A comprehensive framework for the theoretical assessment of the single-well-chemical-tracer tests

Highlights

• Combination of numerical and analytical solutions have been used to highlight different aspects of the SWCT method.

• Shut-in time should be adapted based on the fluid drift and the reservoir properties.

• The geochemical reactions have also been taken into account to study the level of pH-variation during shut-in time.

• In high temperature reservoirs including weak buffer capacity, pH-variation might affect the SWCT test.

Abstract

Single-well-chemical-tracer (SWCT) is the most commonly used field method to determine oil or water saturation in one-spot pilot. This method is a complex process due to many effective parameters and non-ideality factors involved. Understanding the extent to which theses parameters might affect the SWCT test profiles could help us to manage and design the SWCT test more efficient at different reservoir conditions. This paper proposes a comprehensive framework of a new approach to highlight different aspects of the SWCT tests theoretically before implementing the field test. In order to accomplish the task, combining of numerical and analytical solutions have been used.

The devised algorithm has been programmed in six different stages. In the first four stages, all test design parameters in different investigation regions and retardation factors are calculated. The test design parameters are sizing the test volume, test timing (i.e., injection, shut-in, and production), tracer concentration during the test, and the mean residence volume. In the fifth stage, all criteria are taken into consideration to find the most efficient test designs. Then, the achieved parameters are applied in the simulation stage (sixth stage) to investigate the effect of the ester bank and concentration, ester properties, shut-in time. The geochemical speciation code PHREEQC is also used to study the level of pH-variation during shut-in time. The effects of the calcite dissolution, temperature, and initial buffer capacity have been evaluated on the probability of pH-variation. The results show that the probability of pH-variation increases with temperature and lower amount of calcite concentration.

To evaluate the workflow methodology, two different field test cases with different reservoir conditions are employed in order to reflect the influence of different stages of the algorithm. We hope that the workflow developed can be used to minimize the uncertainties and improve the quality of the SWCT tests.