A surface-subsurface study of reservoir-scale fracture heterogeneities in Cretaceous carbonates, North Oman

Abstract

Reservoir-scale structural heterogeneity, especially in terms of mechanical layering and natural fracture systems, is often insufficiently constrained by subsurface data alone. In North Oman, a large dataset in Cretaceous carbonates comprises data from multiple subsurface reservoirs and analogue outcrops. This provides an ideal opportunity to integrate outcrop constraints into the subsurface, and to calibrate the resulting models dynamically. For this purpose, a reservoir-scale analogue outcrop fracture template was created for the Jebel Madmar anticline in the Oman Mountains foothills. The outcrop template provides improved conceptual and quantitative constraints on (i) fracture types and dimensions (e.g. of NE-trending fracture corridors), (ii) fracture heterogeneity, both aerially and stratigraphically, (iii) fracture properties (e.g. cementation evolution, variations due to preferential fault/fracture reactivation) and (iv) structural evolution and history of reactivation. Within a regionally consistent structural framework, the outcrop template has greatly assisted in the creation of geologically realistic models for one of the fractured carbonate reservoirs, complementing the subsurface dataset. Initial dynamic calibration indicates successful application of the outcrop template in that the spatial fracture heterogeneity was succesfuUy captured in the reservoir models and provides a history match to production data. The reduced range of possible fracture system geometries in turn has provided better constraints on the effective fracture properties.

Diagenetic controls on reservoir properties of carbonate successions within the Albian–Turonian of the Arabian Plate

“…Cements are nonferroan to ferroan and may contain petroleum inclusions (Videtich et al 1988;de Keijzer et al 2007;; Fig. 9D).…”

“…9D). Burchette & Britton (1985), Videtich et al (1988), de Keijzer et al (2007 and Taberner et al (2010) all reported the intergrowth of 'exotic' minerals (principally kaolinite, dickite and fluorite), homogenization temperatures of approximately 80-130(C and/or a trend from light to heavy carbon isotope values within burial diagenetic calcite cements. Rare descriptions of cathodoluminescence characteristics document a non-luminescent to dull to bright luminescence within compositionally zoned crystals, with no apparent intra-zonational corrosion (Cross et al 2010;Taberner et al 2010).…”

“…It is beyond the scope of this paper to detail the nature, timing and distribution of fractures across the region, but the intimate relationship between dolomitization, calcite cementation and fractures via robust kinematic models is documented for the Oman Mountains (de Keijzer et al 2007) and the Zagros Mountains Lapponi et al 2011;Casini et al 2011). In both the Zagros and the Oman Mountains, north to NNW trending faults and opening mode fractures, that formed during the First Alpine Event in the Late Cretaceous, are cross-cut by north-easterly orientated faults and fractures of early Tertiary age (Second Alpine Event;de Keijzer et al 2007;Casini et al 2011). Subsurface datasets clearly demonstrate that these faults, fracture corridors and distributed fractures play a fundamental role in hydrocarbon productivity and sweep effieciency (Looseveld et al 1996;Filbrandt et al 2006;Richard et al 2006;de Keizer et al 2007;Moretteni et al 2005;Hollis et al 2011).…”

“…9E-F). Given that precursor (etched and leached) burial calcite cements have emplacement temperatures of over 100 (C (Viditech et al 1988;de Keijzer et al 2007), porosity generation must have taken place at depths of +3 km, and either prior to, or synchronous with, the onset of hydrocarbon migration in the Late Cretaceous to Tertiary. The actual volumes of secondary macroporosity that was generated in the burial environment have not been quantified, but they could be significant.…”

Laser scanning and digital outcrop geology in the petroleum industry: A review

“…Fracture networks from outcrop data were first used in water resource management (Long and Billaux, 1987) and fracture modelling from lidar data is common practice in geotechnical fields (Deparis et al, 2008;Gigli and Casagli, 2011;Schulz, 2007). Fracture studies from lidar data are currently been used with increasing frequency in the hydrocarbon industry (Barr et al, 2007;De Keijzer et al, 2007;Gillespie et al, 2010;Kurtzman et al, 2009;Rogers et al, 2007). A Discrete Fracture Network or DFN approach models fluid flow processes through rock masses via a series of connected fractures (Jing and Stephansson, 2007) and requires statistics on size, density, orientation, position, and aperture of the fractures to generate a stochastic model of the fracture network.…”