--> Abstract: Primary Controlling Factors and Prediction of Absorbed Shale Gas Content in Chang-7 Member, Ordos Basin, by Zhenxue Jiang, Jinyan Xing, Zhuo Li, Yuan Yuan, He Bi, Ye Xu, and Lei Chen; #90180 (2013)

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Primary Controlling Factors and Prediction of Absorbed Shale Gas Content in Chang-7 Member, Ordos Basin

Zhenxue Jiang1,2, Jinyan Xing1,2, Zhuo Li1,2, Yuan Yuan1,2, He Bi1,2, Ye Xu1,2, and Lei Chen1,2
1State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing, China
2Institute of Unconventional Natural Gas Research, China University of Petroleum, Beijing, China

Adsorbed gas is one of the occurrences in shale gas plays, therefore, clarify the main controlling factors of and establish quantitative prediction models for adsorbed gas content can be of both theoretical and practical significance for shale gas resource evaluation and favorable exploration decision. The relationship between adsorbed gas content, the controlling factors and the quantitative model are discussed based on petrology, geochemistry and petrophysics of shale in the Chang-7 member. Adsorbed gas content is determined to be primarily depends on specific surface area, water saturation and formation temperature and pressure via the statistical analysis and cluster analysis. As a significant parameter, specific surface area of minerals determines the reactive capacity and the adsorption capacity of mineral surface. However, different mineral component has different specific surface area. The specific surface area of clay minerals ranges from 15 to 800m2/g, with generally 15m2/g for both of chlorite and kaolinite, 30m2/g for illite, 60m2/g for montmorillonite and 800m2/g for smectite. In contrast, specific surface area of brittle minerals which comprises of quartz, feldspar and carbonate are only about 5m2/g. Therefore, the adsorption capacity of clay minerals is relatively higher than the brittle minerals. Moreover, the adsorption capacity decreases from the montmorillonite through illite-montmorillonite mixed-layer and kaolinite to Quartz and calcite, which have the weakest adsorption capacity. The adsorption gas content in shale has a positive correlation with total carbon content (TOC), which is mostly contributed by the fact that with the organic pore increasing, larger specific surface area raises the content of adsorption shale gas. Especially, while the total volume of micro- to meso-pore occupy more, which results in more specific surface area, the adsorption capacity of shale would become higher. Water preferentially absorbs on the pore surface for gas adsorption in water rich shale, results in the absorbed gas content decrease or even without gas adsorbed. Formation temperature and pressure conditions affect the shale gas occurrence and the absorbed gas content. The adsorption capacity has a negative exponential correlation with formation temperature, but a positively correlation with formation pressure in certain range. After controlling factor and cluster statistic analysis, the quantitative models between the adsorbed gas content and the specific surface area, formation water content, formation temperature and pressure conditions can be established. Shale in Chang-7 member, which is in medium maturity and rich in II1 organic matter, has the similar organic abundance with the Barnett shale. The specific area ranges from 5 m2 /g to 15 m2 /g, with the mean adsorbed gas content ranges from 1.5 to 2.0 m3/t, indicating great significance for industrial exploitation in the Chang-7 member.

AAPG Datapages/Search and Discovery Article #90180©AAPG/SEPM/China University of Petroleum/PetroChina-RIPED Joint Research Conference, Beijing, China, September 23-28, 2013