ABSTRACT:

Several challenges related to pre-salt Santos Basin fields developments were experienced by petroleum engineering and geosciences team, since its discovery in 2006. Mainly caused by the geological environment of the pre-salt and the characteristics of the reservoir rocks. Among the differences from the pre-salt and post-salt fields geology are: high layers of salt to drill the reservoir, large permo-porous properties, providing large areas of loss of circulation and high thickness of the reservoir rock. The main challenges and technological demands have been in terms of special drilling equipment required to drill through the thick salt layers, development of new geomechanical models, new completion settings in order to minimize rig costs and wellheads manufactured to resist the high-pressure conditions. This paper aims to address these pre-salt drilling and completion-related challenges and discuss some key improvement opportunities, such as: 1 - The use of nano-fluids to improve the drilling fluids properties, and artificial intelligence (AI) to provide reliability of drilling fluids selection, aiming to make the whole drilling operation safer and minimize non-productive time; 2 - New intelligent completion settings, to minimize workover costs; 3 - A new probabilistic geomechanical model for pre-salt and post-salt layers, which allows the prediction and analysis of the unconfined compressive strength, in situ stresses and the range of mud density that assures integrity to the wellbore, by computing the gradients to build the mud weight window. Authors present a pre-salt case study where the operational window was planned through field synthetic data, to predict high permeability zones to avoid loss of circulation during drilling operation. 4 - Applied reliability engineering based on stochastic Markovian model to predict the reliability level of main integrity drilling and completion equipments, investigating the influence of operational conditions in the failure rate and providing a framework to promote a reliability growth analysis when researching new equipments. This work also presents the case studies about Blowout Preventer (BOP) and Surface Controlled Subsurface Safety Valve, (SCSSV) reliability used in the pre-salt environment.

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