Análise fluidodinâmica de um solo marinho jateado empregando modelos reológicos

Abstract

Due to the exploration of marine oil fields in ultradeep water regions, the need for different methods of well construction has increased. The technique of laying conductive casing by jetting is the most widely used for the well starting phase in such conditions. In this scenario, in initial layers, where the marine soil is in contact with seawater, this material can present itself as a fine mud, characterizing a cohesive non-drained soil, with low shear strength and that can be considered as a material with viscoplastic behavior. Thus, the use of fluid rheology to analyze it can be a valid option, and it is possible to classify it as a Herschel-Bulkley fluid. One of the alternatives to understand the behavior of the soil during jetting is the use of computational modeling and numerical simulation, due to the accuracy of this technique and its development cost, since the local and budgetary conditions do not always allow more complex studies and experimental analysis. Thus, this work focused on the computational modeling of the jetting of marine soil, based on the soil fluid dynamics approach. For this, the computational fluid dynamics (CFD) software SIMULIA XFLOW©, developed by Dassault Systèmes, version (2020), was used. Firstly, the present work sought to investigate the deformation of the seabed in response to an incident vertical jet, using seawater as the drilling fluid. The profile of the cavity formed by the jet was quantified in terms of depth and width by tracking the position of the fluid-fluid interface over the considered jetting time. This was made possible by the numerical method of the software, the LBM (Lattice-Boltzmann Method), which offers better support for multiphase flow simulations compared to the numerical methods used in conventional CFD softwares, regarding the modeling of the fluid interface region. Next, parametric analyses were performed seeking to understand the influence of jet velocity and drilling fluid on ground deformation in response to the incident jet. The results demonstrated that increasing the jet velocity provided greater depths and widths to the cavity; however, varying the drilling fluid did not cause significant differences in the excavated cavity, except when considering a drilling fluid of higher specific mass, whose jet deformed the soil at greater depths than the other drilling fluids. In order to observe how the jetting of the soil would occur while the conductive casing is being laid, a drill bit was implemented in the analyzed model. The drill bit was modeled according to the information available in the literature and did not perform adequately for jetting, even when varying the rotation of the drill bit and the fluid flow rate, since there was too much soil accumulation in the annulus inside the conductor.