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This presentation summarizes the results of a study undertaken to document and better understand the physical degradation experienced by lost circulation materials (LCMs) in a circulating drilling fluid during drilling operations. In this study, 15 conventional granular LCMs used to remediate and prevent lost circulation were subjected to shear degradation tests, and the effect of shear on the particle size distribution (PSD) was measured. Four chemical families of LCMs were studied: marble; carbon (graphite and petroleum coke); a tough, short-filament fiber; and pecan nut shells. All of these had aspect ratios of length/width/breadth ~1/1/1, hence were classified as granular.

 

The results indicate that, while the carbon-based products are more resistant than the marble-based products to shear degradation, neither one is particularly long-lasting, especially compared to the fibers and nut shells, which exhibited little or no change in their particle size distributions. An exception is a high-resiliency carbon-based LCM, which showed much greater resistance to shear degradation than the other carbon-based products, though slightly lower than the fiber and nut shell products. Both the carbon- and marble-based products exhibited greater resistance to shear degradation with decreasing particle size, and the trend appeared to be stronger for the carbon than for the marble product line. A fine-mesh marble exhibited unusually high sensitivity to shear, which was not consistent with that trend; this may not be surprising, though, considering that it is sourced differently than the other marble products and is ground in a manner that may make it more susceptible to fracturing. Neither the fiber nor the nut shell demonstrated a clear size dependence of shear resistance based on particle size.