This paper discusses a case study including the design, implementation and results of an Interwell Partitioning Tracer Test (IPTT) to measure incremental oil recovery from an ASP flood in a major sandstone reservoir in a field (Field A) in Southern Oman operated by Petroleum Development Oman (PDO).
Conservative tracers have been used over decades to evaluate conformance of a flood in reservoirs. Chemical tracer research and development as well as enhanced interpretation capabilities lead to the availability of a number of unique chemicals that allow remaining oil measurement to be routinely measured at the pattern and field level.
An inverted five spot pattern pilot area was chosen in Field A to apply interwell partitioning tracers with three time lapsed IPTT surveys between February 2014 and January 2017 to quantify desaturation by ASP. First, one unique passive tracer was injected in a central injector of an inverted 5 spot pattern flood to study the conformance of waterflood within the pilot area prior to an ASP application. The second stage was carried out during the pre-ASP water flush where one passive and two unique partitioning tracers were employed to estimate the remaining oil saturation after waterflood within the pilot immediately prior to the ASP flood. The third phase was initiated post the ASP flood where one passive and two unique partitioning tracers were added along with chase water. This final step was aimed at evaluating the effectiveness of the ASP flood through estimation of residual oil saturation within the water contacted pore volume between wells.
The resulting passive and partitioning tracer curves were assessed for their difference in retention times related to the amount of remaining oil saturation and tracer solubility in oil and water. The partition coefficient values were measured at reservoir conditions in a specialist laboratory that was used to estimate the average pre-and post-ASP flood oil saturation within the flooded pilot area of Field A. The results of the study showed an excellent reduction in oil saturation by about 30% within the pilot area. Desaturation level in the pilot determined by IPTT was consistent with other methods.