Deepwater Massive Sandstones: Fans, Channels, Slides and Intrusions on a Seismic Scale

Abstract

Over the past two decades sandstone intrusions have been increasingly recognized as an important component of the deepwater Paleogene petroleum province of the North Sea where entire oil fields are hosted in intrusive traps. In several of the largest developments coming on stream in the UK in the next decade, sandstone intrusions are a critical part of the reservoir volume, geometry and connectivity, highlighting the economical importance of these structures to the petroleum industry. Although the importance of large-scale sandstone intrusions have been recognised for many years in the North Sea, examples from around the world have only started emerging in the past few years, driven primarily by the emergence of high-quality 3D seismic datasets in frontier deepwater regions including Angola, Nigeria, Uruguay and New Zealand. Large-scale sandstone intrusions recognized in seismic data are typically between 50–300 m tall, 200–2000m wide and up to 3–4 km long with limb thicknesses of some 5–100 m. Resulting volumes range from < 0.1 km³ to several km³ for clusters of visibly connected intrusions. This presentation will showcase well documented examples of sand injectite oil fields as well as frontier specimens, highlighting the recognition criteria and their importance to regional and local exploration. We will discuss their interpretation, based on seismic stratigraphic criteria, enabling the distinction of classical lowstand fans and channels from mass transport complexes and their partly remobilised equivalents from fully intrusive sandstones. The importance for exploration and development and production will be demonstrated by means of production data. Sandstone intrusions form thick high-quality reservoirs in unusual basinal locations and violate seals by inserting sub-vertical permeability (several Darcy) conduits that may crosscut hundreds of metres of poorly permeable mudstones. The recognition of deepwater massive sandstones of intrusive origin therefore poses important challenges to deepwater exploration traditionally driven by classic seismic stratigraphic approaches.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015