The Khaviz Anticline: an outcrop analogue to giant fractured Asmari Formation reservoirs in SW Iran

Abstract

The carbonate reservoirs in the Late Oligocene—Early Miocene Asmari Formation in the Dezful Embayment of SW Iran are characterized by low matrix permeability, and effective drainage is dependent on the occurrence of open fractures. Limited information on fracture orientation and fracture density is available from core and borehole image data, and high-quality/high-resolution three-dimensional seismic is often lacking in this area. Well and core data do not contain information on important fracture parameters like length distribution, crosscutting relationships, fracture density v. lithology and bed thickness. The understanding of fracture distribution and formation in the region and their effects on fluid flow has been greatly improved by the use of outcrop analogue data. Exposures of the Asmari Formation in the Khaviz Anticline are in close vicinity to the giant hydrocarbon fields. The Khaviz Anticline has a similar geometry and structural history to the major hydrocarbon fields in the area, and represents an excellent analogue for these. Two types of fracture features were observed: diffuse fracturing and fracture swarms. The diffuse fractures form networks and comprise structures grouped into four fractures sets, which are the typical for this type of anticline. Two orthogonal fracture sets are oriented parallel and perpendicular to the fold axis, and two conjugate fracture sets are oblique to the fold axis with their obtuse angle intersecting the trend of the fold axis. The fractures are typically stratabound, sub-perpendicular to bedding and commonly about the bounding stratigraphic surfaces. To a large extent the density and height of fractures in the Asmari Formation are controlled by the mechanical stratigraphy, which is controlled by the depositional environment and cycles. These outcrop data have been essential in the generation of discrete fracture network (DFN) models and the population of the fracture properties in the reservoir models.

Appraisal of fracture sampling methods and a new workflow to characterise heterogeneous fracture networks at outcrop

“…So, to properly represent relative abundance between the fracture sets, multiple scanlines at different orientations should be used. Many studies have adopted this method (McQuillan, 1973;Hanks et al, 1997;Wennberg et al, 2007;Ortega et al, 2010;Hooker et al, 2011;Barbier et al, 2012;Ellis et al, 2012;Iñigo et al, 2012) whereby a scanline is set up perpendicular to the strike of each fracture set on the outcrop. For each scanline, fracture attributes are measured for that fracture set only.…”

“…To reduce orientation bias for linear scanlines many authors (McQuillan, 1973;Hanks et al, 1997;Wennberg et al, 2007;Ortega et al, 2010;Hooker et al, 2011;Barbier et al, 2012;Ellis et al, 2012) use a technique where a separate scanline is set up perpendicular to each fracture set present. We tested this method against our proposed workflow (Fig.…”

“…Wennberg et al (2007) used an outcrop study of the fractured Khaviz Anticline in SW Iran as an analogue for subsurface reservoirs. Sample sites were located along two transects, spaced over 10 km apart, and oriented parallel to regional compression.…”

La fracturation et les bandes de déformation dans la région d’El Kohol (Atlas saharien central, Algérie): analyse fractale, lois d’échelles et modèle de réseaux de fractures discrètes

“…Wennberg et al (2007) constatent dans leur modèle basé sur celui de Price (1966) R soient des fractures conjuguées suggèrent qu'elles soient ouvertes en cisaillement; mais sur le terrain d'étude, l'effet de ce cisaillement n'apparaît pas beaucoup. De façon intéressante, la même observation a été effectuée au niveau du pli asymétrique d'El Kohol et la figure 10A montre la concordance entre les familles de fractures mesurées dans notre étude et le modèle de Wennberg et al (2007).…”

Joint development and tectonic stress field evolution in the southeastern Mesozoic Ordos Basin, west part of North China

“…Many studies show that joint pattern is controlled by mechanical stratigraphy, and depends on the lithology and layer thickness of stratigraphic units (Hobbs, 1967;Huang and Angelier, 1989;Narr and Suppe, 1991;Gross, 1993;Gross et al, 1995;Engelder et al, 1997;Ji and Saruwatari, 1998;Ruf et al, 1998;Bai and Pollard, 2000;Underwood et al, 2003;Wennberg et al, 2007), but workers have also observed the fact that there are other factors to influence the development of joint spacing, such as the magnitude of tectonic strain to faults and structures (Becker and Gross, 1996;Gross et al, 1997), and the degree of joint set development . The mechanical layer thickness that affects the development of joint spacing in general does not necessarily correspond to the sedimentary stratigraphic beds (Gross et al, 1995;Eyal et al, 2001).…”