A novel approach to the detection of mud-entrained gases while drilling has enable to enrich significantly the quality and quantity of reservoir information available in Real-Time. This approach has involved the development of new detection instruments and the adaptation of existing technology to a new scope, and it was made possible by a constructive workflow involving two separate companies (an oil company and a service provider) and distinct departments within such companies. Such workflow enabled to plan, support and correct the project while drilling in order to maximize the value of the data collected. A gas analyzer able to measure dozens of distinct light hydrocarbon components simultaneously was deployed along with a detector dedicated to the quantification of non-hydrocarbon gas species, focused on the measurement of CO2, He and H2, even in very low concentrations. An interpretation model was applied to such data to infer from it reservoir characteristics. The main result obtained was, in terms of hydrocarbons, an increased depth of investigation of light hydrocarbons composition in Real-Time, obtaining for the first time data normally extracted from production fluid samples at a much later stage. Furthermore, observing the heavy gases behaviour we reached a better understanding of the mechanism of liberation of gas from mud and the effect of contaminant fluids. These observations enable to better assess the value of gas data and to more accurately quantify data uncertainty.
In terms of non-hydrocarbons, high-resolution gas detection was used to identify the presence of Helium and to evaluate the possibility to use it as a tracer to correlate known levels and types of mineralization. The whole system has allowed to identify the passage between the main reservoir formations, secondary lithological contacts (carbonates / clays) and different mineralizations. The noble gas, due to its physical properties, is theoretically differently distributed depending on its solubility in the fluid it is in contact with: in an ideal situation is so possible to identify the types of mineralization on the basis of different quantity of Helium detected in Gas, Water and Oil bearing intervals respectively. The analysis also monitored the levels of CO2 and, where this gas was in significant quantities, we proceeded to the sampling and characterization to determine the type / source of this gas in order to estimate how much of this gas can be present in the well, and consequently, evaluate the productivity of the well and choosing the facilities to be used.
