Maturity
Assessment Of Natural Gas In Tarim Basin: CH4/N2Ratio
As A Tool
Liu, Quanyou1, Bernhard M.
Krooss2, Jinxing Dai1, Wenhui
Liu3, Ralf Littke4 (1) Research Institute of Petroleum
Exploration and Development, PetroChina, Beijing,
China (2) Lehrstuhl für Geologie, Geochemie und Lagerstätten des Erdöls und der Kohle, RWTH-Aachen, Aachen, Germany (3)
Exploration and Production Research Institute, SINOPEC, Beijing, China (4)
Technical University of Aachen (RWTH), D-52056 Aachen, Germany
In this context, the bulk ratio of CH4
/ N2 is examined here as potential alternative geochemical parameter
for the assessment of gas sources and maturity and compared to other previously
used methods of maturity assessment of natural gas. Open-system non-isothermal pyrolysis of the low-mature coal from Manjiaer
Sag, Tarim Basin yielded generation
curves for CH4 and N2. Analysis of the change of vitrinite reflectance indicated a two-stage process of of thermal maturation with increasing temperatures. The
relation between Ro and pyrolysis temperature could
be expressed by the following equations: Stage I : Ro
= 0.0014T + 0.109, r2 = 0.9931(Ro<0.6%); Stage II: Ro = 0.0067T -
1.5855, r2 = 0.9996(Ro>0.6%). A kinetic interpretation of
nitrogen and methane generation characteristics of humic
coal during laboratory pyrolysis indicates that the
bulk ratios of methane and nitrogen as thermal maturity parameter may be
applied to assess the maturity of gas-sources. Thus, the maturity of the source
rocks of natural gases in Tarim Basin was expressed in terms
of the CH4/N2 ratios and compared with other geochemical
natural gas parameters, such as stable isotopes. The predicted results were
found to correlate well with published data of gas-source maturity in these
basins.