CHNG 1: C IM A CHT KHU VC NGHIN CU

1.1 C IM A CHT BN TRNG CU LONG

1.1.1 V tr a l v lch s pht trin bn trng Cu Long

Hnh 1.1: V tr a l bn trng Cu Long trong khu vc bin ng.

Bn trng Cu Long nm pha ng Bc thm lc a pha Nam Vit Nam ko di 340km theo hng ng Bc - Ty Nam v rng 80km theo hng Ty Bc - ng Nam vi ta a l: nm gia 90-110 v Bc, 106030-1090 kinh ng. Bn trng c hnh bu dc, vng ra v pha bin v nm dc theo b bin Vng Tu-Bnh Thun. Bn trng Cu Long tip gip vi t lin v pha Ty Bc, ngn cch vi bn trng Nam Cn Sn bi i nng Cn Sn, pha Ty Nam l i nng Khorat-Natuna v pha ng Bc l i ct trt Tuy Ha ngn cch vi bn trng Ph Khnh. Bn trng c din tch khong 56,000 km2, l bn trng dng rift hnh thnh vo K Tam sm. Kt qu tm kim thm d cho thy bn trng Cu Long c tim nng du kh ln nht v l ni c tp trung nghin cu nhiu nht. Cho n nay, mt khu vc khai thc du kh trn thm lc a Vit Nam c hnh thnh bao gm cc m nh: Bch H, Rng, S T en, S T Vng, Rng ng...

Lch s pht trin bn trng Cu Long c th chia lm ba thi k chnh:

Trc to rift: to nn mng trc Tam, bao gm ch yu l granit v ni la.

ng to rift: xy ra vo thi k Eoxen Oligoxen, hot ng t gy to nn cc khi t gy v cc trng trong bn trng. S kt thc hot ng t gy v bt chnh hp trn nc trm tch Oligoxen nh du s kt thc thi k rift.

Sau to rift: xy ra vo thi k Mioxen sm nay. Cc trm tch Mioxen di ph chm ln cc trm tch c hn, cc tng ni la v tng st bin Rotalit phn b rng khp, l nhng nt in hnh trong thi k ny.

1.1.2 a tng bn trng Cu Long

a tng bn trng Cu Long c th hin trong hnh (1.2) bao gm: mng trc Kainozoi, trm tnh Kainozoi bao gm h tng C Ci tui Eoxen, h tng Tr C tui Oligoxen sm, h tng Tr Tn tui Oligoxen mun, h tng Bch H tui Mioxen sm, h tng Cn Sn tui Mioxen gia, h tng ng Nai tui Mioxen mun v h tng Bin ng tui Plioxen T.

Mng trc Kainozoi

V mt thch hc, mng c th xp thnh hai nhm chnh: granit v granodiorit, ngoi ra cn gp bin cht v cc thnh to ni la. So snh kt qu nghin cu cc phc h magma xm nhp trn t lin vi mng kt tinh ngoi khi bn trng Cu Long, theo c trng thch hc v tui tuyt i c th xp tng ng vi ba phc h: Hn Khoai, nh Qun v C N.

Hnh 1.2: a tng bn trng Cu Long

Phc h Hn Khoai: Ch yu l Diorit. y c th c xem l phc h magma c nht trong mng ca bn trng Cu Long, phc h c tui Triad mun, tng ng khong 195 n 250 triu nm.

Phc h nh Qun: ch yu l granodiorit, i ch gp monzonit-biotit-thch anh a sc. Phc h nh Qun c tui Jura, tui tuyt i dao ng t 130 n 155 triu nm.

Phc h C N: l phc h magma pht trin v gp ph bin nht trn ton bn trng Cu Long. Phc h c trng l granite, thy mica v biotit, thuc loi natri-kali, d nhm (Al=2.98%), Si (~69%) v t Ca. c tui tuyt i khong 90-100 triu nm, thuc Jura. b gip v, nhng mc bin i th sinh yu hn so vi hai phc h trn.

