708 M6 hinh dieu khign he thong bom ep nu 6c khai th^c dau trong cong nghe khai thac dau khi M O HINH DIEU KHIEN HE THONG BCnvl EP N l / O C KHAI THAC DAU TRONG CONG NGHE KHAI T H A C DAU KHI Tran H6n[.]
Trang 17 0 8 M6 hinh dieu khign he thong bom ep nu-6c - khai th^c dau trong cong nghe khai thac dau khi
M O H I N H D I E U K H I E N H E T H O N G BCnvl E P N l / O C
-K H A I T H A C D A U T R O N G C O N G N G H E -K H A I T H A C D A U -K H I
Tran H6ng Phong
XNLD Vietsovpetro
TOM TAT
Bdo cdo trinh bdy phuong phdp mdi gidi hi phuong trinh dgng luc phi tuyin md khdng phu
thudc ro rdng vdo thoi gian nhu hi thdng bom ep - khai thde ddu Phucmg phdp tgm lap khodng
trdng gida md hinh thiit lap vd ly thuyit khong gian - thdi gian Md hinh tgo ra cd khd ndng kiim
tra cdc qud trinh thdng qua cdc cdng thirc thi hiin mdt cdch dinh lugng mdi quan hi xdc sudt giira
cdc yiu td Nd cho phep xdc dinh mirc do tu do cua todn bd cdc yiu td trong hi vd mdi quan hi cua
' ' ^ ' '
chung Nd cung thiit lap dugc cdc hdm ddi tugng dieu chinh di xdc dinh dugc gid tri tdi uu ciia hi,
v.v Nguyin ly ndy dugc dp dung di tdi uu hod bom ip nu&c cho md ddu mdng Bgch Hd
Phuong phdp mdn vd md hinh diiu hdnh ndy cd thi dugc dp dung rdng rdi di kiim
tra qud trinh bom ip nu&c - khai thde ddu trong tucmg lai
DAT VAN DE
Trong c6ng nghe khai thac dau khi, bom ep nuac, khi vao via la phuang phap phi
bien de duy tri ap suat via, keo dai thai gian tu phun cua cac gilng khai thac va la mot
trong nhting bien phap thu h6i dau hieu qua nhat
Ciing vai sir phat trien cua cac phuong phap tren, cac bai toan tii uu qua trinh khai
thac dau tap trung ve ky thuat tinh toan, phat triln phuong phap c l diln Day la each tilp
can kh6ng phan tich chi tiet cac qua trinh phan tir ma khao sat cac hien tugng tren quan
diem duy nhat do la quan diem ve su bien d6i nang lugng trong cac hien tugng do
Toan bg cac bai toan xem xet, chu ylu sir dung phuang phap co hoc dong chay nhilu pha
chuyen dong frong m6i truong x6p He phuang trinh co so bao gIm cac phuang trinh thuy nhiet
dong luc hoc, cac dieu kien ban dau, dieu kien bien va cac he thiic dong kin Ngay nay, vod ky
thuat hien dai, he phuang trinh thu nhan dugc biin d6i vl dang thuan tien dk giai sl va cac loai
chuang trinh tinh dugc hinh thanh hiy theo dang mo ph6ng dl xac dinh gia tri cac biin Pj, Sj, Cj
(i = 1,2, 3) tai tat ca cac diem luod ciing nhu luu lugng gilng theo thoi gian t
Cac m6 hinh da dugc nghien ciiu tren thi gioi dugc bilt cho din nay la:
- Dong tham mgt pha dAu hoae nuoc trong m6i truang xip co chenh ap hay m6 hinh Darcy,
- Dong tham mot pha chat long khae mau hay m6 hinh dong chay "kbac mau",
- D6ng tham mot chieu diing nuoc day dau hay m6 hinh Leibenzon-Masket,
- D6ng tham hai pha dau va nuoc hay m6 hinh Buckly-Leverett,
- Dong tham hai pha c6 tinh den lire mao dan va trong truong,
- Dong tham hai pha hoa nhau theo n6ng do Cj,
- Dong tham hai pha trong moi truong nirt ne hay mo hinh Hell-Shaw,
- Dong tham nhieu pha trong m6i truong x6p
