Lost circulation is one of the major problems encountered in drilling geothermal formations. Consequences and treatment of these lost circulation events can be extremely costly. Underbalanced drilling and LCMs are the two most common methods to address the lost circulation problem. However, some LCMs have proved to be unsuccessful due to the non-predictive nature of fractures, complicated dynamics of LCM, as well as the change of mechanical properties of LCMs under high-temperature conditions. Long-distance circulations in high-temperature environments usually lead to the decline of size, strength and friction coefficient of LCMs in parallel to reduction of drilling fluid viscosity, and eventually failure in sealing fractures. In this paper, we developed a coupled CFD-DEM by combining computational fluid dynamics with discrete element methods to simulate the fracture sealing process by LCMs. The results show that a reduction in particle size, friction coefficient and Young’s modulus lowers bridging’s probability, slows down bridging initiation, but deepens the sealing depth, and tighter but the resultant is an instable sealing zone. We noticed that bridging mechanism changes from single-particle bridging to dual-particles bridging as particle size reduces.

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