ABSTRACT

The Lower Cretaceous Travis Peak Formation in East Texas is a low-permeability gas-bearing sandstone that commonly requires hydraulic fracture treatment to produce at economic rates. Stratigraphic, petrographic, and structural characterization of the Travis Peak has resulted in information that can be used by operators to evaluate and complete these reservoirs more efficiently.

Depositional systems of the Travis Peak Formation in this region include braided to meandering fluvial, deltaic, and paralic systems. Reservoirs in the upper Travis Peak are tidal-channel, tidal-flat, and meandering fluvial channel sandstones, whereas reservoirs in the lower Travis Peak are braided fluvial deposits in wide channelbelts. Mudstones through out the Travis Peak are highly silty and thus do not stop vertical growth of hydraulic fractures created during well stimulation. As a result, hydraulic fractures are circular and may connect several stacked sandstones.

Petrographic studies indicate that extensive quartz cement is the major cause of low permeability in Travis Peak sandstones. Because the volume of quartz cement increases with depth, matrix porosity and permeability decrease. However, natural fractures are more abundant in structurally deeper, more intensely quartz-cemented sandstones than in shallower sandstones. Mean azimuth of natural fractures is N80°E. Drilling-induced fractures and borehole breakouts indicate that maximum horizontal stress (SH_max) is oriented east-northeast, which is the direction in which hydraulic fractures will propagate. Because the hydraulic fractures propagate in a direction subparallel to the natural fractures, hydraulically induced fractures may not intersect as many natural fractures as they might if SH_max had some other orientation relative to fracture strike.