SurfaceLogging Combo: How Continuous Real-Time Isotopic Measurement Enhances the Mud Gas Interpretation Workflow

Abstract

Advanced mud gas logging (AMGL) allows quantitative analysis of light hydrocarbon formation gases during the drilling process with continuous well coverage, improving real-time workflows for understanding fluids distribution and properties very early in the exploration process. With the addition of analysis of the carbon isotope composition of methane with a good accuracy, real-time hydrocarbon fluid analysis provides fast and reliable information to confirm existence and basic fluid properties of the petroleum system and guide sampling strategy, along with wellbore and field safety applications. With both molecular and isotopic, another dimension is added to fingerprint and differentiate the gas shows encountered during the drilling process, particularly on the “dry” gases that can have multiple origins which translate in variations in d13C-C1, with little contrast on the composition. The major advantages of the continuous real-time monitoring are in one hand the very high resolution in depth that can characterize short-scale features, and on the other hand the ability to get real time or close to real time full mapping of fluids, that could either be potential resources or a potential hazard during the drilling process or during the production phase of the field. The goal of this paper is to expose the methodology used to interpret the data. One aspect relates to the interpretation of the expected co-genetic fluid type (potential fluid in place) and resulting sampling program, mixing of 2 fluids of different origin and/or type, and other non-economical fluids in potentially permeable layers that could be the source of drilling-related gas events. The combination of those tools also provides insight on the sealing rock efficiency, migration or diffusion patterns. The interpretation is made through logical decision tree steps, allowing to flag potential in some cases alteration processes, using updated version of diagrams - Schoell and Bernard and derived from them log track representations along with other maturity indicators which will allow to type a fluid in a certain horizon. A complementary approach is to look at global trends as displayed on the above-mentionned diagrams, a full depth log of Isotopic and compositional analysis, and others such as the mixing-diffusion diagrams) will potentially provide useful insights on the migrations pathways, reservoir connectivity and more.

AAPG Datapages/Search and Discovery Article #90332 © 2018 AAPG International Conference and Exhibition, Cape Town, South Africa, November 4-11, 2018