The Potrero del Llanos No. 4 in the Golden Lane of Eastern Mexico, fue el más grande de todos los pozos de petróleo, nunca...was the greatest of all oil wells, ever.
Huasteca Region, Eastern Mexico; circ. 1909
The early morning of 26 December 1910 was oddly cool; a crisp, dry wind blew from the northwest that smelled of mountains and fresh bougainvillea. It was the best that Mexico could offer in the way of winter and for the rig crew; it would do just fine. There had been a party of sorts yesterday in the camp and the mail from the States and Canada was full of packages and letters from home. The men were in good spirits that fine morning. The No. 4 was furthest from camp and they laughed out loud when they caught a ride out to the well on a wagon full of sharpened bits and coils of new hemp rope.
By nine o'clock, the sun coming over the top of thick jungle, the men were back in the hole chipping away on dense shale, the slow monotonous rhythm of the walking beam moving up and down making everyone a little sleepy. They tended to boilers to keep themselves busy, made thick coffee and spoke in low voices of news about the revolution and some killings in a cantina in Furbero. One of the dead was an El Aguila hand from Texas they'd work with before. He had a family.
In the early afternoon mugginess the drill rate picked up and at one point the tool fell some 20 feet, into something that seemed like a cavern. They bailed shale and limestone rubble and remarked about the crystals in the samples that looked like glass. There was a slight gas odor on the floor and the bailer runs had oil in them. They changed bits and carried on. By late afternoon a shadow fell across the floor and total depth was at 1,932 feet. More bailer trips recovered blue, porous chalk, more crystals and brownish looking oil. The well was running low to the No. 1 and they shrugged off installing the big valve on the 8 inch casing until in the morning. They left the bailer on bottom and started to trudge back to camp for dinner and bed.
At 2:00 AM on the morning of the 27th the camp came suddenly to life with mules bellowing in fear and men shouting in both Spanish and English; in the darkness the 4 well seemed to have exploded. They could hear it blowing as they ran to the boilers to close valves, douse fires and latch doors. No one dared walk toward the well with a lantern so they sat and listened. And waited.
By first light they could see the top of the wooden derrick was gone, splinters of thick timbers blown hundreds of feet away. The bailer and drill line left in the well overnight were gone, nowhere to be found, a massive column of oil was towering several hundred feet into the air. Joints of 8 inch casing had been blown up thru the derrick, were broken in pieces and laying everywhere. Oil coated trees and jungle a thousand feet away and gas, like a heavy cloud, burned their throats. The noise was deafening. The ground around them seem to tremble.
El Aguila, Potrero No. 4; June 1909
Most of the oil ran down dry arroyos straight into Buena Vista River and eventually into the Rio Tuxpan. El Aguila company men immediately ceased drilling two other wells in progress on the Potrero hacienda and threw every man it had available at digging ditches, flumes and earthen dams to redirect the oil flow. Men and mules littered the blackened landscape. A primary ditch away from the well was dug to precise measurements and gauge posts were driven in the bottom; it was then possible to estimate flow rates from the Potrero well at something in the order of 112,000 BOPD.
Campesinos found the bailer and one inch drill line hanging in palm trees a half mile from the well.
Some men used a planner table and triangulated the top of the blowout flow to be 450 feet above ground level; now and then chunks of rocks that looked like coral reef were hurled high in the sky.
Weetman Pearson, El Aguila's owner, a man later to be knighted in England as Lord Cowdray, directed the ground efforts himself, often with a shovel. Everette DeGolyer, one of Aquila's geologist responsible for staking the well, arrived on location within the week and helped dig ditches. Pearson ordered DeGolyer and over a hundred men to dam up the Buena Vista River and then set it, and the Tuxpan River, on fire burning an estimated 1.4 MM barrels of oil.
DeGolyer guessed flowing casing pressure of the well around 830 PSI and the oil was a remarkably hot, 145 degrees; too hot to touch.
The Huasteca Oil Co., San Diego de Mar No. 1 blowout and fire in 1909, later renamed, Dos Bocas, represented the northern most extremity of what became known as Mexico's Golden Lane.
After the Potrero discovery other Tamasopo wells were discovered at Juan Casiano, Amarilla and Cerro Azul, between Dos Bocas and the Potrero Del Llanos. Later the trend was extended south toward Furbero.
The first efforts to control the well involved removing what was left of the rig, walking beam and other debris and to clamp the remaining 8 inch casing, some 1500 feet of it still in the ground, and secure it from blowing out of the hole. Tons of railroad tracks were brought to the well to use as dead-men and cables were wrapped around them and hooked to the clamps with heavy shackles. The top of the 8 inch casing had broken off clean and the outer string of 10 inch casing, set to approximately 1100 feet below surface, was still in tact. Thankfully.
