A 3D outcrop analogue model for Ypresian nummulitic carbonate reservoirs: Jebel Ousselat, northern Tunisia

Abstract

A three-dimensional high resolution sequence stratigraphic model of an Ypresian nummulitic carbonate ramp and organic-rich basin is presented based on outcrops in Central Tunisia. The sedimentation pattern is influenced by the interplay of different orders of variations in eustatic sea-level (third to fifth order), the pre-existing palaeotopography, and probably some synsedimentary tectonism (differential subsidence). Time-equivalent rocks deposited in a comparable structural and depositional setting along the northern margin of the African plate are hydrocarbon bearing (Tunisia and Libya). This example may thus serve as an outcrop analogue for this petroleum system, providing valuable information on the sub-seismic-scale distribution pattern, geometries and heterogeneities of both the reservoir and source rock facies. The studied outcrops cover an area of 10 by 20 km where present-day valleys provide three-dimensional access to the rocks. In addition, the transition from the inner/mid-ramp, with nummulitic reservoir facies, to the carbonate source rocks in the basin is exposed in continuous outcrops. This transition takes place in about 3 km, a distance generally beyond the resolution of well spacing. Based on the physical tracing of beds, and the recognition of three orders of depositional sequences (third to fifth) a high resolution time framework is constructed. The accumulation of large nummulites (best reservoir facies) is stratigraphically controlled, and occurs in the transgressive phases of the landward-stepping fourth order cycles (overall transgression). Carbonate production was at that time so high that aggrading geometries are observed during these transgressive pulses. Our observations show that size, morphology and reproduction strategy of foraminiferal assemblages and, particularly, nummulites and Discocyclina , are related to changes in water depth and, consequently, in accommodation space. A regional east–west cross-section shows significant thickness variations of the Ypresian succession that were probably controlled by synsedimentary differential subsidence. The detailed, sub-seismic-scale, geometrical information on stratal patterns and lateral facies change are quantified, and used in a 3D numerical stochastic modelling (HERESIM) of this petroleum system.

Hydrodynamic behaviour of Nummulites: implications for depositional models

“…In the fossil record, several authors consider the shape and wall thickness of foraminiferal tests as a depth indicator (Kulka 1985;Eichenseer and Luterbacher 1992;Loucks et al 1998;Racey 2001;Jorry et al 2003b;Vennin et al 2003;Hasler 2004;Jorry 2004). This assumption is based on observations of LBF from present-day environments.…”

“…The reservoir qualities are mostly induced by the preservation of intraskeletal porosity of Nummulites tests. Numerous sedimentological studies have been made on these deposits in order to better understand the geometry of subsurface reservoirs (Arni 1965;Comte and Lehman 1974;Fournié 1975;Bishop 1985;Moody 1987;Bailey et al 1989;Moody and Grant 1989;Bernasconi et al 1991;Loucks et al 1998;Anketell and Mriheel 2000;Racey et al 2001;Jorry et al 2003a,b;Vennin et al 2003;Hasler 2004;Jorry 2004).…”

Improving the Estimation of Porosity and Permeability Distribution by Linking Basin Modelling to Diagenetic Evolution of Carbonate Reservoirs

“…Time-equivalent strata of these reservoir and source rocks outcrop on land in several locations. The strong lateral variations in formation thicknesses, observed in the outcrop reflect a strong tectonic control of the sedimentation pattern by block faulting along NW-SE trends (Vennin et al, 2003). The G Formation is one of the three lateral subdivisions of the M Group ( Fig.…”

“…H Field, approximately 5 by 3 km, is variously interpreted to be a horst block which trends NNW-SSE, bounded by a system of left stepping en echelon faults (e.g. Klett, 2001;Racey et al, 2001;Vennin et al, 2003), or an anticline created by salt-uplift (Beavington-Penney et al, 2008). The main reservoir in the area of H Field consists of redeposited Lower Eocene nummulitic limestones of the G Formation (Racey et al, 2001; Fig.…”

Correlação gamaespectrométrica de afloramentos e poços: estudo de caso na Formação Ponta Grossa (Bacia do Paraná, Brasil)

“…Slatt et al, 1992Slatt et al, , 1995Alsharhan et al, 1993;Aigner et al, 1995Aigner et al, , 1996Aigner et al, , 2007Bessa & Hesselbo, 1997;Ahmadi & Coe, 1998;Hornung & Aigner, 1999, 2002aNorth & Boering, 1999;Forst et al, 2000;Hadley et al, 2000;Lüning et al, 2000aLüning et al, ,b, 2004Lüning et al, , 2005Svendsen & Hartley, 2001;Brown, 2002;Filer, 2002;Martinius et al, 2002;Brachert et al, 2003;Chiozzi et al, 2003;Hladil et al, 2003;Lüning & Kolonic, 2003;Pawellek & Aigner, 2003Szurlies et al, 2003;Vennin et al, 2003;Doveton & Merriam, 2004;Gehring, 2004;Kostic & Aigner, 2004;Ruf & Aigner, 2004;Collins et al, 2006;Schnyder et al, 2006;Betzler et al, 2007;Evans et al, 2007;Koehrer et al, 2010). Slatt et al (1992), com base na comparação de dados radiométricos de afloramentos e poços do Grupo Jackfork, Arkansas (USA), revelaram que os primeiros foramúteis para o entendimento da geometria e das mudanças laterais de fácies de turbiditos em campos de hidrocarbonetos (óleo e gás).…”