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Introduction
Published in Nwanosike-Warren Quinta, Oil and Gas Engineering for Non-Engineers, 2022
Yet another way of classifying petroleum is by conventional and unconventional reservoirs. Unconventional reservoirs can refer to any way of recovering oil and gas that is outside of the norm. Thus, shale oil and gas, tight gas, heavy oil, and deepwater reservoirs all count as unconventional. Tight gas reservoirs are characterized by low porosity and low permeability, requiring fracking in order for natural gas to be produced. Porosity is the percentage of void space in a rock that can hold liquids or gases. The higher the porosity, the greater the ability of the rock to hold crude oil and other fluids. Shale oil and gas are similarly found in low permeability rock, but instead of the oil and gas being found in reservoir rock, it is found in source rock.
The New Fuel Mix
Published in Michael Frank Hordeski, Alternative Fuels—The Future of Hydrogen, 2020
Natural gas is a fossil fuel found in underground reservoirs. It consists chiefly of methane, with smaller amounts of other hydrocarbons such as ethane, propane, and butane, along with inert gases such as carbon dioxide, nitrogen, and helium. The actual composition varies, depending on the region of the source. As technology advances, unconventional natural gas deposits are beginning to make up a significant part of the supply. Before 1978, natural gas that had been discovered deep underground was left untouched. The passage of market-based regulation and the Natural Gas Policy Act provide incentives to extract these deep deposits and to spur investment in deep exploration and development. Deep gas is usually 15,000 feet underground, compared to conventional deposits which are only a few thousand feet deep. Tight gas is gas that is trapped in hard rock or limestone (tight sand) and represents about 21% of U.S. natural gas reserves. Black shale is another source where the estimated reserves have tripled in the last few years. Coalbed methane is another source that in the past was neglected and considered a problem in coal mining. It is estimated to be about 8% of total reserves.
Petrophysical characterisation of tight sandstone gas reservoirs using nuclear magnetic resonance: a case study of the upper Paleozoic strata in the Kangning area, eastern margin of the Ordos Basin, China
Published in Australian Journal of Earth Sciences, 2018
Y. Y. Huyan, X. Q. Pang, T. S. Liu, F. J. Jiang, X. Z. Chen, X. Q. Ma, L. L. Li, X. H. Shao, D. Y. Zheng
Tight gas is natural gas trapped in unconventional reservoirs of extremely low porosity and permeability. Owing to the decline in conventional oil and gas production, tight gas reservoirs, which are significant sources of gas in China (Feng, Zhang, & Feng, 2011; Hu, Li, Shan, & Han, 2010; Huang, Xiong, Yiang, & Wang, 1996; Lu & Liu, 2015), are hosted in the upper Paleozoic tight reservoirs in the Ordos Basin and the Xujiahe Formation in the Sichuan Basin (Tao et al., 2016; Yang, Li, & Ma, 2005).