A capping stack was built in Aguila's yard in Tuxpan and hauled by mule driven wagon to the well site within the first two weeks of the well blowing out. It had a full opening 10 inch valve and, miraculously, that assembly was stabbed over the flow, winched down over the casing and anchored to railroad ties. The well was put on a one line diverter to the primary ditch and into earthen pits. This "restriction" caused the casing to want to come out of the ground. Small cracks in the ground started bubbling oil 100 feet away from the well bore.
First capping stack, before cement was poured around the base of the well. Men are standing on railroad ties used to secure the well head.
Another view of the first capping stack surrounded by railroad ties and on a single line diverter. Lines coming off the top of the stack were used to send gas to six, large flares surrounding the well.
The first capping stack, called a 'bell-nipple' by Aguila, proved problematic from the start. Surface broaches got worse and soon flow was detected between the 8 inch and 10 inch, as well as around the 13 3/8ths conductor pipe. Cement was poured around the base of the well as a stop gap measure. Several surface broaches occurred along a dry creek bed that grew to such an extent they were blowing an estimated 6,000-7,000 BOPD of oil back into Buena Vista River.
This photo on the right shows that the actual No. 4 wellhead to be encased in an adobe brick 'hut', complete with a vent system on top and entry doors on the bottom. This is believed to have been constructed to keep Mexican revolutionists, like Pancho Villa, from shooting bullets at the wellhead and possibly setting it on fire.
The well was so prolific and such a valuable asset to El Aguila it was guarded by the Mexican government and Aguila employees 24 hours a day until 1918. A gun battle ensued near the well location in the winter to 1915 and numerous men, on both sides of the revolution, were killed.
Things continued to deteriorate around the well head and in March of 1911 the first capping stack assembly on the 8 inch casing was removed and enough of the 10 inch exposed to cap to with a large valve and a segmented seal assembly that had been built in, and shipped from, Tampico. Old cement around the well was dug out and a reinforced concrete foundation some 8 feet deep and 24 feet square was built around the well. The well was shut in just long enough to get three, 10 inch joints of casing laid out and tied into sort of a manifold as a diverter system. It was all nippled up, the well was immediately opened back up and returned to earthen pit production.
On the right, one of three 20 acre earthen pits built by mid 1911 to contain No. 4 production. For some sense of the size of these pits you will please notice a man standing on the levee in the foreground, just right of the tree.
By 1913 the hacienda also contained multiple 5000 bbl. steel tanks.
By early April, 1911, on multiple diverter lines and 89 days after the initial blowout, the well was finally considered fully under control. Aguila was able to pump the oil from the earthen pits onto barges where they were floated down the Buena Vista River to Tuxpan and put on deeper draft ships up to a refinery in Minatitlan, near Tampico. Many 5,000 bbl. steel storage tanks were built in Tuxpan. Work never stopped and thousands were involved, from the No. 4 well head all the way to Tampico.
In the winter of 1912 a large diameter pipeline was finished by El Aguila to the village of Tamiahua and to docks on Tamiahua Lagoon where a steady flow of shallow draft barges stayed within the safety of the lagoon moving massive volumes of oil north to Minatitlan and deep water ports near Tampico. More storage tanks were built in Tamiahua and Pearson was said to have bought every oil barge in Texas he could find.
El Aquila had 3 million barrels of Potrero oil in above ground tanks and/or earthen pits at all times; as fast as they could move the oil to market the No. 4 would fill those tanks back up again.
To facilitate the final pipeline hookup the Potrero well was shut in once again. SICP was found to be 840 PSI, pretty much the same as DeGolyer' estimate two years previously, and surface broaches occurred almost immediately around the well. Problems with the pipeline persisted and the well had to be put back on diverter.
A few weeks later a hurricane hit the Mexican coast and lightning from a storm hit one of the larger surface broaches near the Potrero No. 4 wellbore. Some written accounts of this event suggest the well itself had caught fire but that was not believed to be the case. An enormous earthen berm was built around the well to protect it from the seep fire. Under considerable pressure and flow, the surface broach burned for 2 months until the fire was put out using steam from boilers, seen in this photograph above. To the right, over the boilers, a 5,000 bbl. steel tank is on fire, also from lightning. More oil was burned off the Buena Vista River and all toll an estimated 1.4 MM BO was burned and/or lost in 1913.
A photo of the earthen berm used to protect the Potrero 4 wellhead during the 1913 lightning strikes. Once the nearby fires were contained the berm was removed. The small gauge railroad tracks were used to move dirt to build the berm.
Once the well was finally hooked up permanently to the Tamiahua pipeline it's flow rates were gauged at 39,000-47,000 BOPD. Other than slight turns on the 10 inch master valve no further attempt was ever made to choke the well back or shut it in. Absent of any downstream flow restrictions all surface broaches in the nearby terrain stopped completely. They were actually filled with cement.