Trang 2Tuygn tap bao cao Hgi nghj KHCN "30 nSm Phu khi Vigt Nam: CQ- hoi moi, thach thiic moi" 709
Cae e6ng trinh tren da gop phan lam sang t6 co cbl boat dong ciia cac loai chat luu chuyin dong trong m6i truong via, du bao cac giai doan ngap nuoc, danh gia trtr lugng khai thac c6ng nghiep va can cir vao dae dilm dich chuyen eiia mat phan each dau nuoc de xac dinh nhip do bom ep va khai thac t6i uu Cac nghien ciiu tren da giai quyet nhung van
dl t6ng quat vl phan tich, ting hgp he th6ng nham phuc vu thiet ke khai thae va nho do
ma c6ng nghe thiet ke khai thac co nhimg buoc tien bo dai
Tuy nhien, ban che ehii yeu eiia cac phuang phap c6 dien la 6 ch6: de giai he phuong trinh co so ta phai dat cac dieu kien phu gia dinh (dieu kien ban dau, dieu kien bien) sao cho nghiem ciia bai toan t6n tai duy nhat va phu thuoc lien tuc vao cac dieu kien phu hay c6n goi
la bai toan "dat dung dan" Tren thuc te, he th6ng khai thac dau c6 nhieu nhan t6 ngau nhien kh6ng the doan truoc dugc tac dong: cau true dia chat ciia via va phan b6 cac th6ng s6 cua no nhu dien tich, do day, do r6ng, do tham, do bat d6ng nhat v.v De hieu biet tuong tan ve chiing can phai c6 thai gian thu thap th6ng tin, nen cac dieu kien phu cting bj chi ph6i boi cac nhan t6 ngau nhien nay, va tir do lam cho ca vi tri dat cac gieng khoan trong m6i truong via ciing deu e6 do bat dinh nhat dinh, xac suat thanh c6ng theo du kien tang hay giam phu thuoc vao do bat dinh nay Vi the, ket qua cac bai toan c6 dien trong c6ng nghe khai thac dau khi hau nhu chua bao gio dugc coi la bai toan "dat dung dan" nen con nhiing "viing mo" kh6ng xac djnh dugc Ngoai ra, co nhieu van de nay sinh ma cac phuong phap truyen th6ng kh6ng giai thich dugc tron ven nhu: m6i lien he co ban giiia cac gieng bom ep va cac gieng khai thac dang d6ng thai boat dong, van de bao dam nhjp do khai thac dii va chinh xac phii hgp voi mat
do mang de ban che luai nuoc xuat hien trong via, van de tieu chi danh gia boat dong ciia cac gieng nham chi ra cac phuong phap cai tien kip thoi va co hieu qua Do do, phuong phap truyen th6ng chi co tinh du bao ve t6ng the ma kh6ng dua ra dugc ly thuyet dieu khien theo tinh hu6ng co tinh den nhtrng yeu t6 ngau nhien chi ph6i Trong do co nhting tinh hu6ng bat nga neu sai lech qua can bang se dan den cac phan nhanh khae vi du nhu thay vi c6n duy tri dugc che do khai thac tu phun trong khoang thai gian lau hon ntra thi gieng lai bi ngap nuoc qua nhanh do vi tri dat gieng kh6ng thuan lgi va luu lugng bom ep kh6ng dugc dieu chinh kip thod ma trii lugng khai thac tiem nang trong viing nghien ciiu van c6n nen phai t6n them chi phi b6 sung kh6ng dang co De giai quyet nhung van de neu tren, cac ly thuyet c6 dien xay dung tren quan diem nang lugng voi nguyen ly tat dinh can phai dugc b6 sung bang ly thuyet xay dung tren quan diem thong tin vod nguyen ly tap hgp
XU LY SO LIEU VA XAC DINH DO DO
Xet he th6ng bom ep nuoc - khai thac dau tren quan diem th6ng tin dieu khien theo m6 hinh sau:
