Annales Societatis Geologorum Poloniae (2011), vol. 81: 363–373.

PETROPHYSICAL PROPER TIES OF THE PRE-MIO CENE ROCKS OF THE OUTER ZONE OF THE UKRAINIAN CARPATHIAN FOREDEEP

Ihor KUROVETS1, Hryhoriy PRYTULKA1, Andriy SHYRA1, Yulia SHUFLYAK1 & Tadeusz M. PERYT2

1 In sti tute of Ge ol ogy and Geo chem is try of Com bus ti ble Min er als of Na tional Acad emy of Sci ences of , Naukova 3a, 79060 , Ukraine, e-mail: [email protected] 2 Polish Geolog i cal Insti tute – Nati onal Re search Insti tute, Rakowiecka 4, 00-975 Warszawa, , e-mail: [email protected]

Kurovets, I., Prytulka, H., Shyra, A., Shuflyak, Y. & Peryt, T. M., 2011. Petrophysical prop er ties of the pre-Miocene rocks of the Outer Zone of the Ukrai nian Carpathian Foredeep. Annales Societatis Geologorum Poloniae, 81: 363–373.

Ab stract: The pa per sum ma rizes the re sults of var i ous lab o ra tory stud ies of core ma te rial, in clud ing po ros ity, per meabil ity, lithological-fa cies and struc tural and tex tural char ac ter istics of more than 1,000 samples of Me so- zoic and Palaeozoic rocks. The petrophysical param e ters of siliciclastic and carbon ate rocks are analysed for the to tal of sam ples rep re sent ing dif fer ent lithologies (lime stones vs. sandstones ) as well as for partic u lar stratigra- phic in ter vals (Up per and Lower Cre ta ceous, Up per Ju ras sic, Mid dle and Lower Ju ras sic, and Palaeozoic). The terrigenous rocks with inter gra nu lar po rosity and frac ture-cav ern ous car bonate rocks of reefal fa cies form the best res er voir rocks within the Me sozoic. The terrigenous rocks of frac tured and frac tured-po rous type that are con - trolled by the fault-block tec ton ics pro vide the best Palaeozoic and Ediacaran reser voirs.

Key words: res er voir prop er ties, sand stone, lime stone, Palaeozoic, Me sozoic, Carpathian Foredeep, Ukraine.

Manu script re ceived 12 May 2011, ac cepted 3 November 2011

IN TRO DUC TION Autochthonous de posit s of the Carpathian region, in - Derzhiv, Bohorodchany, and Davydeny, among the others. cluding the substra te of the Outer Zone of the Carpathian In the core sam ples from the Cam brian sandstone s one can Foredeep, are consid ered to be the prime object for pros- observe oil shows, and during test ing of these sandstone s pection and explo ra ti on of oil and gas in western Ukraine the insig nif i cant oil influx has been obtai ned. Oil and gas (Krups’kiy, 2001; Kolodiy et al., 2004). Although Miocene shows in the Silu ria n depos it s have been obtai ned during (Sarmatian) sandstone s rem ain the most im portant tar gets the well drilling in ar eas: Derzhiv, Slobidka Lisna, Davy- for nat ural gas (e.g., Kurovets et al., 2004), there is a num - deny, and Krasnoil’s’k. In parti cu lar , in the latter area, in ber of hy drocar bon fields re lated to the Upper Juras sic and boreholes 1 and 5 one could observe degas sing of the drill - Creta ceous depos it s in this zone; they include Kokhanivka, ing mud. Accord ing to archi val data, several zones of in- , and Orkhovychy oil fields; Letnia gas- creased hy dro car bon con tent were dis tin guished in the conden sat e field; and , Medenychy, Bilche-Volytsia, Cambrian sec tion in the Davydeny 1 borehole. Taking into Uhers’ko, Mala Horozhanna, Hrudiv and Vereschytsia gas accoun t these data as well as the discov ery of the Uszkowce fields (Fig. 1) (Kotarba et al., 2011). In the north-west ern nat u ral gas field oc cur ring in the Or do vi cian–Si lu rian de- part of the Outer Zone, oil inflows from the Up per Juras sic posit s (Karnkowski, 1999) and of several gas fields (Lacho- limestone s were found in the Vyzhomlia, Tyniv and Nyklo- wice-Stryszawa, Zalesie, Niwiska) in the Devo nian de pos its vychi ar eas (Fig. 1). In the south-western part of the zone of SE Poland (Karnkowski, 1999), the Palaeozoic and Pre- under the Carpathian Overthrust, the Lopushna oil field oc - cam brian depos it s of the Outer Zone of the Ukrai nian Car- curring in the Upper Juras sic , Cre taceous and Palaeogene pathian Foredeep are regarded to be prom ising for com mer- de pos its was dis cov ered. cial oil and gas explo ra ti on. The ar chi val data in di cate that oil and gas oc cur rences One of the princi pal factors of the form ati on and pres er- were also record ed in the Palaeozoic de pos its in ar eas of vati on of hydro car bon depos it s is the avail abil ity of the res - Kokhanivka, Rudky, Mostys’ka, Chyzhevychy, Zaluzhany, ervoir rocks and fluid-im perm eable beds. The res ervoir pro- 364 I. KUROVETS ET AL.

