Consequences of Intrusions for Sub-salt, Sub-basalt Exploration and Development

It has long been recognised that the complex overburden affects the propagation of the seismic signal and hence, the imaging of prospective sub-salt Carboniferous reservoirs in the Southern North Sea (SNS). The complexity has consequent impact for structural mapping and depth conversion through a combination of factors, including the presence of a thick salt layer in the Upper Permian (Zechstein Group) and Tertiary igneous intrusions (e.g. Brown et al., 1994; Gauer et al., 2004 & Wall et al., 2010). Moreover, previous work has suggested that the latter have played a major role in today’s Mesozoic and Cenozoic structural and lithological configuration in the SNS including a triggering effect on salt mobility (Underhill, 2009). Nevertheless, our understanding of the effects of the igneous bodies have, until recently, suffered from a lack of well data calibration, so the recently acquired sonic and density logs obtained in well 44/24-6 have afforded us the rare opportunity to model, tie, and map the intrusions. We present the results of research that aims to show the interactions between salt and the intrusions and then to map, quantify, model and understand the implications for the regional overburden and its consequences for sub-salt, sub-basalt exploration of the Carboniferous.