Spindletop: The Original Salt Dome
by Michel T. Halbouty
Geoscientist and Chairman
Michel T. Halbouty Energy Co.
Pattillo Higgins — the true prophet of Spindletop — was too ill to go to the big dinner celebrating the 50th anniversary of the discovery of oil at Spindletop. He listened by radio to the many speeches extolling the virtues of the discovery and what it meant to the people of the world, etc., etc.!
He was disgusted that day in 1951, because although everyone who spoke referred to the oil production, the 100,000 barrels per day and the 60 million bbls. that were produced from "The Hill," no one spoke — not a single reference — about the accumulation of the oil and more particularly about the structure that trapped the oil. He kept yelling at the radio while each speaker was talking: "Say something about the salt dome; tell your audience about how the dome trapped the oil." His outbursts were unheeded, of course, and eventually the occasion was over — the 50th year of the discovery of the "Gusher" was history.
He closed his eyes and began reminiscing about the hardships and ridicule he encountered when he tried to get someone — anyone — to listen to him about finding oil at his spot called "Spindletop." How he finally aroused the interest of one man, the only person to answer an ad he had placed in a magazine. Yes, Captain Anthony F. Lucas, the navy engineer, knew about salt domes and Higgins knew that Lucas was his salvation.
Higgins went back in his memories to the time that he would take his young Sunday School class from his Baptist Church to a picnic at a site where there was a mound that rose some 15 feet above the surrounding prairie. He thought about how he would push a cane into the ground and then light a flame of the gas that escaped from the surface. It was fun for the children and it intrigued Higgins. It was on one of these picnics that Higgins began to believe that maybe the mound was unusual to be located in a flat prairie, and he finally reasoned that something below the mound had caused it to rise above the flat land.
Early Salt Dome Theories
Pattillo Higgins had a belief — a faith — that there was a producing "rock" at Spindletop. He felt that only hard rock could cause the slight uplift of the surface of the earth that formed the mound or hill, and therefore the rock must be somewhere below that mound. He also assumed that there would be oil under or in that rock because he calculated that if the surface was uplifted, the beds under the surface would also be arched. The oil, being lighter than water, would seek its own level, and would thus move through the water in the geological formations until caught in the arched beds. That was probably the extent of Pattillo Higgins’ original knowledge of geology, but it was excellent thinking and was based on sound geological principles, even by today’s standards.
Pattillo Higgins told everyone about his rock, and that it would be found at shallow depths — at approximately 1,000 feet. When the State University geologist visited Higgins and was told about the rock, he publicly refuted Higgins by stating that no such shallow subsurface rock existed in the vicinity of Beaumont and offered as proof a well located in the town of Beaumont which was drilled to 1,400 feet for water, exceeding the depth of Higgins’ theoretical rock layer. Even after the discovery of oil and the drilling of the first few tens of wells at Spindletop, no salt had been penetrated, yet Higgins still believed in his theory of arched beds and his idea of oil being trapped therein.
Higgins even expounded his ideas in a booklet, and he went to great lengths to explain his theories. The remarkable thing about Higgins’ old writings is that they were phenomenally accurate according to present-day geological knowledge. He did not discuss salt or salt domes, as the drill had not yet penetrated salt, but his reasonings as to structure, oil accumulations, drilling and production were very good. Higgins could easily be called the first practical oil man the Gulf Coast produced. He was daring and outspoken, and an optimist, yet so practical that his knowledge borders on that of a scientist and engineer.
It was difficult for the layman in 1901 to comprehend the "why" of the existence of a salt dome — and it still is. Very little professional geology was being done in the Gulf Coast, and there was practically no petroleum geology being practiced anywhere else. The fact that oil would be found only in an area within the influence of the dome was recognized long after the Spindletop discovery. Even Lucas, who was the first to consider the salt-dome theory at Spindletop, leased land for miles from the center of the mound, which indicates that he did not really know what effect a dome would have on oil production.
What Geoscience Has Learned
Just what is a salt dome like Spindletop?
A salt dome is actually a stalklike core of rock salt which has protruded up through the overlying beds of sands, shales and limestones, thus causing the pierced sedimentary beds to dip radially away from the salt core. The effect of the uplift of the salt on the dip of the overlying sediments can be illustrated by laying a flat, unwrinkled handkerchief on a table and gradually lifting the cloth with the fingers from the very center. This will show the radial effect of the plug forcing itself through the strata.
