The effect of testing conditions on lost circulation materials' performance in simulated fractures
"Lost circulation (LOC) problems increase costs of drilling significantly. It is not only the cost of the drilling fluid that is lost into the formation but also the costs of subsequent problems that can be higher than the cost of the drilling fluids. LOC also possibly leads to a serious risk of blowout incident. Lost circulation materials (LCM) are regularly added to the drilling fluids with an expectation of plugging the flow path. Due to the difficulties of testing and monitoring LCM sealing processes in the field, LCM evaluation in the laboratory is often used to prove and assure successful treatment. Investigating LCM behavior and the causation of obtaining different results would expand the reliability of the laboratory evaluation methods. In this study, a steel cylindrical cell was used to simulate downhole high-pressure conditions. Steel discs with precisely sized slots (simulating wellbore fractures) were used to study the effect of testing conditions on the particulate LCM sealing performance. Results show that the fracture wall angles, the disc thickness, the base fluids, the drilling fluid density, the particle size of weighting materials related to the LCM grain sizes, and the dynamic aging conditions all affect the testing results significantly. LCM that performed well in the slow injection rate tests also exhibited sealing behavior effectively in the instantaneous flow conditions. The experiments provided an understanding of the fracture sealing mechanism to be applied in improving the laboratory evaluation methods and field treatment design. This knowledge is useful for both the preventive and corrective LOC mitigating approaches"--Abstract, page iv.
Missouri University of Science and Technology
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