A Coupled CFD-DEM Numerical Study of Lost Circulation Material Transport in Actual Rock Fracture Flow Space

Abstract Fractures are beneficial to the cost-effective development of unconventional reservoirs, which may also induce drilling fluid loss, formation damage and other issues. Fracture plugging is the most common measures to settle those problems. The effect of fracture plugging largely depends on the lost circulation material (LCM) formula. In order to form the plugging zone rapidly in the near wellbore portion of fracture, it is necessary to study the transport process of LCM in real fracture. In this paper, the distributions of fracture aperture of a tight sandstone specimen are captured utilizing the high-resolution and high-precision structured light scanning systems, which is used to reconstruct the geometric model of actual rock fracture flow space. The coupled Computational Fluid Dynamics and Discrete Element Method (CFD-DEM) simulation is carried out to study the interaction between drilling fluid and LCM particles as well as LCM transport in above geometric model with various particle size. The constant directional torque (CDT) model is employed in the part of DEM computation to account the influence of LCM particle shape. The numerical simulation results show the LCM particles would plug in the narrow region of the actual rock fracture flow space, inducing the rapid accumulation of other LCM particles. The compatibility between the distributions of fracture aperture and the size of LCM particles played a decisive role in the transport process of the LCM particles, which directly determined the position of plugging zone. The multigrain bridging phenomenon of small size LCM particles was observed in simulations. This paper presents the idea of combining the reconstruction technique of actual rock fracture flow space and the CFD-DEM simulation to mimic the transport process of LCM particles in real rock fracture. The simulation results show the fracture surface topography has a significant influence on LCM particles transport and plugging zone distribution; the LCM particles considering the nonsphericity may multigrain bridge in the fracture which will greatly improve the efficiency of fracture plugging.