ZNANSTVENO - STRUCNO GLASILO HRVATSKE UDRUGE NAFTNIH INZENJERA I GEOLOGA

SCIENTIFIC AND PROFESSIONAL JOURNAL OF THE CROATIAN ASSOCIATION OF THE PETROLEUM ENGINEERS AND GEOLOGISTS

9nlA] (NJ IGA 68 / | 2 .

I . } IEDUNARODI iA KO\FERI \C I J -q . I I ZLOZB. {

O \ - { F T \ O - P L I \ S K O I I C O S P O D A R S T \ ' I - - T ' S R , E D I S \ - J O J I I S T O C \ O J E I ' R O P I

l s t CENTRAL A \D E - {STER\ ELROPf - \ \I \ T E R N A T I O N A L O I L A N D G A S C O \ F f R . E \ C E A \ D E \ H I B I T I O \

S i r i f o k , I l a t l a r s k a , 1 4 , - 1 6 . r u j n a 2 0 L 1 . - S i 6 f o k . E r r g e r y . S c ; r e r b e r l ' l - 1 6 . 2 0 1 1

KVANTIFIKACIJA VARIJABLI PROIZVODNJE UpTESdENJAdKIIuLEZTSTTVTA U ODNOSU NA DRf GETIPOVE I-,EZISTA U HRVATSKOJQUAt{Tr FICATION O F PRODUCTION VARIAB LES /}SANDS TO]YE HYDRO CARB ON RESERVOIRS VERSL-SOTHER LITHOLOGIES IIY CROATIA

Tomislav Malvi6, INA d.d. Zagreb, SD Naftaplin, RGNfakultet Sveuiiliita u Zagrebu.Josipa Veli6, Marko Cvetkovi6, RGN fakultet SveuiiliSta u Zagrebu

Kljudne rijeii: leZi5ni litofacijesi, srednji miocen, gornji miocen, rezerve ugljikovodika-iscrpak, Panonski bazen, HrvatskaKey words: reservoir lithofacies, Middle Miocene, Late Miocene, hydrocarbon reserves,tec o'v€t !, Pannonian Basin, Croatia

SaZetak

\ajveii dio rezervi ugljikovodika u hrvatskom dijelu Panonskog bazena pripadaju:lesdenjadkim leZi5tima gornjeg panona i donjeg ponta (gornji miocen) te predstavljaju 1..eZi5ni litofacijes. Druga dva leZi5na litofacijesa pripadaju krupnoklastidnim sedimentimaradena (2. leZi5ni litofacijes) i predneogenskim karbonatima, magmatitima I:rretamorfitima (3. leZi5ni litofacijes). Kolidina utvrdenih rezewi ugljikovodika smanjujese prema starijim leZi5nim litofacijesima. Geolo5ke rezerve prvog leZi5nog litofacijesa,p.rpraiene s udjelom u cjelokupnimrezewama, su slijedeie:

- nafta2l7.316.037 m' 168,63 % ukupnih geolo5kih rezerur), ̂- plin otopljen u nafti I plinska kapa 24.391,95 x10' m' (79,08 % ukupnih

geolo5kih rezewl),- plin 2l .199,47x10o m' Q2,80 % ukupnih geolo5kih rezewi),- kondenzat2.63l.l47 m' 112,90 % ukupnih geolo5kih rezervr).

Iz pregleda rezeryrjasno se moZe vidjeti da se u pje5denjadkim leZi5timanalazi elarntna:ezen'i (oko 70 % ukupnih) nafte i plina otopljenog u nafti ili iz plinske kape. \a_ir*c:.."-rpak pak ima 2.leLlSni litofacijes (38,74 %) kojeg slijedi 1. leZi5ni litofaciies s 19.96 ' ':e na kraju 3. leZiSni litofacijes s26,2 % iscrpka. Pje5denjadka leZiSta prete2ntr sd nal:zg,i1

-rrukrurnim i strukturno-stratigrafskim zamkama. Otkriveno je preko ll"ll- le+sra s:rrlsiednom porozno56u 2l % i propusno56u u rasponu od3,73 do 38-tr.l0--' m-. Takoler-- pn om leZi5nom litofacijesu najvelaje vjerojatnost pronalaska nor ih satelitsln-h lezi-ita:-a vec otkrivenim poljima kao i pove6anje iscrpka utiskivanjem r-ode tli plir