^115
i
X,
X2
Xn
Y,
'Y
d d a y :
X = {Xi,X2, Xn}: tap hgp cae phan tir dau vao ciia he th6ng (sir kien bom ep nuoc)
Y = {Yi,Y2, Yn}: tap hgp cac phan tir dau ra ciia he thing (su kien khai thae dhu)
Trang 3™ >16 hinh digu khign he th6ng bom ep nu-pc - khai thac dSu trong cong nghe khai thacdauJvM
^ - Nhieu nen, no "hap thu" mot lugng th6ng tin tir X khi nuac thay thi dau lam nin
de duy tri ap suht via, no co them tinh nhieu cong ti khi nuoc bat dau xuat hien 6 dau ra
Di tim moi quan he nhan qua gitra X, va Yj nao d6 trong vimg la tim each dinh lugng th6ng tin vl sir phan h6i ciia cap d6i tugng tac dong (X|,Yj) Do mau s l lieu bat cap theo hang doc nen kh6ng phu thuoc m6c thoi gian De xac dinh sir thay dii ciia gia tri y, (san lugng khai thac dau tan/thang) theo gia tri Xj (kh6i lugng bom ep nuoc m^/thang) ta sap xep s6 lieu cac phan tir eiia Xj theo hang va phan tir ciia Yj tuong img theo X, Thuc hien phep so sanh timg gia tri phan tir ciia Yj tuong d6i voi nhau theo thir tu truoc, sau Cae dau
© dugc xem la co phan iing tuong quan Ty s6 cac dau duong tren t6ng s6 cac phep so sanh dugc goi la xac xuat tien nghiem ciia sir kien dong thai (X„Yj) do quan he nhan qua
Bang 1
+
9
-i-+
6 +
_
3 -+ +
10 +
+ + + +
+
-1-4 - -t- -1 H
8 +
-1-+
-1-+
-t-
-I-23
n{n-\)
6 day:
P(Xj,yj): Xac xuat tien nghiem gitra 2 sir kien X, va Yj
D (+): T6ng s6 dau + ciia phep so sanh d6i mot truoc sau
n{n-\) X X , , , ,
: I ong so phep so sanh S6 lieu xir ly P(Xi,yj) mang y nghia th6ng tin va phii hgp vai do do th6ng tin l(x,) = -lg[P(Xi)] Tuy nhien, he thong cua chiing ta la dii tugng vat ly cu thi: he thiiy khi trong m6i truang tham, nirt ne bat d6ng nhat, kh6ng dang huong nen chiing c6n phai th6a man cac dilu kien ciia do do tren quan diem tap hgp Do la do do kolmogorov, o day chiing ta tap trung kiem tra sir phii hgp ciia s l lieu xir ly voi do do kolmogorov
Qua trinh bom ep nuoc - khai thac dau duge bilu dien bang ng6n ngii- toan hoc nhu sau: Qua trinh khai thac dau:
1 1 I
lugng dau lugng dau bi lugng dau khai thac duge nuoc chiem ch6 con lai trong via
Trang 4Tuygn tap bao cao Hoi nghi KHCN "30 nam Dau khi Viet Nam: Co" hoi moi, thach thuc moi" 711
Gia sir he thing duy tri ap suat via co dinh, viec thay thi the tieh dau trong m6i
truong via boi nuoc bom ep dugc thu toan bo vao san lugng cac gieng khai thae San
lugng ciia cac gilng chi phu thuoc vao uu the vi tri va van t6c luu chat (kh6ng gian, thai
gian) djch chuyin trong via din cac gieng mot each ngau nhien va dau dich chuyen trong
via hoae din gilng nay, hoae sang gieng kbac ma kh6ng the hien dien o ca nhieu gieng
ciing luc Thing ke san lugng dau khai thae hang thang (la cae phan tir ciia tap hgp Yj (j =
I ^ m) a cac gieng la d6c lap th6ng ke nen tap hgp [Y] kh6ng co phan giao gitra cac phan
tir Nhu vay, [Y] co tinh chat xung khae timg d6i mot va boat dong ciia m6i gieng la mot
phan tir doc lap trong he th6ng nen tap [Y] g6m bo sir kien {Yj, Y2, Ym} la doc lap
