Comparative analysis of lost circulation material particle size and degradation in drilling fluids
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Lost Circulation Materials (LCM) are used to plug natural and induced fractures to minimize drilling fluid loss to formations. Various LCMs are available in field application, such as calcium carbonate and graphite. Design of the particle size distribution is crucial to successfully mitigate loss circulation. It is common industry practice to rely on the particle size distribution as specified by the product data sheet when designing lost circulation pills. During mud circulation, there are several instances where LCMs are exposed to high shear rates, such as during fluid mixing at the hopper, going through mud pumps, and exiting through the bit nozzles. Using sensitive focused beam reflectance measurement (FBRM) techniques, reliable laser diffraction and sophisticated image analysis, we have found that size degradation of calcium carbonate and graphite under such shearing conditions occurs at a lower shearing rate - and to a much larger extent - than previously assumed. This, then, calls into question the effectiveness of calcium carbonate and graphite for LCM applications that rely on size maintenance for effective bridging purposes.. Based on the experimental results, the field personnel can take size degradation effects into account and compensates accordingly. Unexpectedly, particle measurements from sieve analysis, FBRM, laser diffraction and image analysis are quantitatively different. This can be attributed to the various definitions of particle diameters and the limitation of each techniques. Image analysis provides the most accurate particle sizing information but the reproducibility of the corresponding equipment is questionable. Laser diffraction is fast and reliable but will be affected by the sampling method and the degree of dispersion. FBRM requires no dilution to the sample, but provides chord length measurement which is very different from the equivalent spherical diameter (the prevailing diameter definition). In this study, we will show the size degradation results of calcium carbonate and graphite, and the detailed evaluation of the three commercial particle size analyzers used in the experiments.