Analytical model of plugging zone strength for drill-in fluid loss control and formation damage prevention in fractured tight reservoir

Developed fractures are beneficial for the efficient development of tight reservoir. They also lead to drill-in fluid loss and induce severe formation damage. Fracture plugging with loss control material (LCM) is the most common way to control drill-in fluid loss in fractured formation. Fracture plugging effect largely depends on the strength of fracture plugging zone, because in most cases plugging failure is caused by the strength failure of plugging zone. However, the effects of LCM mechanical and geometric parameters on plugging zone strength are still unclear. Moreover, traditional LCM selection is mainly performed by trial-and-error method, due to the lack of mathematical models. This paper develops an analytical model for plugging zone strength accounting for the frictional failure and shear failure of fracture plugging zone. Effects of LCM mechanical and geometric properties on plugging zone strength are analyzed. The proposed model is validated by laboratory data. Application procedure of the proposed model to drill-in fluid loss control is developed and successfully applied to the field case study in Sichuan basin, China. The modelling results show that particle-particle friction angle, particle-fiber friction angle, fiber tensile strength, D90 degradation rate, and friction angle between plugging zone and fracture surface are main mechanical parameters affecting the plugging zone strength. Particle size distribution, aspect ratio and initial angle of fiber, and plugging zone porosity are main geometric parameters during loss control. Single LCM parameters are applied to the selection of LCM type. Plugging zone parameters are used for the determination of optimal LCM concentration. Reasonable combination of rigid granule, fiber and elastic particle can create a synergy effect to optimize the plugging zone strength and loss control effect.