Trm tch Kainozoi

Trm tch Kainozoi l mt b phn quan trng ca bn trng Cu Long c cu to phc tp, nm bt chnh hp trn mt mng kt tinh bo mn v phong ha, vi dy t 2.5 n 8km, cng i v trung tm bn trng, dy cng tng, ch su nht ln hn 8km.

a tng khi qut trm tch Kainozoi ca bn trng Cu Long:

H tng C Ci (E2cc): H tng C Ci c tui Eoxen. Mi trng trm tch ch yu l lc a. B dy h tng khong 400m. Cc ha thch bo t phn hoa c tm thy trong tng trm tch ny bao gm: Soagnum, Pteridaceae, Cyaphidites, Foramea y l tng trm tch mi c pht hin nn cha c nhiu nghin cu.

H tng Tr C (E31tc): H tng Tr C c tui Oligoxen sm. Mi trng trm tch ch yu l sng, chu th, gn vng cao, c th l h phn trung tm bn trng. B dy ti a tng cng ca h tng Tr C ln n 1500m. Cc ha thch bo t phn hoa c trng cho h tng ny bao gm: Trudopoll, Ephedera, Cycas H tng ny rt ng c quan tm do c cc tp st dy xen k cc lp ct.

H tng Tr Tn (E32tt): H tng Tr Tn c tui Oligoxen mun. Mi trng trm tch ch yu l lng sng, h, bin nng, c bit l mi trng tam gic chu (do s c mt phn hoa v Foraminifera). B dy trm tch tng cng khong 1300m. Cc ha thch bo t phn hoa tm thy c trong h tng Tr Tn ny bao gm: Rhizohone, Fussiena y l tng sinh du rt tt, c bit l tp D. Ngoi ra, h tng Tr Tn cng l mt tng chn a phng kh tt.

H tng Bch H (N11bh): H tng Bch H c tui Mioxen sm. Mi trng trm tch: ng bng lng sng, ng bng ven b (phn di nhiu ct, phn trn nhiu st). Mi trng chuyn dn t tam gic chu sang lc a, m h cn kit. B dy ca h tng vo khong 1000m, trong tp st Rotalia c dy vo khong t 100 n 200m. Cc ha thch tm thy c trng cho tng trm tch ny bao gm: Rotalia, Orbuline Univerca, Rhizophora Animia, c bit l Florsfhuetzia Semilobata

H tng Cn Sn (N12cs): H tng Cn Sn c tui Mioxen gia. B dy h tng bin i t 250 n 900m. Mi trng trm tch chuyn dn t bin nng sang trm tch sng, m ly ven bin. Ha thch bo t phn hoa trong tng trm tch kh phong ph thuc: Florsfhuetzia, Foraminifera, Rhizophora, Levopoli H tng ny gn nh khng c trin vng v du kh do khng c tng chn khu vc mc d rng kh ln (15-20%).

H tng ng Nai (N13n): H tng ng Nai c tui Mioxen mun. B dy trm tch bin i t 600 n 900m. Mi trng trm tch bao gm m ly, ng bng ven b v bin nng. H tng ny khng c tim nng du kh do khng c tng chn.

H tng Bin ng (N2-Qb): H tng Bin ng c tui Plioxen T. Mi trng trm tch ch yu l bin nng. H tng ny khng c tim nng du kh.

1.2 C IM A CHT M Y

1.2.1. c im a cht a tng

L 01 & 02 nm bn trng Cu Long thuc thm lc a Nam Vit Nam, cch cng Vng Tu 155 km v pha ng v tri rng trn din tch 1184 km2. M Y c khm ph vo 08/1994 khi khoan vo ging 1X. Mc ch ca ging l tm kim, thm d du kh trong trm tch v mng trc Tam.

a tng m Y bao gm: Mng trc Kainozoi, h tng Tr Tn tui Oligoxen mun vi i gia v i trn, h tng Bch H tui Mioxen sm, h tng Cn Sn tui Mioxen gia, h tng ng Nai tui Mioxen mun v h tng Bin ng tui Plioxen T.

