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The area around Luling, in Central Texas, contains some 6,000 wells, all vertically completed in Creteacous age Austin Chalk and Edwards limestones at depths of less than 3,000 feet. Three signficant fields, Luling-Branyon, Salt Flat, and Darst Creek, and several minor fields, have produced nearly 340,000,000 barrels of oil since the early 1920's.

The first oil well in the Luling area was drilled in 1922, NW of town, on an up-to-the-coast fault that outcrops and can be actually seen in the cut banks of the nearby San Marcos River. The fault strikes Northeast, southwest and its angle to horizontal is about 50 degrees. Oilmen in 1922 mapped this surface fault to deeper depths and the first well drilled on this fault, though considerably down structure, found oil in the Edwards at 1,800 some odd feet below the surface. It was 30 API gravity and very sour.

Most Edwards wells along this Luling fault trend produce water from the get-go and lots of that water has 18,000-25,000 parts per million (ppm) chlorides. The associated gas from the Edwards is high in sulfates and sulfides and H2S concentrations in some fields, like Darst Creek, can border on 200-350 ppm, even above the 500 ppm range in some areas. Down regional dip, to the SE, toward the Gulf of Mexico, Edwards wells along the Stuart City Shelf Margin can contain water with chlorides of 180,000 ppm and H2S conentrations approaching 1,200 ppm.

200-300 ppm H2S will give you a bad headache, 500 ppm will drop you like being hit in the head witha four pound hammer and anything close to a thousand you can't smell the rotten egg odor anymore and you are dead before you hit the ground. I remember 30 years a lease gang in Luling Field cleaning a 5,000 bbl. oil stock tank without air packs and none of them came out that tank alive.

Luling can stink pretty badly on very still mornings when there is no wind and the humidity is low. If then the prevailing wind blows from the South, and occassionally the Southwest, Austinites living 40 miles way will complain about the smell, which tickles me plum to death.

In 1924 the extent of the Luling Field discovery was being extended weekly, both to the SW and NE. Across the Caldwell County line and along strike with the controling fault in Luling Field, in Gudalupe County, a little village grew up to service the new oil boom and besides some boarding houses and a muddy main street with ruts in it as tall as a horse, the OK Cafe came to life, above. The village got so big Mr. Allen wanted to call it Allenstown but some hands named it Gander Slough, instead. In 1945 Gander Slough had a population of 45, including stray dogs; today if you want to take the back road from Luling to Kingsbury, down along Interstate 10, you have to travel Gander Slough Road. This area of Edwards wells was profoundly high in H2S.

Cannan Oil Company drilled into the top of the Edwards formation on the Allen No.3 well in 1924 and most of the floor hands got badly gassed. They knocked out 20 or 30 more feet of Edwards with high H2S concentrations hugging the ground like a blanket of fog. The only way the hands could finish the hole were under World War I vintage gas masks shipped over by train from Houston.

On the right is driller, Charlie Keys on the Allen 3 well drilling in high H2S conditions near Gander Slough, 1924

When running 6 inch production casing on the Allen 3 well the string became plugged with gumbo shale and could not be circulated. The annulus starting blowing gas, rocks and chunks of limestone. Fifty men went down, over come with H2S, and were drug away from the well to safety. Limestone hurled 100 feet in the air hit the first response team causing multiple head injuries. The entire string of 6 inch had to be pulled out of the well and laid back down on the ground to unplug it.

A series of six, six inch back pressure valves were run on the casing string the second time it was run helping control the flow of bad gas. The casing was finally landed at the top of the Edwards. Drill pipe was run back in the casing and the check valves all drilled out. The well was successfully completed, the only fatality was a mule supposedly overcome by gas while tailing out joints of plugged up casing.


Courtesy, Pete Rose, Houston Geological Society

The Luling Fault trend is located just 20 miles south and east of the Balcones Fault Zone along Interstate 35 between Austin and San Antonio. I live on the upthrown block of the Balcones, in the Texas Hill Country. The Austin Chalk outcrops to the surface not very far from where I live and the Edwards formation, the producing interval in the Luling oil field, is 80-90 feet below the surface in my back yard.

As part of the reknowned Southwest Texas State Caving Club, 50 years ago I mapped a cave within walking distance of my house that has about 800 feet of horizontal passage that drops 100 feet from the surface. Back in the back of this cave is a deep pool of water that is acually part of the Edwards Aquifer. I swam in the pool several times. Almost all the caves and sink holes we mapped in this area we carried crude H2S monitors. If shallow passages smelled of rotten, putrid eggs we were always cautious of pushing on.

The Edwards Aquifer is one of the most prolific groundwater sources in Central and Southwest Texas and contains beautiful clean water with chorides of less than 30 ppm. It is the primary source of drinking water for San Antonio and Austin and sole reason Uvalde County is the spinich capital of the world.

The Edwards outcrops to the surface not 5 -10 miles north of the Balcones and when it rains in the Edwards Aquifer recharge zone the cycle time can be counted in days and monitor wells along the aquifer will come up several feet almost immediately.

Some of Texas' most beautiful caverns, karsts and caves are associated with the Edwards Group of limestones north of the Balcones fault zone, Natural Bridge Caverns northwest of New Braunfels, for instance. above. To traverse to the cave's biggest, most spectacular rooms in the Glen Rose formation the trip down is thru the Edwards.

A particular fault of the Balcones zone can be seen in a cut road bank near my house and it shows clearly the base of the Austin Chalk at the surface, a brief period of Eagle Ford mudstone depostion, Buda, Georgetown and Upper Edwards in the wall like a big depostional map of events that occured 80 million years ago.

When I tell people I have skinny dipped in the Edwards Aquifer they look at me like I'm nuts.

When I think just twenty miles south, in the Luling fault zone, the same groundwater aquifer with beautiful crystal clear water has produced 340,000,000 barrels of really stinky oil. it reminds me how really, really cool Mother Earth is.


Texas Portal of History

Gulf Coast Oil & Gas News; 1924

Luling Oil Museum

Texas State Historical Association


University of Texas, San Antonio, Digital Library


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