Abstract

Fast recognition of methane influx into the well and hydrocarbon composition evaluation in the circulated drilling fluid (mud) is of extreme importance for drilling safety and efficiency. IR gas detection was already used for mud logging on the rig floor in fifties¹ but was not accepted for field operation due to the optical unit's size and lack of rigidity. (Mud logging services provide on-rig analysis of samples of the circulated drilling mud to detect signs of fluids which have entered the mud from the formations.) Nevertheless, FT-IR spectroscopy approach is no w considered to be the best for oil "fingerprinting" in the laboratory environment.² Recent progress in industrial applications of attenuated total reflectance (ATR) sampling technique for the on-line chemical process control³ together with the development of a fast computer controlled all-solid-state with no-moving-parts spectrograph^-1 based on the acousto-optic tunable filter (AOTF) principle⁵ allows the design of an IR chemical sensor capable of working in the hostile downhole environment.

© 1999 Optical Society of America