Tracer technology for the oil and gas industry has become an increasingly important tool for reservoir surveying and monitoring. Tracers can help portray reservoir characteristics more clearly, depict fluid pathways, reveal communication—planned or unexpected—between wells, and provide better estimates of remaining oil saturation. Tracer technology in oil and gas has become indispensable for showing fluid transmission paths and connectivity within a reservoir, as well as identifying the relative contribution of oil, gas, and water within the reservoir.
Tracers from different injection sites or stages can be easily distinguished by unique chemical tags. Reservoir engineers can select from a range of water and gas tracers—chemical, radioactive, or nano—based on detectability, stability, solubility, fluid compatibility, environmental impact, and cost for the intended survey. Environmentally friendly gas tracers have a low natural occurrence in reservoirs and therefore are easily detected. The most popular water tracers are fluorinated benzoic acids (FBA) that are detected using analytical techniques such as gas chromatography. Continued improvements in tracer technology are giving management teams a broader range of tools for reservoir surveillance.
An Essential Component of a Reservoir Engineer’s Toolkit
Tracers can be used throughout all stages of the reservoir lifecycle—drilling, completion, hydraulic fracturing, forecasting, and optimization. Tracers can help assess mud infiltration, evaluate wellbore chemical reactions, monitor mud circulation, detect casing leaks, select fracture treatments, and monitor changing reservoir conditions.
In unconventional wells, tracers are injected into the surrounding rock at specific intervals along the wellbore. The diffusion of tracers, once injected can help confirm or refute assumptions that engineers may have regarding evolving reservoir characteristics and performance. Considering the value of tracer surveys in understanding subsurface dynamics, they should be a part of every reservoir engineer’s tool kit.
Tracer Technology in Oil and Gas Finds Multiple Uses
Reservoir engineers are continually discovering new ways to use tracers to better understand reservoir characteristics and performance. Tracer measurements can be obtained from oil, gas, and water production via surface sampling using techniques such as gas chromatography (chemicals in water), pressure cylinders (for gas), or Geiger-Muller tubes(radioactive). A few examples help to show the versatility and value of tracer technology in reservoir surveillance.
- Obtain a clearer definition of an oil well’s fracture pattern by injecting natural gas with tracers into a central well over the course of four months and measuring tracer diffusion.
- Determine the most efficient waterflooding strategy by using tracers to monitor the effects of water and gas injection.
- Monitor the inter-well movement of both injected solvent and water, and use that information to redesign the injection program to achieve better sweep efficiency.
- Determine which, if any, nearby wells intersect the same fracture plane as the injection well using radioactive gas.
- Obtain a better estimate regarding sweep area and relative fluid velocities based on the time it takes tracers to diffuse from the injection site to nearby wells.
- Monitor the evolution of fluid-migration patterns using gas tracers to show which injection rates should be modified to yield additional oil recovery.
Engineers who understand when and where to incorporate tracers into their reservoir surveillance strategy gain additional insight regarding critical factors and decisions influencing reservoir performance.
The Value in Visualizing Tracer Data for Reservoir Surveillance
Reservoir management teams obtain greater benefit from tracers when the results can be visualized and analyzed in the context of other data. The greatest hindrance in interpreting tracer data is the inability to combine it with other relevant reservoir data. Often valuable tracer data remain isolated in a reservoir engineer’s spreadsheet, making it difficult to associate the tracer surveys data with regions of the reservoir they depict.
CoViz 4D enables reservoir engineers to combine tracer data with relevant reservoir detail to visualize the results of tracer surveys. In a shared visualization environment they can correctly analyze and interpret the data in collaboration with others on the reservoir management team, and determine the next steps to optimize recovery.
CoViz 4D enables reservoir engineers to combine tracer data with relevant reservoir detail to visualize the results of tracer surveys.
With CoViz 4D, reservoir engineers can see where along the wellbore tracers have been injected. In three dimensions they can map the location, extent, and flow strength of tracers from source to nearby wells to either assess possible thieving or confirm that frac treatments have achieved their intended result. CoViz 4D can even animate a time series of tracer surveys to help reservoir engineers better understand inter-well fluid movement.
Reservoir engineers who rely on tracers to better assess subsurface conditions can maximize the benefit of tracer surveys by incorporating the data into a visualization environment that facilitates collaborative analysis and interpretation in support of better reservoir surveillance.