Fig. 1. Tec tonic map of the Carpathian oil- and gas-bear ing re gion (from Vul et al., 1998). 1 – 30: Fields of the Bilche-Volytsia oil- and gas-bear ing re gion

perties of the Pre cam brian and Palaeozoic rocks of the GEOLO GI CAL FRAMEWO RK Ukrainian Carpathian Foredeep as well as its Meso zoic de - posit s were studied rarely (Kurovets, 2001; Lyzun et al., Figure 1 shows the tectoni c posi ti on of the Carpathian 2004). Therefore, we have analy sed reser voir proper ti es of oil- and gas-bearing re gion (Vul et al., 1998). The block Meso zoic and Palaeozoic rocks in the Outer Zone of the struc ture, the availabil ity of multi-storey struc tural com - Ukrai nian Carpathian Foredeep aim ing to estab li sh the ba- plexes and the dipping of the eroded surface of the pre-Mio- sic geo log i cal fac tors con trol ling the ca pac ity-fil tra tion cha- cene strata to wards the Carpathians, in the form of sep arate racteristic. steps across the system of longi tu di nal tectoni c frac tures, PETROPHYSICAL PROP ER TIES OF THE PRE-MIO CENE ROCKS 365

Fig. 2. SSW–NNE geo log i cal sec tion along A–A’ line in Fig. 1 (based on Vul et al., 1998)

Ta ble 1 Petrophysical sec tion of the pre-Neogene of the Outer Zone of the Ukrai nian Carpathian Foredeep (based on archi val data and the origi nal result s shown in Table 2)

are char acter istic for the Outer Zone of the Ukrai nian Car- sion) where they occur di rectly under the Miocene form a- pathian Foredeep (Fig. 2; cf. Kotarba et al., 2011). tions and were encoun ter ed in many boreholes (Glushko & Within the limits of the Outer Zone of the Ukrainian Car- Kruglov, eds, 1977; Stupka, 1993), includ ing several wells pathian Foredeep, Me so zoic, Palaeozoic and Up per Pro tero - locat ed in the Chyzhky and Mostys’ka re gions near the bor- zoic de pos its oc cur below the Mio cene (Ta ble 1), the latter der with Poland. However, as stressed by Bu³a and Habryn includ ing the depos it s assum ed so far to be of the Riphean (2011), the rocks consid ered to be Riphean in Ukraine are sim - age (Kruglov & Tsypko, eds, 1988; Stupka, 1993; Mizerski ilar to the Ediacaran flysch depos it s of the Ma³opolska Block & Stupka, 2005). These depos it s are widely distri buted in the in SE Poland, and in addi ti on their Ediacaran age is supporte d north-western part of the Outer Zone (Krukenychy Depres - by palynological studies of Jachowicz-Zdanowska (2011). 366 I. KUROVETS ET AL.

