Down the borehole but outside the box: innovative approaches to wireline log data interpretation

Abstract

Wireline logs record the variation in a number of physical measurements, sometimes 20 or more different properties, with depth down a borehole. They are routinely correlated with, and/or interpreted in terms of, the rock stratigraphic record. Logs are also interpreted with the aim of inferring other useful physical properties not directly measured. In some data-rich exploration industries, such as oil and gas, wireline log interpretation is highly developed. In other industries, such as geothermal and minerals exploration, wireline information is often incomplete and may be inaccurate or inconsistent. The aim of this work is to explore an innovative approach to the analysis of wireline logs. We use an innovative, flexible approach to the identification of ‘change points’, which may indicate boundaries between lithologies or significant intra-formation structure. The number of boundaries/classes is not fixed in advance, being solved for as part of the modelling process. The approaches are applicable in data-rich environments with relatively well-know stratigraphy where they will add to physics and more conventional statistics-based inference. They may also find particular utility in situations with less than ideal data and diverse stratigraphy as they naturally incorporate ways of handling uncertainty. Unforeseen relationships are allowed to emerge and, hence, inform future predictive analysis.