Análise numérica da perda de circulação: utilização de escoamento de fluido pseudoplástico com partículas aplicado ao preenchimento de fraturas

Abstract

Lost cirulation is a common problem in the oil and gas industry, defined as the fluid invasion into the formation being drilled. In this work, the mathematical modeling and numerical simulation of the lost circulation caused by the presence of a single and discrete fracture in the drilling process and its respective obturation applying lost circulation materials (LCM) are investigated. Usually, the drilling fluid presents non-Newtonian characteristics and, therefore, a power law fluid will be used in the simulations. It is expected that LCM, which is represented as spherical particles, will be carried by the fluid up to the fracture location and will deposit inside it, forming a fixed bed. For that, the Dense Discrete Phase Model (DDPM) and the Discrete Element Method (DEM) will be combined to correctly account for particle and fluid motion. The problem will be analyzed by its key control parameters, namely, power (0,4≤ n ≤0,6) and consistency index (0,7≤ m ≤1,3 Pa.sn), particle to fluid density ratio (2,00≤ ρp/β ≤2,50), diameter (0,5≤ Dp ≤0,7 mm) and the flow rate at the wellbore (0,130≤ uβ,CH,i ≤0,392 m/s). The response variables are the flow rate of fluid loss at the fracture end Qfuga and the pressure at the bottom of the wellbore (pent). Moreover, geometric characteristics of the particle bed will also be monitored: position (hpct,i), length (hpct) and vertical filling of the fracture (epct). The goal is to provide guidance for how the control parameters influence the response variables in hopes of providing more adequate parameters for the approach of lost circulation. Results show that, for the range of control parameters studied in this work, the filling time did not show significant variations for the power index and was lower when consistency index and flow velocities were also lower, as well as for higher diameters and density ratios. The flow rate fluid loss at the end of the filling process was more sharply reduced when lower consistency index and fluid velocities are employed, with the same behavior observed for bigger diameters and density ratios. Lastly, the pressure at the fractured channel inlet shows to be more sensible to the particle injection process whenever lower power, consistency index and velocity are applied along with higher density ratios and diameter. This indicate that the mixture of non-Newtonian fluid and particles should be prefferred over Newtonian fluid with particles, whenever possible.