In the north-east ern part, their dis tri bu tion is limited by overlain by the Miocene . Most secti ons exposed by bore- the Fault, and towards the southwest the Edia- holes are known to occur in areas of Uhers’ko, Bilche- caran depos it s are covered by the unit and then by Volytsia, Pivnichni Medynychy and Letnia where their the -Pokuttya unit and Skyba nappe of the Outer thickness is from 570 to 720 m. The Upper Creta ceous is Carpathians. The data of seis mic sur vey in di cate that the to - rep re sented by the Cenomanian–Maastrichtian strata (Pas- tal thick ness of the Ediacaran de pos its is sev eral kilo metres, ternak et al., 1987). and only its top part (maxi m um 199 m in the Tvirzha 3 bore - The Cenomanian is com posed of yellow-gre y and grey- hole) was drilled. green quartz-glauconitic sandstone s with an adm ixture of The Palaeozoic devel oped along the north-western mar- gravels and pebbles of black flints, and then the sandstone s gin of the Outer Zone and is com posed of the Cam brian, Or- are fol lowed by grey and yel low-grey sandy inoceramid do vi cian, Si lu rian and De vo nian sed i ments (Drygant, 2000). limestone s and marls. The Turonian is com posed of white The Cam brian rocks are distri buted alm ost every where and grey bioclastic and micritic, frac tured limestones along the Carpathian Foredeep in the form of a 20-km-wide interbedded with marls, clays, fine-grained sandstone s and strip (with the excep ti on of the Krukenychy Depres sion). aleurolites. The Coniacian–Maastrichtian part of the Up per They are exposed by a num ber of wells in the region of Pid- Creta ceous sec tion consis ts of grey and yel low-grey in col- luby, Kokhanivka, Dobryany, Verbizh, Mala Horozhanna, our, quartz, fine- and medium -grained, poorly sorted, dense Derzhiv, Rudky, , and Davydeny. The greatest sandstone s interbedded with aleurolites, lime claystones, thickness of depos it s, over 1,200 m, was found in the Derz- marls and micritic limeston es. Rapid lithofacies changes, hiv 1 bore hole. The thickness of depos it s in the Davydeny 1 from sand stones to limestones and claystones, are char ac - borehole is 805 m. ter is tic. Sand stones and lime stones are dom i nant lithologies The thin Or do vi cian de pos its are dis trib uted lo cally. in the north-west ern part of the Outer Zone. They were encoun ter ed by the boreholes in ar eas of Chor- nokuntsi, , Kokhanivka, , Rudky, Medy- nychy, and Dashava. MA TE RIAL AND METH ODS The Silu rian de pos its are widely dis trib uted in the Car- pathian Foredeep and occur in the form of strip, recorded by In ves ti ga tion in cluded a com plex of lab o ra tory stud ies boreholes in ar eas of Pidluby, Derzhiv, Stavchany, and of the core ma te rial in clud ing ca pac ity-fil tra tion prop er ties Krasnoil’s’k, among others. of rocks and their lithological and petro log i cal charac ter is- The Lower Devo nian de posit s occur in the far south- tics. True specific grav ity was de ter mined by pycnometric east of the Outer Zone where they were drilled by num erous method and the appar ent vol ume weight by hydro sta tic bore holes. weighting. Factor of total poros it y is deter mined by the clas - The Meso zoic depos it s occur in alm ost the whole terri - sical Melcher’s (1920) method, and fac tor of open poros it y tory of the Ukrai nian Carpathian Foredeep, with the excep - by the classi cal Preobrazhensky’s (1932) method, in which tion of its north-west ern part where di rectly under the Mio - the vol ume of open pores is define d by the volum e of kero - cene de pos its the Palaeozoic and Pre cam brian for mations sene being got into porous space, and the vol ume of the occur (Bu³a & Habryn, 2011). The Meso zoic sequence is sam ple by hy dro static weight ing in ker o sene. rep re sented by Lower Ju ras sic–Up per Cre ta ceous rocks Perm eabil ity is measured by pumping of gas (nitro gen, (Pasternak et al., 1987; Danysh et al., 2004). air) under pres sure through the sam ple of cyli ndri cal shape, The Lower Juras sic depos it s are known from the areas and is deter mined by the vol ume of gas that passed through of Pivnichni Medynychy, Hrushiv, Korolyn, Bortiatyn, and the trans verse sec tion of the sample at given dif fer en tial Chornokuntsi. The Middle Juras sic depos it s occur in the pressure and at given time. north-western part of the Outer Zone (terrigenous rocks of In ad di tion, pre vi ous ar chi val data on lab o ra tory stud ies marine facie s – the Kokhanivka suite) and in its south-west- were com piled. By using stati sti cal methods the petrophy- ern part (basal con tinen tal facies). The Up per Ju ras sic de - sical pa ram eter s of more than one thousand sam ples of posit s, in turn, occur with the excep ti on of the far north- rocks from the Me so zoic and Palaeozoic de pos its were ana - west ern part of the Outer Zone and are com posed of la- lysed. Petrophysical param eter s of terrigenous and carbon - goonal and shal low-wa ter ma rine for ma tions (Karpenchuk ate rocks were analysed sep arately both for the to tal sam ples et al., 2006; Krajewski et al., 2011). and for stratigraphi cal subdi vi sions of the Upper and Lower The Creta ceous de pos its de vel oped in the plat form fa- Cre ta ceous, Up per Ju ras sic, Mid dle and Lower Ju ras sic and cies. In the north-west ern part of the Outer Zone they are Palaeozoic. The fol low ing res er voir char ac ter is tics were lacking. The Lower Cre taceous depos it s were exposed by analysed: open po ros ity and ab so lute per me abil ity, vol u- the major it y of bore holes and are best studied in areas of metric weight, and car bon ate con tent. Bilche-Volytsia, Pivnichni Medenychy, Dashava, Kokha- nivka, Uhers’ko, and Pidluby. They are com posed of grey- green calcar eous sand stones, clayey aleurolites, clayey and RE SULTS sandy limestone s and dark-grey lime claystones. In the north-west, the organodetrital and pseudoölitic limestone s Our origi nal result s are sum mariz ed in Table 2, and our are widely distri buted (Radkovets’, 2005). re sults and ar chi val data are sum marized in Ta ble 1. Be low, The Up per Cre ta ceous de pos its oc cur transgressively we pres ent a short pre senta ti on of main result s for parti cu lar on the Lower Creta ceous rocks and are uncon form ably strati graphi cal in ter vals and prin ci pal lithologies (Figs 3–6). PETROPHYSICAL PROP ER TIES OF THE PRE-MIO CENE ROCKS 367

Ta ble 2 Petrophysical proper ti es of Juras sic and Creta ceous depos it s of the Letnia, Makuniv, Nyklovychi and Susoliv areas

