Pe tro leum ge ol ogy of the Pol ish part of the Bal tic re gion – an over view
Paweł H. KARNKOWSKI, Leszek PIKULSKI and Tadeusz WOLNOWSKI
Karnkowski P. H., Pikulski L. and Wolnowski T. (2010) – Pe tro leum ge ol ogy of the Pol ish part of the Bal tic re gion – an over view. Geol.
Quart., 54 (2): 143–158. Warszawa.
The Pol ish part of the Bal tic re gion is lo cated within the con tact zone be tween two large geo log i cal units: the Pre cam brian plat form and the Pa leo zoic plat form. It com prises the Pol ish sec tor of the south ern Bal tic Sea and the ad ja cent on shore part of North ern Po land (West - ern and East ern Pomerania). The fun da men tal geo log i cal pat tern is de fined by the Teisseyre-Tornquist Zone, sep a rat ing the East Eu ro - pean Craton from the Pa leo zoic plat form. As a re sult of ex plo ra tion ac tiv ity in the on shore Pomerania re gion, four oil fields in Cam brian sand stones, seven gas fields in Car bon if er ous sand stones, six gas fields in Rotliegend sand stones, and eleven oil fields within the Zechstein Main Do lo mite ho ri zon have been dis cov ered. The pe tro leum play of the south ern Bal tic Sea re gion and ad ja cent ar eas must be con sid ered sep a rately for East ern and West ern Pomerania. In the Peribaltic Syneclise we can only take into con sid er ation or ganic mat ter ap pear ing in lower Pa leo zoic rocks but their geo ther mal his tory re fers to the pe riod from the Vendian up to the re cent. The pres ent ex tent of the “oil win dow” in the Up per Cam brian rocks is mainly re stricted to the off shore area. Res er voir prop er ties of the “gas win dow” Cam - brian rocks are rather low due to in ten sive diagenetic pro cesses. Ac qui si tion of gas should be pos si ble by pro cesses of hy drau lic stim u la - tion (tight gas). Lower Pa leo zoic rocks rich in or ganic mat ter (Or do vi cian and Si lu rian), es pe cially in the bor der zone of the EEC (Ro
>1.3%), could be an area of un con ven tional gas fields (shale gas). The West ern Pomerania pe tro leum play shows two sep a rate source rocks units. The older one em braces Car bon if er ous de pos its with or ganic mat ter of ter res trial or i gin and gen er ated gases ac cu mu lated in the Rotliegend and Car bon if er ous traps. The sec ond pe tro leum sys tem is lo cated within the car bon ates of the Zechstein Main Do lo mite (Ca2). This is a closed sys tem, mean ing that the source rocks are at the same time the res er voirs sealed by Zechstein evap o rates. Hith erto dis cov ered hy dro car bon de pos its in the Pol ish part of the Bal tic re gion have con firmed good per spec tives re gard ing oil and gas hy dro car - bon zones. New, con ven tional and un con ven tional dis cov er ies re main pos si ble.
Paweł H. Karnkowski, In sti tute of Ge ol ogy, Uni ver sity of War saw, Żwirki i Wigury 93, PL-02-089 Warszawa, Po land, e-mail:
Karnkowski@uw.edu.pl; Pol ish Oil and Gas Com pany, Kasprzaka 25, PL-01-242 Warszawa, Po land, e-mail:
Pawel.Karnkowski@pgnig.pl; Leszek Pikulski, Ex plo ra tion and Ex ploi ta tion Oil and Gas Com pany “Petrobaltic”, Stary Dwór 9, PL-80-958 Gdańsk, Po land, e-mail: leszek.pikulski@petrobaltic.com.pl; Tadeusz Wolnowski, Pol ish Oil and Gas Com pany-Zielona Góra Branch, Staszica 9, PL-64-920 Piła, Po land, e-mail: Tadeusz.Wolnowski@pgnig.pl (re ceived: Jan u ary 20, 2010; ac cepted: May 17, 2010).
Key words: Bal tic re gion, pe tro leum ge ol ogy, shale gas.
INTRODUCTION
The Pol ish part of the Bal tic re gion com prises the Pol ish sec tor of the south ern Bal tic Sea and the ad ja cent on shore part of North ern Po land (West ern and East ern Pomerania). It is lo - cated within the con tact zone be tween two large re gional geo - log i cal units: the East Eu ro pean Craton (EEC) and the Pa leo - zoic plat form of Cen tral and West ern Eu rope (Fig. 1). The relativly shal low depth of the Bal tic Sea fa vours geo log i cal prospection for hy dro car bon de pos its (Brangulis et al., 1993;
Dobrova et al., 2003; Zachowicz et al., 2004). But pros pect ing and ex ploi ta tion in the off shore area are also harm ful for the nat u ral en vi ron ment so they need to be re al ized with spe cial care to avoid pol lut ing the Bal tic Sea (Elmgren, 2001; San der - son et al., 2009; Szarejko and Namieśnik, 2009).
Re sults of geo log i cal stud ies in North ern Po land have been pub lished sys tem at i cally from the 1950s. A mile stone, sum ma - riz ing the first pe riod of stud ies on the south ern Bal tic area, was the Geo log i cal-struc tural At las of the South ern Part of Bal tic Sea ed ited by Witkowski (1989). Its was sup ple mented by a spe cial is sue of the Geo log i cal Quar terly in 1990, in clud ing de - tailed pa pers on se lected geo phys i cal-geo log i cal prob lems (Kiełt, 1990; Dadlez, 1990; Pokorski, 1990; Ryka, 1990; Wag - ner, 1990; Witkowski, 1990a, b). In next few years sev eral im - por tant pa pers re fer ring to this area were pub lished by Lund et al. (1991), Dadlez (1993), Ryka (1993), Witkowski (1993) and Modliński et al. (1994). Pub li ca tion of the Geo log i cal At las of South ern Bal tic Sea ed ited by Mojski et al. (1995) and Map of the Bal tic Sea Bot tom With out Quarternary De pos its (Kramarska et al., 1999) sum ma rized nu mer ous data ob tained by the be gin ning of the 1990s. Geo log i cal re search, other than
for pros pect ing for off shore hy dro car bons, has en abled de tec - tion of nat u ral raw ma te rial de pos its on the sea bot tom (Kramarska, 1991; Masłowska, 1993, 2002). In this de cade, re - gional geo log i cal pros pect ing ap ply ing the meth od ol ogy of
“Sed i men tary Ba sin Anal y sis” with ad vanced com puter geo - log i cal mod el ling was ini ti ated (Karnkowski, 1996, 2000, 2003; Kotarba et al., 2003, 2004; Kosakowski et al., 2003;
Poprawa et al., 2010). Sev eral pa pers (Karnkowski, 1993;
Wolnowski, 2002, 2003; Domżalski et al., 2004; Pikulski, 2004; Kotarba et al., 2005), ded i cated to solv ing pe tro leum ge - ol ogy prob lems.
