SwRI Structural Geology & Geomechanics

Mesostructures in subhorizontal thinly bedded calcareous mudstones of the Permian Bell Canyon Formation in the western Delaware Basin (west Texas) include vertical tectonic stylolites that are kinematically linked with low-angle thrust faults. Schmidt rebound is high for all but a few beds, indicating generally competent rock. Competent beds exhibit contrasting deformation behavior ranging from (i) no visible tectonic stylolites and numerous small-displacement (<1 cm) thrust faults, to (ii) tectonic stylolites with rare thrust faults. Tectonic stylolites are abundant in beds with 3.5-6.5% clay minerals, and absent from beds with more or less clay. Less competent beds are more clay-rich, and exhibit ductile flowage or internal folding rather than stylolite formation, and tend to terminate small-displacement thrust faults in adjacent beds. These results demonstrate that deformation behavior in otherwise similar calcareous mudstone is extremely sensitive to subtle changes in mineralogy. Check out the full paper: Ferrill, D.A., Cawood, A.J., Evans, M.A., Smart, K.J., King, R.R., Zanoni, G., 2024. Thrust v. stylolite. Journal of Structural Geology, 105113, https://lnkd.in/gkUTgAsG

Our new paper titled “Evidence for regional fluid migration in the Eagle Ford Formation, Austin Chalk, and Buda Limestone of south-central and west Texas, USA.” is now out in Marine and Petroleum Geology. Full reference: Evans, M.A., Ferrill, D.A., Smart, K.J., 2024. Evidence for regional fluid migration in the Eagle Ford Formation, Austin Chalk, and Buda Limestone of south-central and west Texas, USA. Marine and Petroleum Geology, 106896, https://lnkd.in/g7e9MSNA . 

Mesostructures in subhorizontal thinly bedded calcareous mudstones of the Permian Bell Canyon Formation in the western Delaware Basin (west Texas) include vertical tectonic stylolites that are kinematically linked with low-angle thrust faults. Schmidt rebound is high for all but a few beds, indicating generally competent rock. Competent beds exhibit contrasting deformation behavior ranging from (i) no visible tectonic stylolites and numerous small-displacement (<1 cm) thrust faults, to (ii) tectonic stylolites with rare thrust faults. Tectonic stylolites are abundant in beds with 3.5-6.5% clay minerals, and absent from beds with more or less clay. Less competent beds are more clay-rich, and exhibit ductile flowage or internal folding rather than stylolite formation, and tend to terminate small-displacement thrust faults in adjacent beds. These results demonstrate that deformation behavior in otherwise similar calcareous mudstone is extremely sensitive to subtle changes in mineralogy. Check out the full paper: Ferrill, D.A., Cawood, A.J., Evans, M.A., Smart, K.J., King, R.R., Zanoni, G., 2024. Thrust v. stylolite. Journal of Structural Geology, 105113, https://lnkd.in/gkUTgAsG

Small-scale synsedimentary folds in the Eagle Ford Formation in southwest Texas formed during deposition in a shallow epicratonic basin on the North American craton. These folds formed by gravity-driven slumping on very gentle slopes during deposition both above and below storm wave base. Although individual slump intervals are relatively thin (1-2 m thick), they locally represent significant shortening and thickening of slumped intervals, with up-dip absence of the interval represented by missing section, bed terminations, boudinage, or extensional faults. Repeated slumping results in cumulative updip thinning and downdip thickening along depositional slopes. Slump folds are common in unconventional reservoirs in North American epicratonic basins, but underrepresented in the literature. Slump folded intervals add complexity and unpredictability to unconventional reservoirs, with implications for reservoir quality, drilling, and optimal stimulation during completion. Check out the full paper: Ferrill, D.A., Smart, K.J., Lehrmann, D.J., Morris, A.P., McGinnis, R.N., 2023. Synsedimentary slump folding: Examples and consequences of an under-recognized process in epicratonic basins. Marine and Petroleum Geology 152, 106274, https://lnkd.in/ghdvrJXs. https://lnkd.in/ghdvrJXs.

Small-scale synsedimentary folds in the Eagle Ford Formation in southwest Texas formed during deposition in a shallow epicratonic basin on the North American craton. These folds formed by gravity-driven slumping on very gentle slopes during deposition both above and below storm wave base. Although individual slump intervals are relatively thin (1-2 m thick), they locally represent significant shortening and thickening of slumped intervals, with up-dip absence of the interval represented by missing section, bed terminations, boudinage, or extensional faults. Repeated slumping results in cumulative updip thinning and downdip thickening along depositional slopes. Slump folds are common in unconventional reservoirs in North American epicratonic basins, but underrepresented in the literature. Slump folded intervals add complexity and unpredictability to unconventional reservoirs, with implications for reservoir quality, drilling, and optimal stimulation during completion. Check out the full paper: Ferrill, D.A., Smart, K.J., Lehrmann, D.J., Morris, A.P., McGinnis, R.N., 2023. Synsedimentary slump folding: Examples and consequences of an under-recognized process in epicratonic basins. Marine and Petroleum Geology 152, 106274, https://lnkd.in/ghdvrJXs. https://lnkd.in/ghdvrJXs.