Mng trc Kainozoi

Phn mng trc Kainozoi c cao t 2800 4000m so vi y bin. Thnh phn thch hc ch yu l granit. Trong , c t 12 34% l thch anh, 9 38% l feldspar kali (orthoclase v microline), 14 40% plagiocla, 2 10% mica (biotit v muscovit). Nhng khong vt th sinh c th xc nh c l clorit, epidot, zeolit, canxit v cc khong vt ti mu (pirit, oxit st).

Hnh 1.3: a tng m Y bn trng Cu LongThnh phn khong vt ti cc t gy c 10% l biotit nu en, cn li l thch anh (t trong sut n ti mu), feldspar trng xm, canxit, zeolite, clorit v cc mnh vn ca epidote, hornblend v pirit.

S thay i v ch thy nhit c th hin r ti nhng v tr gn cc ai xm nhp.

H tng Tr Tn tui Oligoxen mun i gia

H tng Tr Tn tui Oligoxen mun i gia c cao t 2400 2800m so vi y bin. Thnh phn khong vt ch yu l st mu nu en, giu vt liu hu c, b xen ln bi ct kt, bi kt v vi. st ti i ny c s ng nht cao hn i trn, v vy ti y phn phin hn, cng v c t l st cao hn. st pha trn c mu nu xm, cng tin v gn phn mng, cng c mu m v phn phin hn.

Ct kt c mu t xm nht n xm xanh, ht t th n mn va, trn cnh hnh cu. chn lc t km n va. rng km. Thnh phn khong vt c thch anh, feldspar, kaolin, canxit.

Bi kt c mu t xm nht, xm hng n xm m. cng va phi, gin, d gy. Thnh phn c st, dolomit, mica, clorit v pirit.

vi c mu trng hoc trng vng. cng va phi, gin, d gy. Thnh phn khong vt c canxit v dolomit.

H tng Tr Tn tui Oligoxen mun i trn

H tng Tr Tn tui Oligoxen mun i trn c cao t 2100 2400m so vi y bin. Thnh phn khong vt gm c lp st kt giu vt liu hu c, xen ln l ct kt.Ct kt c mu xm nht. Ht th v mn va, trn cu, chn lc km. rng km. Thnh phn khong vt bao gm thch anh, kaolin, canxit.

H tng Bch H tui Mioxen sm

H tng Bch H tui Mioxen sm c cao t 1700 2235m so vi y bin.H tng Bch H trn c thnh phn khong vt bao gm st kt, ct kt v mt s t vi.

Tp st kt c mu xm nht hoc xm xanh. Thnh phn khong vt bao gm mica, canxit.

Tp ct kt c mu xm nht hoc xm xanh. ht th v mn va. chn lc km. rng km. Thnh phn khong vt bao gm thch anh a dng mu sc, canxit, pirit.

vi c mu trng, trng vng.

H tng Bch H di c thnh phn khong vt bao gm ct kt v mt s t st kt.

Ct kt c mu xm nht hoc xm xanh, ht t th n rt th, chn lc va, rng tt.

St kt c mu t xm nht n xm, mm, ht mn.

H tng Cn Sn tui Mioxen gia

H tng Cn Sn tui Mioxen gia c cao t 1200 1700m so vi y bin. Thnh phn khong vt bao gm ct kt, xen gia l cc lp st kt, c chia thnh 2 dng l st kt 1 v st kt 2.Ct kt c mu xm nht. Ht mn khu vc pha trn, cng xung su ht cng th v trn u. chn lc km. rng km. Thnh phn khong vt bao gm pirit, mica (biotit, muscovit), canxit, dolomit.

Lp st kt 1 c mu vng cam, , cam hoc nu vng. Cng xung su cng cng tng. Ht mn.

Lp st kt 2 c mu xm nht, xm m hoc xm xanh, kh mm. cng tng dn theo chiu su v ht rt mn.

