The Use of Amino-Substituted Naphthalene Sulfonates as Tracers in Geothermal Reservoirs

Abstract

A family of eight commonly available, uv-fluorescent naphthalene sulfonate compounds have proven to be excellent tracers for use in high temperature geothermal reservoirs because they are environmentally benign, very detectable by fluorescence spectroscopy, affordable, and thermally stable. A structurally related compound, Amino G (7-amino-1,3-naphthalene disulfonate), has likewise been used as a conservative tracer or as a thermally reactive tracer in geothermal reservoirs—depending on the reservoir temperature. It has industrial application as an optical brightener in laundry detergents and possesses qualities of thermal stability and detectability similar to those of the naphthalene sulfonates. Several isomers of Amino G, including Amino C, Amino D, Amino E, Amino J, and Amino R, are likewise commercially available. We have screened these compounds and determined them to possess a wide range of thermal stability; some are less stable but most are more stable than Amino G. They are all suitable for use as either reactive or conservative geothermal tracers, depending on the temperature of the resource. The thermal decay kinetics of each compound was determined from experiments under simulated geothermal reservoir conditions using laboratory autoclaves. The results of these studies, including Arrhenius decay rate constants for each, are presented.