Abstract
An integrated approach to characterize natural fractures and optimize reservoir performance for Western Venezuela is presented. Due to poor matrix properties, a thorough reservoir characterization is of key importance. Permeabilities are commonly in the range of 0.01 mD, with natural fracture systems difficult to describe and sensitive to completion fluids and cements.
The approach to fractures includes two main topics: fracture characterization and well design. Fracture characterization comprises the description and analysis of the fracture network at several scales from microfractures up to field size, and includes core, well log images, and seismic data. The methodologies used include microfracture upscaling, core description, image log analysis, petrographic thin sections, scanning electron microscope images, azimuthal coherence seismic processing, and Gaussian curvature analysis. The integration of these analyses together with reservoir engineering data allowed the selection of candidate zones with greater density of open fractures through a semi-qualitative approach.
The well design includes consideration of optimum well trajectory to maximize fracture intersection and the estimation of incremental production based on geometric considerations such as fracture orientation, dip and spacing, presence of more than one set of open fractures, apparent stratal dip, as well as reservoir considerations such as Kh/Kv and geomechanics. These parameters were included in a series of spreadsheets which allow fast estimation of incremental production.
Several completion methods were tested in these reservoirs: cased hole with high penetration perforations, hydraulic fracture with pseudo-point perforating, and open-hole completions. The results of the different completion methods are integrated in this study to optimize well design.
As one of the relevant results of this integration effort, it is concluded that high-angle wells with open-hole completions along the perforated liners is the optimal method of production. This integrated approach allows reclassifying originally sub-commercial reservoirs into economic assets.