Tbstrsct

i:; main ht'drocarbon reservoirs in the Croatian part o-f tle W ICPBSI are.i:s;,-,yered in sandstones of Upper Pannonian and Inw fu FL IfWr lliocene)

l 9

1. MEDU\ . {ROD\{ I io \F f R. f \C IJ . { I IZL0ZBAO ) i A F T \ O - P L I N S K O } I G O S P O D A R S T T ' [ [ S R I D I S \ J O J I I S T O ' \ O J E I . R O P I

l s t C E \ T R . 1 , L _ { \ D f - { S T E R \ E U R O P E A NI N T E R N A T I O N A L O I L . { \ D G , T S C O N F f R E \ C E A N D E X H I B I T I O \

S i r i f o k , M a d a r s k a , 7 4 . - 1 6 . r u j r a l f t l - - S i r i f o k . H u n g a r y , S e p t e m b e r l { - 1 6 . 2 0 l l

ages (Ist reselvoir lithofaciest. Tfu oilt'er ̂ r'o reseruoir tithofacies are Badenian coarse-grained clastites .(1"'' litlwfrciat ud Pre-Neogene carbonates, mapmatites andmetamorphites (3''" lithofixiqt- Tlre discotered hydrocarbon reselyes or"" rorr"quentlylesser toward older lirho-fria- Anwunt ql'geological resewes of hydrocarbons discoveredin I't reservoir n'pe {s@fuel are:

- oil 2I .-115.0-1= i t8-6J"o of^total reserves in all tithofacies),- gas dissolted in cil od gu cap 24,391.95 xl06 *t 179.0go% of totat

t'eset1 es t.- ga-r )-.199-47xlf m] t::.80% of total reserves),- touiensae ]-6i-.11- mj r I2.90bto of total reserves).

It is tietv Ifu saulstone reservoirs are the main reservoir types (about 70o% of totalt'cLcncs/ .fq oil as well as for gas (recovered from oil or gas cap). However, reachedt'€ta\en'k IIE msimal in breccia reservoirs (35.74% in 2'd, 29.96% in I't and 26.2% in-i'' rc-r-tTrtir lrpet. Sandstone reservoirs are mostly found in structural and structural-statiertryhic trops. There are more than 200 separate reservoirs bo.Qies, with averagep"rrtjlh ahout )I?b and permeability in rangefrom 3.73 to 384.00x1a15 m2. This lithotogyr rrra mo-;t probable for discovering new, satellite resen,oirs on existing fields o, th"qp.r,r'ic.rtron o.f-u'ater or gas injectionfor reaching additional recovety.

l. Introduction

The Croatian part of Pannonian Basin System (abbr. CPBS) is divided in four largerdepressions, i.e. hydrocarbon provinces of Neogene age. Those are the Mura, Drava, Savaand Slavonija-Srijem depressions (Figure 1.). The depression margins are generallylocated along several mountains and massifs in the Northern Croatia or their subsurfaceextensions (Velii, 2007; Veli6 et aL.,2002).

Figure l. Croatia and its Croatian geotectonical regions(from: Velic et al., 2008t

20

In the rast 50 years 40 oil and 25 gasfierds had been discor-ered and exploited in GPBS.

The estimatsd geological reserves ur. +!O*tO6 # of equiralent oil' INA Plc' performed

exploration and deve-lopment of more than 60 hydrocarbon fields in Croatia' of which rs

15 not in productiorr. Ti,e recovered hydrocarbon volumes benreenlg-+0-1005 is shown in

Figure 2.Theuno.rul production of -ir.u.tted 3'14x10u tons in penods 19"79--1982 and

1985-1988, uno guJnio; . - ; ; ; i ; iod* 'between 1987-1990 and l '05r10'm- ' in 1993

Neli6 et al., 2008).

