--> --> Abstract: Accumulation Mechanism of Tight-Gas Sands in the 2nd Member of Xujiahe Formation, the Yinshan Structure, North Central Sichuan, China, by Haifeng Yuan, Yong Liu, Jin Qian, Xiao Wang, and Cheng Yang; #90180 (2013)

Datapages, Inc.Print this page

Accumulation Mechanism of Tight-Gas Sands in the 2nd Member of Xujiahe Formation, the Yinshan Structure, North Central Sichuan, China

Haifeng Yuan, Yong Liu, Jin Qian, Xiao Wang, and Cheng Yang
Chengdu University of Technology, Chengdu, Sichuan, China

The Yinshan structure is located in the central Sichuan region. This structure is a part of the rolling anticlinal structure belt in northern Sichuan and its gas pool in the 2nd member of upper Triassic Xujiahe formation is tight gas sands. But, the present exploration success rate of this gas pool is just 32%. The hydrocarbon source rocks from the gas pool is mainly black shale from the 1st member and 3nd member of Xujiahe formation. And the krogen type of the source rocks is type Ⅲ. The porosity of the reservoir is between 4.0% and 10.0%, with an average of 5.99%. The permeability of the reservoir is ranging from 0.0001×10-3μm2 to 0.80×10-3μm2, with an average of 0.103×10-3μm2. At present, the buried depth of this gas pool is between 2500-3000 meters and the trap type is structure-lithology traps. The phenomenon of the high position of the structure producing water and low position of the structure producing gas is quite ordinary, which is due to the uncompleted differentiation of gas and water in the reservoir. The cap rock of this trap is the overlying shale of 3rd member of Xujiahe formation.

In this paper, the methodology of Apatite Fission Track and Easy%Ro Chemical Kinetics Simulation has been used for the reconstruction of the thermal history and the hydrocarbon-evolution history of the source rock of the study area. Combined with the homogenization temperature of fluid inclusions analysis and ESR Dating, the accumulation periods and hydrocarbon accumulation mechanism of the 2nd member of Xujiahe formation gas pool of the Yinshan Structure is explored. The 2nd member of Xujiahe formation gas pool of the Yinshan Structure mainly experienced three important periods. The first period is during the Late Jurassic. The early hydrocarbon fluid primarily charged into the reservoir of the 2nd member of Xujiahe formation during this period; The second period is while the Mid-Late Cretaceous, which is main period for the hydrocarbon charging. In this period, a large-scale hydrocarbon fluid charged into the reservoir 2nd member of Xujiahe formation. The third period is since the late Cretaceous. During this period, the adjustment and transformation of gas accumulation in the 2nd member of Xujiahe formation is made by the tectonization. According to the results of apatite fission track analysis, the tectonic uplift of the central Sichuan region is at least 2400m since the late Cretaceous. And the formation and development of fractures is also due to the tectonization of this period. Mineral ESR dating results of fractures filling quartz demonstrates that the formation time of fractures is mainly in the Himalayan period, and that is also the final period for the formation of gas accumulation. This research shows that the reservoir in Yinshan Structure of the 2nd member of Xujiahe formation is the sweet points of development zone, and the zone of fractures will be the primary area for exploration in the future.

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