“The Maria field in the Norwegian Sea has underperformed”, reports Joe Killen, analyst with Westwood Global Energy.
It came onstream a year ahead of schedule but has experienced a 71% downward revision to the 207mmboe reserves originally claimed.
Westwood benchmarking shows that Maria was under-appraised relative to its peers before the selection of a development concept. Even worse, this is not the only case on the Norwegian Continental Shelf (NCS).
Unanticipated reservoir complexity
“Appraisal practice needs to improve if further disappointments are to be avoided”, Killen writes.
Prior to the declaration of commerciality (PDO), the reservoir at Maria had an anomalously low number of penetrations, increasing the probability of underperformance.
Unanticipated reservoir complexity resulted in a lack of connectivity between producers and injectors and is cited by the operator as the cause of the underperformance at Maria, Westwood reports. Regrettably, Maria is not the only example of a non-performing field on the NCS with an anomalously low number of penetrations prior to PDO. In fact, eight out of the ten fields analysed by Westwood are non-performing. Maria and four other fields have all had downward reserves revision of >50%.
Some companies do seem to be learning lessons from under-appraisal. Spirit Energy, who holds a 20% equity stake in Maria, is reported to have delayed submitting a development plan for the Fogelberg discovery in Norway, citing more complex reservoir than initially thought, Westwood says.
In summary, Maria was put on production ahead of schedule and under budget but has underperformed significantly due to unrecognised reservoir complexity and the lack of connectivity between producers and injectors. The Maria case study shows there is significant room for improvement in appraisal practices including embedding the learning from analogue fields in appraisal programme design.
The reservoir in the Maria field is the Middle Jurassic Garn Formation. It is a well-defined horst block structure with moderate reservoir quality. When all the wells have been drilled, Maria’s 4-slot subsea templates will have a total of five oil production wells drilled approximately 4,500 meters below the seabed and stretching 2,000 meters horizontally into the reservoir. Water injection is provided to pressure-support the field, pumping water into the zone below the oil to help push the hydrocarbons up towards the well producers.