Reservoir Facies of the Kesan Formation: Tight Gas Exploration in the Thrace Basin of N.W. Turkey

Transcription

1 Reservir Facies f the Kesan Frmatin: Tight Gas Explratin in the Thrace Basin f N.W. Turkey Thmas F. Mslw, Mslw Gescience Cnsulting Ltd. Richard H.T. Callw, Statil ASA Rb Sadwnyk, Valeura Energy Inc. Antine Riault, Statil ASA Summary The Yamalik-1 well was drilled in 2017 t test the cncept f basin-centered gas accumulatins in the Thrace Basin, N.W. Turkey. Three cnventinal cres were taken frm different reservir levels and stratigraphic intervals that prvide an excellent example f a brad spectrum f finegrained turbidite facies which have been flw tested with preliminary successful results. Cre #3 frm the Ecene-age Kesan Frmatin is selected fr display as a gd representatin f a reservir target in the basin. Fifty-tw and a half metres f whle diameter cre is displayed and described with respect t sedimentary structures, lithlgy, texture, fractures, diagenetic features and cmpsitin. An extensive cre sampling and data acquisitin prgram prvides additinal data including bistratigraphic age, micrpalaentlgical assemblages, prsity, permeability, XRD/XRF, gechemistry and electrical prperties. Mst f the sandstne facies in the Kesan Frmatin are interpreted as the prduct f sediment gravity flw prcesses that were surced frm a deltaic cmplex t the suth. Apprximately 85% f the sandstne facies bserved in the cre ccur as thin- t thick-bedded turbidites that are interpreted as the prximal t distal depsits f the varius elements f submarine lbe and/r channel envirnments. Reginal 2D seismic lines have been used t cnstrain the depsitinal envirnment f the cred sectin, which culd be challenging in the absence f a gd reginal cntext. It is pssible t link the Kesan Frmatin strata in the Yamalik-1 well t a set f prgrading clinfrms surced frm the basin margin tens f kilmeters t the suth. Cntinued prgradatin in the verlying sectin (bserved in cre #1) indicates that at least sme f the yunger interval may represent mre prximal slpe r prdeltaic depsits. The bservatins indicating a deltaic linkage are als supprted by the presence f abundant terrestrially derived material in the cre, gechemical

2 prfiles frm kergen typing and a strng terrestrial signature recrded in palynlgical assemblages. Gelgical Setting The Thrace Basin, lcated in nrthwest Turkey, is brdered by the Sea f Marmara t the sutheast, the Aegean Sea t the suthwest and Bulgaria and Greece t the nrth and west (Figure 1) and is the mst significant natural gas prducing basin within the cuntry. Figure 1. Physigraphic map f Turkey and adjining land and water masses shwing majr structural lineaments. The Thrace Basin is lcated in the nrthwest crner f Turkey and is bunded t the suth by the Nrth Anatlia Fault Zne (NAFZ). The black rectangle shws the utline f Figure 2 utcrp belt. Blue arrws indicate present day directins f plate mvement. The Istranca Muntain Belt and Nrth Anatlian Fault Zne (NAFZ) are majr tectnic elements that bund the Thrace Basin gelgically t the nrth and suth. Basin frmatin was initiated in the Late Cretaceus by cllisin f the Eurasian and African plates and suturing f terranes within the Anatlian Blck (Fig. 1). Later structural phases included transtensinal faulting beginning in the Palecene that is active t this day (Okay et al., 2004; Siyak and Huvaz, 2007), Micene uplift and inversin, fllwed by right lateral mvement f the Nrth Anatlian Fault in the Plicene. Accmmdatin space generated frm tectnic subsidence has resulted in a Tertiary successin f mstly siliciclastic and vlcaniclastic sediments that is up t 9000 m thick. This is

