Gravitational solid-liquid separation of water-based drilling fluids weighted with hematite through the gamma-ray attenuation technique

摘要

Drilling fluids are injected during the drilling process in order to make the operation viable. Some of the desired functions of these fluids are the following: to be pumpable, to clean the well by transporting cuttings to the surface, to suspend the solids in operational stops, to stabilize the walls of the well, to block the pores of the rock formation, to lubricate and cool the drilling bit and other equipment used, and to be chemically stable and inert in relation to damage to the rock formation. The drilling of an oil well is done in stages, as each rock formation demands a specific fluid formulation. These suspensions have a water, oil, air or synthetic base and different substances and incorporated particles, such as viscosifying, sealing, weighting and thickening agents. The drilling fluids studied in this work were produced by a Brazilian petroleum company, differentiated by the amount of the weighting agent (hematite). In this context, this study simulated a standstill operation and evaluated the stability of particles in four water-based drilling fluids through the gamma-ray attenuation technique to determine an equation for pressure on solids for each system. The rheological behavior of the suspensions was also evaluated. The results showed that fluids with higher amounts of hematite had higher viscosity, pseudoplastic and tixotropic behavior, sediment with higher volumetric concentration, greater stability in relation to sedimentation and a small region of clarified liquid. In addition, constitutive equations were determined for pressure on the solids, and the influence of hematite was also verified.