About Tight Gas

The intricacies of tight gas

While no two tight gas wells or reservoirs are alike, they do share several characteristics that present unique challenges. Those challenges, in turn, affect recovery and ultimate profitability.

Tight gas is trapped in a highly mixed mineralogy sandstone or limestone formation which can be impermeable and non-porous. While conventional natural gas deposits, once drilled, contain gas that can usually be extracted quite readily and easily, a great deal more effort has to be put into extracting gas from a tight formation.

Characteristics

Tight gas reservoirs share a number of characteristics, but these may not all be present in a single resource play.

• Ultra-low permeability values of less than 0.1 mD, generally in sandstone with varying compositions of clays and shales, while experiencing various stress regimes. (Note: Some newly discovered gas plays have been found to have permeability values above 0.1 mD but below 1 mD. Unquestionably, these reservoirs are challenging to develop, and may require stimulation, but classifying them as “tight gas” is not wholly accurate. For this reason, a new classification--“complex gas”--is carried for these plays)
• Discontinuous sweet spots and multi-layers that require precision drilling and production techniques
• Reserves and production that are often evaluated on the offset well and by comparing the high-average-low (production) well to the total asset performance, due to numerous reservoir characteristic variables
• Rapid, efficient drilling and completion processes which maintain gas output as well as minimize unnecessary cost
• Reduced initial and cumulative production that requires more wells and infrastructure when compared to conventional gas wells for the same amount of gas
• Making sure the environmental impact is acceptable for the locale and the world by minimizing the footprint, ensuring fluids meet regulations while using water conservation practices

Complex Gas

Complex gas is a classification of sandstone formations which contain retrograde gas-condensate and have permeability values less than 1mD. These formations can be shallow or deep, and can be normally-to-abnormally pressured.

U.S. Department of Energy (DOE) Resources
National Energy Technology Laboratory - Tight Gas Exploration Technologies  
U.S. Tight Gas Plays