3 disprprtinately thick in cmparisn t the relatively limited 160 x 200 km areal extent. While 900 BCF f recverable gas has been discvered in predminantly cnventinal fault- bunded structural and stratigraphic traps (ie. Cskun, 1997), the current explratin fcus presented here is n basin-centered gas within the Ecene-Oligcene Kesan Frmatin and the Oligcene-age Teslimky Member f the Mezardere Frmatin. Tertiary utcrps including the Middle Ecene t Oligcene-aged Kesan Frmatin, flank the suthern rim f the Thrace Basin (Fig. 2) and prvides the pprtunity t make sedimentlgic and stratigraphic bservatins that can be used t better understand and predict the presence and characteristics f hydrcarbn bearing reservirs in the relatively nearby subsurface. Figure 2. Surface gelgy map alng the suthwestern rim f the Thrace Basin shwing the lcatin and extent f the Kesan Frmatin utcrp belt (green). Nte lcatin f the Yamalik-1 well in the nrtheast crner f the map. The Kesan Frmatin cnsists f high net t grss sandstne and interbedded siltstnes, shales and tuffs with thicknesses exceeding 2000 m (Figs. 3, 5, 6). Fine grained vlcaniclastic and siliciclastic sandstnes and siltstnes are the target f tight gas explratin in the Kesan Frmatin as characterized by the Yamalik-1 cre presented in this study. The hetergeneity in

4 lithlgy and mineralgy f the Kesan Frmatin and much f the sedimentary fill within the Thrace Basin is attributed t multiple phases f tectnism and vlcanism cincident with sedimentatin during basin evlutin (Huvaz, 2005). The sedimentary facies f the Kesan Frmatin utcrps have previusly been interpreted as being depsited in deltaic, fluvial and shallw t deep marine envirnments f depsitin (Siyak and Huvaz, 2007). Figure 3. Stratigraphic clumn shwing frmatins ccurring in the utcrp belt and/r subsurface f the Thrace Basin. The Middle t Upper Ecene Kesan Frmatin which reaches thicknesses f greater than 2000m in the suthern Thrace Basin is ften referred t as the Ceylan Frmatin in the nrthern Thrace Basin (mdified frm Siyak, 2005). Sedimentary Facies and Facies Assciatins An interpreted depsitinal envirnment is prvided fr all facies bserved in cre, which was based n the cmbinatin f physical and bigenic sedimentary structures, and the interpreted physical depsitinal prcesses. A summary f facies assciatins and their sedimentary characteristics, inferred prcesses f depsitin and relevant diagenetic features has been cmpiled. Sedimentary cycles and significant bunding surfaces were identified in the cre and have been crrelated t cre-gamma ray and dwnhle wireline lgs that include ver 1700m f FMI lg data (Fig. 4).

5 Figure 4. Yamalik-1 Cre #3 calibrated t dwnhle gamma lg shwing perfrated intervals. Red arrws shw interpreted cycles f upwards increasing and decreasing gamma ray values which crrespnd t thickening and thinning cycles bserved in the cre. Mst f the sandstne facies in the Kesan Frmatin are interpreted as the prduct f sediment gravity flw prcesses that were surced frm a deltaic cmplex t the suth. Apprximately 85% f the sandstne facies bserved in the cre ccur as either thin r thick-bedded turbidites that are interpreted as prximal t distal depsits f the varius elements f submarine channel and/r lbe envirnments (Fig. 5). Ptentially channelized and the mst prximal lbe depsits cnsist f very fine t medium-grained sandstnes that can in sme cases cntain numerus mudstne intraclasts. These depsits are rganised int thickly bedded, nrmally graded, cmmnly amalgamated Ta, Ta-b and Ta-b-c turbidite beds that may reflect depsitin frm high density turbidity currents. Beds are cmmnly massive in appearance but sedimentary structures include planar and ripple crss-laminatin, cntrted t cnvluted laminae, dish structures, and largescale flame structures (see Fig. 6a-i). The thickest example f the axial submarine channel and lbe facies assciatin ccurs in the upper ne-third f the Kesan Fm. cre frm m

6 where the highest prsity values have been measured frm cre plugs. This uppermst interval f the cre fines upwards frm medium t very fine-grained sandstne, and bed thickness and net t grss rati decreases upwards. Figure 5. Cmpsite graphic lg f the Kesan Fm. in Cre #3 f the Yamalik-1 well.

