The effect of testing conditions on the performance of lost circulation materials: understandable sealing mechanism

Lost circulation materials (LCMs) are added to drilling fluids to mitigate lost circulation (LOC) problems. Designing the fluid requires a good understanding of sealing mechanisms and all the parameters affecting the sealing performance. Laboratory testing apparatus is the key concept for LCM evaluation ensuring successful treatment. The high-pressure test cell containing fracture discs is an effective tool among the broadly designed apparatus. A variety of formulations has been developed from the LCM physical properties. Recently, the testing conditions such as the slot wall angles and the fracture disc thickness were found to have significant effects on the evaluation results. However, the effect of the base fluids, fluid density, types of weighting materials and aging conditions has not been addressed. In this study, two different base fluids, water-based fluids and oil-based fluids, were used to compare the base-fluid effect. Drilling fluid density was raised up using barite and/or hematite to investigate the effect of the weight agents. Barite was sieved to study the effect of fine particles on the sealing. Finally, the dynamic aging tests were conducted in LCM-treated WBF using two temperature levels (200 °F and 400 °F) and two aging periods (24 and 72 h). The results showed that the base fluids affected the sealing performance depending on the complex interaction between the solid particles and the fluids. Adding weighting agents tended to improve the seal integrity. Adding proper size of fine particles improved the LCM sealing performance. Aging conditions affected LCM properties depending on the thermal stability of the materials.