H tng ng Nai tui Mioxen mun

H tng ng Nai tui Mioxen mun c cao t 580 1200m so vi y bin. Thnh phn khong vt bao gm ct kt xen gia l st kt, cc lp dolomit v than. Ct kt c mu xm xanh hoc nu vng. Ht t rt mn n th, gc cnh. chn lc km v rng km. Thnh phn khong vt bao gm thch anh mu trng ng, vng, hng xen ln bi liti, chert, pirit v v vi.

St kt c nhiu mu, ch yu l nu v nu vng. St rt mm, dnh v tan nhiu trong nc.

vi c mu trng ng, xm nht hoc xm vng. rn nhng d b b vn.

Dolomit c mu xm, hng, xm nu hoc trng ng. Dolomit rn, d b b vn. rng km.

Than c mu en nu hoc en, cng va phi, d tch ri, thnh phn khong vt c pirit.

H tng Bin ng tui Plioxen T

H tng Bin ng tui Plioxen T c cao t y bin n 580m so vi y bin. Thnh phn khong vt bao gm ct kt, st kt xen ln l vi v cc lp than mng. Cha nhiu ho thch.Ct kt c mu xm xanh hoc xm vng, kt dnh km. Ht t th n rt th, chn lc km. Thnh phn khong vt bao gm thch anh, glauconit v cha nhiu ho thch.

St kt c mu xm nht hoc xm xanh, rt mm v d tan.

vi c mu xm vng hoc trng. rn, d b vn v ht th. rng t km n va.

1.2.2. Tim nng du kh

m

Cc phn tch v m Y cho thy tng st Oligoxen y rt giu hp cht hu c v c tim nng chuyn ho hydrocacbon ln. Tng carbon hu c TOC trong cc mu st Oligoxen hu nh tt c u trn 1%, ch yu l trn 2% v c mt s trng hp ln n 10%. Gi tr S2 v ch s hydrogen ca cc mu ny cng rt cao.

m tim nng hu ht u tp trung phn ng Nam ca m. Mt s t tp trung phn ng Bc. i gia ca h tng Tr Tn c nh gi l ngun m tt nht, vi lp st dy v ti mu nht. i trn ca h tng Tr Tn cng c nh gi cao, nhng dy lp st mng hn nhiu so vi i gia.

Mt s lp ca tng Mioxen di cng c nhn thy l c tim nng m nhng thiu trng thnh cn thit. Vy nn m ca Mioxen khng c s dng trong phn tch tim nng du kh ca m Y.

cha

i tng cha du chnh ca m Y l mng nt n. Nt n xut hin hu nh trn ton b cu trc mng m Y (hnh 1.4). Cc t gy v nt n trong khi granit c coi l cc va cha tt v c d bo vi tim nng khai thc tt.

Hnh 1.4: Bn cc t gy v nt n ca m Y

Kt qu phn tch thch hc ca cc mu vn cho thy tng mng m Y l biotit granit, thnh phn bao gm 12 32% thch anh, 9 24% feldspar kali (ch yu l orthocla), 20 57% plagiocla v 2 10% mica (biotit v muscovite). Cc khong vt th sinh ch yu l clorit, epidot, zeolit, canxit v cc khong vt ti mu nh pirit, oxit st. B dy ca cc th ny l t di mt mt n 5 10m.

chn

Tng mng nt n c chn bi lp st Oligoxen vi b dy khong t 340 600m, thnh phn ch yu l phin st mu m, giu vt liu hu c, ngoi ra cn ln c ct kt, bi kt, cc lp vi mng v than. Lp st ny bao trm ton b phn trn ca mng.

Ti Mioxen di, tng st Rotalia dy khong 20m l mt tng chn cc k tt cho cc va y, c bit l cho tng ct kt ngay di tng st ny.

Ti cc h tng tr hn h tng Mioxen di v Oligoxen, cc tng st b gim b dy cng nh b ln ct do qu trnh nng ca h tng Bch H v mt ct cao ca h tng Tr Tn. T kh nng chn ca tng st gim