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1. c im cu trc a cht m S T en - S T Vng

Tnh n cui nm 2012, khi mng trc tam m S T en - S T Vng c m ra bi 53 ging khoan (S T en - 38, S T Vng - 15). T kt qu phn tch mu lt mng, mng nt n 2 m trn c chia thnh 2 nhm chnh: (1) magma nn xm nhp ch yu l granite v t phn nh hn l granodiorite; (2) cc ai mch pht trin nhiu giai on khc nhau, xuyn ct khi nn, gm ai mch felsic v mafi c, vi dy t mt vi mt n hng chc mt. Tuy nhin, do phm vi phn b ca cc ai mch kh hn ch nn kh c s lin kt t ging khoan ny ti ging khoan khc. S c mt ca nhng ai mch trong khi mng nng m S T en - S T Vng l yu t a cht quan trng khin mc bt ng nht v thnh phn thch hc v c trng thm cha ca khi nng mng.

Trong thn mng m S T en - S T Vng c 243 t gy phn b su t nc mng n su 4.200m. Trong , m S T en c 113 t gy vi 67

t gy gp ging khoan, m S T Vng c 130 t gy vi 56 t gy gp ging khoan. Cc t gy ny, ct qua vng nghin cu gy ph hy mng, khng ch cc khi kin trc trong mng v to thnh cc i nt n sinh km. Trong , h thng cc t gy phng Ty Bc - ng Nam xut hin vi mt nhiu nht vi 131 t gy, chim 54% tng s cc t gy c trong khu vc nghin cu. m S T Vng, cc t gy ny phn b rng khp v tp trung mt cao nht khi B, xung quanh cc ging SV-4X, SV-9PI, SV-1X, SV-6PST v mt thp nht khi A2 xung quanh ging SV-3X (Hnh 1). m S T en, cc t gy ny phn b tri u trn cc khi A, B, D v t hn hai khi C, E. Cng vi

THN DU TRONG MNG TRC TAM M S T EN, S T VNG V CC YU T A CHT NH HNG

N KH NNG THU HI DUThS. ng Ngc Qu, PGS.TS. Hong Vn Qu

Tng cng ty Thm d Khai thc Du kh

Tm tt

Thn du trong mng trc tam m S T en v S T Vng c cu trc a cht c bit phc tp, c thnh to bi nhiu h magma xm nhp, b ph hy bi nhiu h thng t gy kin to qua nhiu giai on khc nhau, b xuyn ct bi h thng ai mch dy c v b phn chia thnh cc khi c ch thy ng lc c lp v tng i c lp khin kh nng thu hi b chi phi bi nhiu yu t a cht.

Trong bi vit ny, nhm tc gi phn tch cc yu t a cht c nh hng n kh nng thu hi du nh: mc bt ng nht, c trng h thng t gy v nt n sinh km, s phn chia ra nhiu khi vi ch thy ng lc tng i ring bit, nc p sn t cc thnh h Oligocen xm ln trong qu trnh khai thc. Nhng yu t ny cn tip tc c nghin cu, t a ra cc gii php nhm nng cao h s thu hi du.

T kha: Yu t a cht, h thng t gy v nt n sinh km, mc bt ng nht, khi thy ng lc, nc p sn, h s thu hi du, nt n ln, nt n nh

Hnh 1. Bn phn b cc h thng t gy v phn chia khi trong khu vc m S T en - S T Vng ti su 3.250m [ 2 ]

PETROVIETNAM

13DU KH - S 2/2014

h thng t gy phng ng Bc - Ty Nam, h thng t gy phng Ty Bc - ng Nam c hnh thnh do trng ng lc nn p Ty Ty Bc - ng ng Nam xy ra vo cui Oligocen. y l giai on ph hy kin to quan trng nht quyt nh hnh thnh h thng nt n, khng nhng i vi khi mng nng m S T en - S T Vng, m cn i vi khi mng nng m Bch H v nhiu m khc thuc b trm tch Cu Long. V vy, h thng t gy Ty Bc - ng Nam v ng Bc - Ty Nam cng h thng nt n sinh km l yu t a cht quan trng nh hng ti kh nng thm cha trong khi mng nng m S T en v S T Vng.

Kt qu quan st ng thi p sut va trong qu trnh khai thc ca m S T en (Hnh 2) cho thy, d lu lng khai thc tng i n nh nhng mc suy gim ca p sut va nh dn theo thi gian khai thc, chng t c ngun nng lng t bn ngoi h tr cho qu trnh khai thc.