The Spindletop salt core is roughly circular in shape, about one mile in diameter. The uplift of the salt mass had an effect on the surface area overlying the dome, forming a mound or small hill approximately the same diameter as the subsurface salt core, which is quite perceptible about the flat prairie lands of the Gulf Coast. This topographic feature is a characteristic surface expression of most of the piercement-type domes in the Gulf coastal plain. The mound at Spindletop rises barely 15 feet above the general level of the plain, but this rise stands out against the very flat and gently sloping land.
After the discovery of oil at Spindletop, this topographic feature was one of the main "surface indications" that wildcatters looked for in their search for other oil fields. This led to the quick discovery of many domes a few months after Spindletop. Wildcatters did not know what was underneath those surface mounds to cause the accumulation of oil, but the one thing that they did understand was that a mound must first be found before plans were made to drill. This type of "surface" wildcatting resulted in the discovery of many domes in Texas and Louisiana.
Pattillo Higgins was attracted to Spindletop not only because of the mound, but also by the gas seeps, paraffin dirt and sour waters which existed in the vicinity of the mound. These surface indications led to the drilling of the first well at Spindletop and forever after, all wildcatters, geologists, operators and oil men looked for those same indications.
Questions Raised
The existence of a core of salt below the surface of the earth raises a number of questions in the layman’s mind. The two big questions are, when was the salt deposited, and how did the domes rise through the vast thickness of formations to their present positions? These two questions have even stumped many geologists to this day, and many theories have been expounded, discussed and "cussed." The general idea accepted by most students of salt domes is that the mother salt beds were deposited millions and millions of years ago in the old coastal lagoons and embayments during Lower Jurassic or Upper Permian time, or after, and that as much as 5,000 feet or more of salt might have been laid down before the first deposits of sediments were laid down over them.
Many salt domes like Spindletop are located in the Gulf coastal plains of the United States. The area representing the Gulf coastal plains was, throughout early geologic times, either a very shallow basin of water or dry land, and successive cycles of rising and ebbing of the old seas took place, depositing, eroding and redepositing sediments. The thick mother salt bed was deposited during a time when extreme arid conditions prevailed in this part of the world. The climate was very hot, the land dry and the seas shallow. Very little rain fell in the area. The shallow seas became super-saturated with salt, so that salt dropped out of solution from the sea water and solidified on the bottom of the sea. Successive layers of salt thus deposited were packed into a bed of vast extent covering the entire Gulf coastal plain area. This great mother salt bed gave birth to the domes that lie beneath the landscape of the Gulf Coast and under the waters of the Gulf of Mexico.
The depth at which the mother salt bed might be encountered under the Spindletop area is estimated at more than 30,000 feet below the surface. This gives an idea of the thickness of sediments overlying the shale and the overall extent of the movement of the individual salt core through the younger beds. There are many ideas and theories as to the cause of the initial upward movement of the salt plugs from the mother bed. It is believed, however, that movement did not begin until sufficient sediments had been deposited over the salt bed to cause an appreciable static weight on top of the salt.
The weight of the sediments above the salt is a most important factor in the upward movement of the salt. The salt has a specific gravity of 2.19, whereas the average specific gravity of the sediments is approximately 2.7 at great depths. This difference in the specific gravity of the two is likened to that of oil and water. Oil being lighter than water, the forces of buoyancy cause oil to rise through water. This same principle is applied to the salt and overlying sediments. Because the salt is much lighter than the sediments, it rises in a sort of plastic state through the sediments.
The force of buoyancy is one of the factors that causes the salt to move through layers of sediments of higher specific gravity as oil moves through water, not necessarily with the same ease, but by the same principles of the laws of physics. There are other factors that contribute to the movement of the salt mass, such as tectonic forces (internal earth movements) which might have caused the buckling of the mother salt bed, cracking and distorting the salt, as well as the overlying sediments. In turn these movements created lines of weakness in the sediments adjacent to the salt bed, which permitted the initial movement of salt through them. Once the movement of salt begins, the forces of buoyancy are constantly at work, depending on the static weight of the sediments above the salt and on the flanks of the salt core. The main motive force of the uplift of the salt through the sediments is the static weight of these sediments, principally on the flanks of the salt core. The salt stock moves in stages through geologic time, depending on the thickness and the weight of the sediments above and around the salt mass. The sediments at very shallow depths, from the surface down several thousand feet, are less dense than those at greater depths and also less dense than the salt, and afford no contrast therefore to cause the salt to move appreciably. For that reason, the upward movement of the salt core gradually slows down, but does not necessarily stop altogether as it approaches the surface. Generally, when such equilibrium of density is approximated between the sediments and the salt, a stage of semi-dormancy prevails. During this time more sediments are deposited over the salt-core area, which gradually raises the static weight, and increases by compression the density of the beds being buried. This in turn causes an increased compressive action on the peripheral flanks of the dome which, with the forces of buoyancy of the salt thereby revived, causes the accelerated upward movement of the salt stock to begin all over again.
