Numerical Simulation of Jet Excavation in Conductor Jetting Operations in Submarine Soil: Mesh Analysis

Abstract

The more complex exploration techniques and operations in deepwater environment are, the higher become the financial costs involved in the process. The rent of an offshore rig, for instance, can cost hundreds of thousands of dollars per day. Therefore, improving deepwater drilling efficiency can lead to significant cost savings. 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 submarine environments where the seafloor sediments allow the technique to be used. In these environments, the submarine soil consists of a deformable body displaying a behavior that falls between a linear elastic solid and viscous fluid. Therefore, its behavior is governed by general theory of rheology, and it can be described as highly viscous non-Newtonian fluid. Despite the lack of comprehensive investigations, promising works can be carried out by considering cohesive soil behavior as viscous fluid. 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 during the first 30 seconds of examination, considering soil as viscous fluid of Herschel-Bulkley. Ansys Fluent®, which is a CDF software based on the finite-volume method, was applied to simulate the jetting excavation process. The results indicate that all meshes generated in the development of this work have an excellent quality, and they also show that the greater the mesh refinement is, the higher the accuracy and robustness of the model will be. However, the computational cost to simulate the model increases exponentially with the increase in number of elements, highlighting the importance of properly balancing mesh refinement and computational effort. When analyzing the results, we could also identify the excavation profile made by the bit jet, which presented an almost symmetrical shape.