Norway Initiates Water Re-injection Study

Should the water that is produced with oil and gas be discharged to the sea, or injected back into the subsurface? The answer might seem obvious, but what if reinjection leads to lower oil production and lost revenues to the State? The Norwegian Petroleum Directorate (NPD) has initiated a project to examine the potential consequences for oil production when produced water is reinjected into the reservoir.

Norway aims to be a major energy producer as well as a pioneer when it comes to the environment. The oil industry on the Norwegian shelf embraces this principle, and Norway is currently one of the most environmental friendly oil and gas producers in the world. But the goal is to become even better!

Based on the "principle of precaution", the Parliament has decided that no substances shall be discharged to the sea if they may damage the environment. The principle states that the water that is produced together with oil and gas, and which contains minor amounts of potentially environmental hazardous substances, must preferably be pumped back underground. Another alternative is to remove such substances from the water before discharging it to the sea.

Several fields on the Norwegian shelf have started reinjection of produced water in recent years, either for pressure support in the oil reservoir or for disposal in another location. This disposal has no direct impact on the oil production, except that drilling injection wells is expensive. The method requires significant amounts of energy, entails increased emissions to air and has thus far not been utilized much on the Norwegian shelf.

Reinjection of produced water into the oil reservoir gives an increased supply of nutrients to the naturally occurring bacteria, including bacteria that reduce sulphates. These bacteria convert sulphates from previous sea water injection to hydrogen sulphide (H2S). This means more bio-mass and deposits in the reservoir, and higher risk of formation plugging around the wells. If formations are plugged, the effect of water injection to enhance oil recovery will be reduced.

H2S must be removed from the natural gas before it can be exported if the H2S content exceeds the agreed level in the sales contract. The H2S-gas is highly toxic and corrosive and thus represents a challenge as regards both working environment and safety. Handling corrosion can also be very costly.

Due to varying conditions on the fields, it takes a long time to establish a good empirical basis for evaluating the possible future consequences that such environmental measures could have on oil recovery. On this basis the NPD, together with OLF (the Norwegian Oil Industry Association), has implemented a project designed to provide more knowledge on the possible consequences of reinjecting produced water. The project will also examine preventive measures, reveal knowledge gaps that require more research, and possible economic consequences of produced water reinjection. The NPD plans to organize a seminar on this topic in October as part of this work.

This project is an example of the Norwegian Petroleum Directorate's role as a contributor to uniform and long-term management of our common oil and gas resources, a management concept that promotes selecting the environmental solutions that give the best environment for the money.
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