Comprehensive postwell studies indicate oil in place of 1 billion to 1.6 billion bbl, as much as four times earlier estimates, in the Middle and Basal Wealden formations at the Barryroe discovery in the North Celtic Sea basin offshore Ireland, said Providence Resources PLC.
Barryroe is Ireland’s first commercially viable oil field, and the 48/24-10z well completed in March 2012 is the first of a six-well drilling program to continue in the basin in the next 18 months. Other zones could further enlarge the OOIP estimate, and the gas resource is not included in the update, Providence noted.
Providence operates Barryroe with 80% interest on behalf of its partner Lansdowne Oil and Gas PLC with 20%. The discovery is in 100 m of water in Standard Exploration License 1/11 about 50 km off Ireland’s east coast.
The updated assessment incorporated data from the six wells drilled at Barryroe, recent 3D seismic, existing 2D seismic, and other regional data.
The analysis shows that the Barryroe trap at Base Wealden level is situated in the hanging wall side of an inverted major intrabasinal growth-fault system and covers an area of several hundred square kilometers. The crest of the structure is located at 6,400 ft true vertical depth subsea with deepest logged hydrocarbons at 7,300 ft TVD ss with no evidence of an oil-water contact.
Reservoir fluid data from the 48/24-10z well indicate that there is unlikely to be any primary gas cap present at the crest of the structure in the Basal Wealden sands.
The lowest closing contour for the Barryroe structure at Basal Wealden reservoir level is mapped at 7,500 ft TVD ss, 200 ft downdip from existing well control. A mid-case Basal Wealden average net sand thickness of just 23 ft has been assumed across the structure for volumetric purposes and, when combined with well petrophysical parameters, results in an in-place midrange estimate of 756 million bbl of oil and a high estimate of 906 million bbl.
The large increase in Basal Wealden resource versus the previous estimate is based on the ability to use the new high-quality 3D seismic data to image and extend the Basal Wealden sand play across the entire mapped Barryroe structure. The resource figures for the Middle Wealden, midrange of 287 million bbl and high estimate of 706 million bbl) have not been revised and remain as per the previous RPS Energy audit.
As in the recent 48/24-10z well, all of the previous Barryroe wells, which were drilled through the Lower Wealden, encountered a 1,000 ft thick section of interbedded sands and shales with all sands logged as hydrocarbon bearing. These sands are generally thin in eastern Barryroe but thicken considerably to the west as evidenced by the previous Esso-operated 48/23-1 well.
The Esso well, which logged 120 ft of stacked Lower Wealden hydrocarbon-bearing sands, had average porosities of 16% and hydrocarbon saturations of 70%. A failed well test in 1976 over this interval is now interpreted by the partners to be due to mechanical failure. The 48/23-1 well also encountered a 70 ft logged hydrocarbon-bearing sand in Purbeckian lacustrine shales underlying the Basal Wealden that which was not tested.
Deeper exploratory potential has also been identified under Barryroe at Upper Jurassic level, which is as yet undrilled. Mapping confirms the Barryroe closure persists to Base Cretaceous level, and the overpressured shales of the Purbeckian should provide an effective seal for any potential accumulation.
Providence has begun mapping the newly prospective zones and plans to provide a resource update once this work has been completed.