Tuyin tap b^o cao Hoi nghj KHCN "30 nSm Phu khi Viet Nam: Co hoi moi, thach thiic moi" 523
DAC DIEM THACH HOC TRAM TICH TANG
CHLTACAT KET MIOCEN D\f6l - BE CUtJ LONG
Pham Vii Chuong Viin Ddu Khi Nguyen Qu6c Quan Cong ty Thdm dd, khai thde Ddu khi
TOM T A T
Tiim ndng that su cua tdng chira cdt kit Miocen du&i bi Ciru Long dang la mot thdch thuc l&n trong cdng tdc thdm dd ddu khi & nu&c ta. Nhdm muc dich giup cho ngu&i doc cd mdt cdi nhin tdng qudt vi tdng chua ndy, tdc gid trinh bdy nhirng nghiin ciru vi ddc diim thgch hoc trdm tich cua chung trin co s& tdng hgp cdc tdi lieu phdn tich lat mdng, nhiiu xg Ranghen (XRD) vd kinh hien vi diin tu quit (SEM) thuc hiin tgi Phdng Trdm tich, Viin Ddu Khi.
Kit qud nghien ciru cho thdy cdt kit Miocen du&i bi Ciru Long thudc logi hgt min din trung binh, it thd hgt, do chon loc phdn l&n la kem din trung binh. Thdnh phdn chu yiu Id Arkose, it Sub-arkose, Lithic Arkose vd Feldspathic Greywacke. Khd ndng chua phu thudc vdo tdng hdm lugng matrix, xi mdng, khodng vgt thir sinh vd logi khodng vgt thu sinh. Khd ndng chira tdt tap trung a Id 15-1, 15-2 vd 09-1, khd ndng chua khd & Id 01, cdc Id cdn lgi cd khd ndng ehira kem din trung binh.
MdDAu
Dau khi o them luc dja Viet Nam dugc khai thac trong ba d6i tugng chinh: mong phong hoa va nirt ne truoc De tam, tram tich Oligocen va tram tich Miocen. Tuy la doi tugng chira dau dau tien dugc phat hien khi khoan va thir gieng BH-1 vao nam 1975, nhung chi den khi viec khai thac hai tang duoi sau gap nhieu kho khan va dac biet la sau khi JVPC va Cuu Long JOC phat hien dau c6ng nghiep trong tang nay thi tram tich Miocen moi dugc nghien cuu ti mi. Viec phat hien ra dong dau c6ng nghiep trong tram tich Miocen da mo ra mgt huong nghien cuu moi, mgt trien vong mai cho nganh c6ng nghiep dau khi nuoc nha. Tuy nhien, de danh gia mgt each chinh xac tiem nang that sir cua tang chira nay, nham nang cao hieu qua tham do va khai thac, truoc tien can phai xac djnh dugc dac diem thach hgc tram tich ciia chiing. Bao cao trinh bay cac ket qua nghien cim dac diem thach hgc tram tich cua tang Miocen duoi tren co so tai lieu phan tich lat mong, XRD va SEM ciia cac mau cat ket thuge tang tren.
PHLTONG P H A P NGHIEN CtTU
Cac mau cat ket thuoc tang Miocen duoi dugc lira chgn de phan tich lat mong, XRD va SEM. Phan tich lat mong dugc thuc hien bang each dem 500 hat tren m6i lat m6ng qua do xac djnh do hat, do chgn lge, thanh phan khoang vat vun, xi mang va khoang vat thir sinh va do r6ng nhin thay. Phan tich XRD bao g6m 2 phan: toan bg da va khoang vat set nham xac djnh thanh phan khoang vat, phan biet cac khoang vat set ciing nhu cac khoang vat khae ma kh6ng th^ phan biet ro duoi lat mong. Phan tich SEM nhSm dua ra anh kh6ng gian 3 chieu o do phong dai cao nham xac djnh loai khoang vat thii sinh, hinh thai lo r6ng ciing nhu anh huong ciia khoang vat thir sinh den chat lugng chira. Cac kk qua phan tich nay sau do dugc t6ng hgp lai va danh gia theo kien tnic, bao g6m do hat (phan chia theo Udden-Wentworth,
1922), do chgn lge (phan chia theo Folk and Ward, 1957), thanh ph^n khoang vat va xi mang (phan chia theo Folk, 1974), qua do danh gia kha nang chira ciia timg d6i tugng (Bang 1).