The con ces sion pol i tics of Po land en ables for eign in ves tors to start stud ies in the dif fi cult – from a geo log i cal point of view – area of North ern Po land. The de pos its dis cov ered, in clud ing these small ones, are easy for man age ment be cause of the prox - im ity of con sum ers and be cause of a dense pipe line in fra struc - ture. The sta bil ity of po lit i cal and eco nomic con di tions in Po - land dur ing the last 20 years fa vours such pros pect ing ini tia - tives. Many sed i men tary bas ins in the world have now been rel a tively well char ac ter ized and the frame work of pe tro leum prov inces de fined. Lately, there has started a ten dency to pros - pect in ma ture bas ins, where hy dro car bons de pos its have been just dis cov ered and where new find ings are pos si ble due to new ideas. The Bal tic Sea and the ad ja cent ar eas is a good place to test con cepts of ex plo ra tion in ma ture bas ins. Geo chem i cal stud ies (Kosakowski et al., 2003; Kotarba et al., 2003, 2004) and geo log i cal mod el ling (Karnkowski, 1996, 1999, 2000
2003; Kosakowski et al., 2009; Wróbel et al., 2009, 2010) are use ful in such in ves ti ga tions.
GEOLOGICAL SETTING
The Pol ish sec tor of the Bal tic Sea and the ad ja cent on shore part of North ern Po land are the main ob ject of this study. The fun da men tal geo log i cal pat tern is de fined by the Teis - syre-Tornquist Zone (T-T Zone), sep a rat ing the Pre cam brian plat form (part of the East Eu ro pean Craton) from the Pa leo zoic (epi-Cal edo nian) plat form. The north west ern re gion was of ten called West ern Pomerania in re gional geo log i cal lit er a ture but the area lo cated eastwards from the T-T Zone is named the Peribaltic Syneclise (Fig. 1). The last term prac ti cally re fers only to the pre served lower Pa leo zoic de pos its, that pres ently form a gi ant syncline (de pres sion). These de pos its of north east - ern Po land could be con sid ered – in terms of sed i men tary ba sin anal y sis – as a prod uct of Bal tic Ba sin evo lu tion. This ba sin was ini ti ated in the late Vendian in the area of pres ent-day NE Po land, the Kaliningrad re gion, the Peribaltic coun tries and the south ern part of the re cent Bal tic Sea. Its base ment was the west ern part of East Eu ro pean Plat form (Areń and Lendzion, 1978; Jaworowski, 1979, 1982; Dadlez, 1987; Linnemann et al., 2008). The main stage of its de vel op ment took place in the early Pa leo zoic (Modliński and Podhalańska, 2010).
Fig. 1. Lo ca tion of study area with main geo logical and geo graphical units
PALAEOGEOGRAPHIC DEVELOPMENT
Ma rine trans gres sion, ini ti ated at the be gin ning of the Cam brian, was reg is tered in many bas ins world wide, among them also in Po land (Geyer et al., 2008). Dur ing the Mid dle Cam brian a gen eral re gres sion took place due to up lift of the EE Craton. The next transgressive ep i sode was in the Or do vi - cian. Ar eal de crease of the Mid-Late Cam brian ba sin also caused en large ment of land ar eas sup ply ing eroded clastic ma - te rial (Lendzion, 1970; Szczepanik, 2000).
The Cam brian–Or do vi cian bound ary is ero sional over most of NE Po land but in East ern Pomerania sed i men tary con - ti nu ity be tween both sys tems has been doc u mented. Sim i lar con ti nu ity was as sumed for this con tact in West ern Pomerania, where the Tornquist Sea ex tended dur ing the Cam brian (Fig. 2A). Trans gres sion of the Or do vi cian sea flooded the whole area of East ern Pomerania, ac cu mu lat ing mainly clay and marly de pos its and subordinately car bon ate (Modliński, 1982; Modliński and Szymański, 1997; Servais et al., 2008).
Deep ma rine clay sed i men ta tion con tin ued in the Tornquist Sea dur ing the en tire Or do vi cian (Fig. 2B) and Si lu rian (Fig. 2C).
The Si lu rian rocks in the south ern Bal tic area are rep re - sented mainly by siltstones and claystones (Teller, 1974;
Tomczykowa, 1988; Ver ni ers et al., 2008) and they con sti tute re gional seals for Cam brian res er voirs. In the up per part of the Si lu rian suc ces sion there are nu mer ous lime stone interbeds (Usaityte, 2000). At the end of the Si lu rian and be gin ning of the De vo nian the en tire area was up lifted and eroded (Fig. 2D).
Dur ing the De vo nian and the Car bon if er ous the Bal tic Ba sin be came eroded in part and the early Pa leo zoic sub si dence rate sig nif i cantly de creased (Narkiewicz et al., 1998). The Mazurian High – a sig nif i cant and well-known palaeotectonic and palaeogeographic el e ment – was then marked.
The ba sin frame works are well doc u mented by shal low wa - ter de pos its of the shore zone, ob served in sur face out crops or in shal low bore holes in the Bal tic is lands, in the Tallinn and Vilnius re gions and in NE Po land (Poprawa et al., 1997, 1999). The thick ness dis tri bu tion of these de pos its was con trolled by the mar ginal zone of the East Eu ro pean Plat form, where dur ing the Si lu rian the pas sive ba sin mar gin was lo cated and flexed due to load ing by the overthrusted Cal edo nian orogen (Krawczyk et al., 2008). The thick ness of lower Pa leo zoic de pos its in this mar - ginal zone is over sev eral thou sand metres but in the ar eas of the Peribaltic coun tries and in the mid dle Bal tic Ba sin it is sev eral hun dred metres (Modliński et al., 1999, 2006).
This up lifted area of the west ern part of the EEC in flu enced – in the De vo nian and in the Car bon if er ous – the sed i men tary evo lu tion of the West ern Pomerania ba sin (Świdrowska and Hakemberg, 1996; Lipiec and Matyja, 1998; Matyja, 2006).
