Real Time Mud Gas Logging during Drilling Of The CFDDP Drill Hole In Campi Flegrei Caldera, South Italy

In the framework of the International Continental Scientific Drilling Program (ICDP) the Campi Flegrei Deep Drilling project has the aim to understanding in detail the deep caldera structure. More specifically, the pilot hole drilled to date has the specific goal to study the stratigraphy and eruptive history of the easternmost caldera border, which is the less known at depth for lack of previous drillings. In this paper we describe the analysis of the gas phase continuously extracted from the drill mud during drilling of the 506 m pilot hole using a quadrupole mass spectrometer. We report the methods used and present the first results of the gas composition detected during the entirely process of drilling. Because the main components of drilling mud gas are from the air we put particular emphasis on He, CH₄ and CO₂ which are the gas components that should originate from the deep fluids and are most suitable for detection of fluid-bearing horizons such as shear zones, open fractures, and sections of enhanced permeability. Variations in the gas composition show a good correlation with the stratigraphic reconstruction along the drill hole. Lithological changes are often correlated with increasing amounts of gas. The methodology here applied can be hence very useful, in industrial applications (geothermal, oil and gas, etc.), for reservoir and fluid quality characterization.