Reservoir Characterisation of the Jurassic Posidonia Shale Formation and the Triassic Deposits of the Main Buntsandstein Subgroup by Seismic Inversion Methods, Block Q16, West Netherlands Basin

Reservoir Characterisation of the Jurassic Posidonia Shale Formation and the Triassic Deposits of the Main Buntsandstein Subgroup by Seismic Inversion Methods, Block Q16, West Netherlands Basin

Justiniano Cisneros, A.M.

Diephuis, G. (mentor)
Pringle, T. (mentor)

Civil Engineering and Geosciences

Geoscience & Engineering

Reservoir Geology

2014-08-29

The objective of this study was to perform a reservoir characterisation of the Posidonia Shale Formation and the Bunter reservoir, through seismic inversion techniques, in order to obtain several rock properties and analyse how their variations are related to changes in depth, lithology and fluid content. Posidonia Shale is interesting as an unconventional hydrocarbon prospect because it is a bituminous type II kerogen source rock with approximately 5-7% of TOC content. The Bunter reservoir is interesting as it consists of uniform massive stacked fluvial and eolian gas-bearing sandstones of approximately 200 meters in thickness. The study area (256 km2) is located in the Q16 block in the West Netherlands Basin. Structurally it is characterised by half grabens. Posidonia Shale Formation and Bunter reservoir are compartmentalised. Their depths range between 2300 and 2800 meters and between 2500 and 3500 meters respectively. A model-based seismic inversion method and a pre-stack simultaneous seismic inversion method were carried out in order to estimate several rock properties. In addition to the pre and post stack PSTM seismic data, ten wells are located within the study area. As these ten wells did not have recorded shear wave velocities these were estimated by a Xu-White model (Xu and White, 1995 and 1996) and were calibrated at the Posidonia and Bunter intervals with nearby wells that had recorded shear wave velocities. Key horizons were interpreted and were used along with the well logs to generate the low frequency models of acoustic impedance, shear impedance and bulk density. These models were filtered in order to keep the low frequencies, below 10Hz which are missing from the available seismic data. The resultant volumes of acoustic impedance, shear impedance and bulk density obtained from the inversions honoured the well-log data. From these volumes other rock properties were derived namely shear modulus, bulk modulus, Young’s modulus, Vp/Vs ratio, Poisson’s ratio, lambda*rho and mu*rho. At Posidonia Shale, the acoustic and shear impedances and rock properties decrease compared to the bounded shales, which made it easily to follow this Formation laterally. Moreover, at Posidonia Shale interval, the Young’s modulus and Poisson’s ratio were used to estimate a Brittleness index. The southern area of the mapped Posidonia Shale presented the higher brittleness index, which implies that this area has a more plastic behaviour than ductile and thus is likely to be easier to fracture. Furthermore, the west of the mapped Posidonia Shale was selected as a sweet spot area for performing hydraulic fracturing since this zone has a larger continuous extension, it is thicker and it is more brittle. In the case of the Bunter reservoir, the shear modulus and Mu*Rho increased in cleaner sandstones and hence they are considered reliable lithology discriminators, while Poisson’s ratio and Vp/Vs ratio decrease in the presence of gas and, in consequences, they are considered reliable fluid discriminators. The top and base of Bunter reservoir were easier to recognise laterally on these rock property volume than on the original seismic volume.

reservoir characterisation
seismic inversion
rock properties
Posidonia shale
Bunter reservoir
Section Applied Earth Sciences

http://resolver.tudelft.nl/uuid:d9ae1ad5-6f21-478c-828e-40f63e0e4dd3

Student theses

master thesis

(c) 2014 Justiniano Cisneros, A.M.