Elastic Velocity Models of A Stratigraphically Complex Carbonate Reservoir, Midland Basin.
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207
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Nigerian Minning and Geoscience Society
Abstract
Crosswell seismic survey was conducted in a section of midland basin to study a carbonate reservoir of the Wolfcamp formation previously identified on surface seismic data by subtle amplitude and travel-time anomalies. Because the surface seismic data has insufficient resolution to reveal the full geometry of the reservoir and the stratifications around it, crosswell seismic survey having resolution ten-times the surface seismic data was conducted across two wells in the area. The crosswell data was processed for P and S waves travel-time. A finite frequency based optimsed velocity inversion method (OVIM) was applied to image the velocity structure of the reservoir environment after validating the OVIM using synthetic geological model of ‘rainbow’ field. Results of synthetic study gave high resolution complex velocity model comprising horizontal beds and a vertical fracture bearing striking similarities with the true models. The P and S velocity tomograms inverted for the carbonate reservoir show consistent structures that correlate with the well logs from the two well in the area. The velocity tomograms identified the reservoir interval as a low velocity structure adjacent to and overlain by high velocity tight silliciclastic units. The reservoir is delineated as a ~70 m thick stratigraphic trap. Velocity variation within the reservoir interval suggests the presence of facies characterized by variable porosity. The observations in the inverted velocity image are supported by well B velocity log. According to the velocity tomogram, the main pay zone is about 32 m thick extending laterally from well B to the middle of the two wells. Overall, the study demonstrates the enormous potentials of crosswell seismic tomography to address reservoir delineation and characterisation problem usefully.
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Keywords
Velocity tomography, Carbonate reservoir, Cross-well seismic survey, midland Bsin
Citation
Raji, W. O. (2017): Elastic Velocity Models of A Stratigraphically Complex Carbonate Reservoir, Midland Basin. Nigerian Journal of Mining and Geosciences. Vol. 53(1), 1 – 9.