524 Dac diem thach hoc t r i m tich tSng chiia cat kSt miocen duoi - be Ciiu Long
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Tuy^n tap bao cao Hoi nghj KHCN "30 nam D^u khi Viet Nam: Co' hoi moi, thach thuc moi" 525
KET QUA VA THAO LUAN 1. Kien true
Kk qua phan lich do hat dugc trinh bay tren Hinh 1. Hinh ve cho thay hau het cac mau thuge loai nho den trung binh (thanh phan 0,125 - 0,5mm chiem uu the voi 40 - 70%). il trung binh den th6 (thanh phan 0.5 - 1mm chiem 10 - 33%), d6i khi xuat hien hat th6 den rat th6 (16 01 va 02). Do hat co khuynh huong th6 dan ve phia D6ng Bae. Do chgn loc ciia hau het cac mau thuge loai rat kem. kem den trung binh (SQ thay d6i tir 1 - 2.6). chi CO 6 16 15.1 la do chgn lge thuoc loai trung binh den t6t (SQ thay doi tir 0,45 - 1.2).
<0.031 0.031- 0.063
0.063- 0.125
0.125- 0.25-0.5 0.25
Kich thu'cyc hat (mm)
Hinh 1: Do thj phan loai do hat ctia cac mau cat ket Miocen duoi, be Ciru Long 2. Thanh phan khoang vat
Thanh phan khoang vat ciia cac mau cat ket bao g6m chii yeu la thach anh (32 den 55%, trung binh 40 - 45%)), feldspar bao g6m K-feldspar va plagioclase (10 den 28%, trung binh 15 - 20%)), it mica (trung binh 2 - 3%), manh da (5 - 10%) va bao gom cac loai granitoid, phun trao, silic, quartzit, da phien va manh da khae nhu trinh bay trong Bang 1.
Ten da ciia cac mau cat ket theo phan loai Folk (1974) voi thanh phan matrix nh6 hon 15%) dugc trinh bay trong Hinh 2, ket qua cho thay phan Ion cac mau thuge loai Arkose, it Lithic Arkose va Sub-arkose. Vai thanh phan matrix Ion hon \5% chi xuat hien nhieu o 16 01. 02 va 09-2, thanh phan la Feldspathic Greywacke.
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Hinh 2: So do phiin loai cat ket voi thanh phan matrix nho hon 15% (Folk, 1974)
526 Dac diem thach hoc t r i m tich tiing chiia cat kk miocen d u o i he C iru Loiip
Hinh 3: Mau cat ket Arkose chup duoi kinh hien vi phan cue,
thanh phan gom chii yeu la thach anh (Q), feldspar (F) va manh granitoid, mau xanh la 16 rong ciia da (Mau 15-1-SD-3X)
3. Thanh phan matrix, xi mang va khoang vat thii' sinh
Thanh phan matrix, xi mang va khoang vat thir sinh cua cac mau cat ket dugc trinh bay trong Bang 1. Bang tong ket cho thay long ham lugng xi mang va matrix cua cac mau thay doi trong khoang tii- 10,5%) den 23,5%o. Cac mau thuoc 16 09-1, 15-1 va 15-2 CO tong ham lugng xi mang va matrix thap 10 - 14%o, thanh phan chu yeu la kaolinit, it illit/sericit. calcit. silic va smectit (Hinh 4). Trong khi do cac mau thuoc ria phia Tay Nam (16 16, 17) ham lugng xi mang va matrix cao (19 - 23%o) thanh phan nhieu smectit, it hon la cacbonat, kaolinit, illit/sericit va thach anh thir sinh. Nguge lai, a phia Bae (16 01, 02 va 09-2) ciing co ham lugng matrix va xi mang cao, nhung thanh phcin chii yeu illit/sericit. it kaolinit, thach anh thir sinh va smectit.
C.xUSGRPATA^C^0C^le97MD.noU IBTTf.D ICt
(a) (b) Hinh 4: a) gian do phan tich XRD cho thay thanh phSn set gom chu yeu la kaolinit,
it illit, chlorit, smectit va hon hap lop illit-smectit; b) hinh chup duoi SEM cho thay thanh phan xi mang chu yeu la kaolinit (Mau 15-1-SD-3X) 4. Kha nang chua
Dugc danh gia tren co so do r6ng nhin thay khi quan sat tren lat mong. Kha nang chua t6l lap trung o cac 16 09-1. 15-1 va 15-2, noi do r6ng trung binh thay d6i tir 15 - 25%o. L6 01 CO kha nang chira thuge loai kha, do rong trung binh thay doi trong khoang 12-15%o. Cac 16 con lai co do r6ng trung binh tir 3 - 7%o, kha nang chira thuoc loai kem - trung binh.
