Xiomara Marquez

Microfractures Due to Overpressures Caused by Thermal Cracking in Well-Sealed Upper Devonian Reservoirs, Deep Alberta Basin

Microfractures ( 3. This condition is favored by high pore pressures, but failure occurs before pore-fluid pressures reach the lithostatic pressure. Radial and random microfractures are rare and of uncertain origin.

Structural control on sweet-spot distribution in a carbonate reservoir: Concepts and 3-D models (Cogollo Group, Lower Cretaceous, Venezuela)

Numerous major hydrocarbon accumulations are related to burial diagenesis in carbonate reservoirs; however, three-dimensional (3-D) modeling of such reservoirs is a major challenge. The geometries of diagenetic fronts are poorly understood, and few quantitative data on field and outcrop examples for these diagenetic zones exist. The Early Cretaceous Cogollo carbonates (Urdaneta West field, northwest Venezuela) are an example of deeply buried (5000 m; 1600 ft), diagenetically altered limestones producing from a few high-porosity streaks and fracture corridors. Reservoir sweet spots formed because of the interplay of structural evolution and diagenesis. Structural deformation not only generated a fracture network but also influenced primary facies distribution, circulation of diagenetic fluids, and distribution of early charged paleohighs in the reservoir.The prediction of reservoir sweet spots is of key importance for economic success in the Cogollo carbonates but constitutes a major challenge. This article outlines the genetic relationships between structural evolution and sweet-spot distribution, as well as the workflow developed to transfer these concepts into 3-D geocellular models. These 3-D models include a novel approach to fracture permeability prediction based on a geomechanical approach.The reservoir model predicts sweet spots along leached faults, which are best preserved in early charged paleohighs. The Cogollo and other reservoirs suggest that favorable structural development can generate and retain significant matrix porosity even at great depth. The workflow established and applied might help to maximize field potential in similar settings.

Naturally Fractured Reservoir Description Through Well Cutting Analysis. A Case Study: Block IX, Lago de Maracaibo, Venezuela: ABSTRACT

The recognition of variations in sedimentary facies can improve exploration and development strategies for naturally fractured carbonate reservoirs. The evaluation of millimeter-size drill cuttings in well SVS-176 shows that the Cretaceous carbonate sequence consists of five coarse-grained facies: micritized grainstone (G1), algae grainstone (G2), oolitic grainstone (G3), mollusk grainstone (G4), and skeletal packstone (P1), all deposited in a shallowing-upward carbonate sand sequence. The presence of millimeter-size, partly filled fractures and abundant, tiny, euhedral calcite crystals on smooth surfaces of some cuttings indicates that facies G3 is the most prone to have open fractures. This fact was proven by electrical logs, production behavior, drilling, lost zones, and drifting rate information. Sedimentological, petrophysical, and production and drilling data concurrently support that facies G3 controls the presence of open fractures. This information, which confirmed the earliest prediction, was used to propose drilling of well SVS-225. Results obtained with this approach show that by combining independent lines of evidences it is possible to derive an objective and quantitative methodology for naturally fractured reservoir characterization.