Enhancing Dispersion Test Analysis for Shale Drilling: Particle Size Distribution and Cation Exchange Insights

Dispersion, which poses a significant challenge to wellbore stability during shale drilling, is influenced by various factors such as shale petrological and mechanical properties, as well as shale-fluid interactions. The effectiveness of shale inhibitors in alleviating these interactions has traditionally been evaluated using the standardized conventional dispersion test. In this test, measured quantities of sized shale particles are exposed to formulated fluids in a roller-oven cell for a specified duration. Subsequently, the shale particles are washed, dried, and the recovery percentage is determined, with higher rates indicating improved inhibitor performance. While the conventional dispersion test is widely used due to its simplicity, the test provides limited, and at times, misleading information. This paper presents an enhanced dispersion test method and analysis by incorporating particle size analysis and inductively coupled plasma optical emission spectroscopy (ICP-OES) tests before and after the conventional dispersion test. Three standard shales exhibiting diverse reactive and dispersive characteristics are selected along with three fluids containing different chemicals and inhibitors for conducting these advanced dispersion tests and analyses. The study highlights the capabilities of the new method for obtaining comprehensive data, not only the recovery rate at a specific particle size but also the particle size distribution curves before and after the dispersion tests. Analyses of particle size distribution provide valuable insights into the particle size shift after shales interact with different fluids. This detailed understanding of the dispersion properties contributes to a more effective design and optimization of shale inhibitors and enhances borehole cleaning processes. Additionally, the application of ICP-OES analysis enables the identification of cation exchanges between the drilling fluids and shales and the exploration of the relationship between cation exchange and dispersion. A higher release of Ca2+ indicates potentially stronger dispersion.