Abstract

In recent years' helium detection and analysis in real-time while drilling at wellsite has been gaining interest in the oil and gas industry. The quantification of this noble gas from drilling mud could provide interesting insights thanks to its peculiar generation process and because of its correlation in detecting open micro-fractures, faults, and more in general permeability patterns. The presence of helium in the reservoir could be associated to organic matter presence and to good sealing properties of the cap rock, being the atomic size of helium the smallest amongst the other gases and its leaking properties the highest ones. The study has been focusing on the advantage of having real-time wellsite logs, compared to laboratory tests, thanks to the possibility of having a higher depth resolution of analyses and the most accurate gas composition. A comparison of performances at wellsite of two analytical techniques dedicated to helium quantification will be illustrated: μGC (TCD detector) and mass spectrometer (single quadrupole detector). Helium levels can be used in conventional reservoir characterization, where helium peaks and its concentration variations have been used to infer proper fluid identification, i.e. gas, oil or water, and in the evaluation of separation between two geological sequences. A detailed view of the use of helium in unconventional wells will be illustrated; good agreement of the helium traces with the light hydrocarbons has been highlighted, in accordance to lithologic changes as well. In other cases, the helium concentration has been used to build permeability patterns.

Introduction

Noble gases are precious markers for natural fluid characterization. Most of the interest in this topic has been driven by many academic studies on isotopic ratios of noble gases. The common feature amongst all these gases is their chemical inertness; as they are generated and only physical processes govern their migration and isotopic fractionation. This could be used to study migration pathways of hydrocarbons and to trace the mixing processes that a certain formation has passed through (isotopic fractionation).

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