Conforming Uncertainty in Fluid Compositional Analysis Using Advanced Gas Detection While Drilling
Current low oil prices are driving operators to find innovative uses for old techniques. Mud logging with advanced mud gas detection has the potential to optimize logging-while-drilling (LWD) and wireline operations for formation evaluation. By combining reliable and repeatable gas extraction and detection with experienced gas interpretation, valid formation evaluation from low-cost mud logging solutions can be validated using downhole tools. Revitalizing old mud logging techniques with new technology provides a low-cost and reliable solution for accurate fluid identification. Fluid typing from gases while drilling traditionally has been estimated from basic Pixler and Haworth plots using ratios between C1 to heavier C2-C5 and heavier C2-C5 to C1-C5, respectively. While these ratios (Pixler and Haworth) continue to be used as a powerful tool for fluid identification, recent turbine drilling with oil-based mud (OBM) used as drilling fluid caused breakdown of the drilling fluid and increased gas wetness, providing an inaccurate fluid type estimation. Advanced gas service with the ability to measure unsaturated hydrocarbons (ethylene and propylene) as the primary products resulting from OBM cracking, when integrated with basic gas ratios, can help differentiate between gas wetness resulting from OBM cracking and increased wetness caused by actual formational fluid type changes. Additionally, this was a useful tool for identifying hydrocarbon zones. Estimation of oil gravity while drilling is of great importance to differentiate between light oil, heavy oil and tar. Utilization of Mass Spec providing wide range measurements of chemical species was able from two wells presented to identify fluid mobility based on its gravity. Apart from fluid identification is the ability to identify fluid contacts, where areas of water saturation can be identified from advanced gas detection of aromatics as water soluble, and to confirm the basic Pixler ratio for comparison between C3 and C4 abundance (depending on their solubility in water). The case studies presented here show validation of wet intervals estimated from gas ratios and wireline logs.
AAPG Datapages/Search and Discovery Article #90337 ©2019 AAPG Middle East Region GTW, Regional Variations in Charge Systems and the Impact on Hydrocarbon Fluid Properties in Exploration, Dubai, UAE, February 11-13, 2019