Abstract One-dimensional and two-dimensional basin modeling has been performed along a regional transect crossing the Córdoba Platform allochthons and the autochthonous Veracruz Basin in order to infer the burial and kinematic evolution and to determine timing of hydrocarbon migration and charge in this famous Mexican petroleum province. Vitrinite reflectance, Rock-Eval data, and bottom-hole temperatures have been used to calibrate the heat flow and thermal evolution of the Veracruz Basin, where no erosion occurred. The Córdoba Platform and Veracruz Basin in Eastern Mexico comprise the southern most extent of the Laramide foreland fold-and-thrust belt,which developed along the eastern border of the North American Cordillera from Late Cretaceous to Eocene. Unlike in the Canadian Rockies, where pre-orogenic strata are relatively isopachous, this segment of the North American craton has been strongly affected by the Jurassic rifting and opening of the Gulf of Mexico. Substantial thickness and facies changes between horsts and grabens control the lateral and vertical distribution of Mesozoic source rocks and hydrocarbon reservoirs. In the east, thick Paleogene and Neogene sequences in the Cordilleran foreland provide a continuous sedimentary record in the Veracruz Basin. In the west, however, the Middle Cretaceous carbonates of the Córdoba Platform generally constitute the main outcropping horizon in the adjacent thrust belt, making it difficult to reconstruct its burial evolution from the Laramide orogeny onward. Cemented veins were sampled in reservoir intervals of the thrust belt. Petrography, stable isotope analyses, and fluid inclusion studies (microthermetry, Synchroton Fourier Transform Infra-Red analyses) on these samples revealed the diagenetic history of the reservoirs. Where diagenetic phases could be constrained in time and with respect to the tectonic evolution, fluid inclusion temperatures provide an additional paleothermometer in areas where major erosion occurred. Pressure-temperature modeling of simultaneously entrapped aqueous and oil-bearing inclusions indicates more than 4.5 km of erosion of Late Cretaceous-Paleocene sequences in the thrust belt, which can be accommodated in palinspastic sections only by restoring a hypothetical foredeep basin. This implies that the current east-dipping attitude of the basement beneath the Córdoba Platform developed after Laramide deformation, accounting for a major change in paleofluid dynamics. Fluid flow and basin modeling of the Veracruz section has been performed using CERES2D to infer the paleofluid dynamic associated with the petroleum system evolution. Following the initial phase of geometric model building and calibration against the thermal and burial history inferred, the modeling accounted for the past migration pathways for both water and oil and gas fluids. Unlike in most other foreland fold-and-thrust belts, hydrocarbons generated in Jurassic source rocks from the Veracruz foreland are currently migrating westward toward the thrust belt, accounting for a post-Laramide charge of the frontal duplexes of the Cordilleran thrust belt.

