Petroleum: a gaseous, liquid, and solid substance occurring naturally and consisting chiefly of chemical compounds of carbon and hydrogen. It is a renewable resource, albeit over long periods of geologic time. It is an economically important resource that has been the focus of many wars. But its high value has not always been recognized. When it was first discovered, whale oil was the dominant combustible liquid and crude oil was a novelty.

Click to view a chart showing areas of the world that are favorable for the accumulation of organic matter. The shaded areas show both favorable onshore and offshore areas.

Question: Where and when was the first oil produced (drilled and removed from the subsurface)?
Answer: Although the ancients collected asphalt (petroleum) for various uses, it was first drilled and removed from the earth's subsurface in Romania in 1857.

Question: Where and when was the first oil produced in the US?
Answer: Titusville, PA, 1859 The well was 23 meters deep and produced about 25 barrels per day.

Question: When and where was the first oil well of commercial quantities discovered in Louisiana?
Answer: Heywood #1 Jules Clement well, 1,700 feet deep, near Evangeline in Acadia Parish, September 1901

When examining a world map showing areas where large accumulations of hydrocarbons have been located, it becomes evident that hydrocarbons are widespread and not restricted to any particular continent. A notable exception is the Antarctic Continent. But when examining the distribution of sedimentary rocks that provide favorable conditions for either the formation and/or accumulation of hydrocarbons, every continent is represented as are most oceanic bodies down to a depth of less than 2,000 meters . While hydrocarbons are found on all continents of the world, some areas are richer than others. Present major production is concentrated in North America, the Middle East, and in Russia.

Click to view a chart showing the annual production of petroleum by continent.

Question: Virtually everywhere in the United States has some oil and gas production, but there are some notable exceptions (click your "Back" button to return to this page). For example, the New England region appears to be void of appreciable deposits, other than perhaps offshore. Why?
Answer: The answer is two-fold: First, the New England region is old in terms of geologic time, it contains rocks that were formed during late Precambrian time (570 million years ago). While source materials may have existed in the geologic past as well as suitable places to trap the hydrocarbons, subsequent erosion has removed the ancient sedimentary sequence needed for retaining these deposits. Secondly, the New England region is characterized by numerous igneous and metamorphic rocks. All of these rock types are formed by elevated temperatures and pressures over significant spans of geologic time. If hydrocarbons were ever present, they have since been eliminated or "cooked" out of the sediments.

Question: There are no hydrocarbons in Hawaii. What limiting factors can you think of in the context of what has been discussed thus far that would preclude the formation of hydrocarbons at these locations?
Answer: There are a number of reasons, but perhaps the most important is that Hawaii is characterized by volcanic activity. Hydrocarbons are temperature sensitive and tend to vaporize above about 350^o C. If hydrocarbons were ever present, they have since been vaporized.

Question: Can you think of any other reasons?
Answer: The primary ingredients for the formation of hydrocarbons are raw material, planktonic organisms, some sort of a protected environment such as a continental shelf, an influx of abundant sediments to cover the dead planktonic organisms, and geologic time in which to accumulate the materials, transform the carcasses into oil droplets, and move the oil from source beds into reservoir beds. The Hawaiian chain is a series of isolated volcanic cones that rise above the deep ocean floor (Continental Rise). The oldest island formed during the Pliocene and is about 4 million years old while the youngest island is less than 1 million years old. If raw material had accumulated, it has not had sufficient time to undergo transformation and migration . But there are two other equally important reasons: First, we learned in the section on Oil Formation that the accumulation of raw material can only take place in some sort of a protected environment where there is an abundance of plankton and an influx of abundant sediments to cover the dead planktonic organisms. There is no protected environment such as a continental shelf area in which organic matter and planktonic organisms can accumulate in mass. Remember, the islands rise up from the ocean floor. Moreover, because we are dealing with isolated islands in the middle of the Pacific Ocean, there has been no opportunity for sediments to develop in the quantity needed. A massive influx of sediments requires a massive source such as along the edge of a continent, not an island.

Question: So does that mean that hydrocarbons will not be found trapped in igneous rocks?
Answer: No! Not at all. It means that for hydrocarbons to be found in igneous rocks, the rocks must have been intruded into sedimentary rocks, cooled to normal ambient temperature of the surrounding sediments, fractured, and then hydrocarbons migrated into the fractured igneous rocks with the latter now serving as a reservoir material. This requires a lot of geologic time.

