A new environmentally friendly water-based drilling fluids with laponite nanoparticles and polysaccharide/polypeptide derivatives

Abstract

Considering the increasing environmental pressure, environmentally friendly and high-performance water-based drilling fluids (WBDFs) have been widely studied in recent years to replace the commonly used oil-based drilling fluids (OBDFs). However, few of these drilling fluids are entirely composed of natural materials, which makes it difficult to achieve real environmental protection. Using laponite nanoparticles and various derivatives of natural materials, including crosslinked starch, cellulose composite, gelatin ammonium salt, poly-l-arginine, and polyanionic cellulose, a kind of environmentally friendly water-based drilling fluid (EF-WBDF) was built for drilling in environment-sensitive areas. The properties of this EF-WBDF were evaluated by thermal stability tests on rheology, filtration, inhibition, and salt contamination. Besides, biological toxicity, biodegradability, heavy mental content and wheat cultivation tests were conducted to investigate the environmental factor of EF-WBDF. Results showed that EF-WBDF displayed satisfactory thermal resistance up to 150 °C, and the rheological properties did not suffer significant fluctuation, showing potential application in high-temperature wells. The optimal rheological model of EF-WBDF was Herschel–Bulkley model. This EF-WBDF performed an eligible filtration of 14.2 mL at 150 °C and a differential pressure of 3.5 MPa. This fluid could still maintain colloidal stability after being contaminated by 7.5% NaCl or 0.5% CaCl 2 . Meanwhile, rather low clay swelling degree of 2.44 mm and high shale recovery of more than 95% ensured the inhibitive capability of EF-WBDF. Furthermore, EF-WBDF presented a half maximal effective concentration (EC 50 ) of 51200 mg/L and a BOD/COD ratio of 47.55%, suggesting that EF-WBDF was non-toxic and easily biodegradable. The wheat cultivated in EF-WBDF could grow healthily, beneficial for reducing the adverse impact on ecological environment. The formed EF-WBDF has a promising future for drilling in environment-sensitive and high-temperature areas.