Abstract A multi-event tectonic episode that affected the Caribbean and South American Plate boundaries as well as Cenozoic oil generation is based on new structural and geochemical data from the western Falcón Basin, Venezuela. It involves Late Cretaceous to Middle Eocene emplacement of the Lara Nappes followed by Late Eocene to Early Miocene tectonic collapse and graben formation, Middle Miocene inversion and out of sequence thrusting. Oil-source rock correlation of seeps in the northern part of the basin suggests a Cenozoic siliciclastic source rock deposited under suboxic to anoxic conditions. Potential Cenozoic source rocks and Late Cretaceous La Luna Formation were used to evaluate the generation conditions using one- and two-dimensional thermal modelling. A heat flow of c . 190 mW m −2 was reached during the Oligocene–Early Miocene in the central part of the basin. As a result the Cretaceous source rock is overmature, while the primary Cenozoic source rocks are in the oil window. The thermal modelling also suggests that hydrocarbon accumulations are mainly located on the flanks of the graben, with small amounts possible in the centre, due to erosion during basin inversion. This modelling is highly consistent with the proposed polyphase tectonic model.

Abstract Shaly formations are the focus of many research programs and consortia sponsored by petroleum companies and/or waste management organizations; given that they act as seals for oil- or gas-bearing reservoirs or as host rock for underground waste disposals, their integrity (e.g., the possible presence of water-bearing fractures) is a critical factor in risk assessment. To model their rheological properties through time, the observed clastic injectites are used as markers of their mechanical evolution. Aptian–Albian marly formations of the Vocontian Basin (southeast France) are the basis of this study; massive turbidite systems associated with large-scale clastic injectite networks have been described in exceptional outcrops. Field data have permitted the identification of early fracturing in the host formation; the injection of sand is an early event, contemporaneous with the deposition of massive sand bodies. The paleocom-paction curve has been calculated, and the porosity evolution of the sediments has been restored from sea floor to about 500 m (1640 ft) burial. Then, the original configuration of dikes can be reconstituted. Boundary conditions of various numerical modeling have been derived from this extensive reliable data set. Numerical static simulations of the behavior of marly formations are presented, testing the possible function of heterogeneous lithology, bedrock geometry, or loading by sudden massive sand deposition; they indicate that early fracturing is physically possible in the presented scenarios. The next step will be to simulate in dynamic conditions the opening and filling of some of these cracks by hydrofracturing. We dedicate this chapter to the memory of our colleague and friend, Stephen T. Horseman.

Abstract Hardly detected with logs and recognized with difficulty on cores, clastic injectites (sills and dikes) can be troublemakers in oil-field development. Moreover, they provide a precious record of early fracturation. To predict their geometry, extension, and relationship to their feeders, field analysis of selected analog outcrops is conducted to propose some simple rules. In southeast France, the Aptian–Albian formation provides exceptional outcrops (Bevons, Rosans, and Nyons) where it is possible to characterize large sets of injectites: dikes and sills are associated in the same metric-to-kilometric network. The injection occurred per ascensum (more frequently) or per descensum, during or after the sand deposition. Specific geometric-based field methods have been developed to analyze the geometry based on the best conditions. A three-dimensional (3-D) model of the Rosans area injectite network has been built through gOcad ™ tool using outcrop analysis and an original, very high-resolution twodimensional seismic acquisition (0.6 km 2 ; 0.23 mi 2 ). This field analysis, the seismic survey, and the 3-D modeling provide some keys to consider possible occurrences of injectites and associated facies related to a turbiditic channel fill. We dedicate this article to the memory of our colleagues and friends G. P. Allen and D. Claude.

Abstract The data from oil-bearing Ukrainian basins outline the tectonic control of overpressure development in areas characterized by recent episodes of folding and active compression (dominantly horizontal stress regime). Based on the data presented, vertical compaction alone is not sufficient to account for the observed overpressure development. Tentatively, tectonic deformation is proposed as the dominant factor for overpressure development in sedimentary layers in recently folded regions. During folding, the opening of fractures results in local density decrease and helps in driving the migrating fluids, i.e., both hydrocarbon and formation waters, in the carrier beds toward the top of the structures. Ductile flow of shaly interbeds toward anticlinal closures can also enhance the sealing capacity of these layers. In the Ukrainian Carpathians and salt domes of the Dniepr-Donetz Basin, direct relationships have been evidenced to link and predict the amount of overpressure as a function of the amplitude of the folds. The use of measurements and of the monitoring of overpressures for evaluating the horizontal stress intensity and for the forecasting of earthquakes is also suggested.

Abstract The main focus of this study is the origin of the paleofluids in the Late Cretaceous–Oligocene sandstone reservoirs of the El Furrial structure (Venezuela). Basin modeling was performed using Thrustpack®, Locace®, and Ceres® tools. The temperature and nature of the fluids obtained by this modeling were compared to fluid inclusions and oxygen isotope data on quartz overgrowth. Four stages should be considered in this area: (1) From 65 to 20 Ma: Fluids were at thermal equilibrium with the sediments. They were continuously expelled vertically toward the surface during compaction-driven dewatering processes. (2) From 20 to 12 Ma: As a result of the regional tilting and the deposition of the synflexural Naricual Formation, the Cretaceous and Oligocene sandstones of the El Furrial structure became efficient conduits for fluids circulating from the north. These fluids were at thermal equilibrium with the Cretaceous and Oligocene sandstones and seem to be correlated with the first generation of quartz overgrowths. This episode is characterized by an increase in the overpressure of the Oligocene and Upper Cretaceous sandstones that is correlated to a hydraulic fracturing of the sealing Carapita black shales. (3) From 12 to 8 Ma: Fluids were expelled laterally from the Cretaceous sediments of the Pirital hanging-wall unit that is located immediately north of the El Furrial structure. These fluids were likely in chemical disequilibrium, and their temperature was higher than the temperature of adjacent sediments, which probably resulted in additional but minor episodes of quartz precipitation. This hypothesis is consistent with the information obtained from oxygen isotope analyses, which suggest that subsequent generations of quartz cement probably formed from evolved basinal fluids. (4) A reduction of the intensity of the flow and then an inversion of this flow mark the sealing of the southern structural closure of the structure at about 8 Ma. Then, the closure of the northern flank occured at about 5 Ma, as indicated by a present velocity of the fluids close to zero in the El Furrial reservoirs and the filling of the structure by the hydrocarbons.