A Stratigraphic Interpretation of Shear and Compressional Wave Seismic Data for the Pennsylvanian Morrow Formation of Southeastern New Mexico
M. D. McCormack, M. G. Justice, W. W. Sharp, 1985. "A Stratigraphic Interpretation of Shear and Compressional Wave Seismic Data for the Pennsylvanian Morrow Formation of Southeastern New Mexico", Seismic Stratigraphy II: An Integrated Approach to Hydrocarbon Exploration, Orville Roger Berg, Donald G. Woolverton
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Standard surface-recorded compressional and horizontally polarized shear wave seismic data are used to detect lateral variations in lithology and pore fluid within a stratigraphic unit. The analysis technique employed requires determining the horizontal shear and compressional wave interval transit time through a formation using measurements along coincident CDP shear and compressional lines. In addition, at each surface position along these seismic lines, the ratio of the shear-to-compressional transit time across the target interval is calculated. A strong correlation between observed lateral variations in the measured shear and compressional wave interval transit times and their ratio with known changes in the geologic cross section demonstrates the effectiveness of the technique to infer changes in the physical properties of a formation.
The formation chosen for this case study is the Lower Pennsylvanian Morrow formation, which produces gas from isolated channel sand deposits. Detailed geologic cross sections of the producing horizon have been mapped along two nearly perpendicular seismic profiles. Horizontal shear and compressional Vibroseis. surveys were conducted along these surface profiles using data acquisition parameters designed to produce similar signal-to-noise ratios and seismic resolution in both sets of field data. The profiles were located to insure that each line crossed productive and nonproductive regions of the gas field. After standard data processing, the horizontal shear and compressional wave transit times through the Morrow Formation showed significant variation in going from shaly nonproductive regions to productive channel sand areas. These variations, along with diagnostic changes in their ratio, are shown to be reliable indicators of lateral changes in the pore fluid content and the sand-shale ratio within the Morrow Formation.
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The publication of AAPG Memoir 26 opened up a whole new field to the exploration community. The material contained in that publication demonstrated the relationship of seismic data to the geology of the subsurface in greater detail than previously thought possible. In the years that have followed great effort has gone into refining and advancing the principles and methods of seismic stratigraphy. The goal of this Memoir 39 publication is to provide 15 papers which present and document the advances and refinements in seismic stratigraphic princples and methods that have occurred since the publication of Memoir 26. These articles help the geologist, geophysicist, and manager to keep abreast of this rapidly developing field and provide some guidelines for the evaluation of stratigraphically controlled prospects.