This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 187677, “Ten Years of Reservoir Monitoring With Chemical Inflow Tracers—What Have We Learned and Applied Over the Past Decade?” by A.D. Dyrli and E. Leung, SPE, Resman, prepared for the 2017 SPE Kuwait Oil and Gas Show and Conference, 15–18 October. The paper has not been peer reviewed.
Initial development of inflow tracers was designed to provide qualitative information about the location of water breakthrough in production wells. The proof of concept and application for water detection initiated the development of oil tracers for oil-inflow monitoring. The evolution of inflow-tracer-signal interpretation also has provided valuable insight to inflow characterization. A model-based approach to match the measured signals with proprietary models also has been developed.
Unique Chemical Tracers for Reservoir Surveillance
During the past decade, many unique chemical tracers have been designed. The aim of this development has been to obtain many unique signatures with properties as similar as possible. The strategy involved finding families of chemical molecules that had the potential to provide a large number of unique tracers with a small change in the chemical structure. Today, more than 160 unique signatures exist. More than 80 are within one family of oil markers.
The chemical tracers and the polymer matrix need to be stable and inert at a wide range of well conditions. No applicable accelerated test methods exist for polymer materials, so long-term functionality must be tested in the laboratory with an environment as realistic as possible to estimate inflow-tracer longevities.
Another important feature of these tracers is the concept of the detection limit. To be able to mark production over decades with a limited amount of material placed in the well, the detection limit must be extremely low. The amount of material is limited because of space, cost, or environmental concern. In 2005, the detection limits were parts per billion, while the detection limit today is below parts per trillion and is expected to move toward parts per quadrillion.
Years of laboratory work and field experience have proved that designing systems from experience is crucial. The effect of nontarget fluids and treatment chemicals on different materials is tested over specific time periods according to time of exposure under actual conditions. The qualification tests include treatment chemicals, including solvents and strong acids or bases that may affect the tracer or polymer matrix in which the tracers are embedded. Temperature is one of the major parameters affecting release, and stability and functionality tests for the design will be performed at various temperatures. The use of permanent installed tracers to optimize oil production and reduce water production will reduce the need for water treatment and interventions, thereby reducing the overall environmental impact.