The Petrophysics Elephant in the Geomechanics Room
by Colin McPhee, Senergy Energy Services
was presented on the 8 th of April, 2015.
Successful well placement and well construction in geomechanically sensitive formations requires an understanding of the mechanisms that cause formation failure, and the development of a field validated methodology to predict the critical conditions for well and completion instability. The objective is a fit for purpose coupled geomechanical-stability model which can be used for well/formation failure predictions. The key inputs in the geomechanical model come from petrophysical analysis of log and core data. Unfortunately, the deep-seated intellectual compartmentalisation in the industry means that the importance of a rigorous and consistent petrophysical interpretation, which recognises and accounts for shortcomings and uncertainties in the data, is often overlooked by well engineers and production technologists, with serious technical and economic consequences for well construction and completion.
Several case studies and field examples are presented which not only illustrate the common pitfalls in evaluating petrophysical input to geomechanics models but also demonstrates how to avoid them. For example:
- How inconsistent and incorrect log interpretations can invalidate strength models.
- How poor laboratory test practices, inadequate QC, and core damage on coring and core recovery can turn a strong rock into an apparently weak rock, increasing preventable well construction and completion costs.
- How incorrect assumptions in sonic log interpretation can give misleading stress estimates
- How easy it is to misinterpret wellbore failure features from image logs.
The presentation provides best practice recommendations and workflows to ensure that core and petrophysics data are fit for purpose prior to geomechanical analysis. They have demonstrably improved the quality of data input and have ensured a more coherent and consistent data evaluation strategy. Geomechanics has uncertainties which are recognizable and manageable. A pro-active and integrated petrophysical data quality control strategy can eliminate data redundancy and reduce uncertainty in wellbore stability and formation failure evaluation.
Colin McPhee, CV
Colin’s 40 years of industry experience includes petrophysics, geomechanics, core analysis, formation damage and sand management. Currently, Colin is Global Technical Head for Geomechanics and Rock Properties for Senergy based in Edinburgh, UK, advising clients on petrophysical and geomechanical aspects of field development, asset evaluation and well construction.
Colin has delivered over 250 geomechanics projects and 250 core analysis management/interpretation projects in the UK, Norway, Africa, Middle East, Asia, SE Asia and South America; and regularly presents training courses on core analysis, geomechanics and sand management to operators and service companies.
Colin has been a Technical Editor for SPE Formation Evaluation, a SPE Distinguished Lecturer in 2010-11, has authored several technical papers, and has taught over 100 training courses to over 1200 industry professionals, worldwide. Colin has a BSc in applied geology from Strathclyde University and a masters in civil engineering from Glasgow University.