Kinetic Parameters of Methane Generated from Source Rocks and Its Application in the Kuqa Depression of the Tarim Basin

In a thermal simulation experiment of closed-system gold tube-high pressure vessels under a given pressure (50 MPa) and calculation with the specific Kinetics and GOR-Isotope Kinetics software's, kinetic parameters of gas generation and methane carbon isotope from Triassic—Jurassic source rocks in the Kuqa depression of the Tarim Basin are obtained. The ranges of activation energies of methane paralyzed from Jurassic coal, Jurassic mudstone and Triassic mudstone in the Kuqa Depression are 197～268 kJ/mol, 180～260 kJ/mol, and 214～289 kJ/mol, respectively. The frequency ratios are 5.265×10 13/s, 9.761×10 11/s, and 2.270×10 14/s. This suggests that there are different activation energies and frequency ratios for methanes generated from Jurassic coal, coal-associated mudstone and Triassic mudstone in the Kuqa Depression, and reflect their differences of hydrocarbon generation behaviors. The kinetic parameters of methane carbon isotope are also different in Jurassic coal, Jurassic mudstone and Triassic mudstone. Their average activation energies were 228 kJ/mol, 205 kJ/mol, and 231 kJ/mol, respectively. On the basis of the above research, combined with the geological background, the origin of natural gas in the Yinan 2 gas pool was further discussed using these kinetic parameters, and its gas accumulation model is thus established. The natural gas of the Yinan 2 gas pool was primarily derived from Jurassic coal-bearing source rocks at the center of the Yangxia Sag and generally belong to the staged accumulative gas. The Yinan 2 gas was mainly gathered at 5～0 Ma with a R o range of 1.25%～1.95% and lost about 25%～30%.