Annerveen Field: an Integrated Approach to Structural Review

Abstract

The Annerveen high-calorific Rotliegende gas field with approximately 75 x 10[sup 9] m[sup 3] of gas in place is the largest gas field in the Netherlands after the giant Groningen field. It was discovered in 1961, 2 yr after Groningen. Commercial production started in 1973 and, to date, about 59 x 10[sup 9] m[sup 3] has been produced. The field produces from three main clusters, with peripheral wells tied into these production and gas treatment sites. Structurally, the field consists of an east-west-trending elongate horst block, fault bounded to the north and south and dip closed to the west. The eastern closure of the field is contiguous to and separated from Groningen field. After a general description of Annerveen field, this paper focuses on the problems and solutions associated with the structural interpretation of the boundary zone between Annerveen and the Groningen area. The north-eastern part of the Annerveen field is especially difficult to review due to the presence of a large salt wall (the Veendam salt wall), precluding detailed structural data from 3-D seismic; anomalous oil-gas-water contacts and pressure regimes; aquifer uncertainty; and fault evaluation (sealing/non-sealing ). Resolution of some of the field uncertainties has called for an interdisciplinarymore » approach invoking data sources such as 3-D seismic, a vertical seismic profile, gas composition, regional aquifer pressure gradients, initial well logs and Dual-Spacing Thermal Decay Time logs, reservoir pressure decline, and well performance.« less