Specific Electrical resistivity Wm Number of Open Carbonate Interval Permeability density of Area measu- Lithology Stratigraphy porosity content [m] × 10–3 µm2 rock saturated rements Ro % rock g/cm3 solution 103 1,668–2,566 limestone Upper 0.2–8 0.01–1.19 2.46–2.73 41–98.2 6.5–272.2 0.08 87 1,492–2,876 sandstone Jurassic 0.9–12.3 0.01–113.7 2.18–2.68 0.8–48.2 3.2–57.5 0.08 55 1,541–1,850 limestone 1.4–7.4 0.001–0.52 2.5–2.68 56.3–92.9 6.4–114 0.0495–0.08 Letnia Lower 57 1,541–1,850 sandstone Cretaceous 1.5–12 0.1–9.37 2.1–2.7 9.6–49.9 3.5–43.5 0.08 Upper 50 1,285–1,691 sandstone 1.8–28.8 0.01–2 1.71–2.65 0.7–49.6 2–70 0.0495–0.08 Cretaceous 15 2,395–2,416 limestone 0.8–1.4 2.67–2.74 54–72.7 187–295 0.08 Makuniv 10 1,254–2,357 sandstone 1.6–2.8 2.3–2.64 12.8–20.5 26.2–53.4 0.08 60 1,948–2,275 limestone Upper 0.1–5.9 0.02–5.8 2.52–2.71 52–100 18.8–221.3 0.0495–0.08 Nyklovychi 75 1,942–2,161 sandstone Jurassic 0.4–24.6 0.01–175 2.06–2.9 2.3–41.5 11.1–150.8 0.0495–0.08 10 2,637–2,747 limestone 0.9–1.4 2.7–2.71 83.2–87.2 192.5–220.3 0.0495 Susoliv 16 2,999–3,005 sandstone 1.5–5.4 0.01–75 2.4–2.55 1.2–31.0 79.1 0.08

Ediacaran frac tured-po rous res er voirs in the Cam brian de pos its. They are de veloped mainly within the lim its of erosiona l and The Ediacaran de pos its are grey, grey-green and red- tectono-erosiona l upli fts where rocks have under gone the brown schists and phyllites interbedded with quartzit e-like denu da ti on for a long time and thus vari ous pore types were oligomictic fine- and medium -grained sandstone s, aleuroli- formed. Just in such reser voirs gas is enclos ed in the Cam - tes and si liceous claystones. Claystones are dark-grey to brian depos it s at Cetynia in the Pol ish Carpathian Foredeep black in col our, strongly cem ented, frac tured. The rocks are (Karnkowski, 1999). usuall y crushed and fracture d. The dips of beds are often 80 Poros it y in sandy-silty depos it s varies from 0.2 to 7%; to 90°. Labo ra tory studies of the core mate ria l show low po- per meabil ity is less than 0.1 10–3 µm2, ex cept of frac tured rosit y of sandstone s and aleurolites that varies from 0.4 to –3 2 –3 2 rocks where it at tains the value up to 0.53·10 µm . In the 11%, and perm eabil ity does not excee d 0.1 10 µm . In the proces s of well drill ing and dur ing the post-completional area of Khidnovychy and Pyniany, poros it y of sandstone s is –3 2 flow test the water inflows or insuf fi cie nt oil and gas show- 3.6 to 6.9%, and per meabil ity is less than 0.1 10 µm . In ings were obtai ned at many fields and pros pect ing ar eas. In the Kniahynychy 2 bore hole (3,930–3,933 m), poros it y of the Dashava 409 borehole, where poros it y of the Cam brian sandstone s is 4.1 to 8%, and poros it y of claystones is 0.3 to rocks is 4.3 to 5.3% and perm eabil ity is 0.01·10–3 µm2 ac - 2.33%.In the Tvirzha 1 bore hole, sandstone s at depths of cording to labo ra tory data, the brine inflows were obtai ned 3,610–3,655 m show poros it y of 9–11% and perm eabil ity of discharge ranging betwee n 40 and 60 m3/day. In the re- up to 1.0 10–3 µm2. The specif ic densit y of rocks is 2.42– 3 gion of the Kokhanivka oil field, the oil shows were found 2.7 g/cm . in the core sam ples of sandstone s, and during the testing in - The Ediacaran sandstone s and aleurolites belong to the sig nif i cant oil in flow was ob tained. low-po rous, com pli cated frac tured-po rous res er voirs that may con tain the hy dro car bon de pos its in fa vour able con di- tions. Or do vi cian The data on res er voir char ac ter is tics of Or do vi cian grey Cam brian aleurolites and claystone interbedded with lime-quartz sand - The Cam brian rocks (interbedded sandstone s, aleuroli- stones in the lower part and the organogenic-detri tal lime- tes and claystones) are strongly faulted, crushed by a thick stones in the up per part are rare. An analy sis of core mate rial network of frac tures with slicken side s; dips of beds vary has shown that in the Chornokuntsi 1 borehole poros it y of from 10 to 90°. Sandstone s and aleurolites are light- to dark- sandstone s and aleurolites is 0.4–6.7%, and perm eabil ity is grey quartz and oligomictic rocks contai ning abundant feld- less than 0.01·10–3 µm2; in the case of indi vid ual fracture d spars, fine- and medium -grained, fracture d, often resem - sam ples per me abil ity reaches about 0.35·10–3 µm2. bling quartzites. The thickness of interbeds of sandstone s var ies from 1 cm to several metres, and in places it ex ceeds Si lu rian 10 m. Claystones are dark-grey, black in colour, micaceous. To wards the Carpathians, rocks un der went sig nif i cant kata- The Si luria n sequence is repre sent ed by grey and dark- ge netic changes re flected in their den sity. grey calcareous sandstone s with thin (ca. 10 cm thick) inter- With the excep ti on of fracture d rocks that are concen - beds of aleurolites, fine-grained sandstone s, limestone s and trated near the fault zones one can in fer the ex istence of marls. The amount of carbon ate beds is bigger in the lower 368 I. KUROVETS ET AL. - r e v

