Appropriate rock characterization is vital to many oil and gas exploration and exploitation processes. Robust sub-surface models require input data that represent the rocks involved. This paper describes a method for qualifying and integrating physical and mechanical rock property data to assure they provide reliable inputs to geomechanical models.
Rock property data necessarily come from different sources. Physical samples for laboratory testing are usually limited to a few depths. Lab tests are often costly, replicating in-situ conditions can be difficult or impossible, and results frequently show wide scatter reflecting the rock's inherent depth variability and lateral heterogeneity. Electric logs provide near-continuous data, but rarely direct measurements of rock strength properties. All too often data from different sources are inconsistent, leading to uncertainty in models using those data.
Eight mechanical, microstructural and physical properties are shown together to give a good characterization of rock strength behavior in ambient and in-situ conditions. These properties are readily accessible but are individually subject to the above uncertainties. Appropriate data quality assurance and quality control QA/QC review of these properties' values is an essential step in building a representative description of the rock. This paper presents a process for doing this QA/QC review.
Pairs of property values are cross-plotted and compared with correlations from the literature or previously established with qualified data from related formations. Conformance with those correlations gives confidence in the data, whereas outliers are flagged as questionable. Repeating this process with questionable data crossplotted against other parameters for the same depth highlights the property with the greatest uncertainty. The determination of its value is investigated to locate the source of the inconsistency and hopefully to establish a more reliable value. Where this is not possible, the user has a rational basis for rejecting that property value.