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Petrel eyes its Porcupine basin blocks in new light

Ireland’s offshore basins will be increasingly attractive to investors in light of the combination of 3D seismic surveys and directional drilling that allow explorers to map and drain complex reservoirs, said Petrel Resources PLC, Dublin.

Petrel said it has identified several new prospects on its Atlantic margin blocks that lie on the eastern side of Porcupine. Blocks 35/23, 35/24, and the western half of 35/25, and Blocks 45/6, 45/11, and 45/16 total about 1,400 sq km. The company hopes to attract large partners to shoot more seismic and drill exploratory wells.

The expanded size of the 1981 Barryroe oil discovery in the North Celtic Sea basin, appraised by Providence Resources PLC, “shows what is now possible,” Petrel said (OGJ Online, July 25, 2012).

Petrel in October 2011 was awarded licensing options over two sets of blocks in the Atlantic Porcupine basin. Porcupine exploration historically concentrated on Jurassic targets that resemble those of the northern North Sea. Interest waned with lack of success, and no wells have been drilled in the basin in the last decade.

Success in different categories of reservoirs elsewhere, as in the West African and South American offshore, has forced a general re-think and led to a resurgence of interest in similar potential targets in the Porcupine basin, Petrel said.

In making its bid, the company had relied on its large archive of seismic data and reports, supported by the acquisition of a selection of additional seismic lines. This substantial data base has enabled this extensive work to proceed quickly on a modest budget of €1 million over 2 years.

Since the award, Petrel has purchased more substantial coverage of seismic lines and reinterpreted the full integrated data set across both sets of blocks. The data were carefully calibrated against the relevant well logs. This phase of the project was completed in June 2012.

A second phase of interpretation is under way to detail and appraise the potential prospects identified in the first phase of work. This will include the acoustic inversion of selected seismic lines to assess the quality of the targeted reservoir sections. More seismic lines may be purchased if crucial to the interpretation. This phase of the work is scheduled to be completed by the end of September 2012.

A separate seismic project is underway to detail the depositional facies and character of the identified sand bodies.

All relevant well data in the region have been acquired and a full petrophysical appraisal made of 17 wells. Following the upcoming inversion work, this will improve control of the seismic data and potential prospects, Petrel said.

A separate study is being initiated and will focus on the sedimentary provenance of the reservoir successions. This will involve initial petrographic analysis, followed up with the application of the Pb-in-feldspar technique to determine the provenance of first cycle material in the detrital components of the succession. This is important in Porcupine, where sediment input can be along the axis of the basin or from the basin margins.

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