In pursuit of the perfect tracer
Tracers are used in many areas, from medicine to industry. They are widely used to study the insides of oil reservoirs. In this highly specialized field, IFE has an extensive and internationally recognized position. Tracers can be used to estimate how much residual oil there is in a reservoir, the flow of water and oil, and to create a map of an oil reservoir.
At IFE’s tracer laboratories there is currently hard work going on to develop new tracers with different properties. The task for these tracers or chemical substances is to find out how much oil is left in the fields, and to provide information on where in the reservoirs the remaining oil is located. This information is vital to increase oil recovery.
In order to develop this field further, IFE has engaged two skilled scientists, PhD student Mario Silva from Portugal and Postdoctoral Fellow Thomas Brichart from France. Both are affiliated with the National IOR Centre of Norway, with the University of Stavanger (UiS) heading the centre and IFE and IRIS as research partners.
IOR is short for «increased oil recovery», and the centre’s ambitious goal is to raise the exploitation degree from today’s level of just below 50 % up to 70 % on the Norwegian shelf. 1 % increase signifies about 32 billion Euros in increased revenues.
PhD student Mario Silva (from left) from Portugal and Postdoc. Thomas Brichart from France in one of IFE’s tracer laboratories. Both are investigating new tracers at IFE in affiliation with the IOR Centre. Silva has a master degree in chemical engineering from the Polytechnic University of Porto, and worked with analytical and environmental chemistry, and Brichart has a PhD in nanotechnologies and a master degree in inorganic chemistry from the University of Lyon.
The environmental challenge – finding a «green» tracer
One of the big challenges is to find a tracer that is robust enough to survive in one of the world’s most hostile environments; explicitly in an oil reservoir. With pressures up to several hundred bars and temperatures at 100-150 degrees Celsius, many tracers do not survive in these conditions. They disappear or change character so they are impossible to find.
– We are in fact looking for the perfect tracer. One that can handle these conditions, and at the same time is environmentally acceptable and can be detected in very small quantities, explains Brichart.
Small quantities means in this context concentrations down to ppb and ppt, or “parts per billion” and “parts per trillion”, or one nano gram per liter. This puts some specific requirements on the tracers, so they are possible to retrieve.
At the same time as the tracers need to withstand the pressures and temperatures, they need to be acceptable for the environment and as «green» as possible. They should not affect the environment in a negative way, be poisonous, sour or alter the chemical balance in the reservoirs. But they cannot be so “green” and easily degradable that they disappear. One of the most central characteristics for the tracers is to be retrieved in a production well, in order to give information on how it has moved from where it was injected. It can be a challenge to find the right balance between these considerations, says Brichart.
– Because of this I use molecules that have been approved for medical purposes. I mainly work with fluorescent substances, since they are well known and tested, and they have the characteristic that they are easy to find. This makes it possible to use smaller quantities, something that is better for the environment, he explains.
Examples of fluorescent tracers. This property makes it possible to find the substances, even in extremely small quantities.
Brichart is currently testing a dozen different fluorescent substances that may be suitable for the purpose. These tracers are to be used in single well tracer tests, where they are used to measure the amount of residual oil in the area near the well.
– The goal is to reduce the amount of chemicals by a factor to 1000. There are many benefits if we succeed in this. It is not very practical to transport and handle large amounts of chemicals, it is more environmental and of less disturbance to the reservoir if we can reduce the amount of tracers needed, he explains.
All chemicals that are to be injected into oil reservoirs must be reported to the Norwegian Environment Agency and be classified according to a system. The most environmentally acceptable are categorized as «green», following the labels «yellow», «red» and «black», where the latter is the most hostile to the environment. IFE’s ambition is to develop more tracers in the categories «green» and «yellow», thus being acceptable for the environment.
Exploring the residual oil saturation between wells
PhD student Mario Silva is working at developing new oil-water partitioning tracers for tests between wells, also known as PITT-tests or partitioning inter-well tests in the terminology of the petroleum industry. This is a newer field, less developed than the above mentioned single-well tests.
Partitioning tracers are used together with passive tracers. The partitioning tracer is sensitive to oil, while the passive is not. The passive follows the water flow through the reservoir, and reveals patterns of flow and geological information. The partitioning tracer moves between the flowing water and the stagnant oil. The passive tracer passes through the reservoir faster than the partitioning, By measuring and comparing how much time it takes for the two different tracers to pass through the reservoir, one can determine the amount of residual oil in the reservoir.
This is how a PITT tracer works (animation by Mario Silva, IFE/UiS)
The passive and the partitioning tracer are injected simultaneously into a reservoir. The passive moves faster through the reservoir, following the water flow. The partitioning uses more time as it is slowed down by oil on its way. Samples are collected of the production water, and by comparing among other things how much time the passive and the active tracer use, one can calculate how much residual oil is left in the reservoir.
– In my PhD work I will first develop PITT tracers. The next step is to test a selection of these tracers in the laboratory, with simulated conditions resembling a reservoir. Finally I will do pilot test in a real reservoir, explains Silva.
The IOR Centre will help him find a suitable field where he can do the pilot tests. Currently Silva is investigating 16 different molecules with certain characteristics that he will continue working on in the lab.
So far there are few available PITT tracers on the market. Therefore the goal is to develop and qualify more tracers for this purpose. In order to investigate large oil fields many different tracers are necessary, so that they don’t get mixed up and the tests are kept separate. If the same tracer is used in different wells, it is difficult to know for certain which injection well it originates from, and the analysis becomes more uncertain.
Senior Researcher Sissel Opsahl Viig is part of the National IOR Centre’s Management Group, and so far she is very pleased with the collaboration.
– The collaboration in the IOR Centre is very productive. It has been very useful for us to get to know our partners UiS and IRIS better, as well as the industry partners. We have also discovered more areas where IFE has competence and can contribute to strengthen the IOR Centre’s work, she states.
Picture to the right: Senior Researcher Sissel Opsahl Viig, IFE.
Despite the more challenging economic times for the oil industry, none of the twelve industry partners have so far chosen to withdraw from the collaboration.
– This proves that there is much to be gained from this collaboration. The industry recognizes that this research is of high value for them, and the cost of participation is far lower in a “Dutch treat” like this, compared to financing the research alone, concludes Opsahl Viig.
The National IOR Centre of Norway started up in December 2013, and the collaboration will go on for five years with a possible continuation of three more years. A total of 20 PhD students and 6 Postdocs will be affiliated with the Centre during the targeted eight years of operation. The IOR Centre is managed by the University of Stavanger with IFE and IRIS as research partners and 12 industry partners, and is also financed by The Research Council of Norway, The Norwegian Petroleum Directorate and Petoro.
More about the National IOR Centre here.
IFE’s role in the National IOR Centre of Norway
- IFE has a unique competence in tracer technology, a key technology for enhanced oil recovery and mapping of oil reservoirs.
- Tracers are extremely important because they provide a possibility to measure how efficient the IOR processes are and to determine how much residual oil a reservoir holds.
- The use of nano technologies, specifically to design «intelligent» tracers with certain properties may have a role in the Centre’s program, from IFE’s part.
- In addition to tracer technology IFE will contribute with the development of a program to simulate IOR processes, IORSim. Involved in this area is the Process and Fluid Flow Department at IFE, with their wide experience from developing acknowledged simulation tools such as the multiphase simulation tool OLGA.
2015-11-03 Mona Lunde Ramstad