The depositional his tory be gan at the end of the Emsian (Fig. 2E) or at the be gin ning of the Eifelian (Lipiec and Matyja, 1998; Matyja, 2009) pro duc ing mainly shal low ma rine clastics with thin interbeds of car bon ate and evap o rate lithofacies (Fig. 2F). In the Mid dle and Late De vo nian such shal low ma - rine de po si tion con tin ued while deeper open shelf sed i ments also ac cu mu lated (Fig. 2G). Transgressive-re gres sive events were com mon then but it is dif fi cult to de cide whether they re - sulted from global sea level changes or from lo cal tec tonic phe - nom ena. At the end of the De vo nian the ex tremely shal low wa -
ter fa cies of the lower Frasnian (Fig. 2H) were re placed by open shelf marls or by coral-stromatoporoid car bon ates in the prox i mal part of the ba sin (Matyja, 2006, 2009). In the mid dle Famennian shal low ma rine con di tions re turned and from the late Famennian un til the early Tournaisian open shelf de po si - tion pre vailed (Fig. 2I). The south ern Bal tic area, ad joined from the north with West ern and East ern Pomerania, was de fined palaeogeographically dur ing the De vo nian by the Mazurian High and the Fenno-Skania High (Usaityte, 2000). In that time deltaic and nearshore clastic fa cies with a tran si tion to shal low ma rine car bon ates and clastics pre vailed there.
In early Car bon if er ous East ern Pomerania prob a bly be - came a land area and West ern Pomerania was an area of deep (clastics) and shal low (car bon ates) shelf (Fig. 2J; Żelichowski, 1987). Vol ca nic ac tiv ity took place around the De vo nian–Car - bon if er ous bound ary and ma rine de po si tion ter mi nated in the early Namurian (Fig. 2K). Dur ing the whole of the Namurian and the early Westphalian the De vo nian–Car bon if er ous de pos - its of Pomerania were eroded (Fig. 2L). In tense block tec ton ics lo cally caused ero sional re moval of up to 1000 m of strata. The mid Westphalian saw the on set of con ti nen tal de po si tion but only in West ern Pomerania and in the west ern part of the south - ern Bal tic. Black and grey con ti nen tal clastics with thin coal interbeds ac cu mu lated (Fig. 2M). In the late Westphalian red in ter ca la tions were de pos ited, in di cat ing the trop i cal cli mate zone. The Stephanian de pos its in Pomerania are fre quently brown ish-red in col our and they con tinue into the Autunian (lower Perm ian; Żelichowski, 1987; Pokorski, 1990). In the Pol ish part of the Bal tic re gion area De vo nian and Car bon if er - ous de pos its were pre served only in the West ern Pomerania area (Bełka and Narkiewicz, 2008). The Mazurian and Fenno-Scania el e va tions sig nif i cantly in flu enced de po si tion and ero sion of these de pos its. Clo sure of Iapetus Ocean and of Tornquist Sea as well as fold ing of the De vo nian–lower Car - bon if er ous flysch de pos its into the Variscan orogen com pletely re or ga nized the palaeogeographic pat tern in the south ern Bal tic re gion (Kro ner et al., 2008). In the late Car bon if er ous al most the whole area was land but in West ern Pomerania, prob a bly within the foredeep, clastics from the eroded Variscides ac cu - mu lated (Żelichowski, 1987; Ziegler, 1990; McCann, 1998;
Narkiewicz et al., 1998; McCann et al., 2008).
The south ern Bal tic Sea area is mostly de void of Rotliegend de pos its. The Zechstein rocks, over step ping the Rotliegend ba - sin bound aries (Fig. 3), are im por tant for pe tro leum pros pect - ing only in West ern Pomerania. De vel op ment of sig nif i cantly thick Me so zoic de pos its was lim ited to the Pol ish Trough, part of which was lo cated in West ern Pomerania. In the area stud ied the Me so zoic de pos its have not been pros pected for oil but they play an im por tant role as a com po nent of sub si dence his tory in the ther mal evo lu tion of the Pol ish Ba sin (Karnkowski, 1999).
The sed i men tary his tory pre sented of the west ern part of the Bal tic re gion (the Pol ish sec tor of the Bal tic Sea and ad ja cent ar eas) and its Permian–Mesozoic pe riod of evo lu tion is il lus - trated by a typ i cal pro file of this re gion, in lower part of which oc cur lower Pa leo zoic rocks over lain by Perm ian–Me so zoic de pos its. The synclinal (de pres sion) form of the pre served rocks is a rel ict of the Bal tic Ba sin but the fi nal struc tural form of this re gion was a re sult of Variscan tec tonic move ments, which struc tur ally re built the west ern part of the ba sin into the
Fig. 2. Cam brian to Car bon if er ous palaeogeographic maps (Karnkowski, 1999, ex tended and sup ple mented) Other ex pla na tions as in Fig ure 1
Peribaltic Syneclise. The re sultant struc ture is bounded to the west by the Ger man-Pol ish Caledonides and to the east, by the Mazurian High, re cently with out Pa leo zoic cover.
STRUCTURAL FEATURES
West wards from the T-T Zone the older Pa leo zoic de pos its, sev eral thou sand metres thick, in ten sively folded and tec toni - cally de formed, have formed the Ger man-Pol ish Caledonides belt (Franke, 1994; Maletz et al., 1997; Dadlez, 2000). They are doc u mented in bore holes only near the mar ginal zone of the East Eu ro pean Plat form. Dur ing the late Pa leo zoic this belt was cov - ered by plat form de pos its of De vo nian and Car bon if er ous age.
