Tight Gas Sandstones: 25 Years of Searching for “The Answer”

James L. Coleman, Jr.
U. S. Geological Survey, Reston, VA 20192

Exploring for tight gas sandstone reservoirs is much more than looking for a bright spot on 3D seismic or random drilling in a gas-charged basin. It is commonly a complex endeavor intertwined with acreage position, lease obligations, gas sales contracts, strategy for market share, access to pipelines, reservoir and line pressure, proven reserves, daily rates, decline curves, produced water management, structural position, sedimentary context and content, hydraulic frac’ing, Kv-Kh, matrix cement and porosity, grain size, and petrophysical recognition and characterization. The world of science (and business) implies that most problems can be overcome, if one works hard enough and has enough resources to apply. Exploring for, and effectively managing tight gas sandstone reservoirs is a challenge of balancing many elements along a narrow pathway to profitability. It also requires a clear, simple, and correct geologic model upon which exploration and funding strategies can be built. Developing the geologic model requires an understanding of the complete nature of many types of low permeability reservoirs.

Over the past twenty-five years, a number of different tight gas sandstone reservoirs have been brought into the nation’s productive natural gas inventory. These include reservoirs of many different ages, in many different basinal settings. Reservoir discovery and management efforts with select fields in the Silurian Tuscarora, Pennsylvanian Pottsville and Jackfork, Jurassic Cotton Valley, Cretaceous Frontier and Almond, and Eocene Wilcox sandstones will be reviewed, compared, and contrasted. In these case studies, the scope and scale of tight gas sandstone challenges can be illustrated.