Basic and specialized geophysical well logs to characterize an offshore carbonate reservoir in the Campos Basin, southeast Brazil

Abstract

Assessing the geometry, flow dynamics and, petrophysical properties, of a carbonate reservoir has been a key task for a long time, but the challenges presented by these highly heterogeneous rocks seem endless. Geophysical well logs have been, over this time, a very important tool in this type of evaluation. The applications of logs, in the evaluation of the geological formations, range from the estimation of lithology, porosity, permeability and mechanical properties. Commonly, logs are classified as basic or special. The basic logs, used in this work, are the gamma ray, resistivity, density, neutron and sonic. The special ones, utilized in the study, are the acoustic image and the photoelectric logs. From the analysis of the basic logs, the lithologies were identified, the reservoir was delimited and zoned, the fluids and the contact between them were identified and, petrophysical properties, as porosity and water saturation, were estimated. The total porosity was estimated using the empirical relationships from density, neutron and, sonic logs. The identification of the porosity type, such as fractures, vugs etc., although, was determined from the acoustic image borehole wall, as well as different geological structures, such as lithological contacts, inclined layers, natural and induced fractures, besides the identification of caves. The photoelectric log helped to identify the different lithologies, which were compared with those derived from the basic logs. Thus, the main objective of this work was the joint use of the basic and specialized logs, in the characterization of a carbonate reservoir in the Campos Basin, using real data from the post - salt layer. In the end, the advantages and disadvantages, in the usage of these tools, were indicated, as considerably as the applications and care with the occurrence of no geological structures. The joint use of the data and, the adopted methodology proved effective in the characterization of this reservoir.