AAPG Latin America and Caribbean Region Geoscience Technology Workshop

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The construction of predictive risk model to reductions in time and cost of the appraisal or new exploratory well, Santos Basin


Reduced time and costs during well construction using a predictive risk model to understand the pre-salt, salt, and post-salt environment allows drilling with less uncertainty when building the operational window of mud and design, requiring less time and economic investment. The drilling stretch of salt appears to be very complex because of the salt creep, borehole instability, high torque, and vibration during drilling. Some intercalations with igneous rock increase the probability of losing mud weight and the possibility of stuck pipe during drilling is high. Mud weight management is only one of the variables that needs to must considered during drilling in the pre-salt environment. For another hand, the reservoir rock presented low rate penetration due to hard and abrasive carbonate mixed rocks, severe loss of fluids by caves, cavern (Karst) that generated bad hole conditions (Washout) that complicate the evaluation and cementation stage, spending more time that planned. For the mechanical properties, it was necessary to generate the elastic properties for the salt column using the logs of the well drilled and calibrate them with the drilling events observed during the drilling. Information collected from the wells of different characteristics of the same basin to correlate them with the results of the geomechanical curves and drilling events. These results showed that it is possible to identify at least four different sectors in the same basin, each of which has different response to drilling complexity. Geology knowledge is also an important tool to help predict potential drilling problems in the salt section. The previous experience in formation evaluation of the reservoir rocks in different sedimentary models like microbial platforms, complex build up and mixed platform with volcanic influence; were used in many wells to corroborate all the results. The highlight of this new predictive risk model; should be applied to many other pre-salt fields in the Santos Basin.