Geochemical characteristics of the coal from lower-middle jurassic in eastern Junggar Basin and the generation of low-maturity gas

The resource of low maturity gas in eastern Junggar Basin is abundant, and its formation mechanism and source material are the main difficulties and emphases in researches. With Rock-Eval, TOC, RO and GC-MS, saturated and aromatic hydrocarbons are analyzed. The geochemical characteristics of the low-maturity coal in the Middle Jurassic Xishanyao Formation and Lower Jurassic Badaowan Formation in eastern Junggar Basin were systematically studied. The vitrinite reflectance values range from 0.47% to 0.73%, with an average of 0.63%, suggesting the source rocks have entered low-mature stage. Furthermore, the coals are type III organic matter that mainly comes from vascular plants. The results of source rocks evaluation indicate that samples have a great gas-prone. As an important material basis for gas formation, a series of compounds coming from resinites have been detected in saturated and aromatic hydrocarbons. Moreover, saturated hydrocarbons contain abundant benzohopanes, iso-(2-methyl) and anteiso-(3-methyl) alkanes, pristine and phytane, and high abundance is evidence for slight-moderate biodegradation. Besides, the high abundance of diasteranes could also confirm that clay materials have catalyzed the source rocks at low-maturity. Previous research showed that the biodegradation and the catalysis can decrease the activation energy of hydrocarbon, which is beneficial to gas generation at low mature stage. ©, 2015, Science Press. All right reserved.