RMZ â MATERIALI IN GEOOKOLJE

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414 Adewale, A., Olawale, O. O., Martins, O. M.heavy oil with API gravity less than 20° and a specific gravityvalue range of 0.95 g/cm 3 to 1.27 g/cm 3 was determined to rangebetween 1.080 Pa s to 1.360 Pa s. The results obtained agreed withborehole information and earlier published geophysical and petrophysicalresults of the tar sands deposits located in other parts ofthe Nigerian tar sands belt.Izvleček: Električna upornostna tomografija s podzemnim 2-d-prikazomv povezavi s sedimentološkimi in petrofizikalnimi analizami je bilauporabljena za detajlno kartiranje in rezervoarno opredelitev nekaterihnahajališč naftnih peskov v jugozahodni Nigeriji z namenomugotoviti prostorski razpored, opredeliti rezervoarne lastnosti in izvestiprimerjavo z že raziskanimi nahajališči v drugih delih nigerijskegapasu naftnih peskov.Z električno upornostjo je bilo mogoče omejiti razmeroma debelo(povprečne debeline 50 m) visoko uporno (v razponu 1519–5772Ω m) plast peska, prepojenega z bitumnom in ležečega okoli 10 mpod površjem. Granulometrična preiskava osmih vzorcev iz nahajališčanaftnega peska nakazuje razmeroma enakomerno porazdelitevrezervoarnega peska z zrnavostjo med ф = 0,03 mm in 0,55 mm inz do 3 % fine frakcije. Rezervoarni pesek je slabo do srednje dobrosortiran (ф = 0.94–1.63 mm), ugotovljena asimetričnost pa nakazujezelo debelozrnato do zelo drobnozrnato asimetrične (–0.58 to 0.47)rezervoarne peske. Rezultati preiskave poroznosti in prepustnosti sov razponih od 16 % do 24 % in ustrezno 143 mD do 887 mD. Stopnjaimpregniranosti z ogljikovodiki se giblje med 60 % in 90 % instopnja nasičenosti z bitumnom med masnima deležima 18 % in 30%. Viskoznost impregnirane težke nafte, ki ima relativno gostotopod 20° API in specifično maso med 0.95 g/cm 3 in 1.27 g/cm 3 , segiblje med 1.080 Pa s in 1.360 Pa s. Dobljeni rezultati ustrezajomeritvam v vrtinah in objavljenim geofizikalnim in petrofizikalnimpodatkom z nahajališč peskov v drugih območjih nigerijskega pasunaftnih peskov.Key words: tomography, reservoir characterization, tar sands, porosity,permeabilityKljučne besede: tomografija, rezervoarna opredelitev, naftni peski, poroznost,prepustnost<strong>RMZ</strong>-M&G 2012, 59
Geophysical and sedimentological studies for reservoir characterization of ...415IntroductionAsphalt-impregnated sandstones otherwisereferred to as oil sands (tarsands) and active oil-seepages occurin southwestern Nigeria within themarginal pull-apart or margin-sag Dahomey(Benin) basin. The oil sandsoutcrop in an E-W belt, approximately140 km long and 4–6 km wide, extendingfrom Edo, Ondo and Ogun State insouthwest Nigeria. Bituminous sandsare composed of sand, heavy oil andclay that are rich in minerals and water.The heavy oil in the bituminous sand iscommonly called bitumen, which is avery dark coloured, sticky and viscoussubstance. Total reserve of the heavyoil is estimated to exceed 30 billionbarrels (Adegoke et al, 1980).The petroleum habitat is almost exclusivelythe Afowo Formation, a memberof the Abeokuta Group. This litho-unitis of Turonian - Maastrichtian age andconsists of interbeds of coarse-mediumgrained sandstones, siltstones andshale deposited in a transitional to marginalmarine environment (Omatsola& Adegoke, 1981). The oil is found inthe coarse grained clastics within theformation in two discrete bands (the Xand Y horizons), each 30–40 m thickand separated by 6–15 m carbonaceousshales with a thin band of lignite (Akoet al., 1983) and overburden thickness inexcess of 50 m at Agbabu, Ondo State,south western Nigeria (Enu, 1985).This research utilizes electrical resistivitystudies, sedimentological andpetrophysical studies to characterizethe reservoir sands of the tar sand depositsin Gbegude area; a continuum ofthe tar sand belt of North-Eastern Dahomeybasin, South Western Nigeria.The study is aimed at delineating thesubsurface distribution and occurrenceof the deposits as well as determiningthe reservoir characteristics of the tarsand deposits in the study area.Geological settingThe study area is situated in the easternpart of Dahomey basin and locatedwithin longitude 4°22 ’ E to 4° 30 ’ E andlatitude 6° 40 ’ N to 6° 43 ’ N (Figure 1).The Dahomey Basin constitutes partof the system of West African pericratonic(margin sag) basin (Klemme1975; Kingston et al 1983) developedduring the commencement of the riftingand associated with the opening ofthe Gulf of Guinea, in the Late Jurassicto Early Cretaceous (Burke et al,1972; Whiteman, 1982). The crustalseparation, typically preceded by crustalthinning, was accompanied by anextended period of thermally inducedbasin subsidence through the Middle– Upper Cretaceous to Tertiary timesas the South American and the Africanplates entered a drift phase to accommodatethe emerging Atlantic Ocean(Mpanda, 1997).<strong>RMZ</strong>-M&G 2012, 59
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IVTable of Contents - KazaloProfess
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Calculation of stress-strain depend
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RMZ - Materials and Geoenvironment,
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Petrochemical characteristics and g
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360 Akinola, O. O., Talabi, A. O.A
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Page 70 and 71: k =1.05+Dλ = 1+k =( s )396 Shemeto
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Page 74 and 75: у 3 b400 D = f eShemetov, P. A., B
Page 76 and 77: V4BEK Q σBEad = ,commQрσV 01 +
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464 Lajovic, A.njem delu forme. Na
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466 Lajovic, A.Enourni film je mars
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470 Medved, J., Rosina, A., Vončin
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472 Author’s IndexAuthor`s Index,
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Contents476Phase contrast method fo
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Contents47859/4Calculation of stres
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Instructions to authors481Compositi
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Instructions to authors483NAVODILA
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Instructions to authors485Knjige:Ro
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