Structure

Structure maps for 13 of the Permian marker beds, as well as the configuration of the base of the Quaternary Equus Beds, which unconformably overly the Permian strata in the study area, are shown in Figure 3. All of the structure maps show a regional westerly dip of approximately 15-20 ft/mi. Locally, the structure maps show a 1.5-2.5 mi wide zone of structural flattening of the monoclinal westerly dip, centered on a local high in T23S R6W Sec. 3 (at the location of DDV #64). This feature also serves to define the apex of a subtle anticline referred to as the Yaggy-Hutchinson anticline, which extends in an E-W direction from Yaggy to western Hutchinson.

The base of Equus Beds configuration (Figure 3N) is inferred to represent the erosional base of a paleo-incised valley paralleling the Arkansas River, centered approximately 2-3 miles to the south of the present river within the study area. The map illustrates part of a large trunk stream that passes through the Hutchinson area described more fully in Watney et al. (2003). Tributaries draining from north of the modern Arkansas River in the vicinity of Hutchison closely follow subjacent paleotributary valleys that drain into the more deeply incised primary trunk stream of the paleo-Arkansas River. Other depositional and stratigraphic correlations to this paleoriver system are examined in this report.

The Arkansas River follows a distinctively linear course through the area over a distance of 90 miles. In turn, the river valley corresponds closely to the paleo-Arkansas River drainage. Moreover, a linear trend of productive vent wells follows the crest of an anticline between Hutchinson and Yaggy that closely parallels the Arkansas River. These coincidences provided the motivation to evaluate their possible interrelationships and common structural origin, and to use the combined information to help constrain the model to explain the subsurface gas migration in Hutchison.