As delegates meet in Glasgow at COP26, the E&P industry is under the spotlight in its efforts to reduce emissions in oil production and meet Scope 1 and 2 of the Paris Accord. The industry is already doing a lot in terms of improved methods for enhanced recovery, efficient production, digitisation, waste reduction and the reduced movement of people and equipment.
Yet, while, many innovative technologies are now becoming more available to improve operations in these areas, the challenge remains making these technologies part of everyday operations.
One technology, however, that is already a key element of reservoir management and that is playing a major role in production optimisation and the generation of accurate well and reservoir data for greater efficiencies is tracer technology.
The origins of tracer technology
The underlying principle of organic tracers, which can either be installed in the well completion or pumped into an injector well or producing well (depending on the data the operator seeks) is the release of specific molecules which follows the liquid or gas flow in the reservoir. When the permanent tracers are contacted by target fluid (oil, water, gas condensate), they selectively release based on fluid contact, confirming that there is flow.
Tracer concentration is analysed in parts-per-trillion concentrations, and as such, very little organic compounds are used with a small carbon footprint. The Resman tracers also do not contain poisonous substances which pollute the end product, like Cadmium or radioactive isotopes.
While the initial development of tracers was designed to provide qualitative information on the location of water breakthroughs in production wells, the last decade has seen an expansion of the technology’s capabilities to provide zones specific well production data and production trend tracking.
This might include zonal productivity, optimal draw-down of the well, well monitoring, pressure support, oil saturation and the location of water breakthrough or gas coning, as previous mentioned.
Zonal specific information for greater efficiencies
So how can such information lead to great efficiencies?
A non-intervention system of intelligent tracers can be integrated with the completion equipment to monitor segments of the reservoir. At well start-up or in continuous production, oil samples are analysed for tracer parts-per-trillion concentrations which – as mentioned – can generate information on zonal productivity, water breakthrough and gas coning.
For example, if the water cut suddenly increases, a rise in tracer signal from one of the zones will indicate from which zone and at what time the increased water breakthrough occurred, and therefore also what zone to keep under observation and for potential remedial action (such as water shutoff operations).
Furthermore, by optimising the drawdown of the well, the operator can run the well at maximum capacity whilst limiting the production of water or gas, leading to greater sustainability. The production information also gives useful insights into the reservoir which helps the placement and construction of additional wells for maximum efficiencies and recovery.
Comparisons with production logging tools (PLT)
Such zonal information is traditionally collected using a production logging tool (PLT). The PLT contains a series of indirect measurements which are taken over a relatively short time series. At the end, the PLT yields one datapoint in time.
Whilst tracer data will never be able to provide complete accuracy either, it does enable the operator to make sound operational decisions. If the tracer data indicates flow, then there is flow, and the analysis can be repeated over months and years and even continuously to enhance confidence in the results or to monitor the change from a well event.
Thus, the operator can receive actionable data for between 5 and 10 years following a tracer installation or injection, simply by analysing samples from the production. The data and the interpretation will be sent electronically and can also be uploaded in the reservoir model and accessed there. This can be compared to transporting a PLT and crew to the platform with the CO2 saving on one data set with tracers as compared to PLT as much as 99%. This also addresses the reduced movement of people and equipment as outlined in Scopes 1 and 2 of the Paris Accord.
Accessing reservoir-specific information
Traditional interwell tracers are pumped into an injection well and will migrate to the producing wells. By analysing the concentration of tracers in the producing well, the operator can have a good overview of the reservoir’s drainage pattern, as well as an understanding of the pressure support mechanisms and aquifer ingress. Again, all important variables for greater efficiencies and sustainability.
Another important tool for production optimisation is evaluating zone-specific well performance at different operational settings. Analysing tracer profile changes during a multi-rate test, where changes of the well are intentionally induced by the operator, for example, can give important insight and decision support for production optimisation at zonal resolution. If the choke is reduced, the drawdown and production rate are reduced and, from tracer profiles, it will be possible to see if tracers from specific zones disappear.
This would indicate that this zone requires higher drawdown and therefore provides information about differential pressure support distribution along the wellbore. Conducting a controlled multi-rate test and correlating production changes with tracer signals will provide the operator with essential information about the operational modes of the well and can be used for production optimisation and to support well operation decisions for greater efficiencies and sustainability.
A well with early water breakthrough
A simple example of value creation through the use of tracer information can be seen in a recent well with early water breakthrough, where the operator did a tracer test at varying drawdown.
The tracer data confirmed the full wellbore contribution, identified the water producing zone and outlined the optimal choke setting. As a result, water production was reduced by 90%, the lifetime of the well was extended and the net present value (NPV) of the asset increased with wells drilled further away from the aquifer, the pay zone increased, and more efficient operations and environmental management.
Oil saturation and relative permeability
The area between an injector and producer is an area where the operator has limited information, and often relies on stochastic models or expensive 4D seismic data to estimate remaining oil saturation and identify drainage patterns.
By applying Resman’s Partitioning Interwell Tracer Test (PITT) technology, the operator can generate a quantifiable measure of the average oil saturation between an injector and producer. Resmans’s patented tracers also have the potential to access information about fractional flow and relative permeability.
Tracer technology in carbon capture and storage (CCS)
Tracer technology is also an important element in safely storing CO2 as part of carbon capture and storage (CCS) projects that are so key to the oil and gas industry in meeting its climate and emissions reductions goals.
Most CCS applications are planned in existing producing assets, and tracers are the only means of quantifying CO2flow direction, flow velocity and breakthrough to producing wells. Furthermore, the operator can mark the injected CO2 with unique labels and thereby identify the source of CO2 if any leakage occurs, something that has been experienced through old wells. In this event, the operator was able to quickly locate and plug the leak using CO2resistant materials.
Tracer data is a cost efficient and versatile way to better understand operators’ well and reservoirs for better production returns, lower operating and capital costs and greater efficiencies when it comes to environmental management.
With the continued pressures on the E&P industry when it comes to environmental management, technologies, such as tracers, are already delivering.
Gunnar Hviding is CEO of Resman AS. Among his positions prior to joining Roxar in 2002, Hviding was President and CEO of the previously listed Roxar ASA and the CEO of listed Crudecorp ASA. He also has petroleum experience from Shell Internationale Petroleum Matschapij. Hviding holds a MEng in Chemical Engineering from Imperial College and an MBA from INSEAD.