Kele, Zoltán

M. Tóth, Tivadar

Schubert, Félix

Viskolcz, Béla

English

Schubert Félix

M. Tóth Tivadar

Kele Zoltán

Viskolcz Béla

University of Szeged

Acta Mineralogica-Petrographica, Abstract Series 2, Szeged, 2003 IDENTIFICATION OF MULTIPLE GENERATION OIL INCLUSIONS TRAPPED IN QUARTZ SINGLE CRYSTALS USING STEPWISE HEATING CHEMICAL IONISATION MASS SPECTROSCOPY S C H U B E R T . F . ' . M. TÓTH, T.1, KELE, Z . \ VISKOLCZ, B.3 1 University of Szeged, Department of Mineralogy, Geochemistry and Petrology, H-6701 Szeged, P.O. Box 651, Hungary . 2 University of Szeged, Institute of Medical Chemistry, H-6720, Szeged, Dóm tér 8., Hungary. 3 University of Szeged, Department of Chemistry , Juhász Gyula Teacher ' s Training Col lege, H-6701 Szeged, P. O. Box 396, Hungary. E-mail: schubert@sol.cc.u-szeged.hu I n t r o d u c t i o n Quartz is one of the most important cement phases both in sedimentary and fractured hydrocarbon reservoirs. It may fo rm at a wide range of physical and chemical conditions and rather often entraps fluid inclusions of the co-genet ic fluid phases. Besides H 2 0-bear ing inclusions, commonly HC-bearing inclusions also occur, which report about hydrocarbons migrated through the reservoir during quartz precipitation episodes (e.g. Munz et al., 1999, Teinturier et al., 2002). These inclusions can give information both about the P V T properties of charging of the reservoir and the composi t ion of the migrat ing f luids. HC-bearing fluid transport usually takes place in successive migration events, which can be recorded by fluid inclusion (FI) generations trapped along growth zones or as secondary inclusion planes within diagenet ic minerals, like quartz. As a result even a single crystal may contain H C fluids of significantly different composit ion. There are several possible methods on bulk chemical analysis of HC-bearing fluid inclusions (e.g. GC, GC-MS, Karlsen et al., 1993), most of which, however cannot provide valuable information if oil inclusions of different composi t ions are present side by side. Some spectroscopy techniques also are available for quantitative analysis of certain components . The visible R a m a n microspectroscopy can be used even for minute inclusions, but the usually strong fluorescence of the H C inclusions hinder its applicability. T h e most accurate information about the composit ion of a single HC inclusion can be obtained by FT-IR spectroscopy (Pironon et al, 2001) , although this approach is limited in quartz due to its strong absorption above 2000 cm"1. In the present study we introduce a novel approach for measuring composi t ions of d i f ferent hydrocarbons in single crystals. After decrepitating inclusions under closed system conditions we aim detecting liberated fluids by a highly sensi t ive mass spectrometer. Hydrocarbons of different composi t ions are separated by a programmed stepwise heating procedure. T h e method is tested on fracture-fil l ing quartz crystals f rom the Variscan basement of the Pannonian Basin, Hungary. T h e f ractured metamorphic rock bodies in the study area are excellent HC-reservoirs (Nelson, 1985). Geologica l b a c k g r o u n d Békés basin, the deepest sub-basin of the Pannonian Basin system (SE Hungary) is surrounded by metamorphic basement highs, which produce significant amount of hydrocarbons f rom their fractured crystal l ine rocks. One of the largest f ractured basement reservoirs is the Szeghalom dome (SzD), which consists of medium- to high-grade metamorphic rocks; essential ly gneiss and amphibolite. Due to the mult iphase subsidence of the Pannonian Basin, the S z D shows a rather complex Neogene evolution history. The dominantly steeply dipping conjugated microfaults are filled in by a well-defined fracture-f i l l ing mineral sequence. The first cement phase of considerable amount is a free-standing, hydrocarbon-inclusion bear ing quartz phase. Based on stratigraphic, stable isotope chemical and palynological observations, this quartz phase fo rmed prior to the most exhumed state of the SzD (Juhász et al., 2002) and trapped hydrocarbon traces, which should not be identical to the oil produced from the metamorphic basement at present. The quartz crystals trapped H C FIs in several growth zones; in some cases even 15 zones occur. In some drilling cores the HC FIs do not show any change f rom the inner growth zones to the external ones based on petrography, U V f luorescence and Raman microspectroscopy analysis (Schubert , 2003). However , in other cases a clear d i f ference can be recognized f rom one zone to another in both fluorescence and optical properties (colour, V/L ratio, etc.). In these samples , the H C inclusions of the inner zones can usually be characterised by a dark brown liquid phase in normal light and an intense, greenish blue fluorescence colour under the U V excitation (V/L=0.2-0.3). With an abrupt change, in the outer growth zones a new fluid phase becomes dominant. It