Análise e estimação das propriedades de tortas de filtração de fluidos de perfuração não-Newtonianos

Abstract

The oil well drilling process is always evolving and being optimized to ensure maximum efficiency to reduce its cost. In this scenario, the loss circulation is a phenomenon to be continuously studied and minimized to avoid fluid loss and oil reservoirs contamination. It is caused by a pressure differential between the formation pores and the well annular region. As drilling fluid invades the reservoir, a layer of solids is formed and the fluid loss rate becomes a function of cake parameters such as permeability and porosity. To minimize the filtrate loss, drilling fluids are designed to provide a thin cake with low permeability. Several methods of determination of the properties of filtration pies are presented. So, it is noticed the absence of procedures of calculation and estimation of adequate parameters, in which the experimental errors associated with the experimental output variables are adequately described. In this study, the effects of temperature, pressure and solids concentration on the filter cake parameters were evaluated. The mud cake compressibility was analyzed in constant pressure filtration processes. The internal structure of the mud cakes was studied by SEM images. Static filtrations were performed in an HTHP filtration cell with non-Newtonian suspensions with concentrations similar to those used in actual processes. The mud cake parameters were estimated by adjusting the filtration model for non-Newtonian fluids using the Estima package, written in Fortran language. Three different methodologies for parameter estimation were presented, in which they are estimated separately for each experimental condition (implicit method) or directly estimated from filtrate volume data. The effect of the applied pressure differential on the cake permeability and on the filter resistance was considered from appropriate constitutive equations.