Estudo numérico da escavação por jatos de broca em operações de jateamento em solos marinhos

Abstract

The more complex the oil exploration in deepwater environment is, the more expensive and complex it becomes. For instance, the rent of an offshore rig can cost hundreds of thousands of dollars a day. Therefore, improving deepwater drilling efficiency can lead to cost savings and safety improvement in the overall process. The drilling process of an oil well starts with the initial drilling, which is the operation to accommodate the conductor casing. Among the techniques to set the conductor casing, jetting operations have become popular in deepwater environments where the seafloor sediments allow the technique to be used. In these environments, the submarine soil is a deformable body whose behavior falls between a linear elastic solid and viscous fluid, so its behavior is governed by general theory of rheology and it can be described as highly viscous non-Newtonian fluid. Considering cohesive soil behavior as viscous fluid is a promising work despite the lack of study. Problems of this type can be solved using computational fluid dynamics (CFD), a powerful software which solves complex fluid mechanics equations. Thus, this work numerically evaluates the excavation mechanism in conductor jetting operations in submarine soil in the first 30 seconds, considering the soil as viscous fluid of Herschel-Bulkley. Ansys Fluent R , a finite volume method based CFD software, was applied to simulate the jetting excavation process. The results indicate that the jet velocity is the parameter that most influences excavation, because of the soil viscoplastic properties. However, the efficiency of the operation does not depend only on a specific parameter, but on a set of factors. The size and position of the drill bit, inclination of the nozzles, and even the drilling fluid used in the process are parameters that besides reducing the time of this stage in drilling, when optimized, they improve the efficiency of the soil excavation profile and disturb regions close to the conductor casing, facilitating its settlement.