Experimental investigation on plugging behavior of granular lost circulation materials in fractured thief zone

Lost circulation of drilling fluid occurs frequently when drilling in fractured formations. Granular lost circulation material (LCM) is still widely used as a cure to combat the circulation loss of drilling fluid. The placement styles of granular LCM in the fractured thief zone are discussed in this paper. A series of experimental tests to examine the placement style have been carried out using a new developed test equipment. The effects of the material type, particle size distribution (PSD), and concentration of the granular LCMs on the plugging behavior have been investigated. The experimental results proved that t the rigid granules work as an ideal bridging material determining the plugging depth, and the powder material is more suitable as filling material controlling the total fluid loss. The PSD of granular LCM dominates the placement style and efficiency in fractured thief zone, and there exists an optimum concentration for maximum effect of granular LCM additives.