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part of the sec tion. Claystones are strongly ce mented, dense Poros it y of sandstone s and aleurolites shows varies and schist-like. These are crushed and dislo cat ed rocks, and widely, from 1.9 to 24.8%. Reser voir rocks with open po- one can ob serve slick en sides and frac tur ing. Po ros ity of ros ity of 5.5–12.7% pre dom i nate. Per me abil ity of the grea- sandstone s and aleurolites in the Krasnoil’s’k area is 0.9 to ter part of core sam ples does not excee d 0.1·10–3 µm2. Per- 2.5%, and perm eabil ity is <0.1·10–3 µm2. Lithological and meabil ity of some sam ples of sandstone s reaches 190·10–3 petrophysical char ac ter is tics in di cate that this com plex can µm2 that indi cat es the occur rence of highly-porous and serve as a screen. well-perm eable beds in the secti on. Carbon ate content of the sandy-siltstone rocks varies from 1.7 to 45.3%. Porous and frac tured-porous sandy-siltstone rocks may be res ervoir Lower De vo nian rocks in depos it s of the Middle Juras sic . This is confirm ed Lithologically, this is a var ie gated se ries of mica carbo- by the core mate ria l sam pled from the Kokhanivka 9 bore- nate-free claystones, aleurolites and fine-grained quartz hole (depth 1,089–1,100 m), repre sent ed by the quartz ite- sandstone s. Sandstone s are grey in col our, someti mes red, like sandstone cut by a net work of microfrac tures filled with and contai n interbeds of sandy dolomites. The thickness of oil (Dolenko et al., 1969). interbeds of sandstone s and aleurolites is from several centi- metres to several metres. Poros it y of sandstone s in the Up per Ju ras sic Krasnoil’s’k area is 1.7–4.7%, and perm eabil ity is less than 0.1·10–3 µm2. There are com mer cial hy dro car bon ac cu mu la tions con - nected with the Upper Juras sic carbon ate depos it s in the Kokhanivka, Orkhovychy, Rudky, Vereschytsia, Letnia and Lower Juras sic Lopushna fields. The Callovian Rudky suite is com posed of These rocks are al ter nated grey, cal car e ous, me dium- organogenic and oolitic limestone s, occa sion all y sandsto- and vari ously -grained quartz sandstone s and aleurolites, nes, and the Yavoriv suite of sandstone s, aleurolites, gravel- clays and claystones with interbeds of coal. Content of silt- stones and conglom erate s. The Oxfordian depos it s are rep- stone grains aver ages 38%. Clastic mate ria l (55 to 75%) is resent ed by grey, brown-grey, dark-grey to black lime- com posed of quartz grains, 0.02–0.25 mm in size, and also stones interbedded with claystones. The Kimmeridgian de - of pelitized feld spars, zir co nium sil i cates, gar nets, chlorite posit s are in the la goonal-dolomitic facie s com posed of and musco vit e. Cem ent consis ts of sil ica-hydromica, car - limestones, dolomites, dolomitic marls interbedded with bon ate, clay, rarely gyp sum-anhydrite. The type of cem en - claystones, sand stones, and cal car e ous brec cia. Lime stones tati on is porous, filmy-porous and basal. Aleurolites are are light- and dark-grey in col our, someti mes brown, clayey composed mainly of quartz grains with small amount of mu- and aleuritic. The Tithonian de posit s are grey and dark- scovite, fragm ents of micro-grai ned sili con earth and grains grey, bedded, occasionally breccia limestones. of peli- tized feld spars. Ce ment is si der itic, clayey and Reef build-ups and the ad ja cent fore-reef and back-reef clayey-si der it ic. The type of ce men ta tion is po rous, basal- fa cies can be hy dro car bon-res er voir rocks in the car bon ate porous and basal. One can observe the exis tenc e of coalified depos it s. The Oxfordian bioherms (140 m thick) are con- plant organics in the form of long veinlet-like structure s, fined to the Horodok fault and oc cur along it in the form of a lenses and disperse d inclu sions in great quanti ty (Fig. 3a). strip about 10 km wide, and are passing into fore-reef for- Claystones are dark-grey and black in colour, pyritized, and mations in the west and the back-reef ones in the east. Later, en close frag ments and thin lenses of coaly mate rial and re - during the Kimmeridgian–Tithonian time, the form ati on of mains of coalified plant detri tus. The thickness of some reefs occurred in the zone of the Sudova Vyshnia fault. The sandy-siltstone beds reaches 6 m, and coal interbeds are up width of the barrie r reef is there about 10 km, and its maxi - to 2 m thick. Open poros it y of sandstone s and claystones mum thickness is about 1,000 m (Karpenchuk et al., 2006). var ies be tween 1 and 17%, per meabil ity is less than In the Upper Juras sic reser voir rocks, vari ous types of 0.5·10–3 µm2, specif ic densit y is 2.15–2.65 g/cm3, and car - po ros ity oc cur: intragranular, frac ture and frac ture-cav ern - bonate content is 1–32%. ous (Dolenko et al., 1969, Izotova et al., 2005). The reser - Porous and fracture d-porous sandy-siltstone rocks can voir type, its struc tural, tex tural pe cu liar i ties and ca pac ity- be res ervoir rocks in the Lower Juras sic depos it s. They are fil tra tion char ac ter is tics are closely con nected with its depo- connect ed with fluvial sys tems and offshore marine facies. sitional fa cies. Lime stones are of ten cav ern ous; cav erns are from 0.02 to 0.8 mm across. In some cases, caverns are de- veloped throughout the frac tures, form ing a kind of a chain. Mid dle Ju ras sic The caverns are often filled with oil. In the lower part of the Kokhanivka suite, the sandstone The poros it y of limestone s varies from 0.1 to 30.21%, unit (70 m thick) occurs with rare interbeds of gravelstone de pend ing upon the in ten sity of the cav ern de vel op ment. and limestone , and in the upper part the claystone unit is The lime stones are prac ti cally im per me able to show ing per - pres ent. The sand stones are quartzose, fine-grained, cal car - meabil ity up to 100·10–3 µm2 (Fig. 4A). The best reser voir eous. Cem ent is car bon ate and clayey-car bon ate of the po - char acter istics are found in the reefal limestones occur ring rous type. By min eral compo si tion, aleurolites are simi lar to in cores of the reefs, and in the carbon ate rocks re lated to the sandstone s. One can find rocks with si li ceous-clayey-si der- zones of un con formi ties (Dolenko et al., 1969). Intergra nu - itic cem ent of the po rous-basal type. Claystones are aleu- lar poros it y of the carbon ate rocks is low (mainly <5%), and ritic, mica-rich, pelitized, dense. per me abil ity is <0.1·10–3 µm2. There fore, the rocks are 370 I. KUROVETS ET AL.