trong t6ng the vi s6 lieu xir ly P(XY) la ket qua d6ng thoi ciia quan he nhan qua nen ta co
the lap mat phang trang thai ciia cac phan tir nhu sau (Bang 2):
Bang 2
X,
xi
Xn
Yi
P(xi.yi) P(x2,yi)
P(xn,yi)
Y2
P(xi,y2) P(X2,y2)
P(Xn,y2)
Y,„
P(xi,ym) P(X2,ym)
P(Xn,ym)
Va quan he xac suat :
P ( Y , Y J = P(Y,).P(Y2) P(YJ (dge lap, d6ng thai) (3) Mat kbac, trong m6 hinh th6ng tin kh6ng gian - thai gian ciia chat luu chuyen dong
trong via co cau true kh6ng ap dat, no dugc phan b6 theo nhu hien trang tu nhien cua via;
hieu suat thu h6i dau cang cao khi ta tang dan mat do gieng khoan trong mang Vi vay,
neu ta them Ym+i Y^+i vao mang do khoang each gan anh huong qua lai ciia cac gieng
Ion nen san lugng ciia timg gieng se giam Tren quan diem toan hoc ta co the tang cac
phan tir [Y] den vo ban va san lugng m6i gieng tien dan den 0, ta co:
[YnJ CO tinh chat Y^, ^ Y^+i
va Y,Y2 Y,„ = V, thi P(Y,) n T ^ ^ 1 => I(Y„0-l^r^r::r 0 (4) Nhu vay, tap [Y] la truong boren hoan toan th6a man do do Kolmogorov
Tuong tu d6i voi tap [X]
Qua trinh bom ep nuac:
'I n n
lugng nuac bom ep
tir cac gieng
lugng nuac chiem cho lirgng nuoc dau trong via khai thac dugc
Trong kh6ng gian via hai qua trinh [jX, va p | X , la dii lap nhau theo thod gian, khi
gilng khai thac bat dau ngap nuoc, mot phan nuac bom ep tir dau vao chuyin dong thing din
dau ra khong thay the the tich dau trong via nen lugng nuac tren khong mang theo lugng
th6ng tin nao giQ-a dau vao [X] va dau ra [Y] Vi sl lieu xir ly la san lugng dau thu dugc do
Trang 5712 M6 hinh dilu khign he thong bom ep nuoc - khai thac dau trong cong nghe khai t h a c j i a u j ^
nuac chiem eho chir kh6ng tinh phan nuoc ciing chay vao gilng khai thac, vi vay trong m6 hinh th6ng tin ta co the quy nguyen nhan ciia viee suy giam mli quan he gitra nuoc bom ep va dau khai thac do ngap nuoc la vi nhieu va do ngap nuac cang nhilu thi nhieu cang Ion Nhu
vay, khi via bat dau ngap nuoc ngoai nhieu nen £, se xuht hien them nhieu cong £,!• Va tren quan diem th6ng tin lugng tin 6 tap Q X, da tra thanh nhieu eong:
f I N, thong tin ~ ^
Tir(2),(5),(6)tac6:(UJ0)i, < » (fi^^ )m,n
(6)
(V)
Ta dl nhan thay rang, the tich dau con lai la the tich kh6ng xac dinh vi cau triic via la ngau nhien nen no phu thuoc vao vi tri dat gieng va mat do mang khai thac Viec sir dung hieu qua cac gilng hien co trong mang, b6 sung va sira chira kip thod cac phan tir ciia he th6ng, dilu khien nang cao he s l quet la dieu kien tien quyet de tang he s6 thu h6i dau, giam phan
111
PjF^ ciia via (theo (7)) ciia via va day ciing chinh la muc dich ciia bao cao nay
MO HINH DIEU KHIEN HE THONG
^ r r r
2 Tan suat lien thong gifra cac gieng bcm ep va cac gieng khai thac P(Xi,yj)
P(Xj,yj) ve thuc chat la he s6 truyen th6ng tin ciia nuoc bom ep tir gieng bom ep X, th6ng qua dau khai thac dugc tir gieng khai thac Yj trong vimg phan hoach No la ty s6 dau hieu "duong tinh" (tang luu lugng dau) ma Yj nhan dugc khi ta tang mot kh6i lugng nuoc bom ep 6 Xj trong ciing mot don vi thai gian tren t6ng s6 ian tac dong theo ly thuyet P(Xj,yj) ve y nghla co hoc chinh la phan phi tuyen trong he dong lire vi n6 lien quan den s6 gia van t6c khai thac dau va s6 gia van t6c bom ep nuoc trong timg phan tir Dai lugng nay chi ra ty suat m6i quan he nhan qua giiia hai phan tir Xj va y^ co quan he ham s6 (Hinh 1):
