Master Thesis Defense by Dan Friis Tømmerby Jensen

Title: Numerically Modelling of the Seismic Responses from Fractures Inserted into a Caprock

With increasing population, economic growth worldwide and fossil fuels combustion, other means to reduce CO2 emission into the atmosphere is of great interest. Sequestration of CO2 is a favorable method, however serious risk is related to CO2 injection into an underground reservoir and the caprock integrity may be affected by pre-existing fracture or faults. The Tyra Field could provide a safe way of storing CO2 and insight into the detectability of pre-existing fractures or faults and the possible resolution limit would provide knowledge into the security of the Tyra field before initiation CO2 injection. For this thesis, numerical modelling of the seismic response from fractures with difference scale and orientation in a caprock system related to the Tyra Field where conducted. The numerical modelling of the seismic response was achieved through the finite difference method on a structured grid with a Cerjan sponge boundary. The migration of the produced seismogram process was conducted with the reverse time migration method. A Laplacian Filter was used during the Reverse Time Migration procedure in order to minimize low-frequency high-amplitude noise in the migrated image. Results indicate that the pre-existing fractures can’t be distinguish below a 10m scale and the orientation, width and length of these fractures heavily alter the resolution limit.

Supervisor: Klaus Mosegaard