Application of statistical quality control measures for near-surface geochemical petroleum exploration

Abstract

There are four major quality control measures that can apply to geochemical petroleum exploration data: statistical quality control charts, data reproducibility-Juran approach, ethane composition index, and hydrocarbon cross plots. Statistical quality control, or SQC, charts reflect the quality-performance of the analytical process composed of equipment, instrumentation, and operator technique. An unstable process is detected through assignable causes using SQC charts. Knowing data variability is paramount to tying geochemical data over time for in-fill samples and/or project extensions. The Juran approach is a statistical tool used to help determine the ability of a process to maintain itself within the limits of set specifications for reproducing geochemical data. Ethane composition index, or ECI, is a statistical calculation based on near-surface, light hydrocarbon measurements that help differentiate thermogenic, petroleum sources at depth. The ECI data are integrated with subsurface geological information, and/or seismic survey data to determine lower-risk drilling locations. Hydrocarbon cross plots are visual correlation techniques that compare two hydrocarbons within a similar hydrocarbon suite (e.g., ethane versus propane, benzene versus toluene, or 2-ring aromatics versus 3-ring aromatics). Cross plots help determine contamination, multiple petroleum sources, and low-quality data versus high-quality data indigenous to different geochemical exploration tools. When integrated with geomorphology, subsurface geology, and seismic survey data high-quality geochemical data provides beneficial information for developing a petroleum exploration model. High-quality data is the key to the successful application of geochemistry in petroleum exploration modeling. The ability to produce high-quality, geochemical data requires the application of quality control measures reflective of a well managed ISO 9000 quality system. Statistical quality control charts, Juran studies, and data cross plots are basic elements found within such a system. ISO 9000 is briefly discussed in Appendix A.