Inter-Well Gas Tracer Test for EOR Monitoring in a Pilot Project
Tracer technology enhances gas EOR processes
Inter-well Enhanced Oil Recovery (EOR) monitoring projects involve the systematic evaluation and optimization of recovery processes in the context of multiple wells within a reservoir. Tracer technology is commonly used to track fluid movement between wells. Tracer technology has evolved significantly, and it is increasingly used as an effective monitoring and surveillance (M&S) tool in the oil and gas industry, either as inter-well tests or single-well tests. It is used as a successful method to investigate reservoir connectivity and flow performance, measure residual oil saturation and determine reservoir properties that control displacement processes.
In improved oil recovery (IOR) or enhanced oil recovery (EOR) operations, obtaining pertinent data for understanding gas flow paths and gas-phase connectivity for optimizing water-alternating gas (WAG) field operations is increasingly challenging. One of the main challenges includes predicting and monitoring the movement of fluids and fluid flow dynamics during EOR processes in hostile and heterogeneous subsurface environments characterized by high uncertainty, high reservoir pressure and frequent temperature changes.
We implemented tracer technology for a comprehensive monitoring and surveillance program for this GAS-EOR pilot project. An inter-well gas tracer test (IWGTT) is a key monitoring and surveillance tool for EOR projects. Four unique tracers were injected into four individual injectors. In these tests, chemical compounds are used to label injection water and gas to establish well connections and fluid patterns. IWGTT was designed and implemented to provide a better understanding of gas flow paths and gas-phase connectivity between the gas injector and producer pairs as gas-phase breakthrough times (‘time of flight’).
In addition to the reservoir connectivity and breakthrough times between the injector and producer pairs, the results showed different trends for different areas of the reservoir. The gas-phase breakthrough times are slightly different from the water tracer breakthrough times from a previous inter-well chemical tracer test (IWCTT). Residence times for the tracers indicate different trends for three of the injector-producer pairs compared to the last pair. These trends reflect and support conclusions regarding reservoir heterogeneities also seen from the previous IWCTT, which were not anticipated at the beginning of the GAS-EOR pilot.
Tracer technology enhances the monitoring and optimization of gas EOR processes by providing critical data on the movement, distribution and efficiency of the injected gas within the reservoir. The tracer data is very useful in understanding the interconnectivity and the dynamic fluid flow, allowing for better quantification of sweep efficiency of injected gas within the reservoir, identification of the preferential flow paths within the reservoir and optimization of injection strategies. This method can lead to better reservoir description, improved dynamic simulation model and optimized WAG sequence.