The main struc tural fea tures of West ern Pomerania are de - ter mined by the con sol i dated Cal edo nian base ment. In ver ti cal suc ces sion the fol low ing rock suc ces sions have been dis tin - guished: the Cal edo nian (Si lu rian, Or do vi cian and Cam brian), the epi-Cal edo nian (De vo nian, early Car bon if er ous), the Car - bon i f er ous–Perm ian (Westphalian–Rotliegend), the Zech - stein–Me so zoic and the Ce no zoic. Each of these suc ces sions plays an im por tant role in the geo log i cal struc ture of West ern Pomerania. The Cal edo nian suc ces sion con sists of highly folded Si lu rian, Or do vi cian and Cam brian de pos its. In bore - holes Or do vi cian rocks are most com mon, Si lu rian ones are found rarely while Cam brian strata have not yet been found but their oc cur rence in the area is sus pected from the de vel op men - tal scheme of early Pa leo zoic bas ins. Clayey shales with sand -
stone interbeds are the main lithological com po nents of the suc - ces sion, which is highly de formed with beds of var ied in cli na - tion, up to ver ti cal and over turned, that caused an ap par ent thick ness in crease of the de pos its al though their orig i nal thick - ness may reach thou sands of metres. The Cal edo nian suc ces - sion is part of the Ger man-Pol ish Caledonides (Dadlez, 1978, 1980, 1987). Above it, the De vo nian and the lower Car bon if er - ous de pos its (the epi-Cal edo nian com plex) oc cur, be ing com - monly built of red sand stones and siltstones (Old Red) (Miłaczewski, 1987; Żelichowski, 1987). The fol low ing suc - ces sion (Car bon if er ous–Perm ian in age) cor re sponds with the pe riod of late Car bon if er ous and Rotliegend, con ti nen tal de po - si tion when pre vailed, lim ited fre quently to small bas ins con - trolled by fault zones (grabens and half-grabens). The De vo - nian–Car bon if er ous suc ces sions are weakly folded but in ten - sively faulted (Karnkowski, 1979; Dadlez, 1980; Znosko, 1986; Pożaryski, 1987; Knieszner et al., 2000; Matyja, 2006).
Such a block-fault type of tec ton ics de ter mined the in tense ero - sion of the De vo nian–Car bon if er ous rocks so that var i ous De - vo nian and Car bon if er ous for ma tions are ob served on the sub-Perm ian sur face (Karnkowski, 1979; Lech, 1993).
From the be gin ning of re search in Pomerania maps of the sub-Perm ian ge ol ogy were made and up dated as new geo log i cal and geo phys i cal data were ac quired (Witkowski, 1989; Lech, 1993; Pokorski and Modliński, 2007). The last-cited map is a com pi la tion em brac ing not only the area of Po land, but also Rus - sia (Kaliningrad dis trict), Lith u a nia, Lat via, Den mark (Born - holm) and Swe den (Gotland). The fault sys tems dom i nantly
Fig. 3. Sub-Perm ian tec tonic map with ex tent of the Rotliegend strata (sources: Pożaryski, 1987; Witkowski, 1989; Dadlez, 1990;
Lech, 1993; Mojski et al., 1995; Kramarska et al., 1999; Pokorski and Modliński, 2007; Pol ish Oil and Gas Com pany unpubl. data) Fault sys tem ac cord ing to Pokorski (2010); ex pla na tions as in Fig ure 1
have a N–S and E–W ar range ment (Fig. 3). The main N–S fault field ap pears to the north of the Łeba–Gdańsk area (Smołdzino Fault, Karwia Fault, Kużnica Fault; Fig. 3). These faults change di rec tion to E–W at the Pol ish coast line. The char ac ter is tic shape of the Sambia pen in sula re fers to the E–W trending Sambia Fault pat tern. The ex tent of lower Pa leo zoic rocks along the Mazury High is con cor dant with the E–W fault sys tem.
To the west from the T-T Zone the fault ing pat tern has a NW–SE di rec tion. Huge dis lo ca tion zones such as the Koszalin Fault and Trzebiatów Fault limit blocks of base ment which are in ter nally strongly faulted. The re sults of this phe - nom e non are nu mer ous tilted blocks with strongly eroded Car - bon if er ous and De vo nian cov ers. In Pomerania Bay the N–S trending faults are again pres ent. The Kamień Pomorski Block lim its the Pol ish Rotliegend Ba sin from the north. It seems that the NW–SE fault ing pat tern is dom i nant in the wide con tact zone of the EEC and the Pa leo zoic Plat form. N–S and E–W fault di rec tions pre vail in the re main ing area (Fig. 3). The mi - gra tion of hy dro car bons and trap for ma tion were sub stan tially de pend ent on the fault ing pat tern.
In West ern Pomerania ex tended lava cov ers of Autunian age were pre served. De pos its and bound aries of the Pol ish Rotliegend Ba sin in West ern Pomerania are well doc u mented by the bore holes (Nowicka and Wolnowska-Ślemp, 2005). The in - flu ence of the T-T Zone, the strong in flu ence of the Caledonides and of the De vo nian–Car bon if er ous fault sys tems on the fa cies and thick ness dis tri bu tion of the Rotliegend de pos its is very ev i - dent (Lech, 1993; Karnkowski, 1999; Kiersnowski and Buniak, 2006). The Zechstein trans gres sion over stepped the ex tent of Rotliegend clastics in the Pol ish Ba sin and flooded its pe riph ery to form lo cal bas ins (e.g., Słupsk, Mazurian and Podlasie bas ins) as for as Lith u a nia. The De vo nian–Car bon if er ous suc ces sion is over lain by Perm ian–Me so zoic with strata an al most hor i zon tal ar range ment and neg li gi ble de for ma tion be cause the rel a tively small thick ness of Zechstein de pos its pre vented in ten sive halo - tectonics. The Lara mide tec tonic move ments eroded part of the Me so zoic rocks. The Ce no zoic suc ces sion over lies the Me so - zoic de pos its dis cor dantly (Jarosiński et al., 2009).
This re view of the geo log i cal dis tri bu tion of the ar eas stud - ied in di cates they are de ter mined by the age of base ment con - sol i da tion. The pre-Cam brian (pre-Grenvillian) age of con sol i - da tion for the base ment of the Bal tic re gion and the Cal edo nian age of the early Pa leo zoic shelf ba sin of Pomerania and of the north ern part of the Pol ish Ba sin (lo cated in the epi-Cal edo nian plat form) de fine the lim its for dis cus sion of the ge ol ogy and hy dro car bon prospectivity in the Pol ish sec tor of Bal tic Sea and in ad ja cent ar eas (Fig. 1).