can be characterised by translucent liquid and vapour phases of a very weak, bluish f luorescent colour (V/L =0.8-0.9). S t r a t e g y Previous studies clearly inferred presence of fluid inclusions representing di f ferent types of H C in f racture filling quartz crystals of the SzD. As mass spectroscopy is a method to detect even extremely low amount of material, this approach was used measuring composit ions of the multiply generation oil inclusions. To decrepitate inclusions we prefer heat ing to mechanical crushing because mixing of different hydrocarbons must be avoided. Us ing this method we aim determining the temperature of the decrepitation of different inclusion types and detecting their M S spectra independently. In each crystal studied inclusions differ both in V/L ratio and composit ion of the entrapped oil. Assuming identical composit ions, material of the inclusion has larger volume to expand at higher V/L during heating and will decrepitate at higher 174 Acta Mineralogica-Petrographica, Abstract Series 2, Szeged, 2003 T. A s s u m i n g ident ical V / L and d ive r se c o m p o s i t i o n s , the inc lus ion , which con ta ins h y d r o c a r b o n mix tu re of l o w e r bo i l ing point , shou ld o p e n ear l ie r . A s a resul t , it c an be p r e s u m e d that mul t ip ly genera t ion oil inc lus ions in a s ing le crys ta l o p e n at d i f f e r en t t empera tu re s , and so they can be de tec ted independen t ly . B e f o r e m e a s u r e m e n t , the quar tz crys ta ls were pur i f i ed and se lec ted b y s tandard m e t h o d s . In a chemica l ion isa t ion m a s s spec t rome te r ( C I - M S ) the crys ta ls w e r e hea ted with a s tab le 10 K/s ve loc i ty and the m a s s spec t ra were de tec ted at eve ry 5 0 0 mi l l i seconds . S i m u l t a n e o u s l y , the c o n t i n u o u s total ion cu r ren t w a s r e c o r d e d too in o rde r to t r ace the dec rep i t a t ion t e m p e r a t u r e of the inc lus ions . T h e M S spect ra run o n a F inn igan T S Q 7 0 0 0 m a s s spec t rome te r (F inn igan M A T Ltd , San Jose , U S A ) . S a m p l e s w e r e in t roduced to the ion s o u r c e via a d i rec t inser t ion p r o b e that was ope ra t ed at a t e m p e r a t u r e b e t w e e n 3 2 0 and 7 0 0 K. C h e m i c a l ioniza t ion (CI) ion s o u r c e cond i t i ons w e r e as fo l l ows : t e m p e r a t u r e 4 2 3 K ; e lec t ron ene rgy , 4 0 e V ; filament cur ren t 2 0 0 p A ; CI gas: i sobu tane ; the p r e s s u r e of the ion source : 8 torr. Results T h e mos t impor t an t r e su l t s of the e x p e r i m e n t can be c o n c l u d e d as fo l lows : 1) Ion current c u r v e s genera l ly exh ib i t o n l y a f e w s h a r p peaks r i s ing f r o m the b a s e l ine. E a c h p e a k b e l o n g s to a wel l -de f i ned t empe ra tu r e va lue , mos t p r o b a b l y d e f i n e d b y dec rep i t a t ion of a cer ta in FI gene ra t i on (Fig . 1.). 2) C o m p a r a t i v e ana lys i s of M S spect ra , b e l o n g i n g to the d i f f e ren t p e a k s of the total ion cur ren t , sugges t s that they assoc ia te wi th C H mix tu re s of d i f f e r e n t c o m p o s i t i o n s (Fig . 2.) . 3) In all s tudied cases , i nc lus ions r ich in h igh m o l e c u l e weight c o m p o n e n t s o p e n ear l ie r , even if t hese F I s occu r in the internal z o n e s of the crys ta ls . 4) In ca se of t he S z D qua r t z c rys ta l s one can r e c o g n i z e the s ame oil type based on M S spec t ra in d i f f e ren t dr i l l ing co re s . Such a c lass i f ica t ion might lead to cha rac te r i ze d i f f e r e n t f lu id r eg imes in the reservoi r . F i g u r e 2. M S spec t ra of t w o d i f f e ren t oil types f r o m the s a m e quar tz crysta l References KARLSEN, D. A. , NEDKVITNE, T . , LARTER, S . R. , BJORLYKKE, K. (1993) : G e o c h e m i c a et C o s m o c h e m i c a Acta 57 : 3 6 4 1 - 3 6 5 9 . MUNZ,I . , A. , JOHANSEN, H . HOLM, K. , LACHARPAGNE, J . -C. (1999) : M a r i n e and P e t r o l e u m G e o l o g y 16: 6 3 3 - 6 5 1 . NELSON, R . A. (1985) : Con t r ibu t ions in P e t r o l e u m G e o l o g y & E n g i n e e r i n g 1. Gul f P u b l i s h i n g C o m p a n y . PLRONON, J . , THIERY, R. , AYT OUGOUGDAL, M . , TEINTURIER, S., BEAUDOIN, G. , WALGENWITZ, F. (2001) : G e o f l u i d s 1: 2 - 1 0 . SCHUBERT, F . (2003) : P h D Thes i s , p p 158. TEINTURIER, S. , PlRONON, J . , WALGENWITZ, F. (2002) : M a r i n e and P e t r o l e u m G e o l o g y l 9 : 7 5 5 - 7 6 5 . 175 

Identification of multiple generation oil inclusions trapped in quartz single crystals using stepwise heating chemical ionisation mass spectroscopy

http://acta.bibl.u-szeged.hu/31518/1/mineralogica_as_002_174-175.pdf

Identification of multiple generation oil inclusions trapped in quartz single crystals using stepwise heating chemical ionisation mass spectroscopy

Abstract

Similar works

Full text

Available Versions

University of Szeged