--> --> Abstract: The Influence Factors of Shale Gas Occurrence Form and the Quantitative Model of the Adsorbed Gas in Chang 7 Member of Ordos Basin, by Jinyan Xing, Zhenxue Jiang, Lei Chen, Jin Hao, Weitao Chen, and Limiao Yao; #90180 (2013)

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The Influence Factors of Shale Gas Occurrence Form and the Quantitative Model of the Adsorbed Gas in Chang 7 Member of Ordos Basin

Jinyan Xing, Zhenxue Jiang, Lei Chen, Jin Hao, Weitao Chen, and Limiao Yao
Unconventional Natural Gas Institute, China University of Petroleum, Beijing, China

The research of shale gas occurrence influence factors and the quantitative research of adsorbed gas content is the key factor which applied for shale gas assessment and favorable area selection.

By means of combination of comparison, experiment, and simulation methods, this article mainly study the influence factors of shale gas occurrence forms and make a further effort to determine its major control factors. Under consideration of temperature and pressure, we establish the quantitative model between the adsorbed gas content and its major control factors which is used for the gas-bearing evaluation. The achievements have an important reference value for conducting shale gas assessment and favorable area selection in Chang 7 Member, Ordos Basin.

Compared with depositional environment, genetic type, geochemical characteristic, reservoir property, and petrological characteristic between Barnett Shale of the United States and Chang 7 Member of Ordos Basin in China, we can summarize their similar geological features and obtain the relative factors which influence the shale gas occurrence forms of Chang 7 Member. Then, through different methods we can get the content of dissolved gas, absorbed gas, free gas. It gets the content of dissolved gas through PVT simulation experiment which can get the solutions. Well site, laboratory, and mathematical techniques used to determine absorbed gas content, and well logs are used to determine free gas content. And by means of the relative analysis experiments, we can acquire the geological parameters which reflect the shale geochemical characteristics, reservoir physical properties. According to constructing the correlation between the occurrence forms and their relative parameters, we can ascertain the major controlling factors. According to the existing isothermal adsorption experiment datas, we can obtain the curve of shale adsorption and construct the correlation between adsorbed gas content and temperature, pressure, respectively. Thus establishing the model combined with the major control factors which have been identified. The model mainly through 1stOpt software to simulate absorbed gas content, temperature, pressure, and other major control factors. Finally, the quantitative model can predict adsorption ability of non-measure data samples, which can be used to evaluate the gas-bearing in the study area.

By analogy, we discover that shale gas forms in the large black shale of reducing environment. The total shale gas content is determined by the abundance of organic materials content, the type of organic materials is a key parameter which can evaluate gas production capacity, organic maturity influences genetic type of shale gas, rock mineral compositions control the pore structure, pore structure is related to the shale gas occurrence volume, and thus affects the occurrence forms, temperature and pressure are also the main factors that affect shale gas occurrence forms. The free gas of shale in Chang 7 Member occur in a large number of pores and fissures, so the major control factors of gas content are development of porosity and fractures. While, adsorbed gas of shale gas occur in a large number of particles, clay minerals, and the surface of particles, the major control factor is TOC. In the study area, abundance of organic matter is up to 4.5%. It cannot be ignored the soluble gas content in Chang 7 Member, and its content is mainly controlled by crude oil density, temperature, and pressure. Through the study of isothermal adsorption experiments of some representative shale samples in Chang 7 Member, we establish adsorbed gas quantitative model.

The abundance of organic materials of Chang 7 Member is much and its average TOC is 4.5%, which is about equal with the Barnett Shale; the types of organic materials are various and most are the type of II1, which is similar to the Barnett Shale; thermal evolution maturity is moderate. Adsorbed gas is mainly controlled by the organic carbon content, free gas is mainly controlled by porosity, oil-soluble gas mainly controlled by the residual oil content. The gas-bearing of Chang 7 Member is much great, the average gas content is about 2.5m3/t, with great value for industrial exploitation.

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