New Tracers to Measure Residual Oil and Fractional Flow in Push and Pull Tracer Tests

摘要

The well-established single well chemical tracer test (SWCTT), devised by Deans and co-workers in the 1970ies, has been used extensively to assess oil saturation after water flooding and as a method to measure the effect of EOR. The technique is based on separation of two different tracers; one oil/water partitioning tracer that partly hydrolyses in the reservoir to generate a secondary non-partitioning water tracer. Saturation is found from the time lag of the partitioning vs. the non-partitioning tracer and pre-measured partition coefficients. As an alternative to the commonly used tracers (e.g. Ethyl Acetate), a new family of reactive and partitioning chemical tracers was recently developed and field-tested. The new tracers, as well as their in-situ generated secondary non-partitioning tracer counterparts, are not naturally present in the reservoir, and can be analyzed using highly sensitive analytical methods, either on-site or in an off-site lab. The improved sensitivity implies that the required tracer amount can be reduced to a few hundred grams, i.e. about 1000 times less than in a conventional SWCTT. The reduced tracer amount has operational, HSE and several other benefits. In this paper, we review our field experience using the new tracers and explore how they improve and expand the single well tracer test methodology. Results reported in this paper show that off-site analysis is effective and accurate, which eliminates the requirement for on-site field analysis. The paper demonstrates that injecting several reacting and partitioning tracers can be used to measure saturation gradients in the near well zone. By injecting the new tracers in a well where movable oil is present (i.e. without extensive water flooding), information about the fractional flow of oil and water can also be gained. We explore this option and suggest a procedure for in-situ measurement of fractional flow of oil and water in the near well zone.