Tuesday, 20 October 2026

Last week was the annual Earth Science Week, put on by the American Geoscience Institute. This year’s theme was “Critical Minerals for a Thriving Society.” Critical minerals is a field that highlights the significance of what geoscientists do and a great opportunity to promote public understanding of geoscience! You can learn more about Earth Science Week and view its corresponding resources here.

Now, let’s look at some new studies of reservoir porosity and shale reservoirs.

Rasoul Sorkhabi

Editor, Core Elements

New Insights Into Shale Porosity, Pore Geometry, and Permeability

Magnetotelluric survey lines, Guizhong Depression, China (Interpretation, 2026)

Pore geometry and porosity have critical control within the storage and volume of hydrocarbons in reservoirs. Two recent papers on this topic in AAPG Bulletin caught my eye.

Study #1. A Nondestructive Method for Shale Porosity Measurement

A group of Chinese scientists examined how nuclear magnetic resonance (NMR) can help estimate shale porosity without destroying rock sample.

How to measure rock porosity:

1. Image processing of thin sections, transmission electron microscopy (TEM), and focused ion beam-scanning electron microscopy (SEM)
2. Fluid injection methods using probes (helium or mercury), fluid saturation (water immersion or gas adsorption), and mercury intrusion capillary pressure
3. Radiation-based techniques

How NMR works: The researchers propose an improved NMR technique for shale rock porosity measurements.

• The method, called Shale-PorosityT1/T2, detects the amplitude of NMR response signals from internal shale fluids.
• It combines longitudinal relaxation (T1 spectra) and transverse relaxation (T2 spectra) for shale porosity.
• First, T1-T2 spectral-based fluid classification chart and calibrated conversion relationships are established.
• Core samples are stored in liquid nitrogen-cooled, high-pressure sealed vessels.
• The first measurement is the residual fluid porosity (porosity I) in conventional core samples after surface exposure.
• Then, the fluid porosity (porosity II) in pressurized, saturated shale samples is measured.
• Total porosity is then obtained by combining the results of porosity I and II.

Case study:

• The method was applied to core samples from the Eocene-age Shahejie Formation in Dongying sag of the Bohai Bay Basin in China.
• The total porosity of 15 samples ranged between 2.24 percent and 8.00 percent, with a mean value of 4.22 percent.

How NMR was discovered: The physicists who discovered NMR did not have foreknowledge of its applications. Neil deGrasse Tyson explains this well in the linked video.

Study #2. Pore Geometry of Barra Velha Formation in Santos Basin

Scientists from Brazil recently reported on pore geometry and permeability estimation of carbonates from Barra Velha Formation in the offshore Santos Basin.

Basin and reservoir:

• The Barra Velha Formation is a Lower Cretaceous-age sub-salt carbonate reservoir deposited in the post-rift sag stage during the opening of the South Atlantic Ocean.
• Cretaceous-age subsalt plays in the Santos, Campos, and Espírito Santo basins offshore Brazil may contain recoverable hydrocarbon resources of up to 100 billion barrels.

What they did:

• Mansini and colleagues applied digital image analysis to 355 blue-epoxy-impregnated thin sections to quantify total optical porosity and pore geometry of the reservoir
• They also estimated the permeability using the Kozeny equation.

What they found:

• The study found five sedimentary facies within the Barra Velha Formation.
• Facies 1, 2, and 4 show higher porosity and permeability associated with inter-particle and vuggy pore systems.
• Facies 3 and 5 have lower permeability due to diagenetic modification.

Register Now: The West African Margin

West Africa continues to attract attention across the global energy industry, with new exploration activity, evolving plays, and advances in geoscience, technology, and market analysis.

Join AAPG for a webinar that takes a deep dive into the factors shaping the region’s energy landscape.

📢 Featured speakers:

• Rasoul Sorkhabi, geologist, geoscience professor at the University of Utah, and editor of Core Elements

• Benedict Geaghan, Global Business Development Manager at SLB
• Justin Cochrane, African Upstream Regional Research Director at S&P Global

📆 29 October at 9:00 a.m. CT

Magnetotelluric (MT) Survey of Shale Gas Plays

Evolution of a Pleistocene slope channel in Niger Delta (Interpretation, 2026) 

Currently, seismic methods are the main geophysical surveying methods for oil and gas basins.

A group of Chinese geophysicists published a paper in Interpretation that proposes the magneto telluric (MT) method for investigating a shale gas play in China.

Study area:

• The survey was conducted in the Guizhong Depression at the intersection of the Yangtze and Cathaysian blocks in southern China.
• The target reservoir was a shale unit within the Lower Carboniferous-age Luzhai formation.
• The shale has total organic carbon of 3 to 12 percent.

Study methods: The researchers used:

• Three MT survey lines with a total 127 survey points using the instruments and software from Phoenix Geophysics, Canada for data acquisition, processing, inversion, and modeling
• Regional gravity and magnetic data
• Borehole data
• Basin modeling
• Outcrop geology

Survey design:

• The MT survey, based on deep electrical properties, mapped the spatial distribution of the target formation together with fault structures with throws of 40 to 500 meters.
• The survey also mapped various resistivity layers corresponding to the entire Lower Carboniferous lithologies in the basin.
• The target Lushai shale yielded the lowest resistivity range of 100- 500 ohm-meters and a thickness of 200–500 meters, buried 300–3,000 meters deep.

Best Bulletin Articles For 2024 Awarded

From left: Daniel Minisini, Patricio Desjardins, Elizabeth Horne

AAPG has announced the Wallace Pratt Memorial Award for the best paper published in the AAPG Bulletin for 2024.

The winning paper is: “Application of a deep-water stratigraphic framework to the production of the Wolfcampian units in the Permian Basin” by D. Minisini and P. Desjardins, AAPG Bulletin, January 2024.

Additionally, the J. C. “Cam” Sproule Memorial Award was given to the best article written by an author younger than 35 years old. The winner is: “Interpretation, characterization, and slip hazard assessment of faults in the Midland Basin, west Texas, United States” by E.A. Horne, O. Hennings, K.M. Smye, A.Z. Calle, A.P. Morris, and G.C.D Huang, AAPG Bulletin, December 2024.

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