Design of SWTT at High Salinity and High Temperature: Where are the Limits?

The single well tracer test SWTT is a well established method to measure Residual Oil Saturation (ROS) in-situ. The large radius of investigation makes the SWTT a well suited method to evaluate ROS reliably compared with other techniques such as coring and logging.

The partitioning tracer is chosen depending on three basic parameters: reservoir temperature, reservoir salinity and live oil partitioning behavior. These properties control the extent of the hydrolysis reaction that takes place during the shut-in time period to generate the secondary non-partitioning tracer. At high temperature and high salinity (HT/HS), the partitioning coefficient K_d and hydrolysis reaction rate K_h can be significantly high, therefore risking complete reaction of the partitioning tracer and loss of test results reliability.

This paper presents a simulation study carried out to evaluate the feasibility of performing SWTT at HT/HS and help the selection of tracers at these conditions. Using experimental design, a series of SWTT numerical simulations were performed to assess the impact of high K_d and K_h on ROS measurement and interpretability of tracer profile.

Results indicate that conventional rules used for SWTT design would need to be modified or adapted in order to have an interpretable signal from the test. The paper presents also the impact of modified shut-in time and drift on the quality of test.