Monday, 2 December, 2024 / Edition 36

The shale revolution of the past 15 years has turned the Permian Basin of Texas and New Mexico into one of the most prolific petroleum basins in the world. This super-basin currently produces 6 million barrels of oil per day. I came across several interesting papers on the Permian Basin in recent issues of AAPG Bulletin, which I would like to highlight in this edition of Core Elements. Incidentally, my two-year (volunteer) tenure as an associate editor for the AAPG Bulletin ends this month. Huge thanks to my colleagues who keep this journal lively and useful for the community.

Rasoul Sorkhabi

Editor, Core Elements

Induced Seismicity in the Permian Basin

GB Hart/Shutterstock.com

First, let’s take a look at an article written by Peter Hennings and Katie Smye, covering the “knowns, questions, and implications of induced seismicity in the Permian basin.”

History: Induced earthquakes associated with oil and gas production, oil-field water and carbon dioxide flooding for enhanced oil recovery, and wastewater disposal by injection in the Permian Basin date back to the 1960s.

The shale revolution in the region has accelerated these processes at unprecedented rates.

Earthquake clusters: An important observation is that as stress is built up on pre-existing faults, seismic events cluster, associated with earthquake-to-earthquake stress interaction and fault-to-fault activity interaction. This results in spatially and temporally distinct earthquake groupings.

By the numbers: The recent concern around induced seismicity comes mainly from wastewater injection into subsurface formations at multiple levels, thus reactivating basement-rooted faults with frequent and high-magnitude earthquakes.

• Since 2009, shale production has required disposal/injection of about 45 billion barrels of coproduced wastewater in the Permian basin.

• The petroleum industry now handles an estimated 15 million barrels per day of wastewater in the basin.

• Water injection has caused pre-existing faults to slip, producing more than 4,000 magnitude +3.0 earthquakes and 10 magnitude + 5.0 earthquakes as of October 2024.

• Induced seismicity on the most sensitive faults has occurred as distant as 40 kilometers from the deep injection site.

After effects: Wastewater injection in the Permian has caused:

1. Reservoir pressurization

2. Fault reactivation and high rates of induced earthquakes

3. Uplift of the ground surface

4. Threats to the surface environment

Monitoring: Earthquakes in the Permian Basin region are cataloged by the:

• Texas Seismological Network (TexNet)

• New Mexico Tech Seismological Observatory (NMTSO)

• U.S. Geological Survey (USGS)

Better data: With an increasing number of seismometers, uncertainty in depth of earthquake has reduced from 1.8 kilometers in 2017 to 1.0 kilometers in 2023, and uncertainty in XY coordinates decreased from 1.0 kilometer to 0.5 kilometers, according to TexNet’s earthquake catalog.

Recent regulatory work: According to the researchers, “Petroleum regulators in Texas and New Mexico collaborated with operators of injection wells to reduce the rate of injection into deep strata beginning in late 2021, leading to a reduction in the rate of cataloged earthquakes and indicating that retroactive mitigation works in reducing the seismic hazard.”

Go deeper: Read the full article here. You can also read all six articles on induced seismicity in the Midland basin in AAPG Bulletin’s Special Edition for December here.

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Beef Calcite Veins in the Wolfcamp Shale

Calcite veins courtesy of GB Hart/ Shutterstock.com

Have you ever heard of “beef calcite veins?” They are bedding-parallel veins of fibrous calcite found in shale formations with low permeability and high organic content.

This recent article reports on the age and temperature determination of beef calcite veins in the Wolfcamp Shale in the Delaware Basin, the western portion of the Permian.

Why it matters: The Wolfcamp Shale (lowermost Permian age) is the most productive oil formation in the Permian Basin, and understanding its thermal history helps us better quantify its petroleum system evolution.

Findings:

• U-Pb discordia age for the beef calcite vein was determined to be 152.9 ±53.1 Ma (large statistical uncertainty due to high common lead and low uranium).

• The temperature of Wolfcamp beef calcites by clumped isotope thermometry ranges from 142 C to 162 C.

• The consistency between beef calcite temperature range and organic thermal maturity from pyrolysis data indicates vein precipitation at basin thermal maximum in the Mesozoic.

• Peak hydrocarbon generation occurred during the Mesozoic, resulting in overpressure in the formation and followed by precipitation of beef calcite veins.

• The overpressure in the formation persists today.

What’s next: More sample analyses using several techniques will better constrain the thermal history of the Wolfcamp Shale.

Go deeper: Read the full article online.

Quiz of the Week

Last week’s quiz was: The terms geology, geoscience, and Earth Science are sometimes used interchangeably. But they have subtle differences. How do you distinguish the terms geology, geoscience, and Earth science?

Here is how I would answer: Geology deals mainly with the solid earth—its minerals, sedimentary strata, rocks, rock deformation, fossils, evolution, processes, and resources. Geoscience(s) includes geology as well as geochemistry and geophysics. Earth Science(s) includes all physical sciences dealing with the Earth—geoscience(s), atmospheric science, and oceanography.

Now, for this week’s quiz question: What is the largest conventional oil field in the world in terms of reserves and production? Where is it located? What are its producing reservoirs?

Please send your response by December 5 to editorial@aapg.org (subject line: Core Elements Quiz).

Correction: In last week’s edition, “marble” was incorrectly stated as a “sedimentary rock” (I meant to write “meta-sedimentary”). Several readers wrote to mention that marble is a metamorphic rock; yes, that is correct. Thank you very much for your notes and emails. 

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