Characteristics of Light Hydrocarbons of Tight Gases and its Application in the Sulige Gas Field, Ordos Basin, China

Abstract

Tight gas plays an important role in the unconventional natural gas, and the researches of origin and migration of tight gas is of great importance to find the "sweet spots" for exploration and development. Combining the carbon isotopic analysis with light hydrocarbon analysis, it is concluded that the Upper Paleozoic tight gases in the Sulige gas field, Ordos basin are typical coal-derived gas with δ 13C 2 values ranging from -25.3‰ to -22.1‰ (average value = -23.7‰). In addition, methycyclohexane enrichment and a small amount of benzene and toluene are observed in light hydrocarbon composition. The C 7 light hydrocarbons are predominated by methylcyclohexane accounting for 44% to 68% while the content of the naphthene and isoparaffin is relatively higher in C 5-7 compounds. According to the Mango parameters K 1 and K 2 , the Upper Paleozoic tight gases in the Sulige gas field are derived from the CarboniferousPermian coal measures. Besides, the light hydrocarbon parameters such as the content of aromatics, benzene/n-hexane, toluene/n-heptane and other light hydrocarbon indicators show little differentiation which is inferred that the Upper Paleozoic tight gases of the Sulige gas field accumulated near the source rocks without long distance migration. Hence, it is reasonable to regard the district nearby the coal measures as the "sweet spots" in the Sulige gas field.

Using Light Hydrocarbons to Identify the Depositional Environment of Source Rocks in the Ordos Basin, Central China

“…Gases from the Ordos Basin are rich in iso-alkanes ( Fig. 2b), confirming previous conclusions that upper Paleozoic gases in the basin are coal-derived (Yu et al, 2014). Notably, gases from all three Ordos fields strongly overlap in Figure 2, suggesting that either the source rocks were deposited in the same type of environment, or that the parameters are not useful in identifying different depositional environments.…”

Geochemical Characteristics of Shale Gas in Xiasiwan Area, Ordos Basin

“…For C 6 -C 7 compounds, Yanchang Formation shale gas is less than 2.5% in aromatics content, while Shanxi Formation gas is over 4.0% in aromatics content (Table 2). In the Ordos Basin, the aromatics content of conventional gas from Upper and Lower Paleozoic ranges from 2.7‰ to 12.3‰, 7.1‰ on average Yu et al, 2014), changing widest in the Ordos basin. As the aromatics are higher in solubility, and prone to rock and groundwater adsorption during gas migration, the triangular chart of C 5-7 aliphatic compounds is more commonly used to distinguish oil-associated gas and coal-derived gas ( Fig.…”

“…The differences of hydrogen isotopes in this study area are mainly controlled by sedimentary environment and maturity. The Mesozoic oil-associated gas in the Ordos Basin in fresh water lacustrine facies has a δDCH4 value range from -299‰ to -231‰ (Cao and Ni, 2007;Chen et al, 1995), while the conventional gas in Carboniferous-Permian coal measure strata in terrestrial and transitional facies has a δDCH4 value range from -214‰ to -167‰ (Chen et al, 1995;Feng et al, 2007;Yu et al, 2014). Since shale gas in the study area has higher maturity than that in most conventional gas well areas, its hydrogen isotope is more positive.…”

Hydrogen Production from Light Hydrocarbons

“…They are catagenic products, formed between 75 and 140 C. The higher hydrocarbons are too stable to generate the LHs at these temperatures. Additionally, LHs are different from cracking products [50]. Many are structurally like bio-precursors.…”