Monday, 21 April, 2025/ Edition 55

Last week, we covered research around organic-rich mudstones and petroleum generation in deepwater environments—a topic that is important for global carbon-sink and petroleum system analyses. In this edition, I will share even more recent studies and new initiatives by Chinese scientists. Let’s take a look.

Rasoul Sorkhabi

Editor, Core Elements

China Invests in Deep Earth Research With Two New Initiatives

The JOIDES Resolution/ Photo by: Arito Sakaguchi & IODP/TAMU/ Wikimedia Commons

China has stepped into the deepwater scene with a new research vessel named Meng Xiang (“Dream” in Mandarin).

• This drillship, according to a report in Science, “can drill to a depth of 11,000 meters below sea surface compared with the United States’ JOIDES Resolution’s 8,385 meters and the 10,000 meters of Chikyu [Japan’s research vessel].”

• Meng Xiang already has 35 drilling projects scheduled through 2035.

Historical context: Since 1968, the United States’ National Science Foundation has been the world leader in drilling deep into ocean rocks for scientific discoveries. This was made possible by two drillships:

• Glomar Challenger, which was the main vessel for the Deep Sea Drilling Program (DSDP) from 1968 to 1983.  

• JOIDES Resolution, which was used for cruises in the subsequent ocean drilling programs from 1985 to 2024.

Last year, JOIDES Resolution completed its Expedition 403 and retired because of “budget crunch, the end of an international agreement, and the pending expiration of the ship’s current environmental impact statement,” according to the NSF.

SinoProbe II: Another Chinese initiative is the ambitious SinoProble II project launched by China Geological Survey. The project is a follow-up to SinoProbe I, which ran from 2008 to 2016.

According to Science, this year Chinese scientists “will deploy thousands of instruments and drill holes to record-hitting depths, all with the goal of creating a 3D map of the rock layers kilometers below the surface.”

Project goals:

• SinoProbe II aims to map ore deposits and fossil fuels to depths of 3,000 meters.

• Starting in 2027, SinoProbe II will drill wells more than 10,000 meters deep.

• The goal is for China be to be self-sufficient in these mineral and energy resources.

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Ultra-Shallow Gas in Ultra-Deep Waters

Dugguphotovala/ Shutterstock.com

An article in Petroleum Exploration and Development reports on the Lingshui 36-1 field—the first ultra-shallow gas field in an ultra-deepwater basin in China. This study compares ultra-shallow gas accumulations in ultra-deepwater with those in shallow shelf environments.

Basin and field details:

• The Lingshui 36-1 is in the Qiongdongnan Basin in the northern part of the South China Sea.

• The gas field has proven reserves of 100 billion cubic meters, which is 99 percent methane. It is located at water depths of 1,500 to 1,700 meters.

• The basin is a Cenozoic rift basin, sitting atop the Mesozoic basement. It covers an area of 80,000 square kilometers.

Reservoirs: The Quaternary-age Ledong Formation is a submarine fan consisting of siltstone and argillaceous sandstone.

• Two pay zones, L2 and L3, are in the Lingshui 36-1 gas field.

• They contain porosities of 26–48 percent.

• The mud-rich rock type is different from sand-rich reservoirs deposited on the continental shelf.

Natural gas generation: Stable carbon isotope ratios indicated that the natural gas in Lingshui 36-1 field includes thermogenic gas, migrated from deeper parts of the basin, as well as biogenic gas generated at shallow parts.

Source rocks: Oligocene-age Yacheng and Miocene-age Lingshui mudstones, with total organic carbon values of 0.4 to 2.1 percent, and kerogen types II and III, generated the thermogenic gas. 

Migration paths: Pathways for gas migration into the shallow reservoir include vertical fractures, gas chimneys, and lateral routes such as unconformity surfaces and sand carrier beds.

Seal rocks: Unlike the continental shelf, in which the cap rock is mainly low-permeability clay-rich sedimentary rocks, in ultra-deepwater basins, the cap rock is more diverse and includes deep-marine mudstone sediments, mass transport deposits, and gas hydrate layers.

Go deeper: Read the full article.

Asphaltenes in Petroleum Generation and Correlation

Dong fang/Shutterstock.com

A recent article in AAPG Bulletin describes a new method to use asphaltenes in petroleum for correlation of petroleum source rocks in a basin.

About asphaltenes:

• These are the most aromatic, solid, and heavy hydrocarbon compounds. They make up as much as 40 percent of crude oil and 80 percent of bitumen.

• Asphaltene pyrolysates are diagnostic of the parent kerogen in source rocks because they inherit the original kerogen structure and thermal conditions at the time of petroleum expulsion from the source rock.

New method: Researchers from the China University of Geosciences analyzed the pyrolysis products and phase kinetic differences of two shale samples from the Qianjiang Formation in the onshore Jianghan Basin.

Background: In a 2024 study, the same researchers established that these two shale samples represented a source-rock and hybrid source-reservoir rock within the Qianjiang Formation. This indicated intra-formational migration of petroleum in Qianjiang.

New findings:

• Researchers have developed a method named thermo-vaporization/pyrolysis two-dimensional gas chromatography time-of-flight mass spectroscopy (Tvap/Py-GCxGC-TOF-MS) for oil source correlation. (Anyone with a shorter/better idea for a name? It’s definitely needed here).

• The method identifies differences in the composition of pyrolysis yields from asphaltenes, resins, and thermally extractable free petroleum.

• Asphaltene is least overprinted by migrated oil; therefore, its covalently bound biomarkers can be diagnostic of oil source.

Why it matters: This method may be applied to other shale oil systems to examine intra-formational migration of oil. As a new method, it deserves further studies and development.

Go deeper: Read the full article.

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✉️ To get in touch with Rasoul, send an email to editorial@aapg.org.