Testing conditions make a difference when testing LCM

Laboratory studies have been used extensively to evaluate loss circulation materials (LCM) treatments to solve or prevent lost circulation problems in fractured formations. Experiments with slotted disks simulating fractures have been performed with the amount of fluid loss and sealing pressure used as evaluation criteria. This study presents the investigation of LCM behavior with different slot designs and fluid flow patterns for water-based and oil-based drilling fluids. Experiments on tapered-slot discs that simulate fractures with different fracture wall angles and fracture lengths were conducted at high pressure. A bladder-type accumulator was added to the system to provide an instantaneous flow condition. Results showed that increasing the wall angle tended to decrease sealing efficiency. Increasing the fracture length (disc thickness) in tapered discs resulted in higher sealing pressure. In the instantaneous flow tests, LCM formulations used to perform a strong seal in slow injection tests also sealed the slot under the sudden flow condition with a similar bridging and sealing profile, but different in the fluid loss volume. This set of experiments shows that the experimental setup can change the results, so caution should be taken when quantitatively comparing LCM tests on slot disks from different experimental setups.