A common problem in many waterflooded oil reservoirs is early water breakthrough with high water cut through highly conductive thief zones. Thermally active polymer, which is an expandable sub-micron particulate of low viscosity, has been successfully used as an in-depth conformance to improve sweep efficiency of waterfloods.
This paper describes the workflow to evaluate technical feasibility of this conformance technology for proper pilot project designs supported with detailed simulation studies. Two simulation approaches have been developed to model properties of this polymer and its interaction with reservoir rock. Both methods include temperature triggered viscosification and adsorption/retention effects. Temperature profile in the reservoir is modeled by energy balance to accurately place this polymer at the optimum location in the thief zone. The first method considers a single chemical component in the water phase. The second method is based on chemical reactions of multiple chemical components. Both simulation approaches are compared and discussed.
Results show that temperature-triggered polymers can increase oil recovery by viscosification and chemical adsorption/retention, which reduces thief zone permeability diverting flow into unswept zones. Sensitivity analyses suggest that ultimate oil recovery and conformance control depends on the thief zone temperature, vertical to horizontal permeability ratio (Kv/Kh), thief zone vertical location, injection concentration and slug size, oil viscosity, chemical adsorption, and its reversibility, among others. For high flow capacity thief zones and mobility ratios higher than 10, oil recoveries can be improved by increasing chemical concentration or slug size of treatments, or both. Low Kv/Kh (< 0.1) and high permeability contrast generally shows faster incremental recoveries than high Kv/Kh with strong water segregation reservoirs.
The presented workflow is currently used to perform in-depth conformance treatment designs in on-shore and off-shore fields and can be used as a reference tool to evaluate benefits of the thermally active polymer in waterflooded oil reservoirs.