Investigating Surface Roughness Effects on Novel Indentation Testing of Drill Cuttings

Abstract Conventional methods to determine geomechanical properties (e.g., cores, drilling logs) are limited, costly, and usually confined to reservoir intervals. This study explores drill cuttings as an additional data source for geomechanical properties using micro-indentation testing. Specifically, the research focuses on the effect of surface roughness and aims to establish the minimum requirements for a surface finish that ensures consistent and reliable results. Our findings offer a systematic and cost-effective method to obtain geomechanical parameters, benefiting oil and gas projects and energy transition initiatives. The approach involved extracting rock discs from eight different rock types: 2 shales, 3 carbonates, and 3 sandstones, and then polishing them using a series of various grit sandpapers, suspensions, and pastes. The surfaces of the polished rocks were scanned using optical profiling to quantify their roughness. Data preprocessing techniques were applied to remove outliers and correct surface level trends, and then root mean square (RMS) and average roughness (Ra) roughness parameters were calculated for each profile. Grid micro-indentation experiments were then conducted to measure the micro-indentation elastic modulus. The results were analyzed and compared for different surface finishes to identify the minimum roughness requirements for each rock type. The study reveals that the sensitivity of instrumented micro-indentation testing to surface roughness is influenced by grain size and mineralogy. In most cases, rock surface polishing incrementally down to a P4000 grit sandpaper provides consistent microindentation results. By understanding the impact of surface roughness on geomechanical testing, this research contributes to improving the reliability and accuracy of geomechanical parameter determination and applies to most rock types and specifically, to drill cuttings. These insights have significant implications for the energy industry, presenting a cost-effective and accessible approach to obtain comprehensive geomechanical properties along the entire length of a well. This study introduces new insights into the minimum surface finish requirements necessary for consistent and reliable microindentation results. By addressing the challenges in geomechanical testing, this research paves the way for a cost-effective approach to acquire geomechanical properties across entire wellbores.