Geochemical characteristics and genesis of crude oils from Gasikule oilfield in Western Qaidam Basin, China

Abstract

The Gasikule oilfield, including a deep layer E 3 1 and a shallow layer N 2 1 pool, is the largest one in the Qaidam Basin and its crude oil output accounts for 80% of total oil output in the basin. In order to understand the genetic mechanism of crude oils from this oilfield, crude oils from both E 3 1 and N 2 1 pools in the Gasikule oilfield were collected and analyzed using gas chromatography and gas chromatography-mass spectrometry. The geochemical characteristics of biomarkers in the crude oils were synthetically studied. The biomarker compositions indicate that the crude oils were derived from strong anoxic and saline-hypersaline lacustrine environment with a dominance of algal organic matter. It was also observed that the ancient salinity of the sedimentary environments of the source rocks for the N 2 1 crude oils was slightly higher than that for the E 3 1 crude oils. The E 3 1 crude oils were derived mostly from bacteria whereas the N 2 1 crude oils originated mostly from plankton. The maturity parameters of biomarkers reflect that the crude oils were low mature. The maturity of the E 3 1 crude oils was slightly higher than that of the N 2 1 crude oils. These results, together with research of crude oil formation, show that the N 2 and E 3 1 crude oils were yielded from free biological lipids, extractable organic matters and kerogen in the Tertiary source rocks deposited under an anoxic and saline-hypersaline environment at the stage of low maturity.

Distribution and geological significance of 17α(H)-diahopanes from different hydrocarbon source rocks of Yanchang Formation in Ordos Basin

“…Because the Mesozoic crudes in the Ordos Basin generally show multiple distribution horizons, large distribution scope, singular genetic type, and all belong to lacustrine oil type [18][19][20][21][22] , and hydrocarbon generation rocks of I-II 1 types were developed in different scales in Chang 4+5-Chang 9 members of the Yanchang Formation, detailed division of and correlation among lacustrine oil types, as well as accurate determination of dominant hydrocarbon source rocks and their relationships with reservoir groups in various regions and various reservoirs, are issues awaiting urgent solutions in petroleum exploration. The discussion as formulated in this study could provide an effective approach for final solutions to these issues.…”

Large‐scale distribution of bacterial communities in the Qaidam Basin of the Qinghai–Tibet Plateau

“…Because of its richness in natural resources, studies of the microbial communities in the Qaidam Basin have mostly focused on salt lakes and gas fields. These studies focused exclusively on microbial communities and diversity in the salt lakes by isolating halophilic bacteria and studying microbial activity related to the formation of water and gas (Chen, Shuai, Osadetz, Hamblin, & Grasby, ; Duan et al, ; Han et al, ; Jiang, Xue, & Ma, ; Shen, ; Wang et al, ; Zhao et al, ). Soil microbes play an important role in maintaining soil quality and influencing nutrient availability.…”

Origin, migration and secondary processes of oil and natural gas in the western part of the Polish Outer Carpathians: geochemical and geological approach

“…The sulphur concentration below 0.5 wt%, mostly at gravities below 40 °API suggests a connection of the analysed oils with the low-sulphur type II kerogen (Orr 2001). However, generation from type III or type I kerogen is also possible (Duan et al 2009). The CPI values above 1.0 indicate that shales are the dominating source of rock lithology (Moldowan et al 1985).…”