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The role of intelligent tracers in sustainable energy systems

Published by , Deputy Editor
Oilfield Technology,

The last few years has seen the E&P industry come under increasing pressure as demands grow for a more sustainable energy system. The response from the E&P industry has initially been to evaluate its operating practices to reduce emissions in oil production, which covers Scope 1 and 2 in the Paris Accord, and further developing the technologies around Carbon Capture and Storage (CCS), which covers Scope 3.

Central to this strategy for meeting Scope 1 and 2 are methods for enhanced recovery, accelerated production, digitisation, waste reduction and the reduced movement of people and equipment.

The good news is that the technologies are already available and in widespread use. The challenge, however, remains to make better use of the available technologies and move from ‘best practices’ to a ‘standard operating procedures’.

Tracer technology is one of these technologies which can help operators achieve all these objectives through the use of risk-free methods to monitor and optimise production through a better understanding of the underground asset. This article will examine the role tracer technologies are playing in the sustainable energy systems of the future.

What is tracer technology?

The underlying principle of organic tracers is the release of specific molecules which follows the liquid or gas flow in the reservoir. Therefore, if a tracer is detected then there is flow.

The tracers can either be installed in the well completion or pumped into an injector well or producing well, depending on the data the operator seeks. Such data might include zonal productivity, the location of water break-through or gas coning, optimal draw-down of the well, well monitoring, pressure support, oil saturation and a host of other information.

Most often, the tracer data works best when analysed together with other available information from the reservoir.

Zonal specific information for greater 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 can generate information on zonal productivity, water breakthrough and gas coning.

By optimising the drawdown of the well, the operator can operate 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.

The same 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 with unknown confidence.

Whilst tracer data will never be able to provide complete accuracy either, it has the necessary accuracy to 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.

Zonal cross flow or severe multiphase conditions may make quantification more challenging, but in these cases it is possible both to identify the situation and to extract information about the events which are ongoing in the well. Resman is working with a leading oil service provider to enhance simulation capabilities and integrating them in leading industry solutions to enhance the availability of data and to improve reservoir understanding.

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.

Profits and waste reduction

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 and the pay zone increased. Profits and waste reduction often go hand in hand, if tackled in the reservoir.

Oil saturation & relative permeability

Resman’s Partitioning Interwell Tracer Test – PITT – can provide information on oil saturation in producing reservoirs. 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 the 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.

The Single Well Chemical Tracer Test, SWCTT, is also used to estimate near bore oil saturation in production wells through a huff and puff procedure of the partitioning tracers in the production wells.

Reduced CO2 in Operations

Following a tracer installation or injection, the operator can receive actionable data in excess of 5 to 10 years, 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. Compare this to transporting a Production Logging Tool and crew to the platform with the CO2 saving on one data set as much as 99 per cent.

Non-toxic and non-radioactive

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.

Tracer technology in carbon capture and storage (CCS)

Tracer technology is also an important element in safely storing CO2. Most CCS applications are planned in existing producing assets, and tracers are the only means of quantifying CO2 flow 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 CO2 resistant materials.

The road to a sustainable future

In summary, tracer data is a cost efficient and versatile way to better understand operators’ well and reservoirs for better production returns and lower operating and capital costs. The tracer data is always available, over the entire field life, leading to an optimizing value from existing assets whilst reducing CO2 emissions from operations and logistics. Tracer technology will also be an important component in future CCS projects, contributing to a sustainable improvement of the hydrocarbon-based energy system.

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