Reservoir characterization of Maracangalha sandstone using measurements on outcrops and well logs

Abstract

In this research, we performed petrophysical measurements using conventional techniques (Pycnometer and gas permeameter), resistivity and chargeability electrical, besides nuclear magnetic resonance (NMR), on 122 shale sandstone samples collected from outcrops of the Maracangalha Formation in Frades Island, Bahia Brazil. This Formation is an of the main hydrocarbon reservoirs in the Recôncavo Basin in Brazil, but little petrophysical information is available. Electrical measurements were performed using a sample holder build with four-electrode, two for current injection and two for electrical potential measurements, where the rock samples were inserted under condition 100% saturated with multiples salinity solutions. NMR measurements were also obtained with saturated samples and under the condition of partial saturation. The conventional, electrical, and NMR data were analyzed together, resulting in important petrophysical parameters for the lithological characterization of the Maracangalha Formation sandstones. These samples were characterized according to your effective porosity, cementation exponent, volumetric-solid conductivity, clay content, mean grain, and pore-throat sizes. Such laboratory results allowed developing an integrated approach to interpret geophysical well logs of the Maracangalha reservoir. These logs, including gamma-ray, porosity (density, sonic and neutron) and electrical data, were interpreted in terms of shaliness, effective porosity, and partial water saturation, supported by our experimental petrophysical results. In particular, to complete this interpretation was used a combination of electric logs was used to describe the true resistivity at the invaded and in the virgin zone of this reservoir. Taking into account the effects of weathering in the samples used, these results contributed to the formation of a petrophysical database for the Maracangalha Formation, as well as its use as guide values for new interpretations in geophysical profiles in this region.