Tuesday August 25, 2026  Edition 122

Last week, I attended the IMAGE conference in Houston, Texas. About 8,000 geoscientists gathered under one roof and talked about the latest findings, challenges, and prospects related to energy exploration and development. I came back hugely inspired, gratified, and honored as I was one of those who were presented an AAPG Award this year.

For this issue of Core Elements, I have chosen to discuss faults in petroleum basins. Coming from a structural geology background and as co-editor of AAPG Memoir 85, faults are close to my heart. The British geologist H. H. Read famously said that the best geologist is the one who has seen most rocks. He also said: Know your faults!

So here we go! Let’s try to better understand faults in our basins.

Rasoul Sorkhabi

Editor, Core Elements

Fault Seals in the Bohai Bay Basin

Faults in Bohai Bay Basin (AAPG Bulletin, May 2026)

Fault seals used to be a hot topic in the 1990s and 2000s. Not much groundbreaking work has been published in the past 15 years. It is thus encouraging to see a case study of fault sealing in a recent issue of the AAPG Bulletin.

Basin setting: The study concerns the Paleogene-Oligocene normal faults in the Bohai Bay rift basin in east China.

What they did: Song and colleagues analyzed:

• 3D seismic image data
• Well logs
• Structural maps
• Stratigraphic data
• Production test data

What they found:

• Normal faults have behaved as lateral seals supporting hydrocarbon columns as high as 83 meters and buoyancy pressures up to 0.23 megapascal.
• Theoretical hydrocarbon heights calculated from shale-gouge ratio are less than 5 meters, much lower than the actual hydrocarbon column heights sealed by the faults.
• The rocks involved in faulting have low clay content (less than 10 percent), high porosity (more than 15 percent), and moderate burial depths (1 to 3 kilometers).
• The researchers suggest that fault cataclasites have created an effective low-permeability seal.

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A New Seismic Method for Fault Detection

Seismic image with faults, Sichuan Basin (Interpretation, August 2026)

Enji Wang and colleagues discuss a new method for detecting faults on seismic images in the August issue of Interpretation.

Traditional methods: Faults cause discontinuities in seismic amplitudes, which form the basis for several detection methods:

• Variance: Calculation of the normalized correlation coefficient of amplitudes from adjacent seismic traces
• Similarity: Computing similarity of multi-traces in 3D space
• Eigenstructure-based coherence: Calculating the eigenvalues of the covariance matrix of the multi-trace amplitude
• Curvature: Derived from various curvatures of the spatial surface formed by the amplitude
• Gradient structure sensor: Constructing a 2D gradient structure matrix from seismic amplitude and extracting its eigenvalues

Limitations of amplitude-discontinuity methods:

• It is difficult to image small faults that induce weak reflection anomalies.
• Highly sensitive seismic techniques may face interference from background noise.
• Spatial distribution of strike-slip faults is often too complex to image.

New method:

• The researchers offer a planar fault detection method based on seismic horizons.
• It uses the principle that the relative displacement of the same sedimentary layer on both sides of the fault plane is proportional to the local maximum standard deviation of the seismic horizon.

Workflow:

1. Extract the horizon surfaces from high-resolution 3D seismic data
2. Calculate the local standard deviation of the extracted surfaces
3. Extract fault features using a multiscale vessel enhancement filtering algorithm

New method limitations:

• More suitable for stable stratigraphic reservoirs with planar fault distribution
• Poor performance for reservoirs under compressive tectonic stress or basement reservoirs with few stratified layers
• Multiscale vessel enhancement filtering uses methodology from the anatomy of human vascular systems, but faults can be highly complex from one scale to another

Case study:

• The researchers applied amplitude and seismic horizon methods to seismic images in the Sichuan Basin onshore China.
• Target strata included shale gas reservoirs of the Wufeng Formation (Upper Ordovician) and Longmaxi Formation (Lower Silurian).

The bottom line:

• A combination of seismic amplitude and seismic horizons (time domain or depth domain of target layers) would better honor the geology.
• The new method is particularly useful to identify small-scale faults in shale formations.

Seismic Imaging of Faulted Reservoirs

Comparison of fault imaging methods (Interpretation, May 2026)

Asaka and colleagues address the problem of seismic imaging of faulted reservoirs in a recent issue of Interpretation.

Statement of the problem: Seismic imaging around faults is difficult because of:

• Fault shadow or image distortions caused by our inability to resolve the lateral velocity contrast across fault throws
• Noisy images caused by remaining diffracted multiples
• Image dimming or damaging primary events caused by overly aggressive multiple attenuation

Two standard solutions have been suggested:

1. Careful denoising to attenuate diffracted multiples
2. Fault-guided tomography to resolve the lateral velocity contrasts

New method: In addition to using the standard methods, Asaka and colleagues suggest a new imaging method based on multiparameter fault-waveform inversion (FWI).

Workflow:

1. Preparation of initial models for velocity, anisotropy, wavelet, etc.
2. Diving wave FWI with velocity update at 6 and 12 Hertz and to a maximum penetration depth of about 1.2 kilometers
3. Initial density model from smoothing of velocity from tomography
4. Multiparameter FWI imaging based on velocity and reflectivity (density) updates at 9, 12, 15, and 20 Hertz.

Case study:

• The researchers studied an offshore field in the Browse Basin in Western Australia, where a narrow-azimuth streamer (dual source, 10-streamer configuration) dataset almost perpendicular to the strike of main faults was available from TGS.
• The depth target was Jurassic strata at a depth of 5,000 meters and water depths of 290–430 meters.

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