1 . MEDuNARoDNA KoNFERENCTIn ' r r z l oZeA "o NAFTNO_pi lNSX,r l r 'E<i -spoulnsTVU

U Snsl tSNrol t ts to i t ' loJ EUROPI

l S t C E N T R A L A N D E A S T E R \ E U R O P E A N _

TNTERNATlonni ' bi i la 'Ni i Cls coNFERE\cE AND ExtrIRIrIoNu . . ^ ^ o r . q a n t A m h e r 1 4 - 1 6 . 2 0 1 1

S i 6 f o k , M a t l a r s k a ' r 4 ' - l 6 ' t o j " " Z U f t ' - S i 6 f o k ' @

1S50,1959 lgGg -1968-

Recoverable reserves

I oe rr1 I cas (tO',m1

1970.-1979. 198{1.'19ff1 19$'?lo5

Produced teserYes

Z oittml f Gaitvm',

Figure 2' Relation benteen i'clo"cr'rbl'; 'lrl'irt*'ilt;a'l '-i-iir!s-r-i ';- -'"

decorles rti-om. tr ej.r.' ar Ji ' :t:tit'-tl

otroEfo

trorlG'oo!t

I

At the end of the sixt ies avera-qe recoven-rras 15"0" [: ler ' rt rras:=3rr: i3; -:-: : ' i t ier

spectrum of ,e"orref methods" for dift-eient tields- S0 in Sc srr il::= :;J :eel ;'e*i

,ete.al production iegimes reaching reco'en ot-: (al iol5fft n:-j-- ;i:": ::'-'e':lt-\n'

h)20-25o/ousing gu, Jup and (c) 16:20 for soluble ga:{' Gen€f,all}- E3:3: -:-'3': ': ' ' irili

:he most used secondary recovery methods in the CPBS' anrl ah'"u::"-'-: -:::esent

:roduction comes from water flooded resen'oirs lespecialh *s-l*!;-'l:= . ::-lching

i..;6; o-ii1" tnu"ks to production favourable oil r iscositin" Tle :"":' ::; :'" en' does

:,rt depend on reservoir size,but on reservoir lithofacies'

S:,. rhe some largest croatian fields reached recovery from trnlv lbi: rZ-::"; Field)' then

_:-:: tKlo5tar Field), StruZec Field (39%) and e\en 51" tBe:r"r:; t Field) ' The

: -:temporary p.oO.r.tion declining is results of lacking of neu hr;ru-u":'oL]n discovering

,:: ,Jepletion of the most fields, which were mostlr discorere..i ::u'nl i9-;9 to 1989

F: : - - l re 3. ) .

2 l

1 , M E D U N A R O D \ . { K O \ F E R E \ C I J A I I Z L O Z B AO N A F T \ O - P L I \ S K O I I G O S P O D A R 5 T \ t I S R E D I S \ J O J I I S T O ' N O J E U R O P I

l s t C E N T R . { L \ \ D E \ S T E R \ E U R O P E A NI N T E R N A T I O N A I , O I L A N D G - \ S C O \ F E R E \ C E A N D E X H I B I T I O N

S i 6 f o k , M a t l a r s k a , 1 4 . - 1 6 . r u j n a 2 0 1 1 . - S i 6 f r , r k " H u n g a r y , S e p t e m b e r l 4 - 1 6 , 2 0 1 1

Zil.

1940,-1t149. ' Oi

- GG llgn--r!Fg. I Oil l Gas 1 9 S 0 . - 1 9 6 9 . : O i t * G a s

1970.-1979. I ol Z G6 tsl.-l!)8g. I Oil f, Gas 19S0.-2005. lOit EGas

oEoiE!too

oo.9

ooltEz

F istii', -i \ umhet' ol' discot'ered hydrocarbon fields through decades(f'o*: Velit et al., 2010)

2. Reserr oir properties

In CPBS about 3300 wells had been drilled. It offered a lot of data for defining properliesof hydrocarbon reservoirs. Regarding statistical analysis of those properties reseloirs aredivided in three groups (Veli6 et a1., 2008), as it is shown for oil fields and reservoirs inTable 1 (rnain data are derived from Veli6 et al., 2008).

Those groups (Table 1) can be often accompanied with three reservoir lithofacies. Itmeans that properties and group selection is significantly dependant about reservoirbelonging to parlicular sediments of three Neogene depositional megacycles. holr, it isdefined in Velii et al. (2002). The largest and the most productive leserr oirs from the 1'tgroup mostly belong to 2no depositional megacycle (Upper Miocene). i.e. to sandstones ofPattnonian and Pontian age (lst reservoir lithofacies). One, but significanr. e\ception is the3:l ianci Field, where breccia reservoir is part of the 1" megacvcle tBadenian), i .e.2nd-- : - ' r . , ' i r ' l i tho lac ies.

s*l*&ffi**

1 , M E D U N A R O D N A K O N F E R E N C I J A I I Z L , O Z B AO \ A F I ' } - . O - P I . I \ S K 0 I \ I G O S P O D A R S T v U I . S R E D I S \ J O J I I S T O ' \ O J E I R O P I

