Non-destructive strength index testing applications for sand failure evaluation

Abstract

Definitive rock strength data for sand failure evaluation are only available from tests on core plugs, however coverage is limited and core condition and geometry may preclude plugging. This paper presents results from a non-destructive core strength index tester that is less destructive than the Schmidt Hammer and less intrusive, easier, faster and cheaper than the core scratch tester. The portable Equotip index hardness tester measures and compares the impact and rebound velocities of a small steel ball after its collision with a rock surface to determine its hardness which in turn reflects the relative strength of the rock. The tester is run at regular intervals along the surface of the core to provide additional data that complement and enhance core rock mechanics data. Several field examples are presented which illustrate the use of the Equotip to optimise core sample selection, evaluate controls on rock strength, and to calibrate and constrain the development of wireline log-based strength models. Importantly, cases are included to highlight exceptions where the tester can produce misleading and even contradictory results. The integration of Equotip test results with core plug data and log analysis enables development of more robust rock strength models. The methodologies and techniques developed in this work have in turn enabled more accurate sand failure estimates that represent key tools in the development of effective sand management strategies for the reservoir life cycle for a variety of fields throughout the world. Copyright 2012, Society of Petroleum Engineers.