Novel Method for Automated Advanced Mud Gas Extraction Efficiency Correction (EEC) Characterization in Near Real Time

Abstract Advanced mud gas logging is progressing to a more established service throughout the industry over the last two decades. It is more and more recognized as a highly valuable addition to standard and advanced downhole logging data and can be used to a certain extent as a continuous formation fluid composition log often comparing well with pressure volume temperature (PVT) fluid sample analysis. Compared to basic mud gas data, the process involves several correction layers starting from a booster dilution and contamination over to recycled gas correction until the final layer of the extraction efficiency correction (EEC). For this last step a new, fast, and online methodology has been developed and will be presented here together with comparison results between PVT data and corresponding, fully corrected, mud gas data. Mud gas is extracted from drilling mud at surface and measured with gas chromatographs, focusing on the hydrocarbon compounds up to C8s. The boiling point and the interaction of the components is different for each one of them and can be to a certain extent correlated to the number of carbons in the molecule. To derive PVT like quantification, up to normal pentane it is critical to accurately determine the extraction efficiency for each component and to be able to respond in case of fluid changes. Therefore, a fully automatic method is presented that determines the EEC on live mud samples in less than 10 minutes any time a significant change to the mud system is made. The method isolates a fixed volume of mud inside the equipment's extraction chamber and derives the correction coefficients by the integral of concentration extracted compared to a reference integral from before the test was started. This simple and fast method enables the methodology to quickly respond to necessary changes. Several case studies from water as well as oil-based mud demonstrate the applicability of the newly introduced method and unlock the full potential of advanced mud gas data up to normal-pentane.