P(x„yj)
Hinh 1: Quan he ciia P(xi,yj) theo thoi gian t
Trong do:
T| - giai doan hinh thanh ph6ng nuoc
T2 - giai doan hoat dong 6n dinh dieu khien dugc, chua ngap nuoc
T3 - giai doan ngap nuoc: 1) ngap nuoc co luod nuoc; 2) ngap nuoc kh6ng co luoi nuoc Ngoai ra, khi gieng bom ep Xj dugc bom voi do nhan cao nhat Qx, max, ta co tan suat
lien th6ng P(xi,yj) {V j = 1 -=- m} Ion nhat, gia tri ciia Q^j max phu thuoc vao vi tri ciia X, dii
vai cac Yj trong viing Q^j cang thap, P(xi,yj) cang thap Ta co quan he ciia Q^, va P(x,.yj)
theo Hinh 2:
Trang 6Tuygn tap bao cao HQI nghj KHCN "30 nam Dau khi Viet Nam: Co hoi moi, thach thiic moi" 713
v<;xi max Vxi
Hinh 2: Quan he giua P(Xi,yj) va Qxj
Tren thuc te, boat dgng ciia he th6ng phu thupe nhieu vao nhting yeu t6 chu quan cua nha dieu hanh va nhQ-ng thay d6i khaeh quan trong m6i quan he gitra cac phan tir ciia he th6ng qua viec thay doi tinh co hay c6 y luu lugng nuoc bom ep hoae san lugng dau khai thae Do do c6 kha nang dieu khien dugc tan suat P(X|,y|) a giai doan 6n dinh va do cung chinh la ca so cua phuang phap dieu khien he th6ng eiia ehiing ta
2 Entropy dau vao va dau ra ciia he thong
Chiing ta da xem xet, lam sang t6 y nghTa vat ly va th6ng tin ciia s6 lieu xir ly va m6i quan he ham s6 ciia P(Xj,yj) theo thai gian Bay gia, ta tiep tuc xet tinh chat eiia xac suat dau vao va dau ra ciia he th6ng:
Gia sir m6i phan tir bom ep Xj eX c Q dong gop phan minh trong doi hinh bom ep
X voi xac suat th6ng tin P(x,):
[Px] = [P(x,) P(x,)]
Tuong tu, gia sir m6i phan tir bom ep Yj s Y
khai thae Y voi xac suat th6ng tin P(yj):
[Py] = [P(yi) P(ym)]
Tuong tu, tinh cho toan he th6ng ta e6 ma tran xac xuat sau:
r P(xi,yi) P(xi,ymr\
(8)
Q dong gop phan minh trong doi hinh
(9)
[P(X,Y)] = ^ P ( x „ y , ) P ( x „ y ^ (10) Tir day suy ra P(xj,yj) la xac suat tien nghiem dugc tinh theo c6ng thirc (I)
Tir ma tran xac suat [P(X, Y] ta co:
nX,) = Y.^{x,.y^) \ (11)
7 = 1
P{Y,)-±P{x„y,)
i=\
C6ng thire (11) tuong duong voi cac c6ng thire vl xac suht ding thoi
Trang 7714 Mo hinh digu khign he thdng bom ep nu-oc - khai thac d§u trong cong nghe khai thjcjiaujvh|
Tir ma tran xac xuat tren can cii vao eae mli quan he giQra cae phan tii' trong tap hgp
ta CO the djnh nghia 5 truong sir kien:
• Trucmg su kiin ddu vdo
- M6i quan he tuong duong giiia cac gieng bom ep voi Entropy H(X)
- M6i quan he nhan qua giua gieng bom ep Xj voi tap hgp [Y] trong viing voi Entropy H(X,)
• Tru&ng sir kiin ddu ra
- M6i quan he tuong duong gitra cae gieng khai thac voi Entropy H(Y)
- Mli quan he nhan qua giQ'a gieng khai thac Yj voi tap hgp [X] trong viing voi Entropy H(Yj)
Truong t6ng hgp ciia toan he th6ng voi Entropy H(X,Y)
