The Zagros Fold and Thrust belt is one of the world's most prolific petroleum provinces. Most hydrocarbon reserves are stored in naturally fractured reservoirs and such fracture systems can therefore have a significant impact on reservoir performance. Fractures are one of the most important paths for fluid flow in carbonate reservoirs. Fracture data were collected in the outcrops of the Kirkuk Group of Oligocene age around Qara Chauq South and Qara Chauq North anticlines located near the Kirkuk Oil Field. The studied formations outcropping in the Qara Chauq are the main reservoir units in the Kirkuk and Bai Hassan fields. In Kirkuk and surrounding fields, hydrocarbon production comes mainly from primary porosity with assistance from secondary porosity created by dolomitization, karstification, dissolution, vugs and fractures. Fracture attributes collected from outcrops are fracture orientation, density and length. The results show that fractures in the studied reservoir formation are not uniformly distributed due to massive lithologic nature and lack of well bedding. Furthermore, fracture orientations show a clear relationship to the local fold axis in the outcrops. NW-SE fracture set is perpendicular to the NW-SE fold axis. However, some fractures do not show any relation to the local folding. These fractures may have formed in a pre-folding or post folding stage. Other fracture orientations exhibit a symmetrical relation to the maximum horizontal stress direction. The comparative analysis of outcrop data underlines the importance of representative analogue data for reservoir modelling and production strategies.

Deformation bands may show permeabilities that are a few orders of magnitude lower than the surrounding host rocks and therefore have a negative impact on fluid flow in sandstone hydrocarbon reservoirs. Understanding the geometrical attributes of individual bands and their patterns is a critical step in quantifying their connectivity and interpreting how they may compartmentalise reservoirs in the subsurface. In order to gain insights into the shapes, cross-cutting relationships and connectivity of these structures, we developed 3D geometrical models (scaled to centimetres) of deformation bands and joining ladder structures, using a sliced small-scale rock sample from outcrops at Hopeman, Moray Firth (Scotland) and near Goblin Valley, Utah (USA). This 3D geometrical model is used for two-phase flow simulations (water-oil and gas-oil) in order to investigate the effect of deformation bands on time to water breakthrough, waterfront propagation and sweep efficiency. We also investigated capillary effects on flow. Flow simulation results show that the presence of deformation bands led to various time to water and gas breakthroughs, irregular shape of water and gas front propagation and various sweep efficiency for different flow-system. Furthermore, understanding the dynamic behaviour of flow through these structures can lead to better predictions of the influence of deformation bands on fluid flow in subsurface reservoirs.

The productivity of wells in fractured reservoirs depends, in terms of rate and sustainability, on the heterogeneity and variable connectivity of the open fracture network. Outcrop studies in Cretaceous carbonates from the Catalan Pyrenees illuminate this issue and reveal the degree of uncertainty associated with the interpretation of fracture data from wells and seismic. Three examples are chosen to provide verifiable data, parameters and concepts which can be applied to the workflow of fractured reservoir characterization. We discuss fracture properties and distributions in the subseismic volume, the coupled behaviour between litho-mechanical properties, in situ stress and fracturing, and the permeability properties of fault damage zones. The outcrops also highlight some of the difficulties involved in constructing static reservoir models and evaluating fracture interpretations derived from software-based techniques such as surface curvature.

