Điều kiện và các yếu tố ảnh hưởng đến sự hình thành, phân bố hydrate khí trong tự nhiên

PETROVIETNAM ) D l i u KIEN VA CAC YEU l6 A N H Hl/ONG DEN SLJ HINH THANH, PHAN B HYDRATE KHI TRONG TL/ NHIEN TS.Le Van Binh Dai hgc Mo- Dia chdt Email: lebinh55@yahoo.com Hydrate Id nguon ndng luang tii nhien sgch rdt cd tiem ndng tUang lai Theo dU bdo trd luang hydrocarbon chUa hydrate tu nhien dgt 7,6 x 10"m\ Do chi duac thdnh tgo dieu kiin nhiit dp thdp vd dp sudt cao nin 98% lUcfng hydrate ndm dudi ddy them luc dm vd ho, chi 2% d viing bdng vinh cdu trin luc dia Trong do, Canada, Bien Den, ho BaikaL Id cdc khu viic cd trdluang hydrate idn nhdt thi gidi Bdi bdo gidi thieu cdcyeu to dnh hudng din sii hinh thdnh vdphdn bd hydrate tU nhiin; trdlUang vdphdn botrdlugng hydrate trin thi gidi Tdkhda: Hydrate khi, suphdn bo hydrate khi, trdluang hydrate tu nhien Dieu kien va cac y^u t o cinh hadng den sU hinh thanh, phan bo hydrate Trong hda hpc, lien k i t gida elc nguyen tdcd thong sd dac trung I I chilu d i i lien k i t I v l gdc a gida hai lien k i t Trong li^n k i t chuin, chilu d i i lien k i t hydro va gdc 1.1 Biiu kiin hinh thdnh hydrate gida chung cd gia trj chuan: I ~ 2,7A° va a ~ 109,5° phan 1.1.1 Nudc ehda hda tan dmUc dp nhdt dinh t d se b i n vdng nhat Do dai I va gdc lien k i t a eang khae vdi gia trj ehuan thi eang hao phi nang lugng de tao nen Ket q u i nghien cdu ly hda phan t d chc thay: elc clu true va eau true eang kem ben vdng Tuy nhien, lien nguyen t d hydro va oxy p h i n t d nUde ket hgp va k i t hydro la "Hen k i t mem" (dp dai va goc lien ket co the phan bd g i n nhu nam d dinh eiia tam giac can Gde tai thay doi mde tuong ddi) nen ket tinh cae phan t d dinh ed nguyen t d oxy la 109,5°, hai gde edn lai la 37,5° nude CO the ket hap vdi de tao elc tmh the la (Hinh 1) Ddi dien tCr diing chung cua nguyen td hydro nhdng khoi da dien khic ve sd mat, hinh dang mat, v l oxy (trong lien ket dong hda trj) bi hut lech ve phia so canh va tUOng dng se ehda cic khoang trdng khic nguyen t d oxy tao nen tinh phan cUc eho phan td Cue ve kfch thude (Hinh 2) D i y I I nguyen nhan chinh am ve phia nguy§n t d oxy, cOc dUOng ve phia nguyen dan den sU da dang ve clu true tinh t h i ndi ri^ng eung tCr hydro Hydro cae phan t d nude cd sU "gin bd" nhu to hap elc tmh t h i tao nen cau triic hydrate ndi chat ehe vdi eac nguyen t d oxy tao mdi lien ket khdng chung [9] chi vdi nguyen t d oxy phan t d (lien ket ddng hda trj) ma eon tao mdi lien ket tam thdi vdi eae nguyen td Cdng thdc chung ciia hydrate la: M.nHp oxy cua elc phan t d nudc khac, tham ehi nd ed the lien ket vdi oxy trcng p h i n t d khoang chat tac da Do vay, Trong dd: cIcphantLf nUde trcng tu nhien luon "xoo/'trong khdng gian, chc moi nguydn tCf hydro n i m gida nguyen M: Phan td tham gia tao hydrate; t d oxy Lien ket gida nguyen t d oxy cija phan t d nude n: Chi sd hydrate (so phan t d nude tuong Cfng vdi g