Outcrop Characterization and Modelling of Sand Injection Complexes

Sand injection complexes are important components of petroleum systems. They form sub-vertical and sub-horizontal networks of permeable sandstone reservoirs, which often contain commercial hydrocarbons. In the subsurface, defining the geometry and distribution of sandstone intrusions and their reservoir quality is challenging, and constitutes a high level of uncertainty in subsurface models. The Tumey Giant Injection Complex (TGIC) is a well-exposed, excellent analogue for subsurface injection complexes. Herein, outcrop of a km-scale wing intrusion is used to create a 2D geological template as the basis for static and seismic reservoir models. The 2D and 3D static models combined outcrop geometries, injectite facies, and rock properties data to demonstrate spatial relationship between injectite facies and to derive pore volume and their distribution. Seismic modelling used the geological template and petrophysical well data as input for 2D point-spread function (PSF) based seismic modelling to create 2D synthetic seismic data. Results show that seismic data fail to image substantial “sub-seismic” reserve volumes, and that the reservoir geometry is oversimplified. Our models confirm subsurface experience that sandstone intrusions enhance reserve volumes and recovery factors and show that well placement strategy must be cognisant of intrusion architecture to optimize volumetric estimates and hydrocarbon recovery.