Abstract
In enhanced oil recovery (EOR), chemicals are injected into the oil reservoir, either to increase macroscopic sweep efficiency, or to reduce remaining oil saturation in swept zones. Tracers can be used to identify reservoirs that are specifically suited for EOR operations. Injection of a selection of partitioning tracers, combined with frequent sample analysis of produced fluids, provides information suited for estimation of residual oil saturation. Tracers can also be used to evaluate and optimize the application of EOR chemicals in the reservoir. Suitable tracers will follow the EOR chemicals and assist in evaluation of retention, degradation or trapping. In addition to field applications, tracers also have a large potential as a tool to perform mechanistic studies of EOR chemicals in laboratory experiments. By labelling EOR chemicals with radioactive isotopes of elements such as H, C and S, detailed studies of transport mechanisms can be carried out. Co-injection of labelled compounds in dynamic flooding experiments in porous media will give information about retention or separation of the unique compounds constituting the chemical formulation. Separation of such compounds may be detrimental to obtaining the EOR effect expected. The paper gives new information of specific methods, and discusses current status for use of tracers in EOR operations.
Highlights
As the world’s oil fields are maturing, enhanced oil recovery (EOR) is becoming increasingly important to secure supplies of oil
In enhanced oil recovery (EOR), chemicals are injected into the oil reservoir, either to increase macroscopic sweep efficiency, or to reduce remaining oil saturation in swept zones
In particular we will focus on the partitioning inter-well tracer test (PITT), radioactive labelling of EOR-chemicals and the use of tracers to monitor polymer flooding
Summary
As the world’s oil fields are maturing, enhanced oil recovery (EOR) is becoming increasingly important to secure supplies of oil. An important technology used to estimate the amount of oil in a reservoir is the single-well chemical tracer test (SWCTT) It exploits the difference in travel time between injected ester and alcohol generated in-situ by hydrolysis and was pioneered in the US about 40 years ago by Esso [10, 11]. Several pilot tests have been conducted and the SWCTT is used in these projects to measure oil-saturation prior to and after the low-salinity water injection [13,14,15,16]. In several of the reported PITT projects different alcohols have been used as chemical tracers, with detection limits in the order of ppm concentrations This is too high in many large scaled reservoirs relevant for the oil industry.
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