Characterizing Tracer Applicability in Different Mineralogy

Abstract

Abstract Fluorinated benzoic acids (FBA) have been widely used in the oil industry as conservative tracers. However, some of these tracers have been shown to rapidly degrade when tested at temperatures above 121°C within three weeks. Naphthalene sulfonates (NSAs) have been shown to be excellent tracers in geothermal applications. However, a broader study was required to determine tracer conservation in reservoir fluids and formations typically encountered in the oil field. In this study we compare the oil field industry standard FBA tracers to NSA tracers under dynamic test conditions in the presence of reservoir oil, sandstone, carbonates and clays. We also compare the two sets of tracers under static conditions in the presence of four crude oils and different clay mineralogy to establish tracer conservation. Seven different sodium salts of naphthalene sulfonic acids were tested to determine if the tracers were adsorbed onto natural porous media (reservoir rock) at reservoir conditions. A broad range of conditions were selected to target typical reservoirs encountered. In addition, reservoir rock and a pseudo formation containing 10 Wt.% clay in silica sand were used in sand packs saturated with surrogate brine to ensure the tracer recovery under dynamic conditions. High pressure liquid chromatography (HPLC-FLD) separation was used for simultaneous detection of seven NSAs while FBAs were analyzed using HPLC-UV. GC analysis of isopropyl alcohol (IPA) was used as a standard against which the others were measured. Dynamic tracer tests demonstrated that the sodium salts of naphthalene sulfonates behaved similarly to the control, IPA, with none of the tracers adsorbing on to the rock surface or partitioning into the oil phase. The naphthalene sulfonates can be successfully used as conservative tracers most specifically for high temperature applications. NSA tracers are an attractive replacement for conservative FBA tracers in the oil field due to their superior thermal stability, solubility in oil field brine, lower detection limits and cost.