DATA USED AND METHODS
The pe tro leum and re gional ge ol ogy of the Pol ish sec tor of the Bal tic Sea and of ad ja cent ar eas has been dis cussed in nu - mer ous pa pers (Witkowski 1989, 1990a, b; Dadlez 1990, 1993; Kiełt, 1990; Pokorski, 1990; Ryka, 1990; Wag ner, 1990;
Mojski et al., 1995; Karnkowski, 1996, 1999, 2000, 2003;
Karwasiecka and Bruszewska, 1997; Jaworowski, 2000a, b;
Wolnowski, 2002, 2003; Kotarba et al., 2003, 2004; Pikulski,
2004; Fig. 4). The re sults dis cussed here are com piled from their pub lished and non-pub lished ma te ri als. The ba sic geo log - i cal data come from nu mer ous pros pect ing in ves ti ga tions of the Pol ish Gas and Oil Com pany and of “Petrobaltic” Com pany.
These in ves ti ga tions en abled the re al iza tion of sev eral geo log i - cal pro jects, many of which were com pleted with the dis cov ery of new hy dro car bon de pos its (Karnkowski, 2003). It should be men tioned that at the be gin ning of “Petrobaltic” ac tiv ity (years 1975–1990) much geo log i cal in for ma tion was se cret. Dur ing last 10–15 years the geo log i cal re sults of “Petrobaltic” stud ies were made more avail able (Domżalski and Mazurek, 2003).
Data on de pos its lo cated on shore are ac ces si ble e.g., in the mono graph on the pe tro leum ge ol ogy of Po land (Karn - kowski P., 1999). In spite of the dis cov ery of rel a tively small hy dro car bon de pos its in the Pol ish sec tor of the Bal tic Sea and in the ad ja cent ar eas this re gion is still in ter est ing as re gards fur ther pros pect ing.
In the Pol ish part of the Bal tic re gion the evo lu tion of the ma tu rity of or ganic mat ter has been mod elled by the first au thor (Karnkowski, 1996, 1999, 2000, 2003). The meth od ol ogy and in put data have been dis cussed in the pa pers cited. In the pres - ent com pi la tion the re sults of pre vi ous re search have been used.
In the pre vi ous pa pers not all re sults were pub lished and the cross-sec tions with or ganic mat ter ma tu rity zones and map the
“gas win dow” as the po ten tial “shale gas” fields in the Si lu rian de pos its are pre sented here for the first time.
SOURCE ROCKS, RESERVOIRS AND SEAL ROCKS
Pe tro leum plays of the south ern Bal tic and ad ja cent ar eas must be con sid ered sep a rately for East ern and West ern Pomerania. In the Peribaltic Syneclise we can only take into con sid er ation or ganic mat ter pres ent within the lower Pa leo - zoic rocks, par tic u larly as it re fers to the Mid dle and Up per Cam brian, Tremadocian, Caradocian and Llandovery. All these suc ces sions con tain or ganic mat ter of ma rine or i gin (kerogen type II). The best source rocks are the Up per Cam - brian and Tremadocian de pos its where TOC con tent is 1–18%
(Kanev et al., 1994). In the other suc ces sions or ganic mat ter is less than 1% (Kanev et al., 1994).
The West ern Pomerania pe tro leum play shows two sep a - rate source rock units. The older one con sists of Car bon if er ous de pos its with or ganic mat ter of ter res trial or i gin (up per Car - bon if er ous de pos its with 1% TOC av er age and lower Car bon if - er ous rocks with av er age 0.5% TOC).
The sec ond pe tro leum sys tem is re lated to the car bon ates of the Zechstein Main Do lo mite (Ca2). This is a closed sys tem, i.e.
source rocks and res er voirs are both sealed by Zechstein evap o - rates. This is a very prof it able ar range ment be cause the hy dro - car bons gen er ated did not need to mi grate for long dis tances
The con tent of or ganic mat ter within the Main Do lo mite is vari able. The high est val ues of TOC are dis tin guished within the bar rier zone and ad ja cent palaeogeographic el e ments. In the ba sin fa cies the av er age TOC con tent is 0.1–0.2% and in bar rier fa cies it is higher though not im pres sive – 0.3–0.4% TOC (Kotarba et al., 2003, 2004).
The Cam brian quartzitic sand stones are res er voirs in East - ern Pomerania and in the ad ja cent off shore area (Schleicher et al., 1998). Their thick ness var ies be tween 120 metres in the Bal tic Sea re gion up to 60 metres in the on shore. The po ros ity is strongly vari able and de pends first of all on the depth. Gen er - ally the po ros ity is less than 5% be low 3000 metres depth (Weil, 1990; Semyrka et al., 2010). It is in flu enced by diagenetic, tem per a ture-de pend ent pro cesses trans form ing si li - ceous quartz-sand stones into quartzites. In zones char ac ter ized by good petrophysical pa ram e ters po ros ity reaches 14% but per me abil ity has 24 mD max i mum (Weil, 1990). Re gional seal ing is pro vided by Up per Cam brian and Or do vi cian claystones and shales. The Si lu rian claystones give an ad di - tional seal (Zdanaviciute and Lazauskiene, 2004).
In West ern Pomerania Car bon if er ous or the Rotliegend clastics are gas res er voirs sealed by Zechstein evap o rates: if the Rotliegend rocks are miss ing the role of res er voirs be longs to the po rous Car bon if er ous clastics (Kozłowska, 2005). The po - ros ity and per me abil ity of clastic rocks are strongly vari able.
This is par tic u larly so for the Rotliegend con glom er ates char - ac ter ized by very low po ros ity/per me abil ity val ues (Rusek et al., 2005). Res er voirs within the Main Do lo mite unit are grainstones and packstones con nected to the bar rier and la - goonal fa cies. The pres ent good po ros ity/per me abil ity pa ram e - ters are the ef fects of com plex diagenesis pro cesses. As a re sult frac tures have been formed and were later filled with oil (Karnkowski, 1993). The Main Do lo mite de pos its are very well sealed by the Stassfurt evap o rates.
