Experimental study on the updated optimization method for particle size distribution of lost circulation materials

Abstract

The use of laboratory methods to simulate the process of plugging slurry sealing the fracture is an efficient and convenient method for Lost Circulation Materials (LCMs) selection and formula design. However, commonly used plugging evaluation devices have defects such as small-scale fractures and low reproducibility. To address these shortcomings, we applied a wellbore-fracture coupling plugging experimental device to simulate the process of plugging slurry extrusion. We processed a large-scale visualized fracture using Plexiglas based on the geometric parameters of the formation fracture, reproduced the undulation characteristics of the fracture surface using laser etching technology, and characterized the three-dimensional morphology characteristics of commonly used calcite, walnut shells, and flake polybutyl ester at the wellsite to carry out experiments on the transportation of LCMs under wellbore-fracture coupling conditions. The results indicate that the discrepancy between laboratory evaluation outcomes and field application practices, as well as the low success rate of single-attempt on-site plugging, can be primarily attributed to mouth sealing. The migration behavior of the LCMs is dictated by its morphological characteristics. A larger disparity among the three-axis diameters leads to increased irregularity in the LCM. Characterization of irregularity yielded the following results: walnut shell exhibits the highest irregularity, followed by flaky polybutene and calcite. Increased irregularity in the LCM corresponds to a heightened risk of mouth sealing. Entry into the fracture can only be guaranteed when the D90/Wf ratios for calcite, flaky polybutene, and walnut shell are less than or equal to 0.56, 0.42, and 0.39, respectively. The methods and findings presented in this study provide a scientific basis for selecting LCMs in fractured formations and explain the reasons for poor loss control and significant repetitive loss in wellsite practice.