--> --> Abstract: A Fractured Deep Basin Gas Accumulation Model in Eastern Kuqa Depression, NW China, Evidence from Fluid Inclusion Observations, by Zhuo Li, Zhenxue Jiang, Xiaoshi Li, and Feng Li; #90180 (2013)

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A Fractured Deep Basin Gas Accumulation Model in Eastern Kuqa Depression, NW China, Evidence from Fluid Inclusion Observations

Zhuo Li1,2, Zhenxue Jiang1,2, Xiaoshi Li3, and Feng Li1,2
1State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing, China
2Unconventional Nature Gas Institute, China University of Petroleum, Beijing, China
3University of Chinese Academy of Sciences, Beijing, China

The lower Jurassic Ahe Formation in the Kuqa Depression, NW China, is considered a deep basin gas accumulation in which high pressure gas in response to gas generation charge of the low-permeability sandstone occurs under high pore-fluid pressure water layers. This view contrasts with that of other models of low-permeability gas reservoirs in which gas migrates by buoyant drive and accumulates in conventional traps, with fractures an incidental attribute of these reservoirs. The deep basin gas accumulation model in the Kuqa Depression is discussed by determining the timing of fracture growth and associated temperature, pressure, and fluid-composition conditions using microthermometry and Raman microspectrometry of fluid inclusions trapped in fracture cement that formed during fracture growth. Trapping temperatures of aqueous fluid inclusions record systematic temperature trends that increase from approximately 110 to 135°C, which indicates fracture growth during maximum burial conditions. Calculated pore-fluid pressures for methane-rich aqueous inclusions of 115 to 180 MPa indicate fracture growth under near-lithostatic pressure conditions consistent with fracture growth during active gas maturation and charge. Such a process is consistent with gas generation within the Ahe Group or by gas charge from deeper source rocks along fracture but is inconsistent with significant high-pressure generation by compact ion disequilibrium during earlier stages of burial. The results demonstrate that protracted growth of a pervasive fracture system is the consequence of gas maturation and reservoir charge and is intrinsic to deep basin gas reservoirs.

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