Fault trap analysis of the Permian Rotliegend gas play, Lauwerszee Trough, NE Netherlands

Abstract

The Lauwerszee Trough is a northwest-trending sub-basin within the Southern Permian Basin and lies in the onshore area of northeastern Netherlands. Referred to as the ‘Golden Lane’ Trend, it is the classical Lower Permian Rotliegend gas play of the Netherlands, consisting of the prolific, high net-to-gross sandstone reservoirs of the Slochteren Formation. Traps are tilted extensional fault blocks that entrap gas sourced from the Carboniferous Coal Measures. The overlying Rotliegend Ten Boer Claystone and Upper Permian Zechstein evaporitic rocks provide the top and lateral seals for the fault traps. In this study 30 fault traps were analysed in which 22 were found to have gas accumulations. Trap fill is controlled primarily by Slochteren sand-on-sand juxtaposition leakage across a fault; however, some gas accumulations as mapped appear to be filled deeper than this leakpoint and require sand-on-sand fault seal. Retained fault-seal gas columns are relatively small and mostly less than 60 m with one exception of 95 m. Seven potential Slochteren sand-on-sand fault-zone seals were identified in this study. The analysis of these fault traps revealed three possible criteria that may promote the development of such fault seals: (1) juxtaposition against a tight, shale-rich interval; (2) small isolated sand-on-sand juxtaposition area (<25 000 m 2 ) typically associated with fault lengths less than 1 km; or (3) occurrence of a complex narrow fault zone. However, some sealing fault segments are associated with structural interpretation/mapping uncertainty. Minor map changes may eliminate perceived sand-on-sand fault-zone seals and explain trap fill by conventional fault juxtaposition.