Desenvolvimento de fluido aquoso polimérico de baixa densidade com microesferas ocas de vidro para perfuração de poços de petróleo

Abstract

Drilling formations with low pore pressure presents a narrow operating window between the pore and fracture pressures, in which a fluid of inadequate density may cause alterations in the well pressure, resulting in lost circulation and reservoir damage. Under these conditions, reduced-density fluids are necessary that, besides counterbalancing the formation pressure, simultaneously meet filtration, rheology and gel strength criteria. The incorporation of hollow glass microspheres, low-density particles, is an effective strategy for this reduction, but it simultaneously alters these properties, requiring the adjustment among the fluid components. In this work, a study was developed on an aqueous polymeric fluid containing hollow glass microspheres, in two stages. In the first stage, an operational feasibility analysis was carried out with a drill-in fluid, in which the maximum technically sustainable density reduction was 0.50 ppg, with 18 lb/bbl of microspheres; however, field logistics constraints limit this reduction to 0.25 ppg for production volumes between 5,000 and 7,000 bbl. In the second stage, an aqueous polymeric fluid saturated with NaCl was optimized by Central Composite Design (CCD) and Differential Evolution. The CCD was conducted with four independent factors: xanthan gum, HPA, calcium carbonate and hollow glass microspheres; totaling 27 experimental formulations, from which second-order empirical models were fitted for eleven responses: density, filtrate volume, L600, L300, L200, L100, L6, L3, gel strength at 10 seconds, 10 minutes and 30 minutes. For density, the fitted model was linear, with calcium carbonate and microspheres acting independently of each other and as the only significant factors. The shear-rate reading models showed good fit, with xanthan gum as the dominant factor, and the gel strength models reflected the greater complexity and intrinsic variability of this property. The filtrate volume remained below 10 mL in all formulations. From the fitted models, a formulation was identified by optimization that reached a density of 9.10 ppg and a filtrate volume of 1.4 mL, with high- and medium-shear-rate readings within the operational ranges and low-shear readings close to the lower limit. The absence of calcium carbonate in the optimal formulation shows that hollow glass microspheres associated with the xanthan gum polymeric matrix are sufficient to meet the operational criteria of density, rheology and filtration in the investigated domain.