Preparation, characterization and application of modified barite grafted with lipophilic polymers for oil-based drilling fluids

Abstract

With the increasing exploration and development of deep oil and gas resources, the applications of oil-based drilling fluids (OBDFs) have become increasingly prevalent. Accordingly, it places higher demands on drilling fluid density for drilling deep and ultra-deep wells. Conventional weighting materials exhibit limitations in achieving stable dispersion in OBDFs, which often results in poor wall-building performance, unstable viscosity and yield point, and poses risks to drilling operation safety. In this paper, a modified API barite (mAB) was prepared for OBDFs by chemically grafting a lipophilic polymer onto API barite. The mAB was designed to partially replace traditional barite as a multifunctional weighting material. Experimental results demonstrated that the addition of mAB significantly improved the stability of OBDFs, exhibiting a density difference of less than 0.132 g/cm³ and a static sag factor (SF) within 0.53. It indicates superior suspension stability compared to conventional weighting materials, ensuring uniform particle distribution under static conditions. The rheological properties remained stable after aging at 180 °C for 16 h without the addition of wetting agent. Additionally, mAB enhanced the compactness of mud cake, forming a denser and thinner mud cake with reduced filtration loss. Meanwhile, the mAB/OBDFs also exhibited excellent lubricity and reservoir protection performance, achieving a sticking coefficient of 0.0437 and a permeability recovery rate of 95 %. These findings suggest that the mAB developed in this study can serve as a novel multifunctional weighting material for OBDFs, providing an effective approach to optimize the comprehensive performance of high-density drilling fluids.