Tuygn tap bao cao Hoi nghj KHCN "30 n2m Phu khi Viet Nam: Co hoi mdi, thach thuc mdi" 527
KET LUAN VA KIEN NGHI
Tir nhirng nghien cim tren co th^ rut ra kk luan nhu sau:
• Cat k6t Miocen duoi b^ Ciru Long phan Ion thuoc loai nho den trung binh, it tho (16 01 va 02). Do chgn Igc thuoc loai kem den trung binh, hiem khi tot. Thanh phan chii y6u la Arkose, it hon la Sub-arkose va Lithic Arkose, chi co 16 01, 02 va 09-2 hien dien nhidu Feldspathic Greywacke.
• Do nhtrng dac diem tren tuong tu nhu nhau, kha nang chira ciia cat ket tang nay phu thuoc vao tong ham lugng matrix, xi mang va loai khoang vat thir sinh. Kha nang chira tot tap trung o cac 16 09-1, 15-1 va 15-2, noi ham lugng matrix, xi mang va khoang vat thir sinh thap va chu yeu la kaolinit. Kha nang chira thuge loai kha a 16 01, noi ham lugng matrix, xi mang va khoang vat thir sinh khoang 2\% va chii yeu la kaolinit, illit. Cac 16 con lai co ham lugng matrix, xi mang va khoang vat thir sinh cao nen kha nang chua thuoc loai kem - trung binh.
• Cac nghien ciru ve nguon goc, bien doi thir sinh va moi truong tram tich cua tang nay can phai nhanh chong thuc hien, qua do c6 the lap dugc mo hinh tang chiia cua chiing.
TAI LIEU THAM KHAO
1. La Thi Chich, 2001. Thgch hgc. NXB Dai hoc Qu6c gia Thanh ph6 H6 Chi Minh, tr.
265 - 322.
2. F.K. North, 1985. Petroleum geology. Unwin Hyman, USA.
3. G.W. Brindley, 1980. Crystal structures of clay minerals and their X-ray identification. Mineralogical Society, London, UK.
4. Nguyen Van Diing, 2000. Khd ndng chua cua cdt kit diep Bgch Hd bi Ciru Long:
Nguyin nhdn ldm gidm do thdm trong bom ip nu&c. Tuyen tap bao cao Hoi nghi KHCN 2000 ''Ngdnh Ddu khi Viet Nam tru&c thim thi ky 2r, NXB Thanh nien, Ha Ngi, tr. 4 2 6 - 4 3 5 .
5. Howel Williams, Francis J. Turner, Charles M. Gilbert, 1982. Petrography: An introduction to the study of rocks in thin sections. W.H. Freeman and Company, San francisco, USA.
6. Joseph I. Goldstein, et al., 1992. Scanning electron microscopy and X-ray microanalysis. Plenum Press, New York and London.
7. Pham Xuan Kim, 1999. Ddc diim thgch hoc, tu&ng da, mdi tru&ng thdnh tgo vd qui lugt phdn bd cdc tdng chua Miocen s&m - Oligocen bi CUTI Long. T6ng c6ng ty Dau khi Viet Nam.
8. Loren A. Raymond. Petrology: The study of igneous, sedimentary and metamorphic rocks. Wm. C. Brown Publishers, p. 264 - 316.
9. Maurice Tucker, 1989. Techniques in sedimentology. Blackwell Scientific Publications.
5 2 8 Bae diem thach hoc trSm tich thng chira cat kit miocen dudi - bf Cuu L^ng^
10, Ngo Xuan Vinh. 2000. Nhirng yiu td chinh dnh hu&ng din dnh chdt thdm dura ciia da vun luc nguyen Miocen s&m - Oligocen be Ciru Long. Tu\ln tap bao cao Hgi nghj KHCN 2000 "Ngdnh Ddu khi Viet Nam tru&c thim thi ky 21", NXB Thanh nien. Ha Noi. ir. 282 - 294.
11 .Cac bao cao phan lich Ihach hoc cac gieng khoan thuoc be Cim Long. Luu trir lai Vien Dku Khi.
