This emerges from the response given by operators to a circular from the Norwegian Climate and Pollution Agency (Klif) and the Petroleum Safety Authority Norway (PSA).
Sent to all the operators on the NCS on 23 February 2010 [link], the letter requested information on whether they had injection wells for operational discharges.
It also asked how these are monitored and the status for possible leaks, as well as seeking a good deal of additional information on these wells.
Of the 16 operators which responded, 10 report that they do not inject drill cuttings. Statoil, Talisman, BP, ConocoPhillips, ExxonMobil and Marathon have injectors for operational discharges, and have submitted the requested information.
Injected shale zones
The operators report that injection largely takes place in shale zones beneath the Utsira formation, with fracturing to the Utsira at a depth of about 800-1 200 metres.
Some companies have injected from the start in deeper zones, while others have changed their philosophy and shifted from the Utsira to depths of around 2 000-2 100 metres.
During the early years, cuttings were injected in the annulus between 20-inch and 13 3/8-inch casing (alongside production from the well). Newer wells are designed purely as injectors.
The PSA regards feedback from the companies as good. There has also been a positive response to the publication, in consultation with the company, of Statoil’s investigation report on the PSA website [link].
Most of the companies report that they either have implemented or intended to implement measures in line with the recommendations in Statoil’s investigation report.
Status – wells to inject operational discharges
Statoil currently has a total of 20 wells for injection of drill cuttings, cuttings and produced water, gas, carbon dioxide, and some which inject cuttings, produced water and chemicals.
In addition come 50 wells which the company has used for such injection over the years, but which have ceased to be employed for this purpose.
Thirteen of these were shut in because seabed leaks were discovered, including some identified after the Veslefrikk incident.
Others have been shut in because excessive injection pressure was required, and some are temporarily abandoned because faults in the well are suspected after assessing downhole date in the light of the Veslefrikk incident.
Injection wells shut in because of established or suspected leaks are on Åsgard (seven leaks in 1997-2001), Oseberg South, Visund, Veslefrikk A, Snorre B, Oseberg C and Njord.
The company had a cuttings injector on Ringhorne which failed in 2004, with a breakthrough to the seabed. The four other injectors were shut in as a result of this incident, and a new injector was drilled to the Statfjord formation at 2 190 metres.
In addition, the company has injector wells on Jotun B which inject directly beneath the Utsira. Only three of these have been used to inject cuttings, with the other two in reserve.
At present, no drilling or injection of cuttings is under way on Jotun B, but the wells are planned for use in connection with future drilling.
Other operators have provided the following status reports for their injection wells:
Follow-up by the PSA
Because Statoil has had the largest number of incidents with breakthrough to the seabed, the PSA is following up the company’s further work through special status meetings.
It is also checking whether any factors related to cuttings injectors are relevant for other types of injection wells, such as water/gas injectors for production support.
In addition, the PSA is checking that the current well integrity project being pursued by the Norwegian Oil Industry Association covers all types – including cuttings injectors.
Injection of operational discharges affects the regulatory responsibilities of several government agencies:
This means that the problems confronted with the injection of operational discharges have required a coordinated follow-up by Klif, the PSA and the Norwegian Petroleum Directorate.
The NPD has contributed its geoscientific expertise – in part with regard to formation properties for acceptable storage of operational discharges.
The PSA is collaborating with the agencies concerned in order to coordinate other measures where necessary.
Regulatory requirements for injection wells
The regulations set the same requirements for this type of well as for all the others.
As things stand, the PSA takes the view that the regulations it currently enforces take adequate account of the requirements for well integrity and the barriers needed for this type of well.
No indication has been found that the incidents are attributable to weaknesses in the regulations, or that different requirements might have prevented them.
Some of the incidents occurred because of a failure to comply adequately with the regulations. Others have shown that an important requirement for achieving good and secure injection is the selection of suitable zones which can accept the injected medium.