Automated Petrography Solution Onshore Field Test in Papua New Guinea

Haberlah, David¹; Garrick, Mike²
¹Center of Excellence for Natural Resources, FEI Australia, Brisbane, QLD, Australia.
²Halliburton, Aberdeen, United Kingdom.

In conventional surface logging operations, drill cuttings are described by mud loggers by means of optical microscopy. This poses limits on chemical and textural detail, and consistency in reporting. Here, an automated petrography solution compromising a mobile, ruggedized scanning electron microscope (SEM) equipped with energy-dispersive spectrometers (EDS) was tested in an onshore drilling project in remote Papua New Guinea. The field test involved six months of on-site sample preparations, measurements, and reporting throughout 12-hour work shift surface logging operations on a gas injection well, a production well, and an exploration well. The presented results are based on ~200 million x-ray spectra obtained from 1 million genuine cuttings, and demonstrate consistent, high-resolution, quantitative mineral and textural data providing unprecedented detail on the subsurface lithology. Samples were prepared and measured within one hour from collection at the shale shakers. The measurement data consist of high-resolution (20µm) colour-coded 2D compositional maps of physically screened drill cuttings. The data were processed by digital and contextual screens, separating particles into contaminants, drilling fluid additives, and cuttings, thereby allowing to report modal mineralogy on genuine drill cuttings. The cuttings were further categorised into site-specific lithology classes on a cutting-by-cutting basis. Information on the cuttings composition and texture within individual lithology classes were generated, including: average modal mineralogy; quartz grain size distribution; average cutting sizes and quartz grain sizes; matrix density; and the total number and volume contribution of classified cuttings for selected sample (drilling) intervals. The new data were juxtaposed with data from selected downhole measurements and conventional mud log reports. Overall, the automated petrography data show good alignment between geological formation tops, and provide additional detail on clay mineralogy, potassium association with feldspars, and the nature of cements. Near-real time reporting can support the interpretation of seismic data, downhole data, in particular the gamma-ray and resistivity log responses, and thereby assist time-critical drilling decisions. The image-based nature of automated petrography data facilitates interpretation by a range of well-site professionals, including geologists, petrophysicists, drillers, and engineers.

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012