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In this study, 37 samples of Lower Cambrian shale collected from different sections involving shale gas exploration-breakthrough areas (Well WPZK001 from Yichang City, Changyang section from Hubei Province, and Well W001-4 from Weiyuan County) and -failure areas (Kaiyang section from Guizhou Province and Youyang section from Chongqing City) both in the Middle-Upper Yangtze region were investigated by water uptake experiments, with a similar comparative study of Silurian Longmaxi shale samples in the Sichuan Basin. The comparative results showed that the water uptake content for the Lower Cambrian organic-rich shale samples from shale gas exploration-breakthrough areas are primarily controlled by TOC content, showing a positive correlative increase of water content and TOC content, which is similar to that of Silurian Longmaxi organic-rich shale samples in the Sichuan Basin. In contrast, the water uptake content for the Lower Cambrian organic-rich shale samples from shale gas exploration-failure areas generally showed a positive correlation with clay and carbonate contents, and there is no correlation with TOC content. It implies that the characteristics of pore network in the Lower Cambrian organic-rich shales from Middle-Upper Yangtze region, especially the development of organic matter-hosted pores, display significant differences regionally. Importantly, it provides a newly-developed strategy on the study of gas content variation in Cambrian shale from Middle-Upper Yangtze region by investigating the coupling mechanism of pore development and mineral composition as well as origins in organic-rich shales. [ABSTRACT FROM AUTHOR]

An experimental investigation of water uptake on five shale core plugs of Silurian Longmaxi Formation from Well Qianqian 1 in Sichuan Basin was conducted. The saturated water quantities on a series of shale cylinders with different diameters or lengths from one sample were determined, and a linear relationship between water uptake and the skeleton volumes of the shale cylinders was obtained. The slope of line, which is “K” value, represents the saturated water quantity per unit skeleton volume, and the water uptake porosity which is calculated by multiplying “K” value and the rock bulk density is from 3.51% to 8.90%. In order to evaluate the accuracy of the water uptake porosity determined from water uptake method, the nitrogen adsorption porosity and helium porosity of the same series of samples were comparatively measured. The results show that the nitrogen adsorption porosity ranges from 2.38% to 7.04%, which is less than the water uptake porosity, and the difference is about 0.54%-1.96%. The low-temperature nitrogen adsorption method failed to detect macropores with apertures larger than 350 nm in the shales, leading to the lower values of the nitrogen adsorption porosity without accounting the pore volumes of those macropores. GRI helium porosity ranges from 4.55% to 8.09%, and there are good consistency and comparability between the water uptake porosity and the helium porosity except for sample QQ- 45, and the difference is only 0.23%-0.81%. For the sample QQ-45, the helium porosity is 2.65% larger than the water uptake porosity, and the difference is attributed to the microcracks in the shale cylinders. The water uptake experiment can discern the microcracks in the shale cylinders based on the rapid increase of water uptake curve at the early stage of water adsorption. The shale cylinders effectively retain the original pore structures and pore networks of the shales, and the water uptake porosity is a statistical result which was measured with varied sizes of shale cylinders and affected slightly by the shale heterogeneity. Therefore, water uptake porosity is more representative to the actual porosity of the shales. A good positive correlation exists between total organic carbon （TOC） and porosity values, but no direct correlation with clay minerals, suggesting that TOC is the one of key controls on the change of the Longmaxi shale porosity. [ABSTRACT FROM AUTHOR]