GENERATION AND MIGRATION OF HYDROCARBONS
The prob lems of hy dro car bon gen er a tion re gard first of all the re con struc tion of time, place (space) and the ex tent of pro - cesses lead ing to the trans for ma tion of or ganic mat ter into liq - uid or gas eous hy dro car bons. In the on shore part of the Bal tic Ba sin the re sults of com puter-aided mod el ling show that the main phase of hy dro car bon gen er a tion was not later than at the end of Car bon if er ous time (Karnkowski, 2003; Wróbel et al., 2009). The same con clu sions are valid for the off shore area north of the Łeba–Gdańsk coastal line. Perm ian–Me so - zoic palaeotectonic events in the area dis cussed have con trib - uted mainly to the mi gra tion and ac cu mu la tion of hy dro car - bons. The best res er voir prop er ties are in the Mid dle Cam - brian sand stones (Sikorska and Pacześna, 1997) and con se - quently they con sti tute pri mary ex plo ra tion tar gets. On the ba - sis of mod el ling in East ern Pomerania (Karnkowski, 2003) and anal y sis of the Gdańsk off shore area a map of hy dro car - bon zones at the top of Cam brian was pre pared (Fig. 5A): the
“oil win dow” at the top of the Up per Cam brian is rel a tively nar row in the on shore area and con sid er ably wider in the Gdańsk Bay and ad ja cent off shore re gion. The “gas win dow”
dom i nates in the on shore area and con tin ues off shore within the Słupsk Block (Fig. 3). The mar ginal part of the EEC is lo - cated in the overmature zone (Ro >2%), so within the Up per Cam brian rocks only dry gas may be ex pected (Fig. 5A).
Fig. 4. Map of the re cent heat flow in the study area (rect an gle) and ad ja cent re gions (af ter Karwasiecka and Bruszewska, 1997)
Fig. 5. Ex tent of hy dro car bon zones in the main ex plo ra tion tar gets
A – at the top of Cam brian (East ern Pomerania; Karnkowski, 2003, ex tended and sup ple mented); B – in the Zechstein Main Do lo mite (Karnkowski, 1999, 2000, ex tended and sup ple mented); other ex pla na tions as in Fig ure 1
A very im por tant el e ment in the anal y sis of hy dro car bon gen - er a tion here are oil fields dis cov ered in the Kaliningrad Dis - trict. Also, the lack of sig nif i cant pe tro leum dis cov er ies in the on shore Gdańsk re gion de mands ad di tional ex pla na tion. It seems that the pre lim i nary an swer for the above par a dox re - gards the pres ent heat flow dis tri bu tion in the Cen tral Eu rope (Fig. 4), in clud ing the Kaliningrad Dis trict (Plewa et al., 1992; Karwasiecka and Bruszewska, 1997). North to the Pol - ish state bor der (north to the Mazury and Warmia re gion) a high and dis tinct geo ther mal anom aly is marked which em - braces not only the Kaliningrad Dis trict but also all of Lith u a - nia (cf., Karnkowski, 2003). This phe nom e non, a rel a tively high value of the or ganic mat ter ma tu rity in the Lith u a nian part of the Bal tic re gion that Lazauskiene and Mar shall (2002) re cently ana lysed. In Po land, within the Mazury High area, a large neg a tive heat flow anom aly can be ob served. The geo - ther mal field of the north ern slope of the Mazury High is char - ac ter ized by rapid change from a low to a high value of heat flow (Fig. 4). The pres ence of the Lith u a nian geo ther mal anom aly, with a pro lon ga tion to the Kaliningrad Dis trict, can ex plain the good palaeogeothermal con di tions for hy dro car - bon gen er a tion in the Pa leo zoic source rocks de spite their shal low burial.
In the last few years a cou ple of pa pers re fer ring to hy dro - car bon gen er a tion in the Peribaltic Syneclise were pub lished (Nehring-Lefeld et al., 1997; Swadowska and Sikorska, 1998;
Grotek, 1999). For geo log i cal anal y sis, vitrinite reflectance di - ver sity was used. The re sults of the anal y sis sug gest that the Pa - leo zoic palaeogeothermal gra di ent was higher than the pres ent one, and the main fac tor con trol ling the trans for ma tion of or - ganic mat ter into hy dro car bons was the depth of burial. Hence in the bor der zone of the EEC the Ro within the lower Pa leo zoic rocks is rel a tively high.
West ern Pomerania, in the last few years, has been in ten - sively stud ied and geo log i cally mod elled to es tab lish the con di - tions of hy dro car bon gen er a tion for the Car bon if er - ous–Rotliegend and the Zechstein de pos its (Karnkowski, 1996, 1999, 2000; Kosakowski et al., 2009). The re sults of geo log i cal mod el ling of the early Pa leo zoic gen er a tion con di - tions (Karnkowski, 1996) here in di cate high heat flow val ues.
High palaeoheat flow in the late Pa leo zoic de graded cel lu lose into ni tro gen. In north west ern Po land the meth ane con tent in the Car bon if er ous and the Rotliegend res er voirs var ies be - tween 50–15%. A higher ni tro gen con tent is known in the west ern part of Pomerania, close to the Odra River. In East ern Ger many the con tent of ni tro gen ex ceeds 90%.
In the late Zechstein heat flow val ues sig nif i cantly de - creased in re la tion to the pre vi ous pe riod (Karnkowski, 1996).
The heat flow pat tern in West ern Pomerania dur ing the pe riod from the late Perm ian to the pres ent has not changed fun da - men tally (Karnkowski, 1996). These palaegeothermal con di - tions caused that the Main Do lo mite de pos its en tered very late into the phase of pe tro leum gen er a tion, in the early Cre ta ceous, and in a way this pro cess con tin ues un til to day (Karnkowski, 2000). Dif fer en ti a tion of ther mal field and burial his tory caused that the “oil win dow” zone in West ern Pomerania is lim ited to a nar row belt, 5–30 km in width (Fig. 5B). All oil fields in the Main Do lo mite unit dis cov ered within the area dis -
cussed are in the mod elled “oil win dow” (Karnkowski, 1999, 2000, 2007a). This rea son re strict the area of ex plo ra tion to a nar row belt, but it en ables con cen trat ing of ex plo ra tion tar gets in better spec i fied re gions. Un for tu nately, the off shore area of the Main Do lo mite oc cur rence in the area of Pomerania Bay is lo cated in the tran si tion (oil-gas) zone of hy dro car bon gen er a - tion. The chances of oil or gas dis cov er ies are lim ited to the south ern part of Pomerania Bay.
HISTORY OF PETROLEUM EXPLORATION
Pe tro leum ex plo ra tion in North ern Po land be gan in the 1950s. At first the East Eu ro pean Plat form was in ves ti gated, but small oil fields were dis cov ered only in the on shore peribaltic zone (Ta ble 1). As a re sult of ex plo ra tion ac tiv ity (1955–2001) in the on shore Pomerania re gion four oil fields in Cam brian sand stones and seven gas fields in Car bon if er ous sand stones, six gas fields in Rotliegend sand stones and eleven oil fields within the Zechstein Main Do lo mite ho ri zon were dis - cov ered. The oc cur rence of oil fields in East ern Pomerania is lim ited mainly to the coast and off shore Bal tic area in the Pol ish eco nomic sec tor (Figs. 6 and 7; Ta ble 1).
