In-Situ Stress And Wellbore Stability In A Brazilian Basin

Abstract

The knowledge of the in-situ stress has been recognized as a fundamental parameter in planning exploitation activities in the oil industry. Wellbore projects, hydraulic fracturing, prevention of sand production and other activities are highly influenced by the in-situ stress state. In Brazil exploitation projects are usually done considering the paradigm that the Brazilian basins are tectonically relaxed. Nevertheless, a number of evidences indicates that such idea should be reconsidered. Here we show a study prepared for a given oil field to determine the in-situ stress using breakouts analysis, leak-off inversion technique and available information from density logs. The results indicated that the oil field is submitted to a normal stress regime, the horizontal principal stresses are unequal and the maximum horizontal stress (SHmax) is oriented parallel to NNE-SSW. To demonstrate how the in-situ stress could impact wellbore projects, a wellbore stability simulator was used. The input data to the simulator were: breakout information; values of mud weight, pore pressure and leak-off test data; rock mechanics properties; directional characteristics of wells. The program’s visualization tools have shown how important is to determine as precisely as possible the in-situ stress.