What is crude oil exploration?

Processes & factors influencing crude oil exploration?

• factors such as temprature, volume, depth, and pressure affect the rate at which crude oil is being produced from the ground I want to know how all these factors affect the whole process

• Answer:

  It is a complex process, so I will try to hit on the most important factors. In past years oil exploration was done based on the observation of oil seeps at the surface. In many areas oil seeps out of the ground naturally, so these were likely places to drill. As geologic understanding grew, geologists realized that certain structures were likely to contain oil. The first geologist going into Saudi Arabia identified drilling sites from the deck of the ship before he even landed. He could see the structures that were likely to contain oil. As the easy finds have been drilled, the process has gotten much more scientifically rigorous. Often oil exploration starts with an exercise called basin modeling. Geologists look at ancient basins and use available evidence to determine 1) if there is adequate source rock of sufficient organic content and of the proper organic content to generate oil 2) if the burial and subsidence history of the basin was such that at some time in the past the source rock was forced to a depth where the temperature and pressure were ideal for petroleum generation 3) the oil expelled from the source rock had a migration path that allowed it to escape from the source rock 4) there were traps created by structure (anticlines, synclines, fault blocks, etc) or stratigraphy (variations in rock composition) that existed at the same time as the migration took place 5) there was a seal on the trap that prevented escape of the oil or gas over the long period of time that the oil resided there 6) the past heat gradient of the basin was such that the temperature of the source rock reached the ideal temperature range and did not get too hot or stay too cold. As you can guess, a good understanding of a basin's geologic history is necessary, including it's deposition, burial, subsidence, uplift, and faulting history. Misunderstanding or incomplete evidence of any one of these factors results in more risk of failure. The efficiency of the kitchen (the area where the organic material in the source rock is being 'cooked' into oil) can be evaluated with several different kinds of data. Certain organic compounds known as vitrinite can be examined and can give visual evidence of the maximum temperature they have reached. These samples are taken from well cuttings so the approximate depth of the sample is known. Bottom hole temperatures of existing wells are commonly measured and plotted on maps, as well as the temperature gradient coming up through the well. Apatite fission track analysis is another method for determining the thermal history of a sample and can tell the story of the burial history. If there is adequate organic material of the proper makeup and if it can be predicted that it reached a temperature of more than 140 degrees F, then it was likely to generate oil. While it was between 140 F and 320 F it would have been generating oil, and beyond about 200 F, it would have started generating natural gas. If it stayed in the high end of that range long enough, the oil would have changed to natural gas. Beyond about 390 F both oil and natural gas will break down and change to graphite. Understanding this thermal history will lead to predictions about the existence and the potential quantity of oil and gas in a basin. Pressure is also a factor in this process. When the hydrostatic or lithostatic pressure reaches a certain point, oil will begin cracking to form natural gas. Quite often this change can generate what is called overpressure in the reservoir, where the reservoir pressure actually is higher than lithostatic pressure and it can be dangerous for drilling if not anticipated. One of the most fascinating parts of this basin modeling process is that different oil reservoirs can be identified by a geochemical signature that can be traced back to the original source rock. Often when working in a basin there is more than one source rock, and more than one possible migration path to the trap. One of the most fascinating examples of this type of detective work was the identification of oil reservoirs in Brazil that came from source rock that is now in Africa. The oil formed when the two continents were originally splitting apart. If you really want to learn about the process here are the books I recommend: Hunt, John M, 1996, Petroleum Geochemistry and Geology. New York: W.H. Freeman and Co., 743 p. ISBN: 0716724413 Demaison, Gerard, and Roelof J. Murris, editors, 1984, Petroleum Geochemistry and Basin Evaluation, AAPG Memoir 35. Tulsa, Oklahoma: American Association of Petroleum Geologists, 426 p. ISBN: 08911813128 Beaumont, Edward A., and Norman H. Foster, editors, 1999, Exploring for Oil and Gas Traps: Treatise of Petroleum Geology. Tulsa, Oklahoma: American Association of Petroleum Geologists, ~1000 p. ISBN: 0891181602X