Fracture detection using seismic anisotropy at the Weyburn carbon dioxide storage site, Saskatchewan.

摘要

Geological storage of CO2 maybe an effective means of mitigating CO2 emissions to the atmosphere. Cap rock integrity is an essential characteristic of any reservoir to be used for long term CO 2 storage. Focusing on the Midale reservoir within the Weyburn field in southeast Saskatchewan, this study aims to assess the cap rock for the presence of fractures which may provide migration pathways for CO2 out of the containment interval. Seismic AVOA (amplitude variation with offset and azimuth) techniques have been applied to provide maps of seismic anisotropy at the cap rock horizon. These maps aid in identifying areas of potential fracturing; although, the source of anisotropy is non-unique and could also result from differences in the horizontal stress field, aligned mineral fabrics or faults.;Seismic anisotropy analysis shows multiple isolated areas of increased anisotropy which may be fracture-related. AVOA inversion results correlate well with geomechanical modeling predictions, microseismic observations and previous fracture studies on well log and core samples from the reservoir. Anisotropy anomalies are observed to correspond with salt dissolution structures in the cap rock and overlying horizons as interpreted from 3D seismic cross sections.;Modeling is conducted to determine if the effects of anisotropy in the overburden and layers immediately above the cap rock will introduce unacceptable levels of uncertainty in AVOA analysis. Of particular interest are the effects of known underlying fracture induced anisotropy from the reservoir and whether its response can be separated from that of the overlying layers.