d day, ngoai truong hgp H(X,Y) co ngoai dien rgng, bon truong c6n lai co noi ham rat phong phii, chiing cho phep ta xac dinh ham muc tieu de:
• Cue dai hoa kha nang thay the dau boi nuoc 6 trong via den timg phan tir trong he th6ng bang each so sanh va dieu chinh bom ep gitra cac phan tir bom ep tir Entropy H(X)
• Xac dinh thai diem va vi tri b6 sung them gieng khai thac co hieu qua nhat de tang
he s6 thu h6i dau ciia via tir H(Xj)
Nhu vay, qua trinh dieu khien Entropy ciia he th6ng tien den cue dai la qua trinh chuyen quan he tuong duong ciia tap X thanh quan he binh dang trong tap hgp ma cac Entropy chinh la cac ham muc tieu M6 hinh nay hoan toan thoa man viec dieu khien he thong duy tri ap suat via va thay the dau bang nuoc bom ep trong via dat dugc he s6 cao nhat theo yeu cau dieu khien dat ra
Tom lai, tir ma tran xac suat tien nghiem [P(XY)] bang ly thuyit th6ng tin ta co the
"chup anh" trang thai ciia he th6ng dieu khien 6 giai doan vira xem xet dl dilu chinh m6i quan he ciia cac phan tir trong cac tap phan hoach sao cho chiing co lugng tin trung binh (entropy) cue dai
Tir (11) suy ra cac xac suat hau nghiem tren co so d6i voi truong hgp entropy ding thai va entropy dieu kien giiia cac phan tir trong cac tap phan hoach theo quan he ngang hang XY, X, Y:
H(XY) =- Y.llnx,,y,)hP{x„y^)
7 = 1 , = 1
H(X) =- t,P{x,).\gP{x,)
/=!
Tnx„y,)
C)day: P{x,)- '^'
tl III
Yl^nx„y,)
/ = i j=\
H(Y) =- Y^P{y^).\gP{y,)
j = i
Trang 8Tuygn tap b^o cao Hoi nghj KHCN "30 nam Phu khi Viet Nam: Co hoi moi, thach thiic moi" 715
II
/ = i / = ]
3 Lu-o-ng tin co dieu kien ciia phan tu" khai thac Yj khi xuat hien XJ: I(yj\X|)
Bay gio ta xet din xac suat hau nghiem dugc suy ra tir xac suat tien nghiem tren theo
quan he nhan qua:
Lugng tin rieng co dieu kien ciia phan tir khai thac yj khi xuat hien Xj la dai lugng chi
"phan img" ciia phan tir khai thac yj khi bi tac dong boi su xuat hien cua sir kien bom ep
Xj nao do:
I(y>,) = - log P(y>,) (13)
O day, PCV/br,) la xac suat th6ng tin co dieu kien ciia phan tir khai thac yj khi phan tir
bom ep Xj lam viec
Mat kbac, ve y nghia toan hoc ?{yj\Xi) cung la he s6 truyen th6ng tin ciia rieng X, den
cac YJ (j = 1 -^ m) dang hoat dong trong ciing nhom phan hoach
?(yj\xd = -^r-^^^^^^ (14)
Y^Pi^.^yj)
De tim lugng tin trung binh (entropy c6 dieu kien) ciia he th6ng khai thac [Y] d6i voi
tac dong phan tir Xj trong viing phan hoach, ta ap dung c6ng thirc (8) ciia entropy co dieu
kien:
m
H(X,) = -Y^P{x„y^)\gP{y^\x^ (15)
7 = 1
Day la dai lugng dac trung quan trong trong phan tich he th6ng Neu tan suat lien
th6ng P(y/bc,) d6ng vai tro 'do nhay' gitra phan tir dau vao Xj va dau ra yj thi H(X,) chinh
la 'do do' m6i quan he cua Xj vai he thong [Y] trong viing theo quan he nhan qua
4 Lu-oTig tin CO dieu kien cua phan tu- bo'm ep Xj khi xuat hien Yj: I(Xi\yj)
Nhu chiing ta da biet, quan he giQ:a cac sir kien bom ep va cac sir kien khai thac la
quan he nhan qua, sir phan h6i cua quan he nhan qua c6 tinh thuan nghich nen trong
