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Geochemical Characteristics and Geological Significance of Shale Gas from the Fifth Member of the Xujiahe Formation in West Sichuan De-pression

Author: ZouZuo
Tutor: ChenZhenLin
School: China University of Geosciences
Course: Geological Engineering
Keywords: Xujiahe formation Shale gas Geochemistry
CLC: P618.13
Type: Master's thesis
Year: 2011
Downloads: 727
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Abstract

With the enhancing of the exploration degree and further study on the unconventional gas, shale gas exploration and development has become the focus of the world. Shale gas is the natural gas which is found in shale formation with adsorption state and free form. The formation mechanism of shale gas is special, and formation condition is diverse. It is widespread development and wide distributed. The shale gas exploration is still in primary stage in China. In order to fully understand the characteristics of the shale in the study area, we can do some research about organic geochemistry in the shale rock. And it also can offer some foundation for shale gas exploration and constituency evaluation. This paper combined home and abroad shale gas material with the actual situation of the study area, and comprehensive analysis shale which is from the fifth member of the Xujiahe Formation in West Sichuan De-pression with some common organic geochemistry parameters. Until full understanding of the study area, find out some mathematical relationship between geochemistry parameters and electrical parameters, and determine mathematical model. So we can use the well logging data added the shortage of geochemistry data.The western Sichuan depression is a deep depression of Terrestrial Basin in west of Sichuan basin since Late Triassic and a foreland basin in the Longmenshan Nappe structure belt. Through the study of shale, the thickness of this layer is large, and nonmarine shale is mingled with tight sand. Combining the research results of the shale gas, the lower limit of organic carbon is 0.4% in the fifth member of the Xujiahe Formation in West Sichuan De-pression. In the study area, organic content is high, distributed in 0.5～6%, and the organic carbon content of over 95% sample is more than 1%, hydrocarbon-generating ability is strong. In horizontal, the organic carbon content of Longmenshanqian Structure increased gradually from the south to the north; In Nearly Latitudinal direction Structure, the organic carbon content increased gradually from the west to the east, and obviously, the center of hydrocarbon-generating is moving from west to east. In vertical, the organic carbon content became smaller from top to bottom. And the organic carbon content of the first layer and the second layer is better than above layer in the fifth member of the Xujiahe Formation. The organic material in shale is low satisfied hydrocarbon, low aromatic hydrocarbon, high nonhydrocarbon and asphaltene. The organic matter is dominated byⅢtype, including lessⅡtype, and it is mainly produce gas. The thermal evolution of organic matter in the study area is mature-high matural stage. RO distributed in 0.71～1.86%, Tmax distributed in 460～480℃. It is primarily high mature shale. The maturity of shale in Nearly Latitudinal direction Structure is higher than Longmenshanqian Structure, with great potential of hydrocarbon generation.We can analysis Ro、Toc、the buried depth、thickness of carbonaceous shale and thickness of shale in Longmenshanqian Structure、Nearly north-south Structure and Latitudinal direction Structure by radar map. The biggest exploration potential of shale gas area is Hexinchang and Fenggu, followed by is Yazihe.Acoustic travel time, resistivity logging and density logging are effect by mineral composition, clay concentration, compaction and other factors, so we must unite geochemistry target and well logging data. We can know a critical region of organic material type by GR-AC cross-plot. We can give a roughly evaluation about the type of source rocks by AC-DEN-RT cross-plot. And we can use well logging data of DEN and GR to calculate organic content.

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