SECONDARY NATURAL GAS RECOVERY IN THE APPALACHIAN BASIN: APPLICATION OF ADVANCED TECHNOLOGIES IN A FIELD DEMONSTRATION SITE, HENDERSON DOME, WESTERN PENNSYLVANIA

摘要

Two independent high-resolution aeromagnetic surveys flown by Airmag Surveys, Inc. and interpreted by Pearson, de Ridder and Johnson, Inc were merged, processed and reinterpreted by Pearson, de Ridder and Johnson, Inc for this study. Derived products included depth filtered and reduced to pole maps of total magnetic intensity, vertical and horizontal gradients, interpreted STARMAG structure, lineament analysis and an overall interpretation. The total magnetic intensity patterns of the combined survey conformed reasonably well to those of coarser grid, non-proprietary regional aeromagnetic surveys reviewed. The merged study also helped illustrate regional basement patterns adjacent to and including the northwest edge of the Rome trough. The tectonic grain interpreted is dominantly southwest-northeast with a secondary northwest-southeast component that is consistent with this portion of the Appalachian basin. Magnetic susceptibility appears to be more important locally than basement structure in contributing to the magnetic intensity recorded, based on seismic to aeromagnetic data comparisons made to date. However, significant basement structures cannot be ruled out for this area, and in fact are strongly suspected to be present. The coincidence of the Henderson Dome with a total magnetic intensity low is an intriguing observation that suggests the possibility that structure in the overlying Lower Paleozoic section may be detached from the basement. Rose diagrams of lineament orientations for 2.5 minute unit areas are more practical to use than the full-quadrangle summaries because they focus on smaller areas and involve less averaging. Many of these illustrate a northeast bias. Where orientations abruptly become scattered, there is an indication of intersecting fractures and possible exploration interest. However, the surface lineament study results are less applicable in a practical sense relative to the seismic, subsurface or aeromagnetic control used. Subjectivity in interpretation and uncertainty regarding the upward propagation of deeper faulting through multiple unconformities, salt-bearing zones and possible detachments are problematic. On the other hand, modern day basement-involved earthquakes like the nearby 1998 Pymatuning event have been noted which influenced near-surface, water-bearing fractures. This suggests there is merit in recognizing surface features as possible indicators of deeper fault systems in the area. Suggested future research includes confirmation of the natural mode-conversion of P-waves to down going S-waves at the level of the Onondaga Limestone, acquisition of 3-C, 2-D seismic as an alternative to more expensive 3-D seismic, and drilling one or two test wells in which to collect a variety of reservoir information. Formation Imaging Logs, a Vertical Seismic Profile and sidewall cores would be run or collected in each well, providing direct evidence of the presence of fractures and the calibration of fractured rocks to the seismic response. If the study of these data had indicated the presence of fractures in the well(s), and efforts to calibrate from well bores to VSPs had been successful, then a new seismic survey would have been designed over each well. This would result in a practical application of the naturally mode-converted, multi-component seismic method over a well bore in which microfractures and production-scale fractures had been demonstrated to exist, and where the well-bore stratigraphy had been correlated from well logs to the seismic response.