Abstract: Integrated Multi-scale and Multidisciplinary Techniques Applied to the Characterization of an Upper Albian Reservoir, Campos Basin, Brazil

Barroso, A. S.; C. L. Sombra; R. K. Romeu; C. H. L. Bruhn; R. Beer; P. R. S. Johann; Y. Backheuser; L. Bonet; M. M. M. Cortez -Petrobras/E&P/Cenpes

Namorado Sandstone (Upper Albian) Project (PRAVAP 2) is providing Petrobras new reservoir characterization techniques and methodologies. PRAVAP 2 activities were organized according to a multi-scale and multi-disciplinary approach. The basic idea is to define a geological framework coupled with an hierarchical facies model, in which the relationship between genetic, spatial, geometric and effective flow properties are fully and operationally defined. Three main work scales (Fig. 1) were defined according to the processes performed and products generated during the study:

Microscopic scale - "Porous systems" were identified based on microscopic characteristics such as composition, diagenesis, wettability, skin susceptibility, resistivity, petrophysical properties (F, K, Pc, Kr) and rock physics. Several techniques were used, such as petrologic and image analysis, EMS, RXD and petrophysical analysis.

Log and core scale - "Composite facies" were recognized based on the sedimentary and diagenetic features and on their well log responses. Probe permeameter and outcrop studies were also used. Non-parametric statistics and other integration methods were important for identification of facies groups, and quantification of the mutual relationships among rock, well log and petrophysics. Each composite facies was described by a particular spatial arrangement of plug-scale blocks for each "porous systems". These spatial arrangements were statistically defined, and synthetic representative images were generated by Boolean methods.

lnterwell to field scale - A high-resolution stratigraphic and structural framework was defined to constrain the field scale model. Well test analysis and seismic interpretation - with emphasis on inversion techniques - were used in the characterization at this scale. Composite facies were grouped to create "seismic facies" taking in account the statistical correlation between seismic attributes and average reservoir properties. Stochastic seismic-constrained simulations provided possible images of the spatial distribution of the "seismic facies" inside the reservoir at the fluid flow simulation scale.

Effective rock properties were bottom-up determined through this hierarchy. This process began from the plug scale. At this scale petrophysical properties were directly measured at laboratory. The next step was to numerically compute the effective properties for the "composite facies" defined at metric scale. Pseudo-functions for relative permeability were obtained assuming that capillary forces are dominant at this scale. At the "seismic facies" scale, viscous forces are important and the pseudo-functions were computed by dynamic methods, post-processing results of local two-phase flow simulations.

Therefore, the relationship between "porous systems", "composite facies" and "seismic facies" was established, and a fully integrated model was achieved which incorporates the effects of heterogeneities at all scales into the fluidflow simulation model (Fig. 2).

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil