In-Situ Stress And Wellbore Stability In A Brazilian Basin

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