The Zagros-Taurus fold and thrust belt hosts a prolific hydrocarbon system. Most hydrocarbon reserves are stored in naturally fractured reservoirs and such fracture systems can therefore have a significant impact on reservoir performance. Fractures are one of the most important paths for fluid flow in carbonate reservoirs, and industrial geoscientists and engineers therefore need to understand and study fracture patterns in order to optimise hydrocarbon production. The observed fracture patterns in outcrops may have implications on fluid flow and reservoir modelling in subsurface reservoirs, and we have therefore undertaken a case study of fracturing associated with regional folding in Iraqi Kurdistan. In this area, some exploration wells currently target Upper Triassic dolostones (Kurra Chine Formation) and/or Lower Jurassic limestones and dolomitised limestones (Sehkaniyan Formation). In both units hydrocarbon production comes mainly from secondary porosity created by dolomitisation, dissolution and fracturing. Both formations have undergone multiple phases of deformation associated with burial, uplift, folding and thrusting. We investigate some fracture pattern characteristics and some petrophysical properties of these units using selected outcrops around the Gara, Ora and Ranya anticlines that form folds directly traceable for 25-70 km. Our outcrop data is compared with subsurface fracture and petrophysical datasets reported from wells in the nearby Shaikhan and Swara Tika Fields. The 1-2-3D fracture attributes collected from outcrops are fracture orientation, type, spacing, intensity, length and cross-cutting and abutting relationships. Fracture orientations show a clear relationship to the local fold axis in both the outcrop and subsurface, although in some cases they appear to relate more to the present day in-situ maximum horizontal stress direction or local strike-slip faulting. Three stages of fracturing are proposed: pre-folding, early-folding and post-folding fractures. In addition, we report petrophysical properties-porosity, permeability and acoustic velocity of both the Kurra Chine and Sehkaniyan formations in relation to their structural position within folds and faults and stratigraphic level. The highest porosities and permeabilities are recorded in the hinges and backlimbs of the Gara Anticline. The best reservoir quality (highest porosity and permeability) is often found in areas associated with replacement dolomite i.e. solution vugs and intercrystalline porosity. The Kurra Chine Formation displays similar trends in velocity-porosity data at both outcrop and the subsurface. However, the Sehkaniyan Formation displays lower acoustic velocity for a given porosity at outcrop compared to the subsurface. Crown Copyright (C) 2015 Published by Elsevier Ltd. All rights reserved.

Deformation bands can influence fluid flow in sandstone hydrocarbon reservoirs and therefore, understanding the geometrical attributes of individual bands and their patterns is a critical step in quantifying their connectivity. We present a geometrical study of deformation band lozenges, which are rock volumes contained between deformation bands, and fault lenses, which are rock volumes bounded by slip surfaces in fault cores. We investigate the statistical trends among data sets for deformation band lozenges and fault lenses in sandstones from the Moray Firth (Scotland) and southeastern Utah (USA), and explore their potential correlation to other attributes of the fracture pattern and petrophysical properties. The aspect ratio of lozenges, that represents the ratio of length or height to the maximum thickness of a lozenge, displays an oblate-shaped geometry in relation to fault-zone orientation. The length–thickness scaling relationships of lozenges are statistically similar to lenses. The scaling relationships show a slope break between lozenges bounded by deformation bands and lenses bounded by slip surfaces in the fault core. This break is inferred to mark the boundary between the lozenge domain and lens domain, and is likely due to a deformation transition from distributed strain for deformation bands to localised strain for slip surfaces. Furthermore, the integration of geometrical analysis with an understanding of scaling properties can help to make better predictions of fractures and fault properties in subsurface reservoirs.

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.

Subsurface fractures control the flow of fluids through reservoirs containing economic resources. Fractures can act as conduits or barriers to fluid flow and understanding the geometry of the fracture pattern is a crucial step in quantifying the connectivity of fractures, which is the major factor governing bulk permeability. Natural fractures are not randomly distributed and exhibit clustering in various forms particularly in the damage zones around larger faults. We identify the shape of lozenges, which is refer to the area (volume) relatively undeformed sandstone situated between two strands of a composite deformation band. We also mapped and quantified geometry of the deformation band patterns and ladder fractures. The published scaling relationships for attributes across dimensions depend on the assumption of random spatial distributions, and yet fractures are rarely randomly distributed in space. We aim to quantify these relationships and this will guide the construction of testable expressions for multidimensional scaling relationships using empirically derived power law exponents.

Lineaments are one of the most important features showing subsurface elements or structural weakness, such as faults, and are usually extracted by visual analysis of enhanced image data. Individual experts may extract different segments through a visual approach. To detect lineaments under the same objective conditions, this paper proposes a data processing approach using automatically extracted shaded Relief images from a digital elevation model (DEM). The present study is the first study that used digital elevation model with GIS application in the particular study area to extract lineaments and classify lineaments into positive and negative effects on the drainage pattern.