Kt qu phn tch c im a cht cu to m S T en - S T Vng cho thy khi mng nng b bao bc bi trm tch xung quanh vi ng cong khp kn cui cng vo khong 4.000m v tnh cht va gim theo chiu su. Nh vy, c th loi tr kh nng nc trong mng dng cao trong qu trnh khai thc t di thn du. Trng hp khi mng nng m ng Nam Rng, c ranh gii du nc su -2.905m lin tc c nng ln trong qu trnh khai thc do khi mng nng lu thng vi dy nng Cn Sn. V vy, nc xut hin trong qu trnh khai thc thn du trong mng m S T en - S T Vng hon ton c kh nng l nc c p t cc tng trm tch Oligocen k p.

K t qu phn tch PVT ca mu du thu c t m S T en - S T Vng cho thy du trong khu vc ng Bc m S T en ch yu c p sut bo ha Pb = 4.200psi v ngm kh ca du khong 900scf/stb, trong khi du trong khu vc Ty Nam m S T en v S T Vng c p sut bo ha Pb = 1.100psi v ngm kh ca du khong 200scf/stb. Nh vy, khu vc ng Bc m S T en hon ton khng lu thng vi cc khu vc khc trong m S T en v S T Vng. Theo ti liu p sut va thu c trong giai on thm d v thm lng m S T Vng trc khi khu vc Ty Nam m S T en c a vo khai thc cho thy p sut va ca m S T Vng tng ng vi p sut va khu vc Ty Nam m S T en. Nhng khi p sut va ca khu vc Ty Nam m S T en b gim xung hng nghn psi do nh hng ca qu trnh khai thc, ging thm lng SV-5X ghi nhn p sut va ca khu vc m S T Vng b gim. c bit, vo thi im a m S T Vng vo khai thc (sau 5 nm khai thc khu vc Ty Nam m S T en) cc ging khai thc ghi nhn p sut va m S T Vng gim vi chc n vi trm psi so vi p sut va thu c t cc ging thm lng trc . Nh vy, ti liu p sut v kt qu phn tch mu PVT ca du thu c ti m S T en - S T Vng c th chia ra thnh 2 khu vc chnh c chung ch thy ng lc bao gm ton b khu vc Ty Nam m S T en - m S T Vng v khu vc ng Bc m S T en. Tuy nhin theo kt qu kho st ng thi khai thc cho thy mc lu thng trong cng khu vc m cng rt khc nhau.

2. Cc yu t a cht nh hng ti kh nng thu hi du

2.1. C s xc nh cc yu t a cht, nh hng ca cc yu t a cht

nghin cu nh hng ca cc yu t a cht ti kh nng thu hi hay h s thu hi du, trc tin cn nghin cu c s l thuyt nh hng ca cc yu t a cht ti h s y du bi nc v h s qut ca nc khi bm p hoc ca nc t nhin trn vo.

RF = Kd x Squt x (1)

Trong :

RF: H s thu hi du;

Kd: H s y du;

Squt: H s qut hay h s bao trm;

0

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~ Nng lng t du

~ Ngun nng lng bn ngoi

p sut va

Nng lng va

Hnh 2. ng thi p sut va v th tch ngun nng lng cn thit duy tr p sut va n nh

p

sut

va

(psi

)

Ngu

n n

ng

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g v

a

THM D - KHAI THC DU KH

14 DU KH - S 2/2014

: H s ngp nc.

Trong trng hp tnh h s thu hi du cui cng th h s ngp nc lun = 1.

Hin nay cha c kt qu phn tch h s y du i vi thn du trong mng m S T en v S T Vng. Tuy nhin, i vi mng ca m Bch H c thnh phn ch yu l granite, h s y du theo cc nt n macro bng nc bm p xc nh thay i theo hng di chuyn y ca nc l 0,67 - theo hng y t trn xung, 0,71 - theo hng y ngang v 0,89 - theo hng y t di ln. Ring i vi vi nt n h s y du bi nc khng ph thuc vo hng y m ch ph thuc vo rng cc vi l hng do nc thm theo lc mao dn. Nh vy, ngoi cc yu t nh rng, thm, tnh cht du kh nc, mc bt ng nht ca h s y du bng nc cn ph thuc vo t phn l hng macro v micro ca . Trn thc t c im ny cng phn nh mc bt ng nht, quyt nh kh nng thm cha ca mng.

