Developments in resetvoir characterization applied to the Albacora Field (Namorado Sandstone), Campos Basin, offshore Brazil
Authors: Barroso A.S. , Mihaguti M. , Romeu R.K. , Bruhn C.H.L. , Johann P.R.S. , Sombra C.L. , Sarzenski D. , Cortez M.M.M. , Lara A.Q. , Souza O.G. 
Published: October 2008

Namorado Sandstone Project, Albacora Field (PRAVAP 2) is providing Petrobras new reservoir characterization techniques and methodologies in a short period of time. The project key points are: integrated teams from operational and research areas, matrix management, multidisciplinary and multi-scale approach, selective technology acquisition, and synchronism between the field development and the project timing. This paper summarizes the developments acquired and how they impact the field development. High-resolution stratigraphy and facies analysis coupled with a very detailed structural description and fault mapping provide a reservoir deterministic framework and the base for the preliminary geological and fluid flow models. This model has been very useful for drilling and reducing investment risks during early to intermediate stages of field development. More robust models are being constructed using the deterministic framework as a constraint for the stochastic modeling. An hierarquical facies model was established on the basis of porous systems, sedimentary (composite) and impedance facies. An upscaling technique, based on geopseudo concepts, integrates the facies model into a fluid flow model. Geostatistical tools have been applied in reservoir mapping, and facies and porosity stochastic modeling. 3-D seismic inversion improves the definition of inter well reservoir properties and allows a better incorporation of seismic data into geological models. Imaging logs, and core minipermeametry (specially in cored horizontal wells) have been used in the description of the reservoir heterogeneities and facies not identified in conventional logs.

Introduction

Petrobras is exploiting its major offshore oil fields with modern production technology in a scenario of reduced number of wells; more horizontal wells and an intensive use of seismics. Reservoir characterization has to fit this scenario with emphasis on integrated techniques and intensive use of well, seismic and production data. The seismic data for reservoir characterization requires special processing and robust seismic inversion techniques.

Reservoir characterization methodology

PRAVAF' 2 characterization processes were organized according to a multiscale and multidisciplinary approach. Three main work scales were defined according to the common process and products generated during reservoir characterization. The basic idea is to define a geological framework coupled with an hierarquical facies model, in which the relationship between genetic, spatial, geometric and effective flow properties are fully and operationally defined. Microscopic scale - Microscopic characteristics and rockfluid interaction are defined like composition, diagenesis, wettability, skin susceptibility, resistivity and porous systems, described on the basis of rock and ?, K, PC, Kr parameters. Several techniques are used, such as petrologic and image analysis, EMS, RXD and petrophysical analysis. Well and core scale - Basically the sedimentary facies and arrangements of these facies (composite facies) and their well log responses are defined. The common techniques used are the sedimentological analysis, well log interpretation, petrophysics, including the acoustic behavior determination (Vp, Vs, Poison and Young modules). The integration techniques were pursued and the statistics (including nonparametric methods) geostatistical techniques are very important for identification of facies groups, and for quantification of the mutual relationships among rock, well log and peaophysics.

Interwell to field scale

- A high-resolution and very detailed stratigraphic and structural framework was defined and used as a