Pieter Wsk Botha

Sem-Eds-Based Protocol for Subsurface Drilling Mineral Identification and Petrological Classification

Integrated scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDS) solutions have great potential in subsurface drilling applications by providing quantitative cutting-by-cutting information. However, the fine rock cuttings, often contaminated with drilling mud additives, require robust mineral identification and petrological classification solutions.Here, we present an automated SEM-EDS-based elemental identification, mineral and petrological classification protocol for the quantitative characterisation of drill cuttings. Elemental identification is performed on the new QEMSCAN® Spectral Analysis Engine (SAE). Mineral identification and quantification is accomplished by a multi-layered approach, comparing measured low-count energy-dispersive X-ray (EDX) spectra with elemental ranges calculated from synthetic mineral EDX spectra. Individual ranges are adjusted to account for statistical variability, and compositional variation in the rock-forming minerals. Subsequently, the compositional maps of individual cuttings are categorised into lithotype classes, by taking into account textural attributes such as mineral associations and grain sizes.Geological reservoir characterisation can now be enhanced by automated SEM-EDS mineral mapping of drill cuttings.

Petrological Reconstruction of the Subsurface Based on PDC Drill Cuttings: An Advanced Rock Typing Approach

Recent advances in automated scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDS) have transformed the petrological analysis of drill cuttings by replacing qualitative descriptions with ultra-fast, quantitative and repeatable analysis. In this study, 100 m of drill cuttings produced by Polycrystalline Diamond Compact (PDC) bits were mapped on a cutting-by-cutting basis, providing information on mineralogy and texture. The individual cuttings were classified into lithotype categories based on mineral composition and grain sizes. These lithotyping data complement bulk sample mineral and chemical assays, providing detailed information on the nature of cementation, intra-formational seals and changes in mineral grain sizes between reservoir sections. The petrological reconstruction generated from the cuttings analysis compares well with the gamma-ray well log. By combining automated SEM-EDS measurements with advanced digital image analysis, meaningful geological information can be generated from PDC drill cuttings, improving our understanding of lithostratigraphic subdivision and zonation.