Drilling fluid losses are considered one of the major contributors to drilling non-productive time (NPT). Lost circulation materials (LCM’s) have been widely used to avoid or stop losses. Due to the large number of current available LCM’s and their different applications, classification and testing of LCM’s is very important. Conventional LCM’s are currently classified into different categories based on their appearance as fibrous, flaky, and granular or a blend of all three. The most recent LCM classification was published around 50 years ago and this paper intends to fill this gap with an updated classification including conventional and new technologies. We propose to re-classify LCM’s into 7 categories based on their appearance and application as: granular, flaky, fibrous, LCM’s mixture, acid/water soluble, high fluid loss squeeze, swellable/hydratable combinations, and nanoparticles.Particle plugging apparatus (PPA) and HPHT fluid loss apparatus in conjunction with slotted/tapered discs are used to evaluate LCM performance for corrective treatments. Until now, no single standardized testing method or interpretation that evaluates LCM’s performance when preventive treatments are applied in order to increase the fracture gradient has been developed. The difficulty in standardizing the testing methods is due to the disagreement about wellbore strengthening mechanism. This paper discusses the most recent developments in lost circulation materials such as plugging assurance technology and nano-technology, in addition to the presentation of a comprehensive summary of today’s available LCM’s.