truang hgp nay, ta co thi xem phan tir y^ xuat hien truac va he th6ng bom ep [X] bi tac
dong boi Yj nao do, ta c6 lugng tin rieng c6 dieu kien:
\{x,\yj) = -\og?{x,\yj) (16)
6 day, V{Xi\yj) Va xac suht th6ng tin co dilu kien ciia phan tir bom ep x, khi phan tir khai thac y, boat dong Ve y nghla toan hgc P(x,\ yf) cung la he s6 truyen th6ng tin ciia
rieng Y, den cac Xj (i = 1 -=- n) dang boat dong trong ciing nhom phan hoach
P W y , ) = _ ^ ( f i l ^ (17)
I ^(^, •:>',)
( = 1
Trang 9716 Mo hinh digu khign he thong bom ep nu'oc - khai thac dhu trong cong nghe khai thac_daujvh|
Tuong tu, lugng tin trung binh (entropy c6 dieu kien) ciia he thing bom ep [X] d6i voi tac
dong phan tir Y, trong viing phan hoach, ta ap dung e6ng thire (8) eiia entropy co dieu kien :
^(yj) = - X^(^-'>^7)lognx, \;^,) (18)
(=1
5 Do du- va hieu qua cua gieng bom ep
Khdi niem vi do dw Gia sir ta co mot sir kien bom ep Xj phan b6 lugng th6ng tin den m
phan tir khai thac yj trong vung phan hoach, m6i phan tir yj nhan dugc tan suat th6ng tin eo dieu
kien P(yj\x,) Vod lugng tin rieng c6 dieu kien l{yj\x,) va entropy co dieu kien H(X,), khi do ta co:
max I{y^\x,)-H{X,) Rd(Xj) = -^ (19)
max /(>' \x,) Rd(X,) chinh la do du ciia Xj Ve ly thuyet neu tat ca Yj deu co tan suat P(x„yj) nhu
nhau theo dinh nghTa entropy thi lugng tin cue dai ma Xj co the dat dugc khi:
MaxH{x,)= Y.-^(yj \ ^ ' ) = ^(yj^^^ (20)
7 = 1
Tuy nhien, do dieu kien thuc te ve tinh ngau nhien cua cau true via, vi tri gieng va do
bat d6ng nhat ve do tham kh6ng cho phep lugng th6ng tin tir cac phan tir bom ep truyen
den cac phan tir khai thac la nhu nhau, vi vay, entropy ciia Xj thuong kh6ng the dat gia tri
cue dai theo ly thuyet do do:
H(X^, ^maxH(XJ t+i khi I(yj\x)„, -> H(X^ ,{] = \^m) (21)
Do du nay xay ra do tac dong ciia nuoc bom ep tir gieng bom ep Xj thay the vi tri
dau via den cac gieng khai thac Yj kh6ng dugc phan ph6i deu do cac nguyen nhan ngau
nhien da neu tren Mot s6 gieng khai thac san lugng qua mirc, s6 kbac do kh6ng thuan lgi
ve vi tri hoae vi ly do khaeh quan nao do khai thac dugc it (3 day, chiing ta nhan thay:
entropy ciia X, cang tien gan den gia tri cue dai thi Xj lam viec cang hieu qua vi nuac dugc
phan b6 den cac phan tir khai thac a trong vimg phan hoach cang diu Mat kbac, nlu hai
phan tir bom ep Xj va X^ co entropy rieng H(Xi) va H(Xd ciing tiln gan din gia tri cue dai
ciia minh thi phan tir nao co entropy rieng phan thip hon, phan tir ay da lam viec hieu qua
ban (neu giai doan dang xet la giai doan ngap nuoc) hoae co nhilu tilm nang hon (neu
giai doan dang xet la giai doan ban dau ciia qua trinh)
Tir CO so tren, co the danh gia hieu qua cua mgt gilng bom ep bSng gia tri do du:
gieng cang hieu qua, do du cang tien g^n din 0 (Hinh 3) Mat kbac, do du tiln din 0 cung
CO nghTa he s6 hieu dung tiln dan din 1 (Rs=l-Rd)
Rd, Rs
— R j - l - R d
Hinh 3: Moi quan he gifi-a do du Rj va he so hieu dung Rs cua Xj
Trang 10Tuyen tap bao cao HQi nghj KHCN "30 n^m D^u khi Viet Nam: Co- hoi mp-j, thach thiic moi" 7 1 7
