Seeps petroleum

Petroleum—a natural mineral oil—was referred to as early as the Old Testament. The word petroleum means rock oil [from the Greek petros (rock) and elaion (oil)]. It has been found for centuries seeping out of the ground, for example, in the Los Angeles basin in what are now called the La Brea tar pits. Vast deposits were found in Europe, Asia, the Americas, and Africa. 

In addition to large oil spills, petroleum hydrocarbons are released into the aquatic environments from natural seeps as well as non-point-source urban runoffs. Acute impacts from massive one-time spills are obvious and substantial. The impacts from small spills and chronic releases are the subject of much speculation and continued research. Clearly, these inputs of petroleum hydrocarbons have the potential for significant environmental impacts, but the effects of chronic low-level discharges can be minimized by the net assimilative capacities of many ecosystems, resulting in little detectable environmental harm. 

On passive margins, seep flows are caused by (1) the escape of petroleum and natural gas driven by salt tectonics (Figure 19.21b), (2) artesian flows, (3) catastrophic erosion of sediments, and (4) submarine slides. 

Algal sources are ice algae, diatoms, cyanobacteria, dinoflagellates, and picoplankton petroleum sources include eroded bitumens, oil seeps, etc. 

Newtown Creek. Over the years, millions of gallons of oil and petroleum by-products were spilled on land. A significant fraction of these spills seeped into Newton Creek. When first discovered in the 1970s, the oil that had accumulated underground was estimated at 17 million gal and appeared to be spread over 100acres. About 9-3 million gal has been recovered and the spill area reduced to 55 acres. 

Petroleum—a natural mineral oil—was referred to as early as in the Old Testament. The word petroleum means rock oil [from the Greek petros (rock) and elaion (oil)]. It had been found over the centuries seeping out of the ground, for example, in the Los Angeles basin (practically next door to where this review is written) and what are now the La Brea Tar Pits. Vast deposits were found in varied places ranging from Europe, to Asia, to the Americas, and to Africa. In the United States the first commercial petroleum deposit was discovered in 1859 near Titusville in western Pennsylvania when Edwin Drake and Billy Smith struck oil in their first shallow ( 20-m-deep) well.6 The well yielded 400 gallons (gal) of oil a day (about 10 barrels). The area was known before to contain petroleum that residents... 

Petroleum oil has been known for centuries. Petroleum oil seeped through the earth in some places forming small pools of oil or sticky puddles of tar. In some places oil vapour and natural gas leaked through the cracks in the earth s surface and caught fire. 

Long-term exposure of microbial populations to certain toxicants often is necessary for adaptation of enzymatic systems capable of degrading those toxicants. This was the case with the Exxon Valdez oil spill in Alaska in 1989. Natural microbial populations in Prince William Sound, Alaska, had developed enzyme systems that oxidize petroleum hydrocarbons because of long-term exposure to natural oil seeps and to hydrocarbons that leached from the pine forests in the area. Growth of these natural microbial populations was nutrient limited during the summer. Thus the application of nutrient formulations to the rocky beaches of Prince William Sound stimulated microbial growth and helped to degrade the spilled oil. 

The first three together contribute around two-thirds of the total toxic releases. Air emissions alone involve more than 3 x 105 tons per year. In the same vein, approximately 106 tons of petroleum are released annually into the oceans due to natural seeps, or extraction-transportation-consumption processes. 

A petroleum seep is defined as visible evidence at the Earth s surface of the present or past leakage of oil, gas, or bitumen from the subsurface. Seeps have been utilized at least since ancient tribes of the Near East recovered blocks of asphalt from the Dead Sea. Many studies have demonstrated the worldwide correlation between seeps and earthquakes, with most visible seeps being near past or present areas of tectonic activity. The presence of seeps in a basin can considerably reduce the exploration risk because these seeps indicate that petroleum-forming processes have been active in the subsurface. In a situation where the major pathway for seeps is along a fault, the intensity and shape of the seep are significantly different from those situations where vertical leakage has occurred, and this difference permits their distinction. 

Throughout human history, people have collected petroleum to burn in lamps to provide light. They found petroleum seeping from cracks in rocks in certain locations. In fact, the word petroleum literally means "rock oil" and is derived from the Latin words for rock petra) and oil oleum). In the 19th century, as the U.S. entered the machine age and its population increased, the demand for petroleum to produce kerosene for lighting and as a machine lubricant also increased. Because there was no reliable petroleum supply, Edwin Drake drilled the first oil well in the United States near Titusville, Pennsylvania in 1859. The oil industry flourished for a time, but when Edison introduced the electric light in 1882, investors feared that the industry was doomed. However, the invention of the automobile in the 1890s soon revived the industry on a massive scale. 

There is abundant field evidence for the existence of SP cells over petroleum reservoirs. Indeed this evidence itself was used to find petroleum reservoirs for almost 100 years before the cells were recognised. It includes gaseous and liquid hydrocarbon seeps, paraffin deposits, halo-type metal anomalies, iron and manganese deposition, carbonate cementation, hard-drilling areas, magnetic anomalies (associated with magnetite mineralisation) and elevated uranium concentrations (Tomkins, 1990). Chapters 5-7 of this volume and references provided therein document many of these features. 

The preferential pathway model summarises the movement of hydrocarbon fluids through the subsurface to their final destination as a surface seep, either directly or by way of an intermediate trap. It is certainly not definitive nor complete, but illustrates some of the ehallenges eonfronting the petroleum geologist in his quest for new resources. 

In nearly all oil-producing basins, numerous seeps exist. Early usage of petroleum goes back to biblical times in the Middle East. The fact that seeps are often related to faults and fractures was noted, and it was even observed that seepages along the Dead Sea were activated during earthquakes. 

The beginnings of petroleum production are always around seeps. Some petroleum was collected as medicine, for example, near Modena (Fig. 1). In this case, the seep is along a thrust fault and nearby oil fields are not situated directly underneath the seep. However, many seepages take place along crestal fractures of anticlinal structures. The earliest mention of this fact was made by William Logan, the first director of the new Geological Survey of Canada, in 1842. He observed the coincidence of oil seeps with anticlinal crests in the Gaspe peninsula near the mouth of the St. Lawrence. 

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