Innovative experimental method for particle bridging behaviors in natural fractures

Abstract

Lost circulation is a major challenge in drilling naturally fractured formations. The most common solution for this problem is to add particulate lost circulation materials (LCM) in the drilling fluid to plug the fracture loss zones. A successful plugging depends on whether the LCM particles can form an effective bridging and seal the complex loss zones. Therefore, an investigation on the bridging behavior of particles in natural fractures is needed. In this study, a combination of three-dimensional scanning and numerical control mechanical engraving technology is employed to demonstrate a complex transparent model fracture (TMF) which can accurately analyze the internal spatial characteristics of the natural fractures. A series of visualization experiments for different particle size, particle volume concentration, and differential pressure were conducted by injecting regular particles into the TMF. The migration and bridging behavior of the particles in the TMF were recorded using a high-speed camera. Results showed that the particle bridging structures and their distribution in natural fractures are affected by the concentration, size, differential pressure, and the local aperture distribution of the fracture. Two bridging structures, namely, single-particle bridging (SB) and double-particle bridging (DB) were observed at the entrance or inside of the TMF. The type of bridging structure which plays a dominant role in the process of fracture plugging is mainly determined by the particle concentration. SB dominates at particle concentrations of 0.5 vol%, 1 vol% or 2 vol%, whereas DB dominates at concentration of 5%. The visualization experimental results help to better understand the bridging mechanism of the particulate LCMs in natural fractures. The results indicate that irregularity of the natural fracture aperture, which is usually neglected by conventional experiments, has a crucial effect on the structure and position of particle bridging.