Continental Margin Mineral Resources - Petroleum and Natural Gas

The exploration for minerals on the continental margin is an extension of exploration on land in terms of type of rock and processes. Much of the area of exploration (to approximately 100 m depth) was exposed during glacial stages, and the rocks forming the continental shelf and slope are part of the continental crust. However, both exploration and exploitation become much more difficult and expensive when we are searching and developing a seafloor covered with water.

Petroleum and Natural Gas
In our life span, oil has been an important commodity. Human history of oil consumption goes back to the 1870's and will probably end by the mid-21st century. A useful measure of a mineral commodity's life span is the period of consumption of 80% of the available supply. For oil, this is probably the 85 years from 1940 to 2025. The production cycle for the United States and world production potential has changed little since the first plot produced in the 1950's. There is a lot of controversy about the expected life span of petroleum and possible alternative sources. Two viewpoints are presented by the U.S. Geological Survey with geologists that envision expanding resources, large reserves and viable alternatives versus the Association for the Study of Peak Oil whose members embrace impending disaster.

Petroleum and Alternate Resource Use

Petroleum now meets almost half of the energy needs of modern industrial societies, and crude oil is essential to modern agriculture and the petrochemical industry. In 1998, the world consumption of petroleum of 25.3 billion barrels of oil with North America and Europe using almost half (48%) of the oil production. The present world power generation is expected to continue to increase. Oil supplied about 39% of this energy since 1988. A mix of hydroelectric, hydrothermal, nuclear, solar and wind-generated power make up about five percent of the energy supply and the rest comes from natural gas and coal. Oil and gas must continue to supply the major share of the world's energy needs for the next 30 years. Very little is expected from tidal, wave, and current power. Solar and wind power will be expanded on land but the output will remain small. Energy potential as we see it today cannot support a continued population and consumption increase. The alternatives to using petroleum for energy is not a subject of marine mining; but is sobering if we are to understand the importance of increasing oil reserves all that we can. Coal as an alternative presently furnishes 30% of the world's energy (80% in China, 20% in the United States), but it gives off more greenhouse gases per unit of energy than oil or gas. Coal is identified as the primary culprit in acid rain and will be constrained as a source of energy without major pollution control efforts. Coal reserves will reach a peak of production between 2100 and 2150 and the middle 80% of all coal will be produced between 2000 and 2300. Coal can replace oil for a time, but the problems of pollution control, mining, transportation; conversion for its use are awesome. Shale oil reserves are large, but mining and pollution controls as well as cost are something else. Almost 6,000 pounds of oil shale must be processed (requiring energy) to produce 2 barrels of oil. In processing, the loose, powdery residue produced is about ten times the original volume -- it will not stuff back in the same hole. The refining is water-intensive; and the occurrences of oil shales are in arid, semi-desert regions.
Of the energy alternatives, nuclear power is the most obvious and potentially the least polluting. It now furnishes about 5% of the world's power. The number of operable nuclear power units peaked in the summer of 1990. Capacity also peaked in 1990. Nuclear power plants require a ten year start-up and then have a 20 to 30% down time for maintenance and refueling. In the present atmosphere of fear and opposition created by the Three Mile nuclear plant and Chernobyl with clear evidence of engineering blunders, this alternative is less viable. As a bonus problem, uranium is in short supply. The U.S. has only enough to fuel the present reactors for their lifetime.
Renewable sources of energy -- wind, tide, solar, biomass -- have niches, but these are small compared to the overall need. Solar accounts for less than 0.5% of power generated in the US.Despite hopes for improvements in technology and manufacturing, the solar panels sold today for boats (one of the major users of solar power) are the same that were available 15 years ago. Solar panels and windmills simply cannot handle the present or future demand.
Growth of sugar cane for a biomass source in Brazil has introduced major degradation in the nearshore reef and wetland environments of coastal Brazil. But some alternative must be found; petroleum is too valuable a chemical feedstock to burn. Alternate power sources have more potential in underdeveloped nations where distribution systems are expensive and generally not present, and where local manufacture of the components will expand the industrial base.
The potential of present alternatives to petroleum can be put into perspective by comparing how they supply energy. An offshore platform producing 12,000 barrels of oil daily (energy available) equals:

• 10,000 windmills with blades 100 foot diameter
• 36 square miles of solar panels (6 x 6 mile square)
• one nuclear power plant of 1000 megawatt output
• 80 % of the output from Hoover Dam

Since 1985, US demand for energy has fairly steady at about 75 x 10¹⁵ BTU's of total consumption. Most of the energy generation (power plants) comes from consumption of oil, gas, and coal with oil supplying about 46%, natural gas 26%, coal 25% and hydroelectric and nuclear about 1%. Petroleum is also used as feedstock in an active petrochemical industry. Half of the oil consumed in the US is produced from United States reserves and half is imported at a cost of more than $50 billion per year. The cost of imports contributes almost 50 percent of our trade deficit. A study released by the U.S. Department of Energy estimates that at an increase in price of about $7/bbl and development of new recovery technology the U.S. could create an increased oil potential within the United States of 70 to 180 billion barrels of oil.