i n k l , thdng qua nguyen t d hydro trung gian tac phan td khi, thudng dao dpng khoing n = 5,75 mdi lien k i t hydro giOp cho HjO tdn tai trang thai - 17) Vi du: quan sat thUc t l chi cac hydrocarbon ldng d d i l u kien tieu chuan, tao Idp nUde lien ket bao tao hydrate vdi ty le: CH^ x 7Hp: C^H^ x 12Hp; C^H^ x quanh mat d l Do dac diem tren, nUdc cd cae tinh chat MHplM v i t ly khac so vdi hydrua khic ndi rieng va cic c h i t Idng ndi chung nhU: sde cang mat ngoii Idn, nhiet dung cao nhat d d i l u kien tieu chuan, k h i nang truyen nhiet ldn n h i t , k h i nang hoa tan r l t ldn, h i n g so di&n mdi Idn, nhiet hda hoi cao Td cdng thifc ehung ed the nhan thay de tac hydrate khf phli can mdt lugng ldn nddc Theo V.I.Ermcnkin, trcng khoang trdng cua da khong du lupng nude cin thilt, ehi mot phan n i m eau true hydrate, phan edn lai van ton tai trang thai khi"tu iU KHl - sO 3raoi5 67 DAu KHi THf GIOI do" Trong khoang trdng ton tai ddng thdi pha: pha ran la hydrate khf nam bao quanh, pha nam gida khoang trdng [5] Khi luong nUde trcng tich tu vda dii, toan bp tham gia vac phan hydrate khi, nUde thda se ed mdt sd ngan khdng dilcjc lap day bdi phan tu" khf cac dieu kien hinh hydrate ben vdng la nudc phai cd ehda lugng hda tan nhat djnh Neu eae khoang trong tinh the hydrate khong duac lap day bdi cac phan td thi tinh t h i hydrate khdng b i n v l nhiet dpng, de bj p h i huy D i l u kien tdi thieu de cau trije dn djnh la > 70% tdng sd ngan phli dUOe lap day (ty le eae ngan trdng dugc l i p day eang cao thi he hydrate khf eang ben vijfng) Dilu giai thfeh vi mdt tieu chuan tren mat dat (P = at) nddc ket tinh d nhiet dfl 1.1.2 Nhiit dp thdp Nudc chi k i t tinh d nhiet dp t h i p dieu kifn ap suat 4''C song dieu kien ap suit cao, ehda nhieu hoa tan, nddc cd the k i t tinh d nhiet dp cao hcfnnCfa Tuy nhien, p h i n Idn t u nhien cd nhiet tdi ban (Hmh 3) Nhiit tdi hgn tgo hydrate cua mdt logi khi- Id nhiit dp cao nhdt cdn cd thi tgo hydrate cda Niu nhiet dp mdi trUdng vUdt qud gid trj tdi bgn thi du cd tdng dp suat lin mdc rdt cao cung khdng the tgo hydrate Cac cd kich thudc phan t d nhd CH^, O^ N^, Ar, Kr, Xe (d < 0,4n.m) thudng khdng cd nhiet dp tdi han va gin nhi/ chi tham gia l i p day eac khoing trdng nhd tao hydrate khf he eau true CS-I (ben vCfng nhat la he clu true ehda khoang trdng cd kich thude tuong ddng vdi kfch thudc phan t d nam do) Trong t u nhien, khf ehda hydrate khf he eau tnic CS-1 chu y l u la methane Cac khf cd kich thude Idn tham gia tao hydrate khf eae he cau triic CS-il;TS va HS deu cd nhiet tdi han: CjHg -T,^^ = 8,8°C dudi I p suat P = 4at; CjHg - T^^=14,8°C dudi ap suat P = 80at, HjS - T ^ = 29,5''C dudi I p suat P = 21at Hinh I Cdu true phan tim/dc t) Phan ti> methane — ""^ a\^^ / / H2S ••m QH|o ^ / / / iCHm • Wnft 2.7/nft tfte hydriRe methane iuirt-sOMois / C,H« / > 10 15 20 Nhiet dfl T t 25 Hinh edlhinhiel^ too hydrate mdt id logi idil 3