Recognition of turbidite stages in the Massapê oil field, Recôncavo Basin - Brazil, using well logs

Abstract

The integration of rock and well logs data is fundamental for the interpretation of depositional systems and sequences, a fundamental support for E&P activities. This approach was applied on the low permeability turbidite sandstones and slurries of the Maracangalha Formation, in the Massapê Oil/Gas Field, Recôncavo Basin. Well-log interpretation allowed the recognition of 23 turbidite stages, each of which records a specific period of growth of a fan system. These stages are composed of four main facies, all observed in each one of these stages: (a) fine to medium sandstones, with porosities greater than 9%, being the best reservoirs; (b) silty to very fine sandstone slurry facies, that corresponds to very muddy reservoirs with porosities less than 9%, forming important permeability barriers; (c) siltstones and (d) shales. Turbidite stages appear in the Gamma Rays logs (GR) with funnel, block and serrated log motif patterns, corresponding to dominantly thinning and fining upward signatures, recognized in several wells in the Massapê Field. The detailed correlation of these well-logs showed that these stages are present in the whole field. The mapping of high resolution turbiditic stages, considering the correlation of their four facies, will allow a better location of wells, resulting in a more efficient exploration and production development, capable of increasing the recovery of important oil reserves that still exist in the area, optimizing costs and giving greater robustness to E&P processes.