Abstract Reservoir appraisal is commonly a difficult task in fold and thrust belts. Thrust-related folding leads to the development of meso- to microscopic brittle structures that can significantly alter the porosity and permeability properties of reservoir rocks, thus influencing fluid migration and accumulation. The aim of this chapter is to describe at different scales the deformation associated to the development of the Chaudrons thrust-related anticline (Corbières, France) and to discuss its influence on reservoir quality. Pervasive solution cleavage sets at high angle to bedding (ATB) were found and measured along the fold. In addition, collected core samples were used to measure the rock physical properties (anisotropy of magnetic susceptibility and anisotropy of the P-wave velocity). The distribution of deformation in the anticline was used to identify three different deformational panels: crest, rounded forelimb, and constantly steeping forelimb. The crest is characterized by the lowest cleavage intensity. Nonpenetrative solution cleavages and the magnetic foliation are orthogonal to bedding. In the rounded forelimb, bedding dip progressively rotates from 0 to 60°. Cleavage intensity progressively increases, and cleavage and magnetic foliation ATBs progressively increase from 80 to 120° and then remain constant in the steep forelimb. The timing of the development of mesoscale structures, as well as changes of physical properties occurring before and during folding, is also discussed.

ABSTRACT Thrust-related folding is an important and efficient mechanism for generating wide, deformed rock panels at shallow structural levels. In these environmental conditions, three basic forms of deformational features commonly occur: pressure-solution seams (stylolites), extensional fractures (joints and veins), and small-scale faults. Two end-member mechanisms of thrust-related folding can be identified: active-hinge folding and fixed-hinge folding. The spatial distribution of longitudinal deformational features (LDF) induced by fixed-hinge folding is confined within the axial-surface zone, and its intensity is roughly proportional to the fold interlimb angle. Conversely, the spatial distribution of LDF induced by active-hinge folding is arranged in well-defined rock volumes– the deformation panels, each of which is affected by a characteristic LDF intensity. Deformation panels result from the development and interference of deformation domains, which correspond to the rock volumes that underwent deformation during their rolling across the active axial surfaces. The geometry of deformation domains is therefore defined by the architecture of the axial surfaces and the amount of fault displacement. The spatial distribution of deformation panels bears important insights for predicting the distribution of secondary permeability in folded carbonate reservoirs where, in the past, the permeability in the anticlinal crests has been overestimated. The development of deformation panels and deformation domains related to longitudinal deformational elements has been numerically simulated by a hybrid cellular automata (HCA) modeling technique for fault-bend and décollement folding. Model results show that, in many cases, active-hinge anticlines have a crestal zone that is unaffected by folding-related, longitudinal deformational features, and that deformation panels develop along the corresponding limbs. Our numerical results compare favorably with the spatial distribution of deformation in field examples and in analog models. The numerical technique we developed provides an efficient tool for evaluating the spatial distribution of fracture porosity and permeability in folding-related fractured reservoirs.