Abstract

In EOR-operations, the single-well chemical tracer test (SWCTT) has been proven as a secure and stable methodology for measuring oil saturation prior to and after application of EOR-measures. SWCTTs can be used to measure residual oil saturation in a near-well region up to about 10 m from the wellbore, and has been used in several hundred studies, in particular in the US. Current simulation of SWCTT requires a reactive transport modelling tool that allows for a hydrolysis reaction involving four chemical compounds, in addition to other chemical tracers used in specific tests. Today compositional reservoir simulators are usually applied to simulate SWCTTs.

In this paper we show that the SWCTT modelling can be made much simpler, without compromising a correct description of the reactive transport process. The formulation of the solution exploits the fundamental assumption that tracers do not affect the phase transport. A fast post-processing tracer simulation technique is introduced to solve single well tracer transport in real-life reservoir cases. The partitioning and reactions of the tracer components is solved fully coupled with the tracer transport, and partitioning between phases is described by a convenient formulation and the ester hydrolysis reaction is modelled in an efficient manner. The post-processing is based on previously solved reservoir simulation runs and gives significant savings in CPU-time.

Using an experimental case and one field case, we demonstrate the practical improvement achieved by the new method, and investigate effects of numerical smearing. Our main conclusion is that the formulation is important to enhance correct evaluation of SWCTT results.

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