A Structural Model of Jonah and South Pinedale Fields, Wyoming
Despite different structural styles, the South Pinedale anticline and the Jonah gas field share the same timing of deformation. These structures are part of a detached, transpressional system formed in the Green River Basin (GRB) in response to NE-SW compression where the structural strike of the Wind River Range (WRR) changes from a NW-SE orientation to an approximate E-W trend.
The youngest evidence of the deformation is post-early Middle Eocene age, as indicated by faulting and warping of the shallow Wasatch Formation strata seen on seismic and the involvement of outcrops of the Wasatch and basal Green River formations. Coeval folds, thrusts, strike-slip faults, and oblique-normal faults were formed during this time, consistent with transpressional shortening in the GRB, and located above basal detachments fed by slip on basement faults of the WRR. Structural accommodation in Jonah field is controlled by left-lateral (synthetic) displacement on the South Jonah Fault zone (SJF of Hanson and Others, 2004), and associated right-lateral (antithetic) offset along NE-SW-trending faults that terminate downward below the Ericson Fm. Enhanced reserves and rate of recovery on the east flanks of these antithetic, strike-slip faults indicate that production has been influenced by structural development.
Of particular note, is documentation of one mile of left-lateral slip on the SJF by: 1) reconstruction of northeastward-thickening regional isopachs, 2) reconstruction of piercing points defined by depositional patterns on an RMS amplitude attribute map and 3) offset of fold axes.