ABSTRACT

With deregulation and the subsequent rise in gas prices and development of modern evaluation and completion techniques, the "tight gas sands" of the Cotton Valley Terryville massive sandstone complex have become an intriguing play. This study establishes a generalized stratigraphic framework which allows regional correlation of individual productive horizons in the Terryville from east Texas to east Louisiana. It also proposes a sedimentologic sequence for deposition and a diagenetic sequence for reservoir rock modification.

The Terryville is an extensive complex of marine-dominated, massively bedded, predominantly fine-grained, quartz sandstones. It lies stratigraphically between the underlying Bossier Shale and the overlying Knowles Limestone and downdip from the time-equivalent Hico Shale and Schuler Formation.

A series of four prograding marine-dominated, coalescing, deltaic complexes are proposed as the depositional systems for placing the Terryville sands on the stable Jurassic shelf. In this model, fluctuating sea levels and longshore drift spread the sands over a 40- to 50-mile-wide belt.

Burial diagenesis modified the porosity and, in the southeastern portion of the area, created overpressuring in the Terryville sandstones. Subsequent structural movement in certain areas created large fractured reservoirs. Production from the tight gas sands is controlled by distinctive sedimentary and diagenetic effects which divide the area into two subareas: the normally pressured and the overpressured Terryville. Utilization of these concepts should result in a higher degree of success in economically developing the tight gas sands of the Cotton Valley Terryville.