Abstract
Evaluating any subsurface CO 2 storage site comprises the reservoir, seal, and overburden investigation to mitigate injection and storage-related complications. The Upper-Middle Jurassic Sognefjord, Fensfjord, and Krossfjord formation sandstones are potential CO 2 storage reservoirs at the Smeaheia area, northern North Sea. The Smeaheia area is located east of the Troll oil and gas field. The Upper Jurassic organic-rich Heather and Draupne Formation shales are the main seals for the sandstone reservoirs. In this study, we carried out a prestack seismic inversion to obtain elastic property cubes of acoustic impedance ( AI ), velocity ratio ( Vp/Vs ), and bulk density ( RhoB ). From these elastic cubes, we obtained the reservoir properties such as porosity ( Phi ), shaliness ( V sh ), and permeability ( k ) of Sognefjord, Fensfjord, and Krossfjord formations. We introduced two new equations to extract the shale volume and porosity cubes from the inverted elastic cubes in the present study. These equations are nonlinear based on the AI versus Vp/Vs rock physics template. Both equations are correlated first with the well log data and then applied on the elastic property cubes ( AI versus Vp/Vs ) to obtain the V sh and Phi property cubes. An additional porosity cube ( PhiD ) was generated from the inverted RhoB for comparison. Finally, using an empirical equation, permeability was extracted from the porosity cube. The reservoir properties we derived from 3D seismic, in addition to the well log, revealed the vertical and lateral variations of porosity, shaliness, and permeability in the Smeaheia area. We used these reservoir properties to infer the depositional environment and the viability of reservoirs for CO 2 storage. The depositional environments identified were shoreface and deltaic from the extracted sand-body geometries. We found the Sognefjord Formation possessing the best reservoir properties, followed by the Fensfjord Formation as the secondary storage potential. In contrast, the Krossfjord Formation owed the lowest reservoir quality in the Smeaheia area. • Our new equations helped to reveal the lateral variations in reservoirs and their depositional environment. • The Sognefjord is the best, and Fensfjord Formation is the second-best quality reservoir in the area for CO 2 storage. • The Krossfjord Formation is the least suitable for CO 2 storage in the Smeaheia area.
Highlights
Subsurface CO2 storage is one of the many solutions proposed for reducing greenhouse gas emissions in the atmosphere
This study focuses on a prestack seismic inversion to obtain the reservoir properties of Sognefjord, Fensfjord, and Krossfjord formations in a potential CO2 storage site "Smeaheia" offshore Norway (Fig. 1a)
The thickness and porosity within the Sognefjord Formation decrease towards the west in well 32/ 4-1; the net-togross thickness ratio (N/G) 0.36 is low in well 32/2-1 compared to 0.72 in well 32/4-1 (Table 1)
Summary
Subsurface CO2 storage is one of the many solutions proposed for reducing greenhouse gas emissions in the atmosphere. This study focuses on a prestack seismic inversion to obtain the reservoir properties (e.g., porosity, shaliness, and permeability) of Sognefjord, Fensfjord, and Krossfjord formations in a potential CO2 storage site "Smeaheia" offshore Norway (Fig. 1a). Rock physics models link elastic parameters such as impedances and velocities to the reservoir properties such as lithologies, porosity, and fluids. This technique is in a developing stage and needs testing in other fluid-lithology environments The reservoir properties such as porosity, shaliness, and saturation obtained from inverted seismic data (Yenwongfai et al, 2017, 2018) can further be used as input and subsequent calibrations to a 3D reservoir simulation or geomechanical model (e.g., (Herwanger and Koutsabe loulis, 2011). The results from work can be used to develop and calibrate a 3D field scale reservoir, and subsequently a geomechanical model for the potential CO2 storage site Smeaheia in the northern North Sea
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