Lost circulation (LC), complete loss of drilling fluids into subterranean formations through natural/induced fractures, is a recurring problem costing the industry millions of dollars annually. Numerous solutions and drilling practices are applied in the field to mitigate, prevent or cure LC. Among these, the application of lost circulation materials (LCM) in the drilling fluids for plugging flow paths has been a widely accepted practice. LCM like ground marble, graphitic carbon and fibers are well-known to the industry. Different outcomes have been reported in laboratory tests and field applications when LCM is used in aqueous drilling fluids (AF) as opposed to non-aqueous drilling fluids (NAF). The present work provides a novel rheological tool to distinguish plugging performance of fiber-laden LCM in AF and NAF.

The LCM plugging performance is determined by conducting tests on permeability plugging apparatus (PPA) using a tapered slot (TS) on combination of fibers and particulates like ground marble and resilient graphitic carbon. It was observed that several combinations of fibers and particulates formed a plug in TS with minimal fluid loss in aqueous drilling fluids; however, when tested in NAF, LC was difficult to control.

To investigate the above performance difference, tests were conducted with an Anton Paar rheometer. Rotational rheometry is performed to measure first normal stress difference (N1) at low and moderate shears. It is found that the fiber contribution towards N1 in aqueous fluids is remarkably different from that in NAF. Microscopically, this difference in N1 could be attributed to the distinct fiber properties and orientation in these two systems that explain their contrasting performance in PPA analysis. Thus, the rheological technique provides a tool to identify LC control ability of the fiber-laden LCM system and optimize the concentration of fibers and LCM during the planning phase of drilling fluids.

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