OCCURRENCE OF PETROLEUM IN LOUISIANA

Louisiana and the Gulf Coast region lack phosphatic-rich hydrocarbons, the reasons for this were discussed in the last chapter. However being devoid of phosphatic hydrocarbons does not mean that Louisiana is devoid of oil and gas. Quite the contrary. Hydrocarbon reserves occur throughout all of the parishes in Louisiana, albeit some are richer than others.

When we examine the distribution of hydrocarbon reservoirs by age, we notice a distinction between North Louisiana and South Louisiana. The oldest deposits are Mesozoic Era in age, specifically Jurassic Period (54 - 59 millions years in duration) and Cretaceous Period (71 millions years in duration). The youngest hydrocarbons developed during the Tertiary Period of the Cenozoic Era. The earliest Tertiary Period hydrocarbons are mostly south (seaward) a reef structure that formed during the Cretaceous Period (referred to as the "Cretaceous Reef"). Some Tertiary Period hydocarbons (Lower Eocene) occur just to the north of the Cretaceous Reef with the youngest aged hydrocarbons occurring offshore. So hydrocarbon development occurred from north to south.

Question: Based on the information above, where, on this figure, would you place the Cretaceous Reef?
Answer: Look at this figure to see where the reef is located.

This would be expected because Louisiana physiography also developed from north to south. What we see today is not what Louisiana looked like 85 million years ago. During the Triassic-Jurassic Period, the Louisiana coastline was considerably northward from where it is today as was the position of the shelf margin (continental shelf/slope interface). With time, the coastline and shelf margin migrated southward. During the Cretaceous, for example , the reef structure developed at the shelf margin creating a barrier that prohibited organic-rich, upwelling currents from reaching the shallow, warm water zone along the continental shelf.

There is one, perhaps curious, aspect to this discussion of where hydrocarbons are located. The line of demarcation between the northern and southern hydrocarbon provinces in Louisiana appears to contain less oil and gas wells. A similar pattern becomes evident when examining the drilling history of oil and gas wells in the state.

Question: Why do you think this is?
Answer: This area is synonymous with the existence of the Cretaceous reef. The reef lies at greater depths and any hydrocarbons found here are deeper and therefore more costly to explore for and remove from the subsurface. Therefore this area will be the last to be developed until the shallower, less expensive reserves are located and the hydrocarbons have been exhausted.

Question: Why did the hydrocarbons migrate from the source rock into the reef structure? After all, the reef blocked the critical flow of the upwelling current.
Answer: The presence of the reef during the Cretaceous controlled where the source rocks eventually formed later in geologic time. The reef was an inhibitor during the Cretaceous Period when organic matter was being accumulated. But the remnant reef that now exists buried in the subsurface has permeability , is buried beneath a younger succession of sediments that are potential source rocks, and lies atop a deeper sequence of sediments that are also potential source materials. Reservoir fluids are free to pass through both the reef complex and the surrounding sediments.

REFERENCES

DOTT, R. H., and M. J. REYNOLDS, 1969, Source book for Petroleum Geology: Am. Assoc. Petrol. Geol., Mem. No. 5, 471 pp.

JUDSON, SIDNEY A. and R. A. STAMEY, 1933, Overhanging Salt On Domes of Texas and Louisiana: Bull. Am. Assoc. Petrol. Geol., Vol. 17, pp. 1492-1520.

Other Materials Utilized in Preparation of this Section

BATES, R. L. AND J. A. JACKSON, 1980, Glossary of Geology: American Geological Institute, Falls Church, VA., 2nd Ed., 749 pp.

BERGER, B. D. and K. E. Anderson, 1992, Modern Petroleum - A Basic Primer of the Industry: PennWell Books, 3rd Ed., Tulsa, OK., 517 pp.

LEVORSEN, A. I., 1967, Geology of Petroleum: W. H. Freeman and Company, San Franciso, CA., 2nd Ed., 724 pp. SELLEY, R. C., 1985, Element of Petroleum Geology: W. H. Freeman & Co., New York, 449 pp.

NORTH, F. K., 1985, Petroleum Geology: Allen & Unwin, Inc., Winchester, MA., 607 pp.