Gas shale: global significance, distribution, and challenges
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The central geologic properties of a shale gas play are generally assessed in terms of depositional environment, thickness, organic geochemistry, thermal maturity, mineralogy and porosity. Key features of successful shale gas plays include high total organic carbon (TOC) content (>2%), thermally mature (Ro 1.1% to 1.5%), shallow for the given maturity, and a low clay content / high brittle mineral content. However, porosity, in situ stress regime, stress history, and mineralogy are also significant factors. Technically recoverable (although not necessarily economically recoverable) gas shale is abundant across the globe. It is also located in a very wide range of geographical regions, and in many of the nations with the highest energy consumption. For certain nations, shale gas therefore has the potential to reduce energy prices and dependence on other nations, hence impact on both the political and economic outlook. However, the prospects for and significance of shale gas are greater where there is a lack of existing conventional gas production, where there is proximity to demand (i.e. population), and where some form of existing gas distribution infrastructure exists.The definition of a ‘resource’ can follow a number of classifications. However, in the context of this study, the class of ‘technically recoverable resources’ (TRR) has been adopted, which includes both economic and uneconomic resources. The assessment of the global data included the identification of the shale depositional environment and basin type. A brief summary of the shale gas plays is presented for each country, which is followed by a statistical assessment of certain data sub-sets to illustrate where shale gas is located, the expected range of properties in terms of TOC, depth, age, and basin type. There are a number of key challenges that the industry faces, including environmental issues and commercial challenges. The key issues relate to the management of the hydraulic fracturing process, the prediction and improvement of EUR/well, and the consideration of variable production costs in different regions.
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