Dispersion and Filter Cake Removal of Manganese Tetroxide-Based Drilling Fluids

Abstract

Linear and other structures of particle aggregations were identified in Mn 3O4 - based filter cake. Several dispersants showed high potent ial to disperse manganese tetraoxide particles in water -based drilling fluids. Groups A and B dispersants showed particle settling times of 24 and 1 to 3 hrs, respectively. Laser particle analysis showed that aggregation of particles was reduced in the presence of lignosulfonate based dispersant. Zeta potential measurements showed a region of dispersion stability at pH of 6 to 11 based on Mn3O4 /C31 dispersant aqueous solutions . Zeta potential and transparency experiments showed that the optimum dispersant concentration was below 1 wt% and nearly 0.5 wt% based on Mn3O4 /dispersant aqueous solutions . SEM images of filter cake showed that the aggregation of particles was reduced when acrylic/maleicbased dispersant was used in clay contaminated drilling fluids . In most cases, the rheological behavior and sagging tendency of the contaminated and noncontaminated drilling fluids (17.5 and 20 lbm/gal) before/after heat aging at 400°F were improved in the presence of dispersants. The presence of NaCl and CaCl 2 had varying interactions with compatibility and particle settling.

Dispersants for oil -based systems were sorted in Appendix B by the highest potential to disperse manganese tetraoxide particles in mineral oil –based solutions. Particle settling indicated that the optimum concentration for dispersants were nearly between 0.2 and 2 wt% based on Mn3O4 /dispersant S9 mineral oil -based solutions. Viscosity measurements showed a lower viscosity of 13.8 lbm/gal Mn3O4 oil -based drilling fluids at 1 wt% dispersant S9 than that of drilling fluids at 0.25 wt%. In most cases, the rheological behavior and sagging tendency of the contaminated and non-contaminated drilling fluids (17.5 and 20 lbm/gal) before/after heat aging at 400 °F were improved in the presence of dispersants. I lmenite and API barite oil -based drilling fluids showed higher sagging tendencies than those of manganese tetraoxide oil -based drilling fluids, indicating dispersant S5 was more effective with manganese tetraoxide fluids although the three drilling fluids have nearly similar rheological behavior.

Glycolic or HCl acids (4 wt%) dissolved 75 wt% of manganese tetroxide particles. The dissolved manganese ions were higher with glycolic acid ( i .e. 10,000 mg/l) than that of HCl acid (8,500 mg/l). The reaction time when using HCl was nearly 5 times faster than that of glycolic acid reaction with manganese tetroxide particles. The Mn3O4 -based filter removal efficiency was nearly 90 wt% when glycolic acid was used in the single or two -step procedure to dissolve the f ilter cake. Glycolic acid concentrations were 7 and 10 wt% d uring the single and two-step filter cake removal procedures, respectively. The removal efficiencies by flow rate were higher with sandstone core samples ( i .e. 125 vol%) than those of limestone core samples ( i .e. 100 vol%).