Fig. 4. Po ros ity and log a rithm of per me abil ity for Up per Ju ras sic de pos its (A – limestones , B – sand stones) in par tic ular fields

Fig. 5. Po ros ity and log a rithm of per me abil ity for Lower Cre ta ceous de pos its (A – limestones , B – sand stones) in par tic ular fields

prac ti cally im per me able. In di vid ual in creased val ues of po - 2. High-po rous lime stones of or ganic-de tri tal type rosit y up to ca. 20–24% are caused by microcavernous char- that have high poros it y (15–20%) and high perm eabil ity (up acter of dolomites. Three princi pal types of the carbonate to 100·10–3 µm2); reservoir rocks occur in the Upper Jurassic: 3. Pseudoölitic limestone s with high poros it y (20– 1. Low-per me able lime stones with small inter gra nu- 30%), but low perm eabil ity. They may be reser voir rocks if lar po ros ity. The availabil ity of microfractures, caus ing there are fluid-con duc tive frac tures available. their per meabil ity, al lows us to clas sify them as compli cated The poros it y of sandstone s and aleurolites varies from low-porous res ervoirs of the mixed type; 2.2 to 28.4%, in most cases it is 15 to 20% (Fig. 4B). Perm e- PETROPHYSICAL PROP ER TIES OF THE PRE-MIO CENE ROCKS 371

Fig. 6. Po ros ity and log a rithm of per me abil ity for Up per Cre ta ceous de pos its (A – limestones , B – sand stones) in par tic ular fields

abil ity of sandy rocks reaches (80–90)·10–3 µm2. The range ies mainly from 0.01 to 10%, and for sepa rat e sam ples of of the change in densit y is from 1.96 to 2.74 g/cm3, but most rocks from the zones of uncon form iti es it reaches 15.9% com mon are values of 2.3–2.4 g/cm2. Wide de vel op ment of (Fig. 6B). The majo r ity of lime stones is prac tically imper - carbon ate cem ent (5–40%) in sandstone s and aleurolites me able, and per me abil ity of sep a rate sam ples reaches causes a con sid er able wors en ing of their res er voir pro- 34.6·10–3 µm2. perties.

