac gia trj bien dp ciia mach dja chan Phuang trinh (8) liie tra thanh: KR,,{Q,)=A, K Aa + B K Ap (13) Vai cac dai lugng ngoac dugc tinh toan sir dung phan tieh h I i qui Phuang trinh (13) eho thIy, d l tinh toan dugc bien dp tuang d i i tu' bien dp dja c h i n , chiing ta d n phai xac djnh dugc gia trj ciia K N l u khong xac djnh dugc K thi chi phan tich AVO djnh tinh mai CO the dugc t i i n hanh phan tich AVO djnh lugng thi khong t h i Phan tich AVO ngugc sir dung bien dp dja c h i n khong dugc hieu chinh theo cac he so phan xa se eho k i t qua khong chinh xac v l eae tham so van t i e song dpc, song ngang va mat dp Viee xac djnh gia trj cua Kdoi hoi chung ta phai t i i n hanh mo phong tai lieu dja c h i n vai nhiiu khoang each thu no khac sir dung tai lieu sonic luang eye Tiip theo, bien dp RMS (root mean square) dugc tinh toan cho moi mach dia c h i n mo phong va hieu chinh vai mach dia c h i n thyc dja tuang irng Co phuang phap de mo phong tai lieu dja c h i n vai nhiiu khoang each thu no khac nhau: Thuat toan sir dung phuang trinh Zoeppritz va thuat toan sii' dung phuang trinh song - Thuat toan sir dung phuang trinh Zoeppritz xac djnh goe tai eiia song tai cac ranh giai phan xa b i n g phuang phap ve duang truyen song 32 DAU KHi - S6 12/2010 (ray tracing) TO' cac gia trj goc tai va dac tinh thach hpe phia tren va phia d u a l ranh giai phan xa, bien dp phan xa d u g c tinh toan sir dung he phuang trinh Zeoppritz Thuat toan chi ehinh xac cho song phang tren tu'ng ranh giai phan xa rieng le Tren t h y c t l song d u d u g c t r u y i n tai nhieu mat phan xa va tao hang loat cac song phan xa n h i i u l i n va song c h u y i n doi giua cac ranh giai Cac song co the gay anh h u a n g d i n tin hieu phan xa va lam thay doi chung Do thuat toan ehi CO the mo phong tin hieu phan xa va co the cho k i t qua khong chinh xac, dac biet la d i i vai mo hinh phan lap mong co dp t u a n g phan v l tra khang am hpe lan - Thuat toan sir dung phuang trinh song co the khac phuc d u g c nhuge d i l m eiia phuang phap tren bang each mo phong d i n g thai t i t ea eae loai song Vai viec co the mo phong song phan xa n h i i u lan va song chuyen doi, thuat toan v l ly thuylt r I t chinh xae cho mo hinh chilu (khong co sy thay doi theo c h i l u ngang) Tuy nhien, thuat toan duge t i i n hanh tren m i i n f-k nen n l u mo hinh khong dugc xay dyng chi t i l t se gay cae song gia tao Do viec thyc hien thuat toan tren so mo hinh co t h i ton nhiiu thai gian may tinh Ket luan Trong bai bao chung toi da giai thieu tong quan v l phuang phap phan tich AVO cOng nhu thao luan v l each sir dung bien dp dja c h i n truae cpng phan tieh AVO Chung toi chia phan tich AVO loai chinh: Phan tich AVO djnh tinh va djnh l u g n g Trong phan tich AVO djnh tinh co the d u g e tien hanh su' dung bien dp dja ehan tuyet doi thi dp ehinh xac ciia phan tich AVO dinh lugng lai phu thupc rIt n h i i u vao viec hieu chinh bien dp tai lieu dja c h i n theo cac he so phan xa Truae t i i n hanh phan tieh AVO ngugc, tai lieu dja chan thyc dja n h l t t h i l t phai d u g c hieu chinh sir dung hang s i hieu chinh K d u g c tinh toan b i n g phuang phap mo phong va doi chieu vai tai lieu thuc dia PETROVIBTNAM Workstation Workstation Workstation SUN BLADE 2000 LAN/INTRANET & Server/UNIX PC/LINUX PC/LINUX He thing may tinh phuc vu cho cdng tac xir ly va minh giai dac biet Tai lieu tham l