blogger counters

Friday, May 12, 2023

History of Oil-Finders Friday: South Texas Serpentine Plugs

 The 1915 headlines read, ‘Oil in an Igneous Rock,” which certainly piqued the curiosity of oil finders, used to displaying their porous sandstone and limestone cores, stained with oil, in their office display cases.

But, in South Texas, they had done it. They had found oil in a green igneous rock they dubbed “serpentine,” even though it was actually an altered tuff resulting from underwater volcanic eruptions.

Udden, J. A., and Bybee, H. P., and others, 1916

The adventure had started a year earlier. In 1914, Fritz Fuchs, a rancher deep in south Texas near the small town of Thrall, decided to drill a water well for his cattle. He did not encounter water, but at about 300 feet, he brought up a strange mix of oil, salt water, and what appeared to be weathered igneous rock, green in color. Mystified, he called the University of Texas geology department to see if they could shed light. The result was a well drilled in February 1915, which was the discovery well for the Thrall field, and the first of many so-called “serpentine plugs.”

At least one study has pointed out that the deposition of the tuffaceous mounds occurred in conjunction with submarine volcanic vents which emitted volcanic ash which then was deposited in the form of mounds, which subsequently altered to palagonite. The volcanic activity occurred with the deposition of chalk and marl of the upper Austin and lower Taylor Groups, which served as both source and seal. 

Interaction between the submarine volcanic system and carbonates

It turns out that all along a belt of volcanic activity, there were similar submarine volcanic eruptions and they became perfect reservoirs for oil generated in the adjacent source rocks. The stratigraphic traps were found in the porous zones of tuff, and also in porous zones in the surrounding carbonates, and in traps in sands draping over the serpentine plug, and in fracture porosity in the carbonates near the plugs (Loucks, 2022).

The wells could be incredibly prolific, with a feature covering less than 10 acres producing 100,000 barrels. Others were not as prolific. However, by 1986, more than 47 million barrels had been produced (Matthews, 1986).

The serpentine plugs are found associated with the volcanic centers that align with the pre-Tertiary Balcones and Luling regional fault and fracture systems. Some of the minerals in the tuffaceous mounds are magnetic, resulting in magnetic anomalies. 

Some of the minerals in the tuffaceous mounds are magnetic, resulting in magnetic anomalies. While the first oil-rich serpentine plug was discovered by accident, science was used to discover dozens of the features scattered along the belt of pre-Tertiary-age submarine volcanic activity. The fact that the features tended to be shallow and of dramatically different lithology than the surrounding carbonates, and that were often oil seeps, made it possible to use new methods, which included surface geochemistry, in which soil samples were taken, and plants observed to see if they were affected by hydrocarbons in the soil. Second, newly developed magnetometers were used. Most were truck-mounted, and they were able to detect anomalies by means of differences in the magnetic field.

Source: Loucks, 2022

The features were small, and it took a lot of patience to find them, but when they did, the wells could be extremely prolific. Ranging from just a few feet deep, to 5,000 feet deep, the wells were inexpensive to drill.

Today, with high-resolution drone-mounted magnetometers, and highly accurate surface geochemistry, it’s possible to revisit a fascinating play, which to this day is one of the few areas of the world where oil is found in igneous rocks.

I love this play, and I’m thrilled to have an original copy of the November 25, 1916 Bulletin of the University of Texas published by the Bureau of Economic Geology and Technology which is dedicated to the Thrall Oil Field. 


Loucks, R. G., R. R. Reed (15 April 2022) Implications for carbonate mass-wasting complexes induced by volcanism from Upper Cretaceous Austin Chalk strata in the Maverick Basin and San Marcos Arch areas of south-central Texas, USA. Sedimentary Geology. Vol 432. 

Matthews, T. F. (1986) The Petroleum Potential of "Serpentine Plugs" and Associated Rocks, Central and South Texas. Baylor Geological Studies Bulletin, Spring 1986.  

Udden, J. A., and Bybee, H. P., and others, 1916, The Thrall Oil Field, by J. A. Udden and H. P. Bybee [and] Ozokerite from the Thrall Oil Field, by E. P. Schoch [and] The Chemical Composition of the Petroleums Obtained at Thrall, Texas, by E. P. Schoch and W. T. Read: University of Texas, Austin, Bureau of Economic Geology and Technology, Bulletin 66, 93 p.

