Tracers in wells increase reservoir understanding

Based on input from the IFE:

Tracers are substances pumped down wells together with water or gas, or positioned in completions. Measuring them in the liquid or gas produced can reveal which zones are active, what type of liquid is flowing where, and how much is being produced. That provides information on which parts of the reservoir are flowing well and which require additional measures to improve recovery.

The first internationally reported use of tracers dates to 1946, when helium gas (He) was injected in California’s Elk Hills oil reservoir to study gas flow in the reservoir. Several scattered trials were conducted during the following decade with helium and radioactive hydrogen (HT) in other reservoirs. But it was not until the 1970s and 1980s that tracer technology began to acquire a certain position in the petroleum industry.

Tracers were first used on the NCS in 1984 to study how drilling fluid influenced well cores. Titrated (radioactive) water (HTO) was added to the drilling fluid during exploration drilling on Snorre.

The first use of tracers in production occurred on Ekofisk and Gullfaks in 1985-87 in order to study the flow of injected water and gas between wells. All the tracers were radioactive. Since the results were positive, the industry wanted to develop non-radioactive alternatives. This was first achieved by the Norwegian Institute for Energy Technology (IFE) in 1988 to measure gas on Ekofisk on behalf of Phillips Petroleum.

In 1990, the “tracer club” was established at the IFE as a programme sponsored by large oil companies, and with the NPD as an observer. This work has resulted in the qualification of new non-radioactive tracers for gas, water and oil.

Considerable work has been done in recent years to develop tracer-based methods for measuring remaining (immobile) oil. The IFE has developed and qualified methods both for waterflooded areas between wells and for investigating the immediate vicinity of an individual well. This plays an important role in efforts to qualify various EOR methods through pilot projects.

One or more tracer injections have been performed in many of the reservoirs which are or have been on stream. The aim is to improve the reservoir description by acquiring the better understanding of fluid dynamics required to ensure optimal drainage. Although the value of applying this technology on the NCS and internationally is difficult to measure directly, estimates indicate that it amounts to billions of kroner.