H s y du bi nc i vi mng nt n c xc nh theo cng thc sau [3]:

Kd = Kdmacro x macro + Kdmicro x micro (2)

Trong :

Kdmacro, Kdmicro: H s y du ca i nt n macro v micro tng ng;

macro, micro: T phn nt n macro v micro theo th tch trong khi mng nng.

H s S qut l t phn gia th tch cha c qut bi nc trn tng th tch ca cha du. H s qut ca thn du ph thuc vo c trng thm cha v mc bt ng nht ca chng theo khng gian. Ngoi ra, h s qut cn ph thuc vo h thng khai thc ngha l ph thuc vo h thng cc ging khai thc v h thng cc ging bm p.

Theo [1, 3] h s qut c tnh theo cng thc:

Squt = Squt(s) x Squt(h) (3)

Trong :

Squt(s), Squt(h): H s qut theo din tch v theo chiu thng ng tng ng.

H s qut theo din tch Squt(s) ph thuc vo kh nng bao trm thu hi v kh nng bao trm bm p hoc nc p y hay nc p sn. H s bao trm thu hi ngha l kh nng bao trm ca mng li ging khai thc. Khng c ging khai thc th h s bao trm thu hi = 0. H s qut bm p l kh nng bao trm ca mng li cc ging bm p hoc nc p y hay p sn.

H s qut theo din tch l t phn din tch c bao trm bng h thng ging bm p hoc khai thc tng ng. H s qut theo chiu thng ng xc nh c theo tng ging khoan nh t phn chiu dy cha du c kh nng b nc bm p xm nhp trn tng chiu dy hiu dng cha du. Nh vy, h s ny ph thuc vo c yu t cng ngh v yu t a cht. Yu t cng ngh l khong chng ng, i bm p; yu t a cht l c trng lu thng gia cc ging.

Cui cng, h s thu hi c tnh theo cng thc:

RF = (Kdmacro x macro + Kdmicro x micro) x Squt x (4)

2.2. nh hng ca cc yu t a cht n kh nng thu hi du

Trn c s cng thc (4), nhm tc gi tin hnh phn tch nh hng ca cc yu t a cht n kh nng y du v kh nng bao trm hay kh nng qut ca nc bm p hay nc p sn.

Hnh 3. S phn b cc loi magma xm nhp chnh v cc ai mch dc theo cc ging trong m S T Vng

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2.2.1. H thng t gy, nt n v c trng thm cha

Kh nng y du bng nc bm p hoc nc p sn hay p y ph thuc vo c trng thm cha. Nh phn 1 nu i vi khu vc Ty Nam m S T en v m S T Vng mt t gy h thng t gy Ty Bc - ng Nam v h thng nt n sinh km c mt cao hn, c trng thm cha cao hn, tr khi C, so vi khu vc ng Bc m S T en, c bit l khi E (Hnh 1). Cng vi mt t gy v nt n sinh km, t phn l hng (nt n) macro khi Ty Nam v m S T Vng cao hn khi ng Bc m S T en. Ni cch khc, h s y du bi nc ca mng khi Ty Nam m S T en v S T Vng s cao hn h s y du bi nc khi ng Bc m S T en.

2.2.2. Mc bt ng nht ca mng

c tnh thm cha ca mng ph thuc vo mc t gy v nt n do nh hng ca qu trnh kin to, v vy cc loi khc nhau s b dp v cc mc

khc nhau. Do , mc bt ng nht v thnh phn thch hc (Hnh 3) v tnh thm cha ca mng m S T en v S T Vng kh cao, nh hng rt ln ti kh nng qut hay bao trm ca nc bm p v nc p sn y du vo khu vc nh hng ca qu trnh khai thc. V vy, mt trong nhng gii php nng cao kh nng thu hi tr lng i vi thn du trong mng nt n m S T en v S T Vng l phi tng h s qut y du ti vng nh hng ca qu trnh khai thc.

2.2.3. Nc p sn

Nu ly tng t khi mng m Bch H, h s y du bng nc p y khu vc Ty Nam m S T en v S T Vng c th t ti 0,71, trong khi i vi khu vc ng Bc m S T en thp hn hn do c trng thm cha km. Hnh 4 cho thy khi mng nng m S T en v S T Vng tn ti nc p sn t cc thnh to Oligocen. Do nc xm ln khng u so vi nc p y hoc nc bm p dng ln t di nn h s y du khng cao, ch yu theo hng ngang. V vy, nc p sn l mt trong nhng yu t a cht c bit quan trng i vi m S T en v m S T Vng c nh hng ti kh

nng thu hi du, cn phi c ch khai thc ph hp nhm nng cao h s thu hi. Ring h s y du bi nc p sn (y theo chiu ngang) cng nh hn h s y du bi nc p y.

