Caracterização geologica de um reservatorio fluvio-eolico da Bacia do Reconcavo-Bahia, Brasil

AUTOR(ES)
DATA DE PUBLICAÇÃO

1994

RESUMO

This dissertation presents a detailed study of an Early Cretaceous, fluvial-aeolian reservoir from the Recôncavo Basin, northeastern Brazil. This study, developed at the oil field scale, inc1uded essentially: (1) the description of lithofacies and lithofacies associations, as well as their depositional processes; (2) the interpretation of depositional systems, high-resolution stratigraphy and geometry ofthe studied reservoir; (3) log-rock correlation, and identification of electrofacies toallow the mapping of reservoir heterogeneities and petrophysical properties; and (4) the study of rock and fluid quality, and of reservoir behavior. The studied sandstone reservoir was deposited in low-sinuosity fluvial and aeolian (dune settings) systems. Eight lithofacies (two aeolian and six fluvial) were identified. There is good correlation between lithofacies and well log signatures, which are related main1y with the rock texture and diagenesis. The eight lithofacies were grouped into four electrofacies (one Aeolian and three fluvial). Statistical techniques were used to trace these electrofacies in the uncored wells.Production and pressure data suggest reservoir compartmentalization along the studied oil field, which are related with variation fi the quality of the oil. There is very low oi! production from the reservoir upper portion, despite of the fact that it contains the most permeable lithofacies. This is probably related with paraffin precipitation, as suggested by the high content (26 %) of paraffin in the recovered oil, and the low reservoir temperature (25 - 40 °C, around the pour point). Erosion of a thick section of over1ying sediments may have been responsible for the present reservoir low temperature. The mid portion of the reservoir is the best production zone, despite its lower permeability; this is explained by the fact that this portion presents temperatures above the pour point of the oil. Four classes of reservoir rocks where recognized on the basis of porosity, permeability, and types of oil shows. Major reservoir heterogeneities that control oil flow are: (1) discontinuous beds of low-permeability sandstones and mudstones; (2) frequent interbedding of distinct lithofacies; and (3) occurrence of oil with low temperature (around pour point)

ASSUNTO(S)

petroleo - geologia geologia estratigrafica reservatorios - reconcavo (ba)

ACESSO AO ARTIGO

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