7 Marginal r weakly channelized t verbank facies cnsist f medium bedded (cm-dm scale) heterlithic, interbedded silty very fine-grained sandstne and sandy carse siltstne t mudstne. Sandstnes with high clay cntents are als bserved cmmnly in this facies assciatin. Dewatering structures ccur cmmnly in the frm f small sand injectites (Fig. 6b), and dish and flame structures (Fig. 6c). Anther cmmn attribute f this facies assciatin is the ccurrence f relatively thin beds characterized by parallel r ripple crss laminatin, including aggradatinal climbing-ripples that display carbnaceus debris as resedimented plant detritus n freset laminae. Inferred prcesses include depsitin frm sediment gravity flws (mstly lw-density turbidity currents) and suspensin depsitin Figure 6. Examples f facies in Cre #3 including descriptin and interpretatin f prcesses and depsitinal envirnments including turbidites (a-d), rganic rich facies (e), slumps and debrites (f, g, i).

8 The majrity f turbidite beds bserved in the cre are thin bedded (mm-cm scale) sandstnes (Fig. 6a, b, h) with ripple crss laminatin, parallel laminatin and/r starved ripples, that are interbedded with fine-grained siltstne t mudstne depsits (Fig. 6b). This thin-bedded facies is interpreted as distal channel verbank and/r distal lbe depsits f lw density turbidity currents. Internally defrmed r cntrted beds are interpreted as sft-sediment defrmatin and pssible mass-wasting due t subaqueus slumps (Fig. 6f). Petrlgy Sandstne facies f the Kesan Frmatin in Cre #3 cnsist primarily f mderately t prly srted, very-fine t fine-grained feldspathic vlcanic-arenites. The largest measured grains are mid-upper medium grain size. Prsity is reduced and pre thrats are ccluded by cmpactin f minr vlumes f clay matrix and cmmn ductile grains alng with the emplacement f mderate vlumes f pre filling and replacive irn rich calcite. Framewrk cmpsitin in mst sandstne samples is dminated by mncrystalline quartz (MQ), feldspar (FD) and ductile vlcanic rck fragments (VRF) (Fig. 7). Other cnstituents bserved in thin sectin include: resedimented plant detritus; recrystallized biclastic fragments (BIO); heavy minerals, likely rutile: (HM); cmpacted mica rich metamrphic rck fragments (MRF); ductile micas (M); phsphate clasts (PH); variably preserved chert grains (CT); and plutnic rck fragments (PRF).

9 It is estimated that apprximately half f the measured ttal prsity is represented by micrprsity, preserved within leached grains and minr vlumes f matrix and authigenic clays. Figure 7. Thin sectin phtmicrgraph f a feldspathic vlcanic-arenite frm a turbidite lbe facies assciatin at m. Cre prsity is 6.5%; cre permeability is mD at 5.5MPa net cnfining pressure. See text fr descriptin and identificatin f cnstituent grains. (Phtgraph and anntatin by GR Petrlgy Cnsultants Inc.).

