Development and evaluation of an electropositive wellbore stabilizer with flexible adaptability for drilling strongly hydratable shales

Abstract

In order to overcome serious instability problems in hydratable shale formations, a novel electropositive wellbore stabilizer (EPWS) was prepared by a new approach. It has good colloidal stability, particle size distribution, compatibility, sealing property, and flexible adaptability. A variety of methods including measurements of particle size, Zeta potential, colloidal stability, contact angle, shale stability index, shale dispersion, shale swelling, and plugging experiments were adopted to characterize the EPWS and evaluate its anti-sloughing capacity and flexible adaptability. Results show that the EPWS has advantages over the conventional wellbore stabilizer (ZX-3) in particle size distribution, colloidal stability, inhibition, compatibility, and flexible adaptability. The EPWS with an average particle size of 507 nm and an average Zeta potential of 54 mV could be stable for 147 days and be compatible with salt tolerant or positive charged additives, and it also exhibited preferable anti-sloughing performance to hydratable shales at 77, 100, and 120 °C, and better compatibility with sodium bentonite than ZX-3 and KCl. The EPWS can plug micro-fractures and pores by forming a tight external mud cake and an internal sealing belt to retard pressure transmission and prevent filtrate invasion, enhancing hydrophobicity of shale surfaces by adsorption to inhibit hydration. The EPWS with flexible adaptability to temperature for inhibition and sealing capacity is available for long open-hole sections during drilling.