Seismic and sub-seismic deformation prediction for the assessment of possible pathways – the joint project PROTECT

Abstract:

In the joint project PROTECT (PRediction Of deformation To Ensure Carbon Traps), we determine the specific potential of communicating systems that occur between reservoir and surface in the framework of CO2 underground storage. The development of a new seismo-mechanical workflow permits an estimation of the long-term storage integrity.

The study target in the Otway Basin in south-western Victoria is Australia´s first demonstration of the deep geological storage of CO2, operated by the CO2CRC. Our objective is to predict and quantify the distribution and the amount of sub-/seismic strain caused by fault movement in the proximity of the reservoir. For this purpose, we applied three independent approaches to fill the sub-seismic space, and validated them.

Firstly, we built a geometrical kinematic 3-D depth model based on 2-D and 3-D seismic data that are provided by the CO2CRC Consortium. This interpretation was stabilized by additional seismic attribute processing that images small-scale lineaments with high resolution by multi-attribute displays that combine curvature and coherency. Retro-deformation, i.e. kinematically restoring the strata in 3-D, was performed on the reservoir seal. The highest strain magnitudes are around 4-5%. They are not observed where the fault displacements are highest, but where the fault morphologies were the most complex, i.e., there are rapid changes in displacement along the fault plane. Benchmarking this approach by numerical forward modelling yields further constraints on stress variation. In areas where we had preliminary predicted critical deformation we carried out new reflection seismic measurements to calibrate our predictions. This not only yields high-resolution structural images, but, in addition, also allows to determine petrophysical parameters by the acquisition of shear-wave reflection seismic data.

With this seismo-mechanical workflow we obtain a better overview of possible fluid migration pathways and communication between reservoir and overburden. As such we will provide a tool for prediction and adapted time-dependent monitoring strategies for subsurface storage in general.