Improved Formation Evaluation While Drilling With a New Heavy Gas Detector

A series of cases are presented showing how a wider range of hydrocarbon gases detected in Real-Time improves the accuracy of formation evaluation while drilling, in terms of identification of formation fluids contacts and fluid characterization. The results have been obtained with a chromatograph exploiting the benefits of FID technology, optimized for the high resolution detection of heavier hydrocarbon gas components, thanks to a dedicated chromatographic system. Flame Ionization Detector (FID) technology is not new to gas detection on the field; however it had never been applied on the field to the detection of gases heavier than n-pentane. The components analyzed by the system span from n-hexane to toluene. The instrumentation has been run on a number of wells in different fields and countries, and it has operated as a complement of an advanced surface logging system. Unlike other technologies presently utilized for this scope, this system reduces the required equipment and personnel to a minimum. The reliability of the system has also been quantified in this paper, with a procedure that the authors propose as standard for all gas detectors. The case history presented documents the clear identification of formation fluid contacts with higher accuracy than standard light gas detectors, the recognition of contaminants within the drilling fluid, and the practicality of operating an advanced gas detection system with minimal operational and logistic footprint. The new gas chromatograph has been run as a complement of an advanced gas detection system, which comprise a series of crucial elements, all crucial to obtaining high quality, repeatable gas data. The system comprises a constant volume gas extractor, a mud heating system, a sample flow control system, a high-resolution chromatograph for the light fraction of hydrocarbon gases, in parallel with the heavy gas detector, and an automated gas data quality check system.