No abstract

Synthetic data were analyzed to determine the most cost-effective tomographic monitoring system for a geologic carbon sequestration injection site. Double-difference tomographic inversion was peiformed on 125 synthetic data sets: five stages of COJ plume growth, five seismic event regions, and five geophone arrays. Each resulting velocity model was compared quantitatively to its respective synthetic velocity model to determine accuracy. The results were examined to determine a relationship between cost and accuracy in monitoring, verification, and accounting applications using double-differencetomography. The geophone arrays with widely varying geophone locations, both laterally and vertically, peiformed best.

Shale gas has become an increasingly important clean energy, which has been explored worldwide in recent decades. In the shale gas production, supercritical CO2 acts as a fracturing fluid. For preventing any kinds of leakage of the injected supercritical CO2, it is essential to monitor the stability of its storage hundreds of kilometres beneath the Earth's surface. Seismic tomography is an imaging technique that uses induced seismic waves to create three dimensional images of the subsurface. It is an effective monitoring method to evaluate the caprock integrity in the CO2 sequestration storage (CCS). In this experimental research, a simulated uniaxial compressive load was applied on a granite sample to analyze the stress redistribution for long-term in-situ caprock integrity during CO2 injection. The induced seismic waves were recorded, and seismic events were located according to the Geiger algorithm. The frequency of seismic events correlates with the caprock failure evolution. Based on the frequency of seismic events and the failure process, the seismic data is divided into four regimes to examine the failure evolution. Finally, the double difference tomography (TomoDD) algorithm using arrival time was adopted to recalculate to modify the locations of seismic events and velocity structure in each regime. The results indicate that the passive seismic system can map the caprock stress distribution and allow for imaging of the caprock integrity. TomoDD exhibits sound improvements to relocate seismic events both in relative and absolute locations as well as to characterize the local velocity structure. The study further reveals that seismic monitoring along with TomoDD could evaluate the caprock failure accurately in the CCS.

Shale gas has become an increasingly important clean energy, which has been explored worldwide in recent decades. Supercritical CO2 acts as fracturing fluid for shale gas production. The safety monitoring is essential to prevent any kinds of leakage from the reservoir as the supercritical CO2 physically stored hundred kilometres underground. Seismic tomography is an imaging technique that uses induced seismic waves to create three dimensional images of the subsurface. It is an effective monitoring method to evaluate the caprock integrity in the carbon dioxide sequestration storage (CCS). In this experimental research, a simulated uniaxial compressive load is applied on a granite sample to analyze the stress redistribution for long-term in-situ caprock integrity during CO2 injection. The induced seismic waves are recorded and seismic events are traced based on the Geiger algorithm. The frequency of seismic events correlates with the caprock failure evolution. The acquired seismic data is divided into four regimes based on the frequency of seismic events and the failure process to examine the failure evolution. Furthermore, the travel time and distance is plotted to analyze the variation of velocity. Finally, the double difference tomography (TomoDD) algorithm using arrival time is adopted to recalculate the locations of seismic events and velocity structure in each regime. The results indicate that the passive seismic system can map the caprock stress distribution and allow for imaging of the caprock integrity. TomoDD exhibits sound improvements to relocate seismic events both in relative and absolute locations as well as to characterize the local velocity structure. The study further reveals that seismic monitoring along with TomoDD could evaluate the caprock failure accurately in the CCS.