The foun da tion of the “Petrobaltic” Joint Ven ture (1975) gave a new im pulse to ex plo ra tion in the eco nomic zones of Po - land, the for mer So viet Un ion, and the for mer Ger man Dem o - cratic Re pub lic. To date in the Pol ish eco nomic sec tor off shore hy dro car bon fields have been dis cov ered only in the Cam brian de pos its north of Gdańsk Bay (Figs. 6 and 7A). Po lit i cal and eco nomic changes in East ern Eu rope at the end of the 1980’s trans formed the In ter na tional “Petrobaltic” Com pany into the solely Pol ish “Petrobaltic”. The main ac tiv ity of the pres ent
“Petrobaltic” has fo cused on ex ploi ta tion of the fields dis cov - ered. New bore holes were drilled and field B4 started pro duc - tion in 1996. The next oil field B3 was ready for ex ploi ta tion in 2006. From 2003 “Petrobaltic” started to trans form as a pri vate com pany and now the LOTOS Group (a pet ro chem i cal com - pany) is al most the sole owner of it.
The sig nif i cant in crease in re sources in the West ern Pomerania re gion was in the years 1970–1980 due to nu mer ous bore holes (about 100). Oil fields were quickly de vel oped and al most all oil re serves were ex ploited. Gas in this re gion con - tains 50–60% meth ane and some times less (Ta ble 1). Not all gas fields were de vel oped and only half of the re sources were ex ploited. The last 25 years of ex plo ra tion in this area did not yield sig nif i cant suc cesses.
NON-CONVENTIONAL PETROLEUM RESOURCES
A gen eral over view of the pro spec tive ex plo ra tion area with re gard to con ven tional el e ments of pe tro leum play was pro vided by Karnkowski (2007b) in the pa per con cern ing pe - tro leum prov inces in Po land. For the Cam brian de pos its – in the area of Peribaltic Syneclise – the oil pro duc tion ho ri zons are the
Mid dle Cam brian sand stones. The oil and gas fields dis cov ered up to now (es pe cially in the off shore Bal tic area and Kaliningrad Dis trict) show that main type of trap is a close-to-fault anticline. Res er voir prop er ties de crease with in - creased depth. Con sid er ing the large oc cur rence of Cam brian rocks it was stated that al most in whole area of the Pol ish part of the EEC these de pos its have ex plo ra tion per spec tives. There is a prob lem of res er voir rocks with low petrophysical pa ram e - ters such as the Cam brian sand stones ly ing deeper on the slope of the Peribaltic Syneclise (tight gas sand stone type).
A gen eral re view of the tight gas and shale gas po ten tial in Po land is given in pa per of Poprawa and Kiersnowski (2008).
For the shale gas per spec tives the Up per Or do vi cian and the lower Si lu rian shales in the Pol ish part of the EEC are in di cated (Grotek, 2009; Klimuszko, 2009). The re sults of geo log i cal mod el ling (Karnkowski, 2003) sug gest the pos si ble oc cur rence of such gas de pos its in the Peribaltic Syneclise. The mod elled geo log i cal as well as eco nomic con di tions will be a pos i tive
fac tor if the petrophysical-geo chem i cal pa ram e ters of these rocks en able re al iza tion of the “shale gas” pro jects.
The pres ent world ex plo ra tion ten den cies in di cate in creas - ingly more pos si bil i ties for gas from un con ven tional (tight gas and shale gas) de pos its. Spec i fi ca tion of ex ploi ta tion of un con - ven tional pe tro leum re sources does not pre fer (at least pres - ently) off shore ar eas for ex plo ra tion of this type of de posit in the south ern Bal tic re gion. Rather good per spec tives, how ever, ex ist within the on shore Peribaltic area (Fig. 8). It seems most rea son able was to con cen trate on con ven tional gas struc tures with low po ros ity/per me abil ity val ues. The ob jects are known and only a stim u la tion pro cess is nec es sary. To pre pare such stim u la tion a large amount of geo log i cal in for ma tion is re - quired con cern ing:
– tech nol ogy of stim u la tion,
– con tent of gas in res er voir rocks and pos si bil i ties of its ex ploi ta tion,
Field name Dis cov ery Res er voir stratigraphy Main fluid type Dis cov ered re sources Re marks WESTERN POMERANIA
Międzyzdroje E 1970 Rotliegend (P1) Gas 0.41 Bcm 20–22% HC
Międzyzdroje W 1971 Rotliegend (P1) Gas 0.40 Bcm 20–22% HC
Międzyzdroje 1971 Main Do lo mite (Pz2) Oil 0.118 MMt
Przytór 1971 Rotliegend (P1) Gas 0.48 Bcm 20–22% HC
Wierzchowo 1971 Car bon if er ous (C1) Gas 0.55 Bcm 70% HC
Kamień Pomorski 1972 Main Do lo mite (Pz2) Oil 4.7 MMt as so ci ated gas: 12% H2S, 80 HC
Petrykozy 1974 Main Do lo mite (Pz2) Oil 0.027 MMt
Rekowo 1975 Main Do lo mite (Pz2) Oil 0.096 MMt as so ci ated gas: 5% H2S
Wrzosowo 1975 Car bon if er ous (C2) Gas 0.73 Bcm 40% HC
Gorzysław N 1976 Car bon if er ous (C2) Gas 1.68 Bcm 40–45% HC
Gorzysław S 1976 Car bon if er ous (C2) Gas 0.59 Bcm 40–45% HC
Trzebusz 1978 Car bon if er ous (C2) Gas 0.14 Bcm 40–45% HC
Wysoka Kamieńska 1978 Main Do lo mite (Pz2) Oil 1.4 MMt as so ci ated gas: 91% HC
Błotno 1980 Main Do lo mite (Pz2) Oil 0.165 MMt as so ci ated gas: 5% H2S
Daszewo 1980 Main Do lo mite (Pz2) Oil 0.567 MMt
Daszewo N 1980 Car bon if er ous (C2) Gas 1.79 Bcm 65% HC
Daszewo N ropa 1980 Main Do lo mite (Pz2) Oil 0.1 MMt
Ciechnowo 1981 Rotliegend (P1) Gas 0.83 Bcm 45–47% HC
Białogard 1982 Rotliegend (P1) Gas 0.74 Bcm 52% HC
Brzozówka 1989 Main Do lo mite (Pz2) Oil 0.124 MMt
Tychowo 1989 Main Do lo mite (Pz2) Oil 0.042 MMT
Sławoborze 2001 Main Do lo mite (Pz2) Oil 0.155 MMt 0.475 Bcm of gas
EASTERN POMERANIA
Dębki 1972 Cam brian Oil 0.43 MMt as so ci ated gas: 95% HC
Żarmowiec 1972 Cam brian Oil 0.5 MMt as so ci ated gas: 95% HC
Żarnowiec W 1973 Cam brian Oil 0.055 MMt
Białogóra E 1990 Cam brian Oil 0.0145 MMt
OFFSHORE (Pol ish part of the Balic Sea)
B3 1981 Cam brian Oil 5.3 MMt wa ter depth: 80 m
B4 1981 Cam brian Gas 2.0 Bcm wa ter depth: 60 m
B6 1982 Cam brian Gas 1.8 Bcm wa ter depth: 70 m
B8 1983 Cam brian Oil 3.7 MMt wa ter depth: 80 m
T a b l e 1 Oil and gas fields in the Pol ish part of the Bal tic re gion: his tory of dis cov er ies and re sources
– geo chem i cal and petrophysical prop er ties of source and res er voir rocks,
– pe trol ogy of the rocks in terms of their sed i men tary en - vi ron ment, lithofacies, min er al ogy, pore struc ture and types of ma trix,
– pat tern of joints (both ex ist ing and fu ture – those which have to arise as re sult of the stim u la tion pro cess), – geomechanical prop er ties of the rocks,
– com par a tive study on sim i lar con di tions and tech nol ogy in other pe tro leum prov inces.
