The characteristics of fracture networks in the Shiranish Formation of the Bina Bawi Anticline; comparison with the Taq Taq Field, Zagros, Kurdistan, NE Iraq

Abstract

The Zagros Fold and Thrust Belt of NE Iraq hosts a prolific hydrocarbon system. Reservoirs are commonly found in fractured Cretaceous carbonates (Shiranish Formation) such as in the Taq Taq Field located in the Kirkuk Embayment of the Zagros foothills. Data providing information on fractures in the Taq Taq Field are core, image logs and flowmeters from wells, and surface observations. For comparison, an outcrop study has been undertaken around the Bina Bawi Anticline (10 km from Taq Taq Field), where the same stratigraphical unit is exposed in a continuous, lenticular-shaped belt. Fracture data have been collected using scanlines on bedding surfaces in the limbs and hinge of the anticlines. Both the Bina Bawi Anticline and Taq Taq Field show a systematic relationship between fracture sets and fracture lineaments, with a dominance of NE–SW-oriented structures. This orientation is perpendicular to the major folds and parallel to the maximum horizontal in situ stress. There are three fracture populations in the Bina Bawi Anticline, classified according to their relationship with the fold axis and bedding: (i) NW–SE-striking fractures normal to bedding: (ii) NE–SW-striking fractures normal to bedding; and (iii) conjugate oblique fracture sets subnormal to bedding. Both fracture intensity and fracture terminations are controlled by the location within the anticline; the hinge zone displays the highest intensity and the most fracture-abutting terminations. Cross-cutting relationships suggest that a prefolding stage of NE–SW tensional fractures predates folding-related tensional and shear fractures. Few uplift fractures can be indicated. We propose that the former fracture set (joints) formed in a foreland setting and was controlled by the far-field stresses, whereas later fracturing occurred due to outer arc extension during flexing of the Bina Bawi and Taq Taq anticlines. Our comparative analysis of outcrop and well data underline the importance of representative analogue data for reservoir modelling and production strategies.

Influence of structural position on fracture networks in the Torridon Group, Achnashellach fold and thrust belt, NW Scotland

“…Understanding the mode of fold formation and strain history is critical for prediction of fracture attribute variations, which can be used in a range of applications, including fractured reservoir exploration, carbon capture and storage, aquifer characterisation and civil and mining engineering. Many studies have been conducted to investigate how fracture attributes vary in carbonate thrust belts for hydrocarbon exploration, such as in the Zagros foldand-thrust belt of Iran (McQuillan, 1973(McQuillan, , 1974Wennberg et al, 2006;Wennberg et al, 2007;Awdal et al, 2013), the Italian Apennines , the Rocky Mountains of the USA and Canada (Ghosh and Mitra, 2009;Barbier et al, 2012) and the Northeastern Brooks Range, Alaska (Hanks et al, 1997). Studies on fracturing in sandstone thrust belts are much less well documented; examples include Florez-Niño et al (2005) and Iñigo et al (2012) who use fractured outcrops as analogues to low porosity, low permeability (tight) sandstone hydrocarbon reservoirs in the Sub-Andean thrust belt.…”

“…McQuillan (1973) also suggests fracture density is constant within fold structures of the Asmari Formation, SW Iran, providing bed thickness and lithology are constant. Many studies show an increase in fracture intensity in high curvature and high strain regions of individual fold structures in a range of lithologies (Hobbs, 1967;Jamison, 1997;Ortega et al, 2010), for example fracture intensity is often seen to be higher in fold forelimbs and crests than backlimbs (Barbier et al, 2012;Awdal et al, 2013).…”

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

“…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). Dans leurs études des réseaux de fracturation des structures de Bina Bawi et de Taq Taq dans les monts Zagros (Kurdistan), Awdal et al (2013) arrivent aux mêmes constatations. De façon intéressante, la même observation a été effectuée au niveau du pli asymétrique de Sheep Mountain (Wyoming, USA) (Bellahsen et al, 2006).…”

Late Campanian–Maastrichtian sequence stratigraphy from Kurdistan foreland basin, NE/Iraq

“…The top of the Shiranish third order coincides with a mass extinction surface and is characterized by a turbidite facies with bioturbated sandstone bed that points to a sequence boundary of type two overlain by a shelfmargin system tract. Awdal et al (2014) propose that the NE-SW fracture in the Shiranish formation set (joints) was formed in a foreland setting and controlled by far-field stresses, whereas later fracturing occurred due to outerarc extension during flexing of the Bina Bawi and Taq Taq anticlines.…”