Seismic Evaluation of the Fruitland Formation with Implications on Leakage Potential of Injected CO2

Subsurface characterization activities undertaken in collaboration with the Southwest Regional Carbon Sequestration Partnership on their San Juan Basin pilot test include acquisition of geophysical logs, time lapse VSP and analysis of 3D seismic data from the site. The project is funded by the U.S. Department of Energy and is managed by the National Energy Technology Laboratory.CO2 injection began in late July of 2008 and appears it will continue at least into early August of 2009. Total CO2 injection volume to date (mid July, 2009) is approximately 300MMcf. Subsurface characterization activities are critical to the evaluation of reservoir integrity and the potential that leakage of injected CO2 might occur. Work discussed in this presentation focuses primarily on the analysis of 3D seismic from the area. 3D seismic interpretation reveals that the Late Cretaceous Fruitland Formation forms a well defined seismic sequence bounded by high amplitude reflection events at its top and base. The pattern of internal reflection events is parallel and conformable near the top and base of the sequence. The 3D seismic view of the Fruitland Formation shows considerable detail not inferred from well log correlations in the area. The pattern of internal reflection events is marked by significant internal discontinuity. Fruitland coal reflection events reveal the presence of local fold-like structures with wavelengths of 1 km to 3.5km accompanied by relief of 6 feet to 60 feet. The origin of these structures is uncertain. Some of the structures observed in the Fruitland are present in overlying Paleocene and Late Cretaceous intervals. Post-stack processing of the 3D seismic is undertaken to enhance subtle discontinuity in the data that might be indicative of small faults or fracture zones that could jeopardize reservoir integrity. 3D seismic from the area is processed using edge enhancement, event similarity and spectral decomposition algorithms. Additional seismic attributes are also evaluated for evidence of faults or fracture zones. The analysis raises questions concerning local variations in Fruitland coal depositional systems, the influence of differential compaction within the Fruitland coal section, and local structure of possible tectonic origin. The vertical extension of larger wavelength structures into shallower strata suggests that local deformation of the area continued through the Paleocene and may include minor deformation of Eocene strata exposed at the surface in the areas surrounding the pilot site. Extensive tracer monitoring at the surface for evidence of CO2 escape ensures that escape very small amounts of CO2, should that occur, will be detected.