The Investigation of Broad-Spectrum Sealing Drilling Fluid Based on Horsfield Close-Packing Theory

Abstract

In shale gas drilling operations, oil-based drilling fluids have proved to be effective in addressing the issue of shale reservoir hydration expansion, serving as the primary working fluid for complex subsurface shale formations. However, the presence of shale laminations and the development of microfractures with varying widths require drilling fluids with excellent sealing capabilities. In this study, a comprehensive investigation was conducted to develop a drilling fluid system with broad-spectrum high-sealing performance. The porosity of bridging particles was determined by using the Archimedean drainage method. The bridging particle size and quantity at each level were meticulously designed through leveraging the Horsfield close-packing theory. The incorporation of deformable nanoscale polymer sealing materials further enhanced the sealing performance of the drilling fluid system. Additionally, hydrophobic nanoscale silica particles were introduced as coemulsifier to prepare Pickering emulsions, thereby improving emulsion stability and enhancing particle-size distribution for improved sealing. Through formulation optimization, a drilling fluid system with broad-spectrum, high-sealing performance capabilities was developed. The study revealed a reduction in porosity of closely packed bridging particles from 35.36% to 11.38%. The drilling fluid system exhibited a remarkable sealing efficiency of 99.2% for microfractures in the 1–10 μm range and 95.8% for microfractures in the 30–50 μm range. Furthermore, it demonstrated excellent sedimentation stability, with a sedimentation factor of less than 0.52 after 48 hours of static sedimentation at 150°C. The drilling fluid system also exhibited favorable rheological, lubrication, and inhibition properties, thus meeting the demands of field applications.