Tracer Flow Testing for Determination of Mass Flow Rates and Enthalpies, Case Study for KenGen-Olkaria Production Wells

Abstract

Tracer flow testing is the routine measurement of well output in terms of mass flow and enthalpy in two phase pipelines and is of utmost importance in understanding reservoir performance. This is carried out by injection of exclusively non-radioactive and non-toxic tracers of high chemical and thermal stability- greater than 330oC. High precision multi-phase tracer metering systems with rapid-pulse tracer injection is used as the injection equipment to maximize concentrations at high flow and pressure. Multi-phase sampling separators are used for water-brine and gas-steam sampling. Analysis of samples is carried out by use ultra-specific and sensitive methods which include Gas chromatography and UV-Vis/fluorescence. Interpretation of data is carried out by numerical reservoir simulation services and not just qualitative and quantitative interpretation of results. This kind of tracers are injected in the flow line and sampling is downstream of the injection point. Liquid tracers injected must be conservative- cannot partition significantly to the vapor phase, decay chemically or thermally while in the reservoir for the measurement period. They must also be very detectable at ultra-low concentrations without interference from high concentrations of dissolved minerals in the produced water. Naphthalene sulphonates (NSA) are used for brine phase and Sulphur Hexafluoride (SF6) for gas phase. Interpretation of tracer flow test data is only used quantitatively.