10 Depsitinal Mdel Generalized depsitinal mdels fr the Kesan frmatin cred facies in the Yamalik-1 well are shwn in Fig. 8. These mdels were develped in the Laingsburg depcenter, Kar Basin, Suth Africa, where laterally extensive expsures prvide superb prximal-distal and stratigraphic examples f submarine lbe systems. Many similarities in terms f lithfacies, stacking patterns and interpreted prcesses have been nted between the Kesan Fm. and the Laingsburg utcrps. Figure 8. Generalized mdels fr submarine fan turbidite channel and lbe mrphlgy, terminlgy and stratigraphic hierarchy. These mdels were develped in the Laingsburg depcenter, Kar Basin, where laterally extensive expsures prvide superb prximal-distal and stratigraphic examples f submarine lbe systems that may be cmparable t the Keşan Fm. A. Sketch f the rganisatin, hierarchy and terminlgy within deepwater channel t lbe cmplexes (frm Prélat et al., 2009, 2010). B. Ptential vertical and lateral bed thickness changes in submarine lbes frm updip t dwndip psitins, i) lbe cmpsed f a single prgrading lbe element, ii) lbe is cmpsed f multiple stacked lbe elements. (frm Prélat and Hdgsn, 2013). Cnclusins The Yamalik-1 well was drilled t test a basin-centered tight gas play, hsted in Ecene-Oligcene sediments. Three cres ttalling 135m were taken in rder t better cnstrain the envirnment f depsitin, net t grss, grss thickness and reservir quality. Cre descriptin revealed that the cred sectins were dminated by fine t medium-grained, thin t thick-bedded sediment gravity flw depsits with minr mudstne-dminated intervals. Lw density turbidity current depsits dminate the sectin with minr cmpnents f high density turbidity current depsits and debris flw depsits. On the basis f facies analysis and study f stacking patterns Cre #3 presented here has been interpreted as representing axial t distal lbe fringe depsits, ptentially cnsisting f several stacked lbes frming a thick submarine lbe cmplex. Facies, facies assciatins, bed thicknesses and stacking patterns are cmparable t field analgues such as the lbe depsits f the Laingsburg depcenter f the Kar Basin. The cre data prvides imprtant data

11 n net t grss, especially f the thin t very thin bedded facies. Thin bedded intervals can appear as nn-reservir n cnventinal lg data, but may in fact cntain up t 50% f sand in thin mm t cm thick turbidite beds. The integratin f cre data, cnventinal lg data, cnventinal cre analysis and seismic data has been vital in the accurate understanding f depsitinal envirnment, and lateral extent, thickness and reservir quality f the Kesan Frmatin. References Cskun, B., Oil and gas fields transfer zne relatinships, Thrace Basin, NW Turkey. Marine and Petrleum Gelgy, v. 14, p Huvaz, O., 2005, Investigatin f the thermal gradient histry f the Thrace Basin, NW Turkey, by using a mdified Easy%R maturity mdel; PhD. Thesis, Middle East Technical University, Ankara. 106p. Mslw, T. F., Sadwnyk, R., Luxtn, P., Umul, B., Smith, I., Fine grained turbidite reservir facies f the Kesan Grup: tight gas explitatin in the Thrace Basin f N.W. Turkey. Canadian Sciety f Petrleum Gelgists Gecnventin Cre Cnference, Cre Abstract Bklet, p Okay, A. I., Tuysuz, O., Kaya, S., 2004, Frm transpressin t transtensin: changes in mrphlgy and structure arund a bend in the Nrth Anatli Fault in the Marmara regin; Tectnphysics, v. 391, Prélat, A., Hdgsn, D.M., The full range f turbidite bed thickness patterns in submarine lbes: cntrls and implicatins. Jurnal f the Gelgical Sciety, v. 170, p Prélat, A., Hdgsn, D.M., Flint, S.S., Evlutin, architecture and hierarchy f distributary deep-water depsits: a high-reslutin utcrp investigatin frm the Permian Kar Basin, Suth Africa. Sedimentlgy, v. 56, p Prélat, A., Cvault, J.A., Hdgsn, D.M., Fildani, A., Flint, S.S., Intrinsic cntrls n the range f vlumes, mrphlgies, and dimensins f submarine lbes. Sedimentary Gelgy v. 232, p Sadwnyk, S., 2013, Tight gas develpment within the Thrace Basin, NW Turkey; Canadian Sciety f Petrleum Gelgists Reservir, vl. 10, p. 14. Sadwnyk, R., Luxtn, P., Mslw, T. F., Mezardere Slpe Fan Explratin Mdel, Thrace Basin, Turkey: Integratin f Cre, Outcrp, Seismic and Well Lg Data. Canadian Sciety f Petrleum Gelgists Gecnventin Cre Cnference, Cre Abstract Bklet, p Siyak, M. and Huvaz, O., 2007, Ecene stratigraphic evlutin f the Thrace Basin, Turkey. Sedimentary Gelgy, v. 198, p Siyak, M., 2005, Trakya Ve Yakin Cevresinin Tersiyer Stratigrafisi; TPAO