Reserves and Production

At the present, enough oil can be produced worldwide to meet current use, but increasing demand brings the amount of reserves and the rate at which they can be produced closer to the worldwide needs for consumption. The present estimate of total world oil reserves is 2100 x 10⁹ bbls and gas reserves are 10,000 x 10¹² ft³. The value of oil in our current economy is an important factor in conservation, and the present low prices have led to higher consumption and reduced efforts to search for new discoveries of oil and alternate methods for energy generation. This is very different from 1982 when major conservation efforts and a serious economic recession led the U.S. consumption to decline from a peak of 19 million to 15.3 million barrels per day. Not only do most of the reserves of oil and gas lie outside the United States, but the effort by American companies to find new oil is now directed to foreign exploration. Domestic production has dropped from 10.2 million barrels a day in 1975 to less than 7 million barrels a day by 1995. The 1990's have seen a major reduction in the size and efforts in exploration by U.S. companies. US production has been falling since 1985, except for a modest increase in 1991. As use climbed about 13 percent reliance on imports increased from 28 percent to 52 percent. US drilling activity is close to record low rates and provides little hope that the production decline can be slowed. Most drilling in the US now focuses on natural gas. Most of the major oil companies are turning to foreign exploration for new sources of petroleum and natural gas. The total number of drilling rigs operating in the U.S. dropped below 700 in 1992 and has remained low through 1995 and more than 400,000 jobs were eliminated in the oil and gas industry. The increase in crude oil prices in 2000 resulted in an increased drilling effort in the United States. After an eight year lag, workers were so hard to find that company recruiters were waiting at prison gates for released oil field hands.
Although oil reserves are being exhausted in the United states resources of natural gas remain high. The US has almost 1,300 trillion cubic feet of recoverable gas. Offshore hydrocarbon reserves are substantial and potential reserves are large, with possibly 40 percent of the world's undiscovered petroleum resources and production has been developed on the margins of every continent except Antarctica. High latitude regions are the present focus of exploration and development - Argentina, Chile, Canada, Norway, USSR, US. Offshore prospects are favorable off Asia in India, Burma, Vietnam, and China, and around South American and Central America and Mexico. Since 1965, record water depths for drilling have gone from 190 m to 2,120 m with production pushed to a water depth of 413 m. The intensity of exploitation reflects: the reserves and complexity of the geology; financial and legal incentives and environmental protection constraints imposed by national governments.
Halbouty estimated the area of the world's prospective offshore petroleum basins at about 31% of the world's total petroliferus basins. With increasing world petroleum consumption, the offshore will become increasingly important. In 1986, the offshore production accounted for more than 24% of total annual crude oil production, and offshore gas was about 19% of the world total. By 2000, the offshore could provide 50% of the total oil production.
link to petroleum
Another energy resource is gas hydrate which are crystalline substances composed of water and gas in a cage-like structure called clathrate. These are widespread beneath the sea in sediment of outer continental margins. Methane, propane, and other gases can be included in the clathrate structure, but methane hydrates appear to be the most common. The estimated amount of gas in the hydrate reservoirs of the world greatly exceeds the volume of known conventional gas reserves. In 2000, Congress appropriated 50 million dollars for research grants to fund develop of technologies for gas hydrate recovery.
The production history of the Russian Messoyakha gas hydrate field demonstrates that gas hydrates are an immediate source of natural gas that can be produced by conventional methods. World estimates for the amount of natural gas in gas hydrate deposits range from 1.1 x 10⁵ to 2.7 x 10⁸ trillion cubic feet for marine sediments. If estimates are valid, the amount of methane in gas hydrates is almost two orders of magnitude larger than the estimated total remaining recoverable conventional methane resources and offer an alternate to our dwindling oil supplies.

Pollution and Legal Problems Associated with Petroleum Exploration

Oil and gas drilling and petroleum pollution in general have become hot topics during recent years. The Amoco Cadiz and Exxon Valdez oil spills caused much of the present interest--both from the public and the scientific community. Attention has been focused on the possible effects of oil spills on coastlines and benthic, neritic, and pelagic organisms. The problem of floating oil will increase with tanker traffic. But it is not the only source of problems. Rig blow-outs can create massive oil spills , and these rigs are usually near a coastal region. The presence of tar and oil slicks are the most conspicuous effects. Tar may seriously soil beaches, and the clean-up may bring, as a secondary effect, beach erosion. Many marine organisms may accidentally feed on tar and become toxic. Both oil and gas drilling and petroleum pollution affect water quality, accumulate in sediments, change the distribution of marine organisms, and cause illness to marine organisms and human beings--that is, similar effects as from inland waste disposal. The increasing public concern with oil spills and pollution from drilling operations has been a factor in major cutbacks in the United States offshore drilling program.





Source

www.geology.uprm.edu