Abstract Several advances have been made for the reconstruction of fluid circulations and diagenetic history in subthrusted petroleum reservoirs because of the combination of the in-situ microanalysis of hydrocarbon fluid inclusions by Synchrotron Fourier transform infrared spectroscopy and PVTX modeling coupled to diagenetic history and tectonic setting. Integrated study has been made in the Eocene Chorgali formation (North Potwar Basin, Pakistan), where the shallow-marine carbonates formed important fractured reservoirs. Hydrocarbon fluid inclusions recognized in authigenic quartz and calcite from hydroveins show atypical association of CO 2 -rich light oil depleted in H 2 O in sulfates-quartz-calcite along simultaneous dissolution recrystallization processes at micrometer scale. Synchrotron Fourier transform infrared spectroscopy analyses, microthermometry, and pressure-volume-temperature modeling led to the beginning of quartz and calcite recrystallization at no more than 75–85°C and 150–180 bar in conditions of sulfate-calcite transformation. Temperatures of 150°C measured in aqueous fluid inclusions from calcite hydroveins are in favor of a thermosulfatoreduction mechanism. Early diagenetic sulfates are reduced by organic acids, and CO 2 comes from organic matter decomposition and/or previous decarbonation. A second phase of quartz growth is evidenced by the homogeneous entrapment in fluid inclusions of more mature oil in 60% CH 4 and a large amount of water at temperatures reaching 150–170°C. This late production of CH 4 agrees with δ 13 C depletion (−20 and −36%o) measured in veins and the crystallization of saddle dolomite. Thrustpack ® modeling shows that the onset of hydrofracturing and quartz precipitation at 1.5 km (1 mi) depth and 15–10.8 Ma (middle Siwalik) began when temperatures of 65 ± 10°C were reached at the end of sedimentation in the basin. It lasted until 4–6 km (2.5–4 mi) depth at temperatures as much as 170°C and reached the development of the thrust sheet at 5 Ma. Thus, circulations of hydrocarbon-rich fluids may be considered in thermal equilibrium with host rocks in both cases. The oil could then be derived from source rocks in the deep Mesozoic formation for the first input. The second input originated from the deep part of the basin itself and mixed with tectonic and meteoric water along the circulation pathways. The fluids are mainly driven by tectonics. They are expelled from the hinterland farther to the north and move updip toward the south in the Chorgali conduits, below the Kuldana seals. The potential source rock for organic matter is known as type II and type III kerogens in coal and black shales from the Paleocene.

Abstract Major oil discoveries in the foothills of the Venezuelan and Colombian Andes have recently focused the interest of exploration companies toward sub-Andean basins. Seismic, well, and core data from the El Furrial (Venezuela) and Cusiana (Colombia) productive fields have been integrated herein with other regional information to document the evolution of the thrust belt and the history of the petroleum systems, and to propose practical guidelines for prediction of sandstone reservoir quality in such a complex geodynamic environment. Although timing of deformation is slightly different in these areas of eastern Venezuela and Colombia, sedimentary and tectonic burial of the foreland autochthon in both regions led to the maturation of prolific Cretaceous marine source rocks, resulting in successive and diachronous hydrocarbon migration and trapping episodes. Early sedimentary burial at the current location of the Serranía del Interior (Venezuela) and the Eastern Cordillera (Colombia) resulted in long-range migration of early-generated hydrocarbons toward the foreland, forming the large accumulation of hydrocarbon along the Faja Petrolifera (Eastern Venezuela). Early entrapped hydrocarbons also have been preserved in pre-Andean prospects of the Andean foothills, as evidenced by the complex charge history of the Cusiana field. However, wide areas of source rocks in the Andean foothills and adjacent foreland reached the oil window only during the late Neogene and Pliocene-Quaternary, when maximum burial was attained. This produced a second migration episode, coeval with the growth of frontal anticlinal prospects. The main reservoir in Cusiana is fluvial sandstone of the Mirador Formation (Eocene); in El Furrial, it is sandstone of the Naricual-Merecure Formation (Oligocene). Pressure solution and quartz cementation decreased permeability of these sandstones. Results of studies of the anisotropy of the magnetic susceptibility (AMS), coupled with studies of fluid inclusions in quartz overgrowths and thermal modeling, demonstrate that sandstone reservoirs of these oil fields were compacted both vertically, by the load of the synflexural sequence, and horizontally, by tectonic stress (layer-parallel shortening) prior to being tectonically emplaced into the allochthon. Layer-parallel shortening by pressure solution is a major source of silica in the underthrust foreland. Venezuelan and Colombian sandstones still have reasonably good reservoir characteristics, although they have been buried to great depths. Overpressure that developed in these reservoirs as a result of rapid foredeep sedimentation probably caused a delay in compaction. Early carbonate cements also may have contributed locally to prevent compaction until secondary porosity developed as a result of dissolution of this early diagenetic phase. Finally, development of structural closures and hydrocarbon trapping has resulted progressively in the shutting down of the hydraulic system, preventing the transport of exotic silica by regional fluid flow.