Cycle after cycle of this procedure took place until the domes gradually pierced their way through the overlying beds to their present positions under the surface of the earth. It must be emphasized, however, that it appears that there was variation in the rate of the upward rise of the original salt stocks. Some of these moved upward rather slowly, so that they could not keep pace with the rapid deposition of sediments and eventually became buried beneath many thousands of feet of overburden. These domes are referred to as "deep-seated," and gas and oil production is generally found in the arched, but unpierced, formations lying over the super-dome area. Other salt stocks, including the one at Spindletop, seem to have developed under conditions that resulted in the salt stocks remaining near the surface throughout their growth history. These are commonly referred to as the "piercement-type" domes, because the salt pierced the overlying sediments with growth and remained, therefore, only a few thousand or hundreds of feet below the surface. Gas and oil production at these domes is therefore likely to be important in the pierced formations that butt against the sides of the salt mass. It was one of these salt cores that finally settled under an area that is known as Spindletop.
At Spindletop, oil had accumulated in the arched beds — many abutting against the salt — and they were perfect traps for the accumulation of oil. These flank oil traps were the cause of the second boom in 1925. Some of the arched zones abutted against the caprock, which literally sucked the oil from the sedimentary beds into the porous caprock. The "gusher" was from that source. Higgins repeatedly stated that oil would be found at 1,000 feet. He missed it by 20 feet — the depth was 1,020 feet.
The Futures of the Domes
Salt domes, irrespective of their past production or lack of it, still remain as major sources of the oil reserves yet to be discovered and produced. It is anticipated that every salt dome will eventually produce oil if properly tested, and those which have already produced will again yield additional reserves from down-structure, away from the old production — just like Spindletop, which will continue to produce new oil as long as wildcatters have the courage and incentive to drill deeper and farther away from the center of the dome. And this can be said for all of the other domes. Most salt domes are still the most important geologic features in the coastal plains and they will surely be explored deeper and deeper, each additional foot probing into a vast unknown, eventually through the entire group of sediments, 30,000 feet or more, to the mother salt bed. How many millions of barrels of oil or trillions of cubic feet of gas are hidden in the lower depths is a question that can be answered only by the drill.
The answer will be supplied by the imagination, inventiveness, courage and determination of those who immortalized Spindletop. It will require geological, mechanical and operational daring. It will require great risks and great losses, bolstered by tremendous financing and continued incentive for the wildcatters without whom nothing has been nor will be accomplished toward bringing greater abundance and prosperity to the nation and the world. There will be greater prosperity in terms of sources of new energy and chemical advancements. These in turn provide individual comfort and convenience and national power and security. Oil will be found wherever and whenever these forces are combined. For Spindletop and domes like it there will undoubtedly be more action on "The Hills."
Michel T. Halbouty is an internationally renowned earth scientist and engineer whose career and accomplishments in geology and petroleum engineering have earned him recognition as one of the world’s outstanding geoscientists. He received his M.S. and B.S. in geology and petroleum engineering from Texas A&M University. He also earned the Professional Degree in Geological Engineering from Texas A&M University. The Montana College of Mineral Science and Technology conferred the degree of Doctor of Engineering (hc) upon him. He was awarded the degree of Doctor of Geoscience (hc) by the USSR Academy of Sciences, the only such honor bestowed on a scientist outside Russia. The University of Nanjing (People’s Republic of China) presented him with an Honorary Professorship in Geology for his numerous contributions to the advancement of petroleum geology in China. He was also elected a member of the Chinese Academy of Engineering. A former president of the American Association of Petroleum Geologists, Halbouty is widely sought as a speaker by scientific and lay groups all over the U.S. and the world. Halbouty was the first independent to explore in Alaska. The finding of the West Fork gas field on the Kenai Peninsula in 1959 was the first discovery by an independent in Alaska. He is recognized as the petroleum industry’s preeminent wildcatter. He chaired President Reagan’s Energy Policy Advisory Task Force and later was appointed by President Reagan as leader of the Transition Team on Energy.
|