I s T C E N T R A L A N D E A S T E R N E U R O P E , { NI N T E R N A T I O N A L O I L A N D G A S C O N F E R E N C E A n - D E X H I B I T I O N

S i 6 f o k , M a t l a r s k a , 7 4 . - 1 6 . r u j n a 2 0 1 1 . - S i 6 f o k , H u n g a r v . S e p t e m b e r l 4 - 1 6 , 2 0 1 1

Tuble i. Grottping oJ oil resetvoirs based on depositionol, structttrol. petrophysical,, r o dLtct io n and fluid p rop ert ies

ltt group , 3'd group

Neogenerr,qegaCycle whieh the most

r rrr 'rof reservoirs belong

2nd

lrarely 1'1)

,.,;,',,,1,,itil,tand 2td

:,:,,:(.-|, N€. basement)

lo and 2nd(+ Ng basement)

Dominmt,, ieservoir lithofaciesl t t 200

i r dJ

(U; Mioc., Baden..

:PZ-Mz basement)

I s I ?no l ro

(U. Mioc., Baden.,

Pz-Mz basement)

Portion of total production (%) 84.8 | 2 . 3 2.9Number of oil fields that mostly

oroduct from srouo8 t1 1 8

Abs. depths to reservoir top (m) -570 to -1700 -310 to -2280 -790 to -2350

Average number of reservo[s l 6 9 ^

Prognosis of e-rploitation (years) 55 46 36Ar eraqe porosin' (%) 2 1 . 0 8 t5.62 t2 .6s

Avera.se penneabrlin ( l0 ' ' urnr) 3.73-384.00 8. l6 -196.60 2.9-92.3Arerage recrr \en r : ' ) 33.87 / -+. / ) t 4 ) 1

Averase oil densin , k: ni 8 7 3 . 6 869 :8-l

Tire 2nd and 3'd groups rnclude resentr i rs ol \en hete:r . ,gcnitrJ- i l i tholouic Ctr: iFrrSirrol l,::d ages alld can belons tt-r 1' and I - 'Jept-rsitrrrnai rnegacrc-ie. St-rile ol thent incluoe pre-\eogene reservoir rocks. i ike in the Deletorci Field (Sranites. gneisses. s.-his is and- .rbases of Palaeozoic). Kuiancr-Kapelna Field tTnassic doiomit ic breccia). Obod-Lacici1- retaceous carbonates) etc.

. .:ere is only a few reserv.oir in CPBS which are discovered in the sediments of 3'o-_racvcles up to now (Pliocene sandstones), and they are still considered as potential

- ;r, that need to be evaluated numerically with Probability Of Success (abbr. POS); : - r r 1 l ?11V .

: ::Jla oir lithology, lge, depth, porosity and recoveries are generally correlative with::-.ted and reached recoveries (e.g.in Velii, 2007 Veli6 et al., 2002; Malvii et al.,

- j: Saftii et aI.,2001). So, average porosity decreases fi'onr 1" group toward 3'd group.,. ', i.1 as the maximal penneability (Table 1).

- - -- -:riire remaining recoverable reserves in the CPBS are shown on Figure 4 fir the-,-..r-...-rlS ol-. and upiated (Table 2) for the end of l't decade of the 21th century. in fact.

: : :ri se\ elal newer sources for hydrocarbon reserves in the CPBS published in the last- : - : - ; , : ie Dobrova et a l . (2003) and Vel i6 et a l . (2008. 2010) .

1. MEDUNARODNA KONFERENCIJ A I IZLOZ'B AO NAF'TNO-PLINSKOM GOSPODARSTVU U SREDISNJOJ I ISTOENOJ EUROPI

ls t CENTRAL AND EASTERN EUROPEANINTERNATIONAL OIL AND GAS CONFERENCE AND EXHIBIT ION

Si r f fok , Madarska , 14 . - 16 . ru jna 2011. - S i6 fok , Hungary , September 14 - 16 ,2011

1 20000

lTAd rw#gc rcs€rrr€s (x10nf)

lfaa parcogG Es€ry€s (x1drr)

fl fca lwriiB gc Eserrres (x10ni)

lrcarec*decre (xt(}m)

lroa p*-rd ee glom)

!rorqdEtcre 1rl0rd)

Figure 4. Recoverable (+ produced + rarfifr) ltcmes of oiland gas in the CPBS (from: YeIiiAJilnS)