Friday, May 05, 2023

History of Oil Finders Friday: Dunkirk Black Shale Gas Well, 1825, in Fredonia, New York

In the 1820s in Fredonia, New York, William Aaron Hart, a local gunsmith long curious about the gas seeps emanating from the nearby Canadaway Creek, decided to investigate. According to a historical report, he first tested the gas by collecting it in a flipped-over washtub, inserting a gun barrel in a hole, and then lighting the gas as it flowed through the gun barrel.  

Encouraged, Hart started to investigate the origin of the gas seeps, and soon found that they were coming from what he referred to as “slaty rock,” which was later classified as the Dunkirk shale, an upper Devonian black shale, typified by prominent and numerous joints and fracture networks. Early geologists such as Lewis Caleb Beck (1798-1853) studied not only the geology and mineralogy, but the surrounding vegetation as well. 

The Dunkirk shale is a very low-permeability source rock which reached the oil window for hydrocarbon generation during the Permian.  Heat flow occurred at the same time that the tectonic events were propagating the joints throughout the Devonian section in the Finger Lakes District (Lash, 2014). In other words, Gary Lash and his fellow researchers found that petroleum generation was a joint-driving mechanism, due to thermally-driven phase change.

Randy Blood, who studied under Gary Lash, has continued to do extensive fieldwork and to make further connections between thermal maturation and the development of massive joint systems which create a robust and persistent gas reservoir and migration pathway. The exploration implications are significant. 

Gas generation from the upper Devonian black shales resulted from the desorption of methane from the surface of residual organic material (kerogen and bitumen) and clay minerals, principally illite. Production, however, depends the size, frequency, and interconnectedness of natural jointing.  

After continuing to investigate and experiment, in 1825 Hart drilled a 27-foot hole into the rock, and encountered gas that would flow at a rate sufficient for him to invent and implement a small pipeline (first made of bamboo) and to use the gas in gas lamps, first in farms, a mill, and later in a hotel and a lighthouse. 

Several years later, Preston Barmore, a creative engineer unfazed by what might happen as one ramped up the production volumes of natural gas, decided to drill a well to 127 feet in depth, and, when frustrated by the low volume of gas, decided to ignite the gas, causing downhole explosions (Martin, etal, 2008). This early version of fracing was highly effective. 

Within a few years, hundreds of wells were drilled in the shallow Dunkirk shale, and pipelines were constructed to distribute the gas to street lamps, making Fredonia one of the first towns in the world to have gas street lamps (Martin, et al, 2008). Other pipelines were built in western and upstate New York, including ones constructed of hollowed-out tree logs, used for transporting produced salt water to evaporation ponds.

Whether or not the shallow, low-volume gas reservoirs of the Dunkirk shale might still have economic potential given current regulatory frameworks is something to be pursued. Because there were so many active gas seeps in the past, it might be worthwhile to conduct airborne surveys to detect methane and to see if there are any concentrations around natural seeps. There could be local uses for low-volume gas for innovative geologists and engineers today as well as almost 200 years ago. 


Blood, R., and Lash, G. (2019). Horizontal Targeting Strategies and Challenges: Examples from the Marcellus Shale, Appalachian Basin, USA. Conference: Unconventional Resources Technology Conference (URTeC),2019 - Denver, CO. 

Lash, G., Loewy, St., and T. Engelder (2004). Preferential jointing of Upper Devonian black shale, Appalachian Plateau, USA: evidence supporting hydrocarbon generation as a joint-driving mechanism. Geological Society of London. Special Publications. Vol. 231:1, p 129-161. 

Lash, G. G., and E. P. Lash (2014) Early History of the Natural Gas Industry, Fredonia, New York. Search and Discovery Article. August 29, 2014.  

Lash, G., and E. Lash (May 2015) The Unsung “Father of the Natural Gas Industry” AAPG Explorer. May 2015. 

MacDonald, Ronald (2002) Application of Innovative Technologies to Fractured Devonian Shale Reservoir Exploration and Development Activities, Proceedings of the Forty-First Annual OPI Conference, Ontario Petroleum Institute, November 4-6. 

Martin, J P., Hill, D. G., Lombardi, T. E., Nyahay, R. (2008). A Primer on New York’s Gas Shales. New York State Geological Association: NYSGA Online.

Blog Archive