6 Entropy boro ep via H(X)
Trong phan tren chung ta vira xet dai lugng H(Xi) bieu diln tac dong cua su kien bom ep
nuoc Xj vod he thing dau khai thac trong vimg theo quan he nhan qua Trong phan nay, de
lam ro uu thi vl vi tri cua phan tir bam ep d6i voi su kien bom ep nuoc, chiing ta de cap den
m6i quan he ngang hang gitra cac phan tir bom ep trong he th6ng vod entropy H{X) Dieu
nay CO y nghia toan dien trong viec nang cao he s6 quet tren toan vimg phan hoach, H(X)
chinh la chi s6 dinh lugng bae tu do ciia he th6ng That vay, trong mot he th6ng, m6i quan he
tuong h6 gitra cac phan tir rat quan trong, neu su tu do qua miic ciia mot phan tir nao do lam
giam tu do cua cac phan tir kbac trong he th6ng thi ciing lam giam bae tu do ciia ca he Vi
vay, dieu chinh lugng tin rieng ciia he th6ng sao cho entropy bom ep via dat cue dai d6ng
nghTa vod viec dieu khien nuoc bom ep chiem nhieu ch6 cua dau khai thac trong via nhat
Tinh toan H(X) va he s6 hieu dung cua he th6ng theo cac c6ng thiic tir 2,8 -f 2,12
7 Entropy khai thac dau H(Y)
Entropy khai thac dau a timg viing cung phai dugc dilu chinh sao cho: lugng tin rieng
cua cac gieng khai thac phai tien gan den nhau de entropy ciia he thing khai thac dat cue dai
Dieu nay c6 nghTa la: chiing ta dieu chinh he th6ng sao cho vimg anh huong ciia su
kien khai thac dau [Y] d6i voi m6i truong via la Ion nhat (do Ion phu thuoc vao dieu kien
dia chat, vi tri xay ra cac su kien (vi tri dat gieng) va mat do mang) nham tao dilu kien cho
nuac bom ep chiem ch6 mgt each trat tu trong via de phu deu via voi he s6 quet cue dai
Tuy nhien, kh6ng phai luc nao cung dieu khien dugc san lugng timg gieng theo yeu cau
dat ra, nen tren thuc te, viec dieu khien H(Y) la rat ban chi, chii yeu ta quan tam din dilu
khien H(X) Dii vay, ta cung can nhan xet rang: khu vuc nao kh6ng bao dam dugc cue dai
H(Y) do he s6 hieu dung qua thap thi nen b6 sung them gieng khai thac vao mang neu co
lgi ve kinh te, hoae phai each ly nuoc C6ng thiic tinh theo (12)
8 Kiem soat va dieu chinh he thong
Mu6n kiem soat dugc he th6ng, truac bet chiing ta can phai dieu chinh dugc cac
phan tir trong cac tap hgp cua chiing Nguyen ly dieu chinh nhu da trinh bay a cac phan
tren la dieu chinh ty suat lien th6ng gitra cac phan tir bang each tang - giam kh6i lugng
bam ep nuac va san lugng khai thac dau hang thang cua timg phan tir sao cho cac
entrpopy tuong iing tien den cue dai D6i vai toan he thong, entropy cue dai d6ng nghTa
vai he so hieu dung ciia he thong tien dan den I va chiing ta da sir dung t6i uu c6ng suat
cua timg phan tir trong he thong nghTa la phai dieu chinh sao cho:
a Doi v&i quan hi ngang hdng
• Diiu chinh khdi lugng bcrm ip
De dieu chinh entropy bom ep dat cue dai ta dilu chinh theo nguyen tac quan he
giQ-a P(Xj,yj)va Q^i nhu da trinh bay 6 phan tren:
I{X,\^, -> H(X}, {1=1 ^n) <^ H(X), -^ max.H(X),^,
Tang kh6i lugng bom ep 6 cac gilng co I(Xj) > H(X)
- Giam khii lugng bom ep a cac gilng co I(Xj) < H(X)
- Gitr nguyen cac gilng co I(x,) « H(X)