Morphology of Turbidite-Channel Reservoirs, Lower Hackberry (Oligocene), Southeast Texas: ABSTRACT

Abstract

ABSTRACT Hackberry sandstones produce gas at depths of from 9500 to 11,500 ft (2900 to 3500 m) in the western part of the Hackberry embayment. Adjacent shales contain a microfauna generally believed to represent bathyal depths. The Hackberry sandstones have long been known to be turbidites in the form of dip-trending, channel-like bodies. Recent cores from fields in southeast Texas provide more details concerning reservoir character and morphology. Hackberry reservoirs are found in narrow channels only 3000 to 4000 ft (914 to 1219 m) in width. Channel sandstones thicken abruptly to 200 to 300 ft (61 to 91 m). Middle-channel locations are characterized by stacked, massive sandstones which represent the A division of the turbidite sequence. Stacked channel beds are apparently on the order of 10 ft (3.5 m) in thickness, but no intervening shales separate bed sets. The channel-margin sections consist of interbedded sandstone and shale. The beds are on the order of 3 to 5 ft (1 to 1.5 m) in thickness and consist of massive and laminated sandstones that form turbidite sequences of the A and AB type. The immediately adjacent overbank sections are composed dominantly of shale but contain thin sandstones and siltstones that are massive to laminated and rippled and form more complete turbidites of the ABC type. All of the sandstones have graded texture and are volcanic-chert arenites of moderate quartz content. The channels appear to be of constructional origin, and log correlations above and below the channel facies suggest that they are inserted in the sedimentary section rather than filling eroded channels. The several facies illustrated by cores have characteristic responses on borehole logs which permit recognition of channels and overbank sections by logs alone. These distinctive log characteristics may permit the prediction of channels in exploratory and development drilling.