Gas-Bearing Characteristics and Its Affected Factors of Shale of Upper Paleozoic in the Depression of Central and Southeast Hunan

Guosheng Xu, Zhen Zhang, Shao Feng Bu, Peng Yang, and Wenjun Liu
Chengdu University of Technology, Chengdu, Sichuan, China

The Shale gas is one of the most important unconventional natural gas, which mainly accumulates in adsorbed and free phases, and is characterized by a typical in-situ accumulation. The shale of Devonian-Permian of the Upper Paleozoic is widely distributed in the depression of central and southeast Hunan, and is characterized by big thickness, high TOC rate, moderate thermal evolution and highly developed fractures, which indicates a large resource potential of shale gas. In order to better calculate resources of shale gas and predict available areas of shale gas in the depression of central and southeast Hunan, this paper is based on the regional geological setting in the depression of central and southeast Hunan and the analysis of geological characteristics of the marine shale, using outcrop observations, drilling data, experimental testing and other methods, 24 shale samples in 7 targeted layers of Devonian-Permian have been studied by such mineral x-ray diffraction quantitative analysis, field emission scanning electron microscopy, and isothermal adsorption simulations experiments. This study emphatically analyzed the influence of the organic geochemical parameters, mineral composition and microcosmic pore structure on gas-bearing characteristics. It can be concluded from these results that the adsorbed gas of Devonian-Permian, the Upper Paleozoic mainly exist in a large number of micro pore and nano pore within the organic matter, reservoir space of free gas is mainly composed of frame pores, dissolution pores, diagenetic micro-fractures and tectoclase in the depression of central and southeast Hunan. The adsorbed gas of shale sample is 0.63~2.17 cm³/g, on average 1.51cm³/g, and the adsorbed gas of coal sample of Longtan Formation is 19.28cm³/g in the depression of central Hunan; the adsorbed gas of shale sample is 1.24~2.12 cm³/g, on average 1.60cm³/g, and the adsorbed gas of coal sample of Datang Stage is 7.12cm³/g in the depression of southeast Hunan; The exploration of shale gas in Xiangye 1 Well is successfully finished and the natural deliverability is available. The maximum value of adsorbed gas of crushed coal sample from Xiangye 1 Well is up to 1.413 8 cm³/g, which indicated an grateful prospect of exploration of the shale gas in the study area. The adsorbed gas is mainly affected by the content of organic carbon, the content of clay mineral, the maturity of organic matter, pore size and specific surface area, which revealed a intrinsic link among the properties of the reservoirs, the composition of minerals, geochemical features and the gas-bearing characteristics of the reservoir. The research has gave the important guiding significance and practical value to the exploration and exploitation of the shale gas of the Upper Paleozoic in the depression of central and southeast Hunan.

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