Table 2. Croatian recoverable (+ produced + nil-f lfiuarbon (*reserves givenin brackets are condensate volumes) resertw

3. Conclusions

Some studies for the CPBS stated that that there is 2-4 times more oil had been generatedthan it was proven in existing reservoirs. Although iL can be overestimated value, there isfor sure some signifrcantpart of hydrocarbon reserves that could be:

(a) Producing with increased maximal estimated recovery from existing fields, especiallyfrom the reservoir belonging to 2"o depositional megacycle, i.e. in Pannonian andPontian sediments ( 1't reservoir lithofacies) ;

al,

E-o

oooo-ooot

24

1 . MEDUNARODNA KONFERENCIJA I I ZLOZBAO N A F T N O - P L I N S K O M C O S P O D A R S T V I U S R E D I S \ J O J I I S T O ' N O J E U R O P I

I s t C E \ T R A L A N D E A S T E R N E f R O P E A NI N T E R N A T I O N A L O I L - { N D G A S C O N F E R E N C E A \ D E X H I B I T I O N

S i 6 f o k , M a i l a r s k a , 1 4 . - 1 6 . r u j n a 2 0 1 1 . - S i 6 f o k , H u n g a r r . S e p t e m b e r l 4 - 1 6 , 2 0 l l

(b) Discovering the new ones resenroirs as satellite to existins l'lelds or maybe in the pre-Neogene basement or 1st\eogene megacycle (Badenian):

(c) Estimation of gas potential for the youngest part of 2nd and the oldest of 3'd Neogenemegacycle (Upper Pontian and Pliocene sediments).

Potential reselvoirs can be discovered using different geological models. especiallymodels of regional and local hrdrocarbon systems in the CPBS. In anv case. the furtherexploration need to be onented to regionally weaker explored chronostratieraphic units.like Badenian, Upper Pontran or Pliocene sediments. Stratigraphic traps in the sandstonesof 2"" Neogene megacycle. located in the margins of larger anticlines ri ith smaller closure.maybe can be primary goal tbr erploration of existing hydrocarbon fields.

References

1. Dobrova, H., Kolly. E. & Schmttz. U. (2003): Ventures in the Eastern-CentralEurope Transformation States after 1989 - a Review of Expectations and Results.Oil gas European Magazine. 19. +. 172-182.

2. Malvii, T., Velii, J. & Peh. Z. (1005): Qualitative-Quantitative Analyses of theInfluence of Depth and Lithological Composition on Lower Pontian SandstonePorosity in the Central Part of Bjelorar Sag (Croatia). Geologia Croatica, 58, 1,73-85.

3. Safti6, B., Peh, Z.,Yelic, J. & Jrittner, I. (2001): Interdepence of PetrophysicalProperties and Depth: Some Implications of Multivariate Solution on DistinctionBetween the Lower Pontian Hydrocarbon-bearing Sandstone Units in the WestemPart of the Sava Depression. Geologia Croatica, 54,2, 259-277 .

4. Velii, J. (2007): Geologija leLilta nafte i plina (Geology of Oil and Gas Reservoirsin Croatian). Faculty of Mining, Geology and Petroleum Engineering, Universin

of Zagreb,342 p.5. Velii, J., Malvi6, T., Cvetkovi6, M. & Vrbanac, B. (2010): Characteristics ri

Hydrocarbon Fields in the Croatian Part of the Pannonian Basin. Oil gas Eurore.:.Magazine, 36, 3, 146-147 .

6. Veli i , J., Malvi i , T., Cvetkovii , M., Weisser, M. & Curi, V. (2008): Obs.:,. : -

useful for increase of hydrocarbon fields exploitation period u.ithin Cr,,.,- :,.::of the Pannonian basin. SGEM congress "Modern Management ot ,\! ' . .- .; -.

Geology and Environmental Protection", Intemational Scienti:-: i, --- -,== .:SGEM (ed.). Sofia. Proceedinss. 567 -57 4.Velii, J., Weisser, M., Safti6, B., Vrbanac. B\aftnogeoloSke znadajke i istraZenost triju neogenski:-,diielu Panonskog bazena (Petroleum-geologicttl,jr-;'.;.!et'e/ of lhe three Neogene depositiona/ ntegut.', i'J-i ;,;PLtttnoniotl basin). Nafta. 53. 6-7. 239-219

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