Early-Time Analysis of Tracers for Use in Enhanced-Oil-Recovery Flood Optimization

Abstract

Summary Tracer testing is a powerful tool for reservoir surveillance. Conducting and analyzing an interwell tracer test (IWTT) before starting an enhanced-oil-recovery (EOR) flood provides specific information required to balance the pattern's swept pore volume (PV) and to optimize chemical or solvent use. Tracer testing also plays an important role in EOR by establishing a baseline for estimating incremental volume swept and recovery factor. A key limitation to tracer testing is the time required to obtain a complete interpretation of the test results. Conventional interpretation methods require observing exponential decline in the tracer concentration from all producers; depending on the pattern size and processing rate, this can take many months or years. Meanwhile, the EOR flood is delayed, thereby eroding its value and reducing the remaining oil target. We have developed a method for analyzing tracer data from relatively early times that is based, in part, on a new way to extrapolate the tracer data, providing timely information to optimize flood performance. The extrapolation can be performed soon after the peak tracer concentration is observed in the well with the slowest response. We illustrate the extrapolation procedure with a synthetic, yet realistic, data set showing that the new methods result in a good approximation at much earlier times. We then compare ‘early time analysis’ swept PVs with the (correct) swept PVs using the complete tracer data set. We also discuss how early-time approximations can thus provide the opportunity to optimize chemical-flood performance and to enable field startup of EOR floods in a timely fashion.