Lower Cre ta ceous DIS CUS SION Rocks of the Lower Cre taceous are char acter ized by a The main geo log i cal fac tors de ter min ing the res er voir con sid er able het er o ge ne ity. Po ros ity of sand stones var ies charac ter isti cs of terrigenous rocks and their physi cal prop- within the lim its of 0.8–21.5%, and per meabil ity is (0.01– er ties are: the min eral compo sition, the shape, the size of 178)·10–3 µm2 (Fig. 3, 5B). As a rule, poros it y of calcar e ous fragmental grains and pores, their mutual loca ti on, the in- sandstone s is < 9.5%, and perm eabil ity is <1·10–3 µm2. ten sity of katagenetic trans for ma tions and ther mo dy namic Densit y of sandstone s-siltstones varies betwee n 2.17–2.71 condi ti ons (Aagaard & Jahren, 2010; cf. Kurovets & Pry- g/cm3. Intergra nu lar poros it y of limestone s is low (<6%) tulka, 2001). (Fig. 5A). In the Kokhanivka field, fracture d and cavern ous The po ros ity (F) of sandstone s and siltstones in the Me - limestone s are known to be oil-reservoir rocks. so zoic and Palaeozoic de pos its var ies be tween 0.1 and 28.8%, with the aver age value of 10.1% (Fig. 4). The coef fi - cient of varia ti on of the poros it y is 0.72. The great est range Up per Cre ta ceous of vari ati on of the coef fi cie nt of open poros it y is charac ter - The poros it y of Cenomanian sandstone s is 5–16% (Fig. isti c of sandstone s and aleurolites from the Creta ceous (0.1– 6B), and that of Turonian limestone s is <5.5% (Fig. 6A). 28.8%) and the Upper Juras sic (0.4–24.6%), which is The Coniacian–Maastrichtian sandstone s contai n carbon ate caused by a con sid er able lithological-fa cies het er o ge ne ity and clayey-carbon ate cem ent. The poros it y of sandstone s and a dif fer ent struc ture of the pore space. The smallest ranges betwee n 0.1 to 28.8%, and the perm eabil ity is (0.01– range of varia ti on is re corded for the Palaeozoic terrigenous 940) 10–3 µm2. The rock densit y is 1.71 to 2.89 g/cm3. The rocks (0.2–6.7%) that have under gone katagenetic pro- high est po ros ity is char ac ter is tic of sand stones of the basal cesses to a con sid er able ex tent. cement type from the Uhers’ko and Bilche-Volytsia fields. In the to tal ana lysed set of samples of Meso zoic and North-westward and south-east ward of these fields the res er- Palaeozoic rocks, the per meabil ity (K) var ies from voir charac ter isti cs of sandstone s becom e worse (Fig. 6A). 0.01·10–3 to 1138·10–3 µm2 and the aver ag e perme abil ity is The inter granu lar poros it y of limestone s and marls var- 1.901·10–3 µm2 (cf. Table 1, Fig. 3). The lgK-param eter is 372 I. KUROVETS ET AL. char ac ter ized by the great est co ef fi cient of vari a tion, equal CON CLU SIONS to 4.80 in com pari son with other petrophysical parameters. The petrophysical char ac ter is tics of the car bon ate res er - The reser voir rocks in the pre-Miocene strata of the voirs are more vari able than the terrigenous ones due to suf- Outer Zone of the Ukrai nian Carpathian Foredeep contai n fi cient va ri et ies of sed i men ta tion con di tions and sen si tiv ity hy dro car bon de pos its. In the Me so zoic de pos its, the best to the pro cesses of lithification, recrystallization and al ka li - res er voir rocks are Cre taceous siliciclastic rocks with inter - zati on. As a re sult of the diagenetic dis solu ti on, caverns and gra nu lar po ros ity and Ju ras sic frac ture-cav ern ous car bon ate great karst pores are formed in the carbon ate rocks. The rocks of reefal fa cies be tween Lubaczów in Po land and Gai. most in ten sive dis so lu tion of min er als oc curred dur ing the The greatest hydro car bon depos it s are known to oc cur in the subaerial expo sure of rocks and circu la ti on of the reser voir reef fa cies locat ed upon most strongly upli fted blocks. If flu ids. As a re sult of recrystallization, the coarse-crys tal line there are fa vour able struc tural con di tions, the hy dro car bon calcite was formed, in ciden tally the vol ume and the shape accu mu lation may be expected also in the fore-reef and of the pore space changed. Most in ten sively are recrystalli- back-reef depos its. In the Palaeozoic and Ediacaran depos - zed first of all high-per meable or ganic, coarse-detri tal and its, siliciclastic reser voirs of frac tured and fractured- po rous fragmental and then oolitic limeston es. In micritic lime- types are de vel oped. Their dis tri bu tion in the geo log i cal stones, the pro cess of recrystallization oc curs more slowly sec tion is control led by fault-block tecton ics . They are pro- (Knishman et al., 2001). In the carbon ate rocks fracture s are spec tive within the lim its of the Krukenychy Depres sion, in distri buted throughout the secti on. The fractur ing and fur- which po rous-frac tured and