Natural Gas Production from Unconventional Low-Permeability Sandstone, Fractured-Shale, and Coalbed Reservoirs--Analogs from the U.S.A

Christopher J. Schenk, Richard M. Pollastro, and Troy Cook
U.S. Geological Survey, Denver, CO

Production of natural gas from low-permeability sandstone, fractured-shale, and coalbed reservoirs accounts for more than 20 percent of total annual gas production in the U.S. These types of unconventional reservoirs are now being examined for potential production in many other parts of the world. The availability of production data from several thousand wells in low-permeability sandstone, fractured-shale, and coalbed reservoirs in the U.S. has allowed the U.S. Geological Survey to construct production-decline curves and Estimated Ultimate Recovery (EUR) distributions by reservoir. Median EURs of wells from many low-permeability sandstone reservoirs range from 100 to 700 million cubic feet (3 to 20 million cubic meters) of gas and maximum EURs range from 5 to 15 billion cubic feet (140 to 420 million cubic meters) of gas. Although there is less production data for fractured shales (such as the Mississippian Barnett Shale in north-central Texas), median EURs of wells from fractured-shale reservoirs range from 300 to 600 million cubic feet (9 to 17 million cubic meters) of gas and maximum EURs range from 1 to 7 billion cubic feet (30 to 200 million cubic meters) of gas. Median EURs for most coalbed wells range from 100 to 400 million cubic feet (3 to 12 million cubic meters) and maximum EURs range from 4 to 7 billion cubic feet (110 to 200 million cubic meters). Geologic “sweet spots” within all types of unconventional reservoirs can have higher median and maximum EURs. The EUR distributions might also be valuable as analog production curves for the screening and assessment of similar low-permeability sandstone, fractured-shale and coalbed reservoirs in basins worldwide.

AAPG Search and Discovery Article #90072 © 2007 AAPG and AAPG European Region Conference, Athens, Greece