Stratigraphic Pinchout Traps: Large Hackberry Lower Reservoir in Port Acres Field, Texas

JACKSON, MARY, Bureau of Economic Geology, Austin, TX

Port Acres gas field is located on the upper Texas Gulf Coast on the east side of the Houston Salt basin. The principal producing zone in the field is the Hackberry Lower reservoir, with a cumulative production of 308 Bcf; the Hackberry Lower ranks 35th in productivity among gas reservoirs in the Texas Gulf Coastal Plain Province. Although the Hackberry Lower reservoir is a candidate for coproduction, secondary recovery has been hindered by difficulties with brine disposal. The reservoir has been abandoned since 1978 except for one shut-in well.

Port Acres field lies within a submarine fan complex at the western edge of the Hackberry embayment, which contains strata equivalent to the Oligocene middle Frio Formation. From core data, log patterns, and sand-body geometry, the Lower Hackberry reservoir is interpreted to be a dip-oriented submarine canyon and fan system containing incised channel-fill sandstones and upward-fining sandstones interpreted as intermediate suprafan deposits.

Growth fault systems and salt-related structures are abundant in the Port Acres field area. The field discovery well was drilled into a fault-bounded structural trap identified on seismic sections, but the true stratigraphic nature of the trap was identified much later. Stratigraphic pinchouts, common in submarine-fan reservoirs, compartmentalize reservoir-quality sandstones and can be identified through depositional and structural analysis. In modern exploration practice, integrated studies of reservoir stratigraphy using depositional systems analysis, paleontologic data, 3-D seismic data, and interpretations of the time of emplacement and the geometry of salt structures may be used to identify subtle Gulf Coast stratigraphic traps.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)