In 1914, to protect the well head from further lightening strikes and to help defend it from revolutionists, a concrete bunker was built around it, on top of the 1911 concrete foundation, see above. Its walls were a foot thick and believed to offer some defense against artillery rounds. As the Mexican revolution escalated in 1915-1916 the entire Potrero No. 4 location was surrounded by high fence with guard towers.
Everette DeGolyer (1886-1956) and colleague, Leon Russ (standing) at the Potrero No. 4 "bunker;" 1914. This photo was taken days before DeGolyer left Mexico for the last time.
There is some debate as to who was actually responsible for determining the location of the Potrero 4 well, DeGolyer or his boss at El Aguila, Dr. Willard Hayes (1858-1916). With two other Potrero wells in progress at the time of the No. 4 blowout (oriented to test the concept of a three way closure) it is believed DeGolyer had the final say. For the record, it was structurally low to the first well drilled on the hacienda.
The year after the No. 4 was fully contained the other two Potrero wells were re-entered only to find relatively minor, commercial amounts of oil. A total of seven wells eventually produced on the hacienda and the oil from those wells was also sent down the pipeline to Tamiahua. At one point six 'other' wells on the Potrero hacienda totaled 5,000 BOPD.
In 1916, six years after the Potrero discovery, Edward Doheny (1856-1935) and his Huasteca Oil Company drilled the Cerro Azul No.4, just north of the Hacienda Potrero and into the same carbonate, Tamasopo formation. It too blew out and its estimated flow was gauged at 260,800 BOPD. The Azul No. 4 marks the highest known blowout rates of any well anywhere in the world; it was produced by Pemex sporadically until 1996 and may actually still be producing small quantities of oil, in heads, today The actual christmas tree on the well is maintained in a little park in the village of Cerro Azul and there is a sign nearby describing the unique history of the No. 4 well. Its known cumulative production including waste, is believed to be 79,000,000 barrels. 
Another Doheny well in the Golden Lane, the Casiano No. 7, produced approximately 70,000,000 BO 
The El Aguila, Potrero del Llanos No. 4 well produced until December 1918 when it went to 100% water, virtually overnight. It's known market production and estimated losses from the initial blowout flowing into the river, ground loss from earthen pits, lightning strikes and ensuing fires were 73,000,000 BO thru the end of 1914 when Everette DeGolyer left Mexico and stopped maintaining production records .
From 1915 to 1918 the well produced an additional 43,000,000 BO. Its estimated total cumulative production in eight years was over 115,000,000 barrels, making it the most productive oil well in world history .
 Everette DeGolyer became a legendary geologist in America and formed the American Association of Petroleum Geologists. I relied heavily on his photographs and papers on file at The DeGolyer Library, Southern Methodist University and book titled, The Oilfields of Mexico, Tuxpan and Tampico Regions; 1916.
Note: El Aguila* made its founder, Sir Weetman Pearson (1856-1927), one of the wealthiest men in the world. His company was eventually sold to Royal Dutch Shell in 1919 for $75,000,000. Mexico nationalized its oil resources in 1938 and turned all the oil wells in the great, Golden Lane, over to what eventually became, Pemex.
Some 1.6 BO of 21 to 23 gravity oil was produced from Tamasopo formation in the Faja de Oro between 1906 and around 1938, all above 2,200 feet vertical depth.
The great Pozo Rico Field (1930), a giant, lies to the south and west of the southern most extremities of the Golden Lane reef in similar, deeper Cretaceous aged, Tamabra carbonates.
* El Aguila was also known as the Mexican Eagle Oil Company
 Oil Weekly (World Oil Magazine); July 1933:
 National Petroleum News Vol. 13
 Fuel Oil Journal Vol. 5
 Pan American Magazine Vol. 35
 Mexico's Oil, Government of Mexico 1940
 The Golden Lane, Faja de Oro; Sam Pfiester, 2012
 Structural Evolution of the Golden Lane; HH Wilson, JPG Volume 10
 Oil and Revolution in Mexico; J. Brown, 1993
In response to El Aguila's magnificent Mexican production volumes it created the Eagle Shipping Company. It had an entire fleet of shallow draft barges and deep water ships operating around the world to move its Golden Lane oil.
Mexico confiscated all of El Aguila's oil wells in 1938, as well as many of its other assets in Mexico, including the oil tanker, SS Potrero de Llano. In 1942 the ship, sailing under the Mexican flag, was carrying diesel oil from Tampico to New York and just off the coast of Florida it was torpedoed by a German submarine.
Siempre es por gran privilegio escribir sobre la historia del petróleo Mexicano.