Genesis and Geometry of Oligocene Sandstone Intrusions in North Sea Basin

Key words: 
• North Sea Basin /
• sandstone intrusions /
• polygonal fault systems /
• hydrocarbon emplacement /
• overpressure

Abstract: Sandstone intrusions are a common class of soft-sediment deformation. They are formed by the forceful intrusion of fluidization sand into overlying sealing sequence during early stages of burial. Based on 3-D high-resolution seismic data and logging data, we utilize methods of seismic reflection configuration analysis and coherence cube slice to illustrate geometry and induced mechanism of sandstone intrusions. Results indicated that sand intrusions appear V-shaped or W-shaped high amplitude anomalies in seismic sections; conical bodies are 1-2 km on the plane and up to hundreds of meters high; fluid emplacement and polygonal fault systems inducing cap-rock fracture are the key factors for overpressure of depositional sand body and fluidization of sand. After injection, sandstone intrusions may serve as high-permeability fluid flow passage for a long term and has great significance for vertical migration of fluid. More importantly, sandstone intrusions may serve as favorable reservoirs. So it has a great guiding significance to evaluation of cap-rock sealing capacity and hydrocarbon exploration.