Secondary Natural Gas Recovery: Targeted Applications for Infield Reserve Growth in Midcontinent Reservoirs, Boonsville Field, Forth Worth Basin, Texas - Volume II Appendix

This report documents an assessment of Midcontinent sandstone natural gas reservoirs in Boonsville (Bend Conglomerate Gas) field by integrating four key disciplines: geology, geophysics, reservoir engineering, and petrophysics. Pressure and production data confirm the existence of compartmented or poorly drained gas throughout much of the Bend Conglomerate and suggest that additional gas will be found when well spacing is reduced to 80 acres, although multiple stacked completion opportunities will typically be needed to ensure the economic viability of new infield wells. As part of this analysis, the Lower Atoka Group was divided into 13 third-order genetic sequences, and to our knowledge, this is the first public, comprehensive genetic sequence analysis that relates these Pennsylvanian reservoirs to their seismic response and to gas productivity. A 26-mi², 3-D seismic survey was done to test methods for reservoir delineation in thin-bed, hard-rock environments and identified a previously unknown structural component of reservoir compartmentalization in the form of low-displacement faulting commonly associated with karst collapse in deeper carbonate rocks. These karst collapse features extend vertically as much as 2,500 ft and may be a widespread influence on the deposition of younger sediments in the Midcontinent. The ability of the 3-D survey to define stratigraphic entrapments was more variable. Some sequences were imaged quite well, and seismic attribute analyses provided excellent agreement with net reservoir distributions generated from sequence stratigraphic interpretations. In other instances, individual systems tracts and reservoir sandstones that were subsets of genetic sequences proved difficult to trace precisely in the 3-D data, especially when those units were associated with a subtle impedance contrast or were extremely thin.