Thick reservoirs (about 100 m, 330 ft) have been discovered in the northern part of the North Sea, with effective permeabilities less than 0.1 md. In spite of this poor transmissivity, it has been planned to study the development of these blocks, lying under 160 m (525 ft) of sea water. Reservoir engineering evaluations have already suggested that profitability could be reached, but only if the wells are significantly stimulated. This is why an extensive fracturing feasibility study, focused on the Brent formation, was carried out.

The Brent formation appears to be a sandstone which would easily be stimulated using normal hydraulic fracturing techniques and this study has revealed (1) that sufficiently conductive propped fractures with fracture half-lengths at least equal to 150 m (500 ft) are feasible and have a reasonable chance of success, and (2) that this size of treatment will satisfy the production increase requirements.

However, it is not possible with the data available today to guarantee that this design would in fact reach the expected target in all drilled and planned wells. The main reason is that the minimum horizontal in-situ stress profile versus depth is not known and, that fully three-dimensional numerical simulations based on laboratory results have emphasized that 50 bar (725 psi) is the minimum excess pressure to contain a facture to less than 10 m (33 ft) of vertical growth and thus, to prevent fluid penetration in the underlying coal strata during the pumping period. In a coal layer, horizontal stresses are suspected to be very low and in the case of connection between such a layer and the perforations, the gel would preferentially fracture the coal rather than the sandstone, thus setting the proppant out of the pay zone. In-situ measurements of stress become essential for each relevant layer.

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