Tectonic evolution of the Sichuan Basin, Southwest China

Numerous large gas fields with large proven reserves occur in the deep formations of Songliao Basin, NE China. However, some challenges remain as follows: (1) the main source rock is poorly studied and (2) the origins and genetic types of the natural gases are controversial. In this study, these problems can be addressed by the research of the paleoenvironments during shale deposition, the organic matter sources, the source rock potential, the gas origin and genetic type, and gas–source correlations. The redox conditions of the water column during the Huoshiling to Yingcheng depositions were transitional (suboxidizing to subreducing) environments, and the Huoshiling deposition corresponded to reducing conditions. The paleosalinity of water was brackish to fresh from Huoshiling to Yingcheng depositions. The organic matters of the Huoshiling–Yingcheng shales mainly originated from terrigenous and/or lacustrine materials. The shales are evaluated as the fair to good source rock potential, and the Huoshiling is the best. The gases in the Huoshiling and Shahezi were mainly organic and thermogenic origins, with some inorganic origins. The gases of organic origins are mainly the mixed sources of coal-derived and oil-associated gases and are predominant products of secondary cracking, suggesting the well gas exploration potential in deep formations of Songliao Basin. The gases in the Shahezi formation are predominantly sourced by the Shahezi shales, indicating an approaching-source accumulation. 

Characteristics of Source Rocks and Genetic Origins of Natural Gas in Deep Formations, Gudian Depression, Songliao Basin, NE China

The Zhang 22 well was drilled in the Ordos Basin, penetrating the Chang 7 Member of the Triassic Yanchang Formation, which, cumulatively, has more than 80 m (>260 ft) of black organic-rich shale of oil window maturity. Using 76 samples collected every 1 m (3 ft) from the well, the effects of stratigraphic fractionation and petroleum expulsion within five intervals of the Chang 7 shale were qualitatively and quantitatively documented. The organic-rich intervals 1, 2, and 5, having an average total organic carbon (TOC) of 6.79 wt. % and pyrolyzable hydrocarbon potential of 9.40 mg/g rock (i.e., the amount of hydrocarbons generated by pyrolysis between 300°C and 650°C [S2]), are defined as “generative units” in the Chang 7 shale system, compared to the “in-source reservoirs” or “sweet spots” (i.e., the third and fourth intervals), which contain a lower average TOC of 4.19 wt. % and an average S2 value of 7.17 mg/g rock, but the highest amount of free oil (average total oil of 7.35 mg/g rock). Geochemical and molecular compositions display distinctive differences between samples from these source and reservoir groupings. For example, bitumens from the generative units proportionally possess lower saturated hydrocarbons (56%–66%) than those from the in-source reservoirs (up to 81%). The proportions of aromatic and polar compounds in the generative units are accordingly higher than in their counterpart. The individual molecular weight distribution of sample extracts displays more light-end moieties being enriched in the generative units. By applying the compositional mass balance calculation, the overall and compound-specific expulsion efficiencies in the in-source reservoirs are abnormally negative compared to the positive values in the generative intervals. This finding, in conjunction with the effects of the preferential retention of aliphatic hydrocarbons and the differential expulsion of light molecular weight compounds in the in-source reservoirs, indicates a short-distance intrasource migration of generated petroleum into the sweet-spot intervals (intervals 3 and 4) from the overlying units (intervals 1 and 2) and the underlying interval 5. Furthermore, when quantifying the total amount of retained petroleum in the shale system, an amended assessment has been introduced to overcome the systematic misestimations if only unextracted values for the amount of thermally extractable hydrocarbons volatilized at 300°C (mg HC/g rock) were considered. Thus, the oil crossover effect, temperature at which the rate of S2 generation is at maximum shift phenomenon, and the hydrogen index being shifted to higher values after extraction all account for identifying intervals 3 and 4 as the in-source reservoirs. In this study, we have not only identified a set of promising in-source targets for shale oil exploration and production, but we also presented the chemical and molecular composition for these shale oils. We have additionally speculated for the intrasource migration model and further discussed the different expulsion efficiencies in the shale system upon the compositional mass balance calculation as well as the stratigraphic fractionation on differentiating the chemical compositions during migration. The improved oil quality by fractionation, the extra storage potential derived from microfossil quartz, the weak adsorptive affinity of oil to organic matter, and the good shale susceptibility to hydraulic fracturing all give a promising prospective for exploring and producing shale oil from the Chang 7 shale system in the Ordos Basin.

/pdf/oil-retention-and-intrasource-migration-in-the-organic-rich-t3lmr514dw.pdf

Oil retention and intrasource migration in the organic-rich lacustrine Chang 7 shale of the Upper Triassic Yanchang Formation, Ordos Basin, central China

Generation and expulsion process of the Chang 7 oil shale in the Ordos Basin based on temperature-based semi-open pyrolysis: Implications for in-situ conversion process

Pore structure of Triassic Yanchang mudstone, Ordos Basin: Insights into the impact of solvent extraction on porosity in lacustrine mudstone within the oil window

Geochemical characteristics of the Triassic Chang 7 lacustrine source rocks, Ordos Basin, China: Implications for paleoenvironment, petroleum potential and tight oil occurrence

Handle everyday research tasks with reliable, citation-backed results

Your personal Research Agent to handle research tasks with citation-backed results

Popular Tasks used by Researchers

How can I help with your research?

Meet SciSpace

Get more enhanced response by uploading the PDFs you want me to reference.

No relevant PDFs in your library

SciSpace is the AI research assistant for academics. Run systematic literature reviews on 280M+ papers, and write papers with cited sources. Trusted by 1M+ students, PhDs & researchers.

SciSpace | AI for Research

Analyze PDFs

Code & Manuscripts

Funding & Grants

Literature & Patents

Medical & Clinical Data

Systematic Review

Visualize & Present

Web & Data

Build a Google Scholar-like website for your research.

Build a website

Create charts and images for your research

Create a Chart

Write a paper for submission to a journal

Draft a manuscript

Patent Search

Design eye-catching scientific posters in minutes.

Scientific Poster Generation

Systematic Literature Review

One task is running at the moment. Your messages will be shown right after.

Drag and drop or click here to browse

Loved by <highlight>1 million+</highlight> researchers

Extract a list of specific topics and their sources from unstructured text

Topics

Compare and analyze relevant papers that matches with your search

Papers

Get insights from PDFs and bookmarked papers from your library

My library

Recent searches

Try searching for:

Catch AI-generated content in scholarly and non-scholarly content

{ai} Detector

Ai Writer

Get PDF Summaries, highlighted text explanations 

Chat with PDF

Effortlessly create in-text citations and bibliographies in APA and 2,500 other formats

Citation generator

Get explanations, summaries, and answers on academic papers

Ease up your research workflow with {scispace}'s cohort of exciting AI tools

Elevate your academic writing skills and convey your ideas the way you want

Paraphraser

Explore our range of reading and writing tools

Your file is being prepared and should be ready in a few minutes. If it's a large file, it might take a bit longer. You can close this window, and we'll email you the file when it's done.

You have reached a maximum limit of <strong>{limit}</strong> columns in the table. Remove at least <strong>1</strong> column to add or create another one.

Benjieming Liu

Author Tools

Chat about Author

Papers

Geochemical characteristics of the Triassic Chang 7 lacustrine source rocks, Ordos Basin, China: Implications for paleoenvironment, petroleum potential and tight oil occurrence