The Harlingen field, the only gas field in the Upper Cretaceous chalk of the Netherlands

Abstract

The Harlingen gas field, at the top of the Chalk, is situated in Petroland's Leeuwarden Concession in the province of Friesland, northern Netherlands. The structural closure developed partly during the Early Oligocene, after approximately 500 m of sediment had been deposited on top of the Chalk. Shortly hereafter, gas migrated into the structure. The presence of the gas strongly reduced the further loss of porosity and permeability by diagenesis, whereas the overpressuring reduced further compaction. A final deformation phase, probably at the end of the Early Miocene, slightly enhanced the curvature at the top Chalk and gently folded the then relatively porous gas cap, resulting in a folded gas-water contact. Unlike the situation in the Chalk fields in the Central North Sea, fracturing of the reservoir is very limited and has not resulted in increased effective permeability. This is probably due to the weak curvature of the structure. Notwithstanding the low average permeability (1-2 mD), a production rate of over 60 000 m3/day was maintained for a period of five months after stimulation, without any signs of pore collapse, common in many unfractured chalk reservoirs-elsewhere. A field development plan is being considered.