The discovery of the Fat Sand Play (Solling Formation, Triassic), Northern Dutch offshore – a case of serendipity

Abstract

In 1992, the well L9-7, drilled by the Nederlandse Aardolie Maatschappij (NAM) unexpectedly found a thick previously unknown sandstone interval with excellent reservoir characteristics in the Middle Buntsandstein (Triassic) of the Dutch Northern Offshore: the ‘Fat Sand’. A follow-up well, L9-8, found this reservoir gas-bearing in an accumulation that turned out have recoverable reserves of circa 1 Tcf of gas distributed over several fault compartments. This serendipitous discovery led to a frantic period in NAM's office trying to understand the setting of this local sand development and, most importantly, assess follow-up potential; could this sand be present elsewhere in a trapping configuration? The local depocentre in which the Fat Sand accumulated is considered to be caused by local extension along a strongly listric fault soling out on the top of the Zechstein Salt. This supra-salt fault seems to be caused by early east-west extension in the Dutch northern offshore. The shape of the fault plane was strongly influenced by the presence of the nearby Zechstein Salt, and by early salt flow, which was also triggered by E-W extension.