cav ern ous res er voir rocks are ther widen ing of the frac tures by the flow of underground de vel oped that are widely dis trib uted within the limits of water promoted the origin of new fractures and caverns. erosion escarpments and in zones of unconsoli- dated rocks The poros it y measured on sam ples of small size is in- confined to the faults. suf fi cient, and it char acter izes capac ity of the rock matrix, be cause fractures and cav erns are prac tically lacking. The Ac knowl edge ments inter gra nu lar po ros ity of the car bon ate rocks var ies from 0.1 to 15.4%, with the aver age of 3.0%; rock sam ples with po - This research was under taken as a research project No. ros ity of 0.1–5% pre dom i nate. The co ef fi cient of vari a tion UKRAINA/193/2006 of the Polish Minis try of Sci ence and of poros it y is 0.87. The great est range of varia ti on of inter- Higher Ed u ca tion, car ried out at the AGH Univer sity of Sci ence granu lar poros it y is observe d in the carbon ate rocks of the and Tech nol ogy and the Pol ish Geo log i cal In sti tute – Na tional Re - Upper Creta ceous . The poros it y of limestone s in the Upper search In sti tute, and was fi nanced from the sci en tific fund of 2007–2010. Thanks are due to J. Golonka, Y. Koltun and P. Such Juras sic depos it s ranges within 0.1–11.9% (Fig. 4A), with a for help ful com ments and sugges tions. mean of 2.3%, and in the Lower Creta ceous – 0.1–7.4%, with a mean of 3.8% (Fig. 5A). Most of sam ples of the car- bon ate rocks are prac ti cally im per me able: the per me abil ity REF ER ENCES is <0.1·10–3 µm2. How ever, to gether with im per me able sam ples one can observe limestone s with perm eabil ity of –3 2 Aagaard, P. & Jahren, J., 2010. Special issue in tro duc tion: Com - about 73.2·10 µm . The de crease in poros it y and perm e- pac tion pro cesses – Po ros ity, per me abil ity and rock prop er - abil ity of sandy-clayey rocks with depth of their oc currence ties evo lu tion in sed i men tary bas ins. Ma rine and Pe tro leum is char ac ter is tic of the geo log i cal cross-sec tion of the Outer Ge ol ogy, 27: 1681–1683. Zone of the Ukrai nian Carpathian Foredeep. Coef fi cie nts of Bu³a, Z. & Habryn, R., 2011. Pre cam brian and Palaeozoic base - cor re la tion of F and lgK with depth are 0.61 and 0.50, re- ment of the Carpathian foredeep and the ad ja cent Outer Car- spec tively (Fig. 3A). The most no ticeable changes in ca pac - pathians (SE Po land and west ern Ukraine). Annales Societatis ity–fil tra tion pa ram e ters with depth of oc cur rence are ob - Geologorum Poloniae, 81: 221–239. served in the Me so zoic de pos its bur ied to in suf fi cient Danysh, V., Hnylko, O., Kopach, I., Krupskyy, Yu., Pavlyuk, M., depths that did not undergo consid er able katagenetic chan- Pobihun, I., Rizun, B., Savchuk, O., Shcherba, O. & Stupka, O., 2004. Lithological-strati graphic out line. In: Kolodiy, V. ges. In the Palaeozoic rocks the gradi ents of changes in V., Boyko, G. Y., Poychevs’ka, L. E. et al. (eds), 2004. petrophys i cal pa ram e ters de crease with in creas ing depth. Karpats’ka naftogazonosna provintsiya. (In Ukrai nian, Eng - The Palaeozoic de pos its are at the stage of deep-seated kata- lish summary ). Ukrains’kyy Vydavnychyy Tsentr, Lviv- gen e sis. They are strongly con sol i dated and un der went suf- Kyiv, 12–43. fi cient struc tural changes caused by recrystallization of peli- Dolenko, G. N., Yarosh, B. I., Khomenko, V. I. & Ulizlo, B. M., tomorphic car bon ate and si li ceous ce ment and by re gen er a- 1969. Zakonomirnosti naftogazonosnosti Peredkarpats’kogo tion of quartz (Gurzhiy et al., 1983). As a result , changes in i Zakarpats’kogo progyniv. (In Ukrai nian). Naukova Dumka, petrophysical pa rame ters with depth are prac tically un no - Kyiv, 204 pp. ticed. Drygant, D., 2000. Lower and Mid dle Palaeozoic of the Volyn – In carbon ate rocks the change in petrophysical pa ram e- Podollya mar gin of the East-Eu ro pean Plat form and Carpa- ters with depth is less no tice able. Thus, the co ef fi cient of thian Foredeep. (In Ukrai nian, Eng lish summary ). Naukovi zapiski Derzhavnogo prirodoznavchego muzeyu, 15: 24–130. cor re la tion be tween pa ram e ters F and lgH is 0.56 (Fig. 3B) Glushko, V. V. & Kruglov, S. S. (eds), 1977. Obosnovanie and di rect de pend ence of de crease in per me abil ity with napravleniy poiskov nefti i gaza v glubokozalegayuschikh depth is not observe d. The coef fi cie nt of corre la ti on be- gorizontakh Ukrainskikh Karpat. (In Russian). Naukova tween the K-pa rame ter and the lgH-param e ter is equal to Dumka, Kiev, 176 pp. 0.21. Gurzhiy, D. V., Gabinet, M. P., Kiselev, A. E. et al., 1983. Lito- PETROPHYSICAL PROP ER TIES OF THE PRE-MIO CENE ROCKS 373

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