Application of a New Class of Chemical Tracers to Measure Oil Saturation in Partitioning Interwell Tracer Tests

Abstract

Abstract This paper introduces six new oil-water partitioning tracers suitable for use in oil reservoirs to estimate remaining oil saturation in inter-well regions. The tracers were tested in a field pilot in the Total-operated Lagrave field located in the South- West of France in 2011. The tests were successful for all six tracers. Measurement of remaining oil saturation in a near well region, using a single-well chemical tracer test (SWCTT) is commonly used in the oil industry. This method exploits the time lag of back-produced ester vs. hydrolysed alcohol. Partitioning inter-well tracer tests (PITTs), which can be used to assess inter-well oil saturation, are frequently used to investigate the presence and remediation of non-aqueous phase liquids (NAPLs) in aquifers. However PITTs are rare in the oil industry, with a few notable exceptions dating back to the 1990's. Consequently, few tracers are available for such tests in oil reservoirs. In addition, several of the tracers previously used were radio-labelled, which may restrict their application in many fields. Our main objective is therefore to expand the portfolio of environmentally acceptable partitioning tracers for PITT operations, and we present results from a field pilot where we successfully tested six new PITT tracers with oil-water partitioning coefficients ranging from 1.5 to 2.9. Lagrave is a relatively small carbonate field with fast injector-producer communications, which allows for relatively low- cost field qualification of partitioning tracers. Six partitioning tracers were injected in February 2011, together with a well-known non-partitioning tracer (2-FBA). The pilot area encloses one injector and three producers. Frequent sampling (2-3 times per week) yielded concise tracer response curves well-suited for estimation of remaining oil saturation. The response curves from the partitioning tracers were compared to the non-partitioning tracer to estimate saturations. The results are also compared with other reservoir data. The class of new partitioning water tracers enables testing of oil saturation in inter-well regions and may become a vital tool to investigate the potential for enhanced oil recovery and assess the effect of EOR measures. Outside the oil industry, the new tracers should also be useful for NAPL identification and evaluation of NAPL remediation processes.