In the au thor’s opin ion the Cam brian rocks of the EEC should be the first ob ject of in ter est: a pe tro leum sys tem is proved by the ex is tence of oil and gas fields in the Cam brian de pos its, seis mic ac qui si tion and pro cess ing gives good re sults in struc tural in ves ti ga tion and the pres ent state of and suc cesses in hy drau lic stim u la tion of tight gas res er voirs in Po land guar - an tees a rea son able level of ex plo ra tion econ omy. Fur ther ac - tiv ity should be to ex plore the Up per Or do vi cian and the lower Si lu rian shales lo cated in the mar ginal zone of the EEC.
CONCLUSIONS
1. The anal y sis of burial and ther mal his tory of the Paleozoic suc ces sions in the southern Bal tic area (west ern part of the Bal tic Ba sin) shows a vast area within the oil win dow. It is much greater than in the on shore area, ex plain ing the oc cur - rence of oil fields in the off shore Bal tic.
2. Cam brian traps for oil have a struc tural form and they are as so ci ated with faults along which mi gra tion of hy dro car bons occurred.
3. In the area of the “gas win dow” and of “dry gas”
(Ro >2%) res er voir prop er ties of the Cam brian rocks are rather low due to in tense diagenetic pro cesses (tight gas). Ac qui si tion of gas should be pos si ble by pro cesses of hy drau lic in ten si fi ca - tion of ex ploi ta tion.
4. Lower Pa leo zoic rocks rich in or ganic mat ter, es pe cially in the bor der zone of the EEC (Ro >1.3%), could be an area of un con ven tional gas fields (shale gas). The most pro spec tive area is on shore lo cated, and may be prof it able as re gards the econ omy of fu ture shale gas.
Fig. 6. Oil and gas fields in the Pomerania re gion and ad ja cent off shore area (af ter Karnkowski, 1993 and “Petrobaltic” data) Ex pla na tions as in Fig ure 1
Fig. 7. Se lected ex am ples of the oil and gas fields in the Pomerania re gion and ad ja cent off shore area
A – B8-2/05 (oil field); B – Żarnowiec W (oil field); C – Wrzosowo (gas field); D – Kamień Pomorski (oil field; af ter Karnkowski, 1993 and
“Petrobaltic” unpubl. data); PCm –Pre cam brian, Cm1 – Lower Cam brian, Cm2 – Mid dle Cam brian, Cm3 – Up per Cam brian, O – Or do vi cian, S – Si - lu rian, D1 – Lower Dewonian, D2+3 – Mid dle and Up per De vo nian, C2 – up per Car bon if er ous, P1 – Rotliegend, P2 – Zechstein, A1G – Up per Anhydrite, Ca2 – Main Do lo mite, A2 – Basal Anhydrite, Na2 – Older Ha - lite, A2G+Z3 – Screen ing Anhydrite and Leine cyclothem
Fig. 8. Po ten tial “shale gas” fields in the Pomerania area A – ex tent of the “gas win dow” in the Si lu rian de pos its;
B–D – cross-sec tions show ing ex tent of hy dro car bon zones (af ter Karnkowski, 2003, sup ple mented)
5. The southern Bal tic ly ing on the west to the T-T line has pe tro leum sys tems: the up per Pa leo zoic (Car bon i f er - ous– Rotliegend) and the Zechstein (Main Do lo mite car bon - ates) ones. This lat ter one is marked as a pro spec tive area only in Pomerania Bay.
6. The Carboniferous–Rotliegend pe tro leum sys tem in the south ern Bal tic is weakly ex plored. Partly the Rotliegend clastic rocks there are eroded or non-de pos ited. The Car bon if - er ous rocks of Pomerania are strongly dis lo cated which make ex plo ra tion of gas fields dif fi cult. A content of gas with more than 50% of meth ane could be a pos i tive el e ment in eval u a tion of pros pects. Shale gas ex plo ra tion is not out of the ques tion.
7. Hith erto dis cov ered hy dro car bon de pos its in Cam brian rocks, es pe cially within the off shore zone, con firmed the good per spec tives of the Gdańsk Pe tro leum Province.
8. To the west of the T-T Zone ex tends the Pomerania Pe - tro leum Prov ince the per spec tives of which are only partly proved by bore holes. Off shore in the Pomerania Bay is an ex - plo ra tion chal lenge.
Ac knowl edg ments. The au thors wish to ex press their grat - i tude to Dr. Hilmar Rempel and the sec ond anon y mous re - viewer who gave their time and en ergy en sur ing the qual ity of the pub lished pa per. We are ex tremely grate ful for their com - mit ment and ded i ca tion to the peer re view pro cess.
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