ADVANCED MUD GAS DETECTION SYSTEM IMPROVES FORMATION FLUID CHARACTERIZATION WHILE DRILLING IN CHALLENGING INDONESIA DEEPWATER: A CASE HISTORY.

摘要

In this paper, a new gas detection system operating while drilling is presented. Such system comprises an array of solutions which greatly reduce the uncertainties historically attached to mud gas data, especially in deepwater environment where, due to the very low temperature of the mud flow out, the degassing efficiency of conventional gas extractor is quite poor. A series of analysis and cross comparisons with independent datasets and measurements demonstrate the reliability, and accuracy of the gas data obtained with such system and how they have supported Real-Time formation evaluation in deepwater operations. The system deployed addresses all sides of gas extraction and detection, implementing solutions which enable to optimize every aspect of the process. A drilling mud heater supplies mud to a constant volume gas extractor. The sample is sent to the surface logging gas detectors via a controlled sample flow system. An accurate FID detection system analyzes a wide spectrum of hydrocarbon gases (CI to C8) to maximize the information about the formation fluid. The gas analysis techniques utilized comprise a rigorous QC system. The system has operated in the past months on a drillship involved in deepwater exploration drilling. It has enabled to obtain high quality gas data, unaffected by the typical issues which often damage the quality of mud gas data in such operating conditions. The data were QC and analysed using the Gas While Drilling (GWD~(TM)) methodology to obtain gas ratios curves and cross-plots enable to characterize the hydrocarbon phase. A good match with LWD, wireline logs and fluid analysis emphasize the reliability of the Gas in mud data suitable for the formation evaluation The results obtained challenge common beliefs associated with gas detection; the system has effectively overcome the main reliability issues associated with gas detection in deepwater environment, and give an effective and suitable cost saving tool for safety (trustable semi-quantitative fluid ID). The consistency and repeatability of the data are also suitable for integrate Formation Evaluation from LWD or wireline datasets.