No abstract

Fluids produced from oil reservoirs typically contain oil, natural gas, water, sediments, in varying amounts, and contaminating gases. Considering that economic interest usually targets mostly oil and gas, primary processing is used to separate water/oil/gas, in addition to treating these phases. Therefore, the well stream should be processed as soon as possible after reaching the surface. Separator vessels are among the main equipment used at surface production facilities, being responsible for the separation of the produced phases. This work focuses on studying the fluid dynamic behavior in a horizontal three-phase separator. To accomplish this goal, we used the computer fluid dynamics software ANSYS CFX. First, we performed a detailed analysis of a “Standard Case” to understand in detail the entire separation process within the vessel. The results show the three phases through the simulation time, analyses of the separation efficiency, different fluids flow lines, pressure gradient inside the vessel, and effect of the diverter baffle. It also considers a variation of fluid flow at the inlet of the separator. These analyses include pictures of all cases studied. Afterwards, some parameters of the standard case were altered to evaluate its influence on fluid dynamics behavior and the functioning of the separator vessel. At last, we analyzed the influences of oil density and viscosity on the separation. The oil quality affects the primary separation directly, as the oil density and viscosity increase, for example, increases the drag between the fluids and decreases the rate of sedimentation, which stickles the separation process difficult. Two out of the three cases generated satisfactory results. The simulation with the heaviest oil presented the worse results.

The fluids produced and transported to the surface by the production manifolds do not have the necessary conditions to be economically viable. Produced fluids consist of at least three fluid phases (oil, water, and gas), besides impurities and contaminants. Therefore, the well stream should be processed as soon as possible after bringing it to the surface. Separator vessels are among the main equipment used at surface production facilities, being responsible for the separation of the produced phases. This work focuses in studying the fluid dynamic behavior in a horizontal three-phase separator. For this, we used the computational fluid dynamics software ANSYS CFX. First, a detailed analysis of a "Standard Case" was performed to better understand the entire separation process within the vessel. The results showed the three phases through simulation time, an analysis of the separation efficiency, an analysis of the different fluids flow lines, an analysis of the pressure gradient inside the vessel, and an analysis of the effect of the diverter baffle, as well as, a variation of fluid flow at the inlet of the separator.

With the exploration of marine oil fields in deep and ultra-deepwater regions, the need for studying different methods of well construction has increased. Nowadays, the technique of laying conductive casing by jetting is the most widely used for the starting phase of a well in such conditions. In this scenario, in early 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, being considered a material with viscoplastic behavior. Thus, as such, using fluid rheology to analyze it may represent a valid option; being possible to classify it as a Herschel-Bulkley fluid. The use of computational modeling and numerical simulation represent an alternative to understand the behavior of soil during jetting. In this context, this work focuses on developing a computational modeling of the jetting of marine soil, based on the soil fluid dynamics approach, using computational fluid dynamics (CFD - Computational Fluid Dynamics) software SIMULIA XFLOW, version 2020. This work aims to investigate the deformation in the seabed in response to an incident vertical jet using different drilling fluids, also modeled as viscoplastic materials. Drilling fluids suitable for jetting and a fluid with a higher specific mass were considered. For the proposed modeling of the soil and drilling fluids considered, the main parameters used were the yield point, consistency index, behavior index, and the boundary viscosity. The latter was necessary to implement the modified Herschel-Bulkley model used by the software. Results show that the excavated cavity presented a similar behavior for the drilling fluids suitable for jetting, indicating that the rheology of the drilling fluid does not interfere with the deformation of the soil. However, a significant influence on the profile of the excavated cavity was observed when implementing the drilling fluid of higher specific mass in the jetting, which deformed the soil at greater depths.

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.