Theo nghin cu [1], nhm tc gi thy h s qut du bi nc ph thuc rt nhiu vo v tr nc trn vo v y du ti i khai thc. Nu nc trn vo ni c ngp nc hon ton (SW = 100%) th h s qut c th t ti 85 - 90%; nu nc trn vo ni cha du vi bo ha nc d, c ngha l phn thn du cha c nc xm chim th h s qut ch t ti 40 - 50% hoc thp hn. Hin nay cha c s liu xc nh v tr v kch thc chnh xc ca nc p sn xm nhp nn vic a ra gii php nng cao kh nng qut ca nc p sn l vn c bit kh khn, cn c nhng nghin cu b sung. Tuy nhin, v tr v kch thc ca nc p sn trong mng m S T en v S T Vng l yu t a cht c bit quan trng nh hng ti h s thu hi du.

Hnh 4. Hng cung cp ca tng nc c p nm trong cc tp ct Oligocen [4]

Hnh 5. Cc khi trong khu vc m S T en [4]

A

B

C

DE

THM D - KHAI THC DU KH

16 DU KH - S 2/2014

2.2.4. S phn chia thn du thnh nhiu khi vi ch thy ng lc ring bit

Khi mng m S T en, S T Vng c chia thnh cc khi, mi khi c c trng thm cha khc nhau vi ch thy ng lc ring bit (Hnh 5). S phn chia khi mng nng m S T en thnh nhng khi thy ng lc ring bit nh hng rt ln ti h s thu hi du ca ton m. Ngoi ra, h s thu hi cn ph thuc vo kch thc m hoc kch thc cc khi. y cng l yu t quan trng nh hng n kh nng thu hi du. M cng b chia ct ra nhiu khi nh c ch thy ng lc ring bit th kh nng thu hi cng thp. T thc t tham kho thn du trong mng m Bch H ta thy yu t chia nh ra thnh nhng khi thy ng lc ring bit ca m S T en v S T Vng l yu t a cht nh hng ln, lm suy gim kh nng thu hi du.

3. Kt lun

Thn du trong mng trc tam m S T en v S T Vng c cu trc a cht rt phc tp, nh hng

ln ti kh nng thu hi du bao gm: mc bt ng nht v thnh phn thch hc, c trng nt n v hang hc, ngun nng lng nc p sn v s phn chia thnh nhiu khi c ch thy ng lc ring bit y l nhng yu t a cht chnh nh hng ln ti kh nng thu hi du, cn c nghin cu k tm gii php nng cao kh nng thu hi tr lng m.

Ti liu tham kho

1. N.P.Lebedinhes. The study and the production for oil fi eld in fractured reservoirs. Nauka, Moscow. 1997.

2. Cng ty Lin doanh iu hnh Cu Long. Geological and reservoir simulation - advance halo model - Su Tu Vang. 2013.

3. Hoang Van Quy and others. Development and construction project of White Tiger fi eld. Vietsovpetro. Vung Tau. 2008.

4. Cng ty Lin doanh iu hnh Cu Long. Bo co nh gi tr lng du kh ti ch v thu hi tng mng m S T en v S T Vng. 2009.

Summary

Oil bearing Pre-Cenozoic basement reservoirs of Su Tu Den and Su Tu Vang fi elds are quite complicated and they are created from the deformation of many magma complexes by tectonic faults and dykes in diff erent geological peri-ods, which divided the basement into many domains with independent or semi-independent hydrodynamic blocks, thus oil recovery is directly infl uenced by many geological factors.

In this paper, the authors analysed the geological factors that directly infl uence oil recovery such as the geological heterogeneity, the fault and associated fracture systems, diff erences of hydrodynamic resumes, and the presence of Oligocene aquifer during production processes. In order to have suitable approaches for increasing and enhancing oil recovery factor, further studies of the above geological factors will be necessary.

Key words: Geological factor, fault and associated fracture system, reservoir heterogeneity, adjacent aquifer, hydrodynamic block, oil recovery factor, macrofracture, microfracture

Geological factors influencing oil recovery from Pre-Cenozoic basement oil reservoirs of Su Tu Den

and Su Tu Vang fields Dang Ngoc Quy, Hoang Van QuyPetrovietnam Exploration Production Corporation