Real Time Formation Characterization from Advanced Mud Gas Analyses for Improved Geological Operations Decisions

Abstract

Exploration progressing into deeper and more challenging environments has led to a drastic increase in drilling costs. Therefore the importance of evaluating formations while drilling has become crucial for more efficient geological operations decisions. Traditionally, mud gas analysis from mud logging has consisted of a low efficiency mud gas extractor coupled to a gas chromatography analyzer. Data from these systems were qualitative and with limited applicability for fluid characterization although still acquired routinely. However, developments of more advanced mud gas logging technology over the last 10 years have produced a step change in the quality and utility of mud gas data. To date, advanced mud gas analyses from atomic mass spectrometry associated to efficient mud gas extraction and transport provides data and interpretation suitable for “formation evaluation” rather than basic gas mud compositional assessment. In this paper we are presenting two examples from offshore Brazil, one exploratory well and one appraisal well, where advanced mud gas analyses and real time interpretation have helped in selecting depths for fluid sampling from wireline.