Robust Procedure for Measuring Particle Size Distribution of Non-Aqueous Drilling Fluids Using Laser Diffraction

Abstract

Abstract Since particle size distribution (PSD) affects drilling fluid performance, devices for measuring particle size have been widely used in the field and in laboratories. Laser diffraction (also called laser light scattering) is the technique most often employed, because it is easy, rapid, and provides reproducible results. However, variations in laser diffraction instrumentation and operating protocols in different testing facilities/laboratories can cause the PSD results to vary significantly. The problem is serious for water-based drilling fluids, but it can be even more severe for non-aqueous drilling fluids (NADFs) because of variations in base fluid and the presence of emulsified water. To address this, a work group was formed by the American Petroleum Institute (API) to develop a general and robust testing procedure for measuring PSD of NADFs using laser diffraction instruments. After identifying fundamental variables (including sampling method, instrument, sonication treatment, dispersant) that can affect PSD results, pilot testing was carried out with various instruments to determine general operating settings regardless of the specific instrument. Based on these studies, a measurement procedure was developed and evaluated with a round robin test in which five NADFs possessing different base fluids, solids content, and water/oil ratios were measured by several laboratories using different particle sizers. The PSD results of these five fluids measured by different laboratories agreed well, confirming the robustness of the measurement procedure. The developed measurement procedure has been accepted and will be included as a recommended procedure in the API RP 13I 2019 revision. This paper will discuss the development of the procedure and the round robin test results in detail.