Fluid losses are still today one of the most challenging problems in well construction. The scenarios faced by operators during development and exploratory campaigns in the deep water pre-salt area are characterized by natural fractures, vugs and caves. Therefore, problems related to loss of circulation are critical, increasing the non-productive time and consequently, well construction costs. Additionally, in several situations, conventional drilling limitations prevent the reaching of the well target. The present study proposes the application of a methodology to define optimum loss control material (cross-linked pills, fluid loss squeeze, bridging agents, cement), among those available for each situation, to minimize lost circulation events during drilling operations. An Artificial Intelligence strategy based on Supervised Learning was defined to generalize data collected from five hundred lost circulation events over a three years period. Human Computer Interaction principles were used on the development of an interface where the field engineer can interact with training data while having little to no Machine Learning knowledge. The use of empirical analysis and learning strategies as tools to assist the decision making process in the form of lost circulation countermeasures is described by this paper. The method was validated on data collected from several different wells in the Santos Basin, Brazil, pre-salt area. The strategy was already applied in two real cases resulting in a six days well construction time saving.

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The drilling of the evaporitic section using water-based mud (WBM) was always a challenge: even though there are already some wells drilled with saturated aqueous fluid, their use still divides opinions within the technical-academic community of the oil industry. Basically, there are two currents: one that believes that salt drilling with WBM causes an enlargement so great that it becomes impracticable to cement the casing and, consequently, to obtain a leak off test (LOT) or a formation integrity test (FIT) sufficient for drilling of the next phase. The other line of thinking is based on that the break-in created by the WBM is similar to that caused by the synthetic-based mud (SBM) and this increase in diameter would not have a negative influence on the quality of the cementing job. In 2015-2016, Petrobras drilled 13 wells in Santos Basin Pre-Salt using WBM for bottom hole drilling (BHD). In this way, this work aims to report the lessons learned in each well, comparing fluid costs with correlation wells drilled with SBM's. The use of WBM, besides not negatively impacting the drilling time of the phases, allows a reduction of the costs with chemicals products and a decrease in equipment costs, since the drying system of cuttings is not used. In addition, rig and borehole cleaning are simpler and require less time and WBM is less aggressive for people working in direct contact with the drilling fluid. To compare the costs of fabrication and treatment of fluids, an average calculation was used for the correlation wells. Thus, an economy achieved is the difference between average cost for correlation wells and the well in question. The drilling of the evaporitic section with WBM's makes: (i) no significant salt washout than that obtained when using SBM and (ii) as WBM does not require a cuttings drying system, rate of penetration (ROP) obtained during a salt drilling are higher than those obtained when working with SBM. For the drilling of the carbonate reservoir, the performance of WBM is similar to that of SBM and the use of WBM in BHD allows faster fluid exchange and generates less residue for wells with open hole single completions. By drilling 13 wells using WBM, it was possible to save 576.9 hours of rig time.