Quantitative identification of coal-type gas and oil-type gas in source-mixed gas at the northern margin of Qaidam Basin

31 natural gases in the western Qaidam Basin of China were collected and analyzed for gas composition including light hydrocarbons (C5-C7) and carbon isotopic characteristics. Based on genetic type obtained from C1-C3 and C7 fractions, four types of gases are identified: oil-type gas, coal-type gas, biodegraded gas, and mixed gas. The oil-type gas is the predominant-type gas in the western Qaidam Basin; coal-type gas is mainly distributed in the Zhahaquan and Nanyishan fields; mixed gas is mainly in the Zhahaquan, Wunan, and Nanyishan fields; and biodegraded gas is mainly distributed in the Huatugou and Yuejinerhao fields. According to the empirical relationship between δ13C1 and the equivalent vitrinite reflectance (Ro, %) of source rock, the Ro values of gas range from 0.6% to 1.5%, with an average value of 0.9%. The generation temperatures of major reservoired hydrocarbons (GTMRH) calculated from the C7 components range from 115.6°C to 141.7°C, with an average value of 126.5°C. These two maturity indicators have relatively positive correlation and reveal that the maturity of gas increases from west to east in the southwestern Qaidam Basin. Moreover, combining GTMRH with the homogenous temperature of petroleum inclusions, it is inferred that major petroleum charge in the western Qaidam Basin mainly occurred during the late period of the Himalayan movement. Deep hydrocarbon fluid sources were found in the Shizigou, Yingdong, Zhahaquan, and Nanyishan fields; thus, the deep reservoirs of paleouplifts adjacent to the hydrocarbon-generating depressions are estimated as a favorable area for further exploration in the western Qaidam Basin.

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95/03478 Quantitative analysis of coal type gas and oil type gas in the mixed gas reservoir in the northwest boarder of Junggar basin

Fuel and Energy Abstracts ◽

10.1016/0140-6701(95)95125-o ◽

1995 ◽

Vol 36 (4) ◽

pp. 254

Keyword(s):

Quantitative Analysis ◽

Junggar Basin ◽

Mixed Gas ◽

Gas Reservoir ◽

Oil Type ◽

Coal Type

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Impact of Diagenesis on the Low Permeability Sandstone Reservoir: Case Study of the Lower Jurassic Reservoir in the Niudong Area, Northern Margin of Qaidam Basin

Minerals ◽

10.3390/min11050453 ◽

2021 ◽

Vol 11 (5) ◽

pp. 453

Author(s):

Wenhuan Li ◽

Tailiang Fan ◽

Zhiqian Gao ◽

Zhixiong Wu ◽

Ya’nan Li ◽

...

Keyword(s):

Physical Properties ◽

Oil And Gas ◽

Qaidam Basin ◽

Isotope Analysis ◽

Lower Jurassic ◽

Low Permeability ◽

Hydrocarbon Generation ◽

Northern Margin ◽

Pore Evolution ◽

Sandstone Reservoir

The Lower Jurassic reservoir in the Niudong area of the northern margin of Qaidam Basin is a typical low permeability sandstone reservoir and an important target for oil and gas exploration in the northern margin of the Qaidam Basin. In this paper, casting thin section analysis, scanning electron microscopy, X-ray diffraction, and stable isotope analysis among other methods were used to identify the diagenetic characteristics and evolution as well as the main factors influencing reservoir quality in the study area. The predominant types of sandstone in the study area are mainly feldspathic lithic sandstone and lithic arkose, followed by feldspathic sandstone and lithic sandstone. Reservoir porosity ranges from 0.01% to 19.5% (average of 9.9%), and permeability ranges from 0.01 to 32.4 mD (average of 3.8 mD). The reservoir exhibits robust heterogeneity and its quality is mainly influenced by diagenesis. The Lower Jurassic reservoir in the study area has undergone complex diagenesis and reached the middle diagenesis stage (A–B). The quantitative analysis of pore evolution showed that the porosity loss rate caused by compaction and cementation was 69.0% and 25.7% on average, and the porosity increase via dissolution was 4.8% on average. Compaction was the main cause of the reduction in the physical property of the reservoir in the study area, while cementation and dissolution were the main causes of reservoir heterogeneity. Cementation can reduce reservoir space by filling primary intergranular pores and secondary dissolved pores via cementation such as a calcite and illite/smectite mixed layer, whereas high cement content increased the compaction resistance of particles to preserve certain primary pores. δ13C and δ18O isotopes showed that the carbonate cement in the study area was the product of hydrocarbon generation by organic matter. The study area has conditions that are conductive to strong dissolution and mainly occur in feldspar dissolution, which produces a large number of secondary pores. It is important to improve the physical properties of the reservoir. Structurally, the Niudong area is a large nose uplift structure with developed fractures, which can be used as an effective oil and gas reservoir space and migration channel. In addition, the existence of fractures provides favorable conditions for the uninterrupted entry of acid fluid into the reservoir, promoting the occurrence of dissolution, and ultimately improves the physical properties of reservoirs, which is mainly manifested in improving the reservoir permeability.

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Petroleum accumulation history of Nanbaxian belt — Study of gas generation and fluid phase, northern margin of Qaidam Basin, West of China

Journal of Petroleum Science and Engineering ◽

10.1016/j.petrol.2019.03.060 ◽

2019 ◽

Vol 178 ◽

pp. 449-458 ◽

Cited By ~ 1

Author(s):

Deliang Fu ◽

Shixin Zhou ◽

Yu Ma ◽

Jing Li ◽

Guosheng Xu ◽

...

Keyword(s):

Qaidam Basin ◽

Fluid Phase ◽

Gas Generation ◽

Northern Margin ◽

History Of ◽

Petroleum Accumulation ◽

Accumulation History

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Geochemical Significance of Clay Minerals and Elements in Paleogene Sandstones in the Center of the Northern Margin of the Qaidam Basin, China

Minerals ◽

10.3390/min10060505 ◽

2020 ◽

Vol 10 (6) ◽

pp. 505 ◽

Cited By ~ 1

Author(s):

Guoqiang Sun ◽

Meng Wang ◽

Jiajia Guo ◽

Yetong Wang ◽

Yongheng Yang

Keyword(s):

Clay Minerals ◽

Chemical Weathering ◽

Qaidam Basin ◽

Sedimentary Environment ◽

Climatic Conditions ◽

Northern Margin ◽

Magmatic Arc ◽

Average Value ◽

Geochemical Significance ◽

Continental Magmatic Arc

The average thickness of Paleogene sandstones reaches about 3000–4000 m at the northern margin of the Qaidam Basin. However, the provenance and sedimentary environment of these sandstones are uncertain; thus, more comprehensive research is needed. Integrated research is conducted on the provenance and weathering process based on petrographic characteristics, clay minerals, and geochemical compositions of sandstones in the center of the northern Qaidam Basin. The results of lithofacies analysis show that the Paleogene sandstones were mainly derived from an active continental magmatic arc, subduction accretion, or a fold-thrust belt. The average illite content in the Paleogene clay minerals is more than 50%, followed by chlorite and smectite, which reflect climatic and environmental characteristics that were arid to semi-arid, whereas the characteristics of carbon–oxygen isotopes reveal a mainly freshwater sedimentary environment. The corrected chemical index of alteration (CIAcorr) is between 56.3 and 75.7, with an average value of 66.5. These results indicate that the provenance of the Paleogene sandstones in the center of the northern Qaidam Basin mainly formed under cold and dry climatic conditions and experienced limited chemical weathering with a small amount that underwent intermediate chemical weathering under warm and humid conditions.

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