Have you ever thought where does Gallons of petroleum come from and why is that Petroleum is so Scarce…. Let us know the Industrial technique to find the availability of petroleum in a particular region.

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Petroleum refers to any naturally occurring hydrocarbons that are found beneath the surface of the earth, no matter whether these hydrocarbons are solid, liquid or gas. The solid and semi-solid forms of petroleum are called asphalt and tar. Whereas liquid petroleum is called crude oil if it is dark and viscous, or condensate if it is clear and volatile. And of course there is natural gas, which can be associated with oil, or found entirely by itself.

Mankind has used the various forms petroleum for centuries. The Babylonians used asphalt to pave paths and caulk boats, and the ancient Egyptians used tar to prepare their mummies. In fact, mummy is a derivation of the Arabic word for tar. Condensate was an essential ingredient of Greek fire, the secret weapon of Byzantium, and the ancient Chinese used natural gas to light their imperial palaces. These ancient cultures found petroleum by simply looking for oil seeps or gas seeps and hoping that an adequate source was nearby, but the search for oil and gas today is much more complicated.

Petroleum Geology

Several geologic elements are necessary for oil and gas to accumulate in sufficient quantities to create a pool large enough to be worth producing. These elements include an organic-rich source rock to generate the oil or gas, a porous reservoir rock to store the petroleum in, and some sort of trap to prevent the oil and gas from leaking away. Traps generally exist in predictable places – such as at the tops of anticlines, next to faults, in the updip pinchouts of sandstone beds, or beneath unconformities.

To find a convergence in the subsurface of the geologic elements necessary to form an oil or gas pool requires a careful blend of science and art. To discover what geometries and compositions the rocks might possess deep underground, geologists examine the rocks where they are exposed in surface outcrops, or they examine aerial photographs and satellite images when surface access is limited. Geologists also work closely with geophysicists to integrate seismic lines and other types of geophysical data into their interpretations. 

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The collection of seismic data involves sending shock waves into the ground and measuring how long it takes for the subsurface rocks to reflect these waves back to the surface. The shock waves that are used today are usually generated by pounding the earth with giant vibrator trucks, but in the past gephysicists preferred to explode small dynamite charges in shallow holes. However, environmental restrictions in most places today prevent using explosives to collect seismic data.  

 When shock waves created by the vibrator trucks travel into the earth, boundaries between the rocks reflect the waves back, and the arrival times of the waves back at the surface are detected by listening devices called geophones. Computers then process the geophone data and convert it into seismic lines, which are nothing more than two-dimensional displays that resemble cross-sections.

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Seismic lines in the old days were just that . . . two-dimensional lines created by laying the geophones out in single line. But today, the data is commonly collected as an intersecting grid of seismic lines referred to as 3-D seismic volume. Data collected in this fashion may even be used to help create 3-D computer models of the underground geometries of the rocks.

Geologic and geophysical clues are enticing, but drilling is the only way to learn if an oil or gas field really exists. Once a well is drilled, well logs yield data on the types of rock present and, most important, what fluids these rocks contain. The information interpreted from the logs is used to decision whether a well should be completed and used to produce oil and gas, or filled with cement and abandoned. The logs are also used to update the geologic models originally used to locate the well.

Known Facts

Today, the average wildcat well has only one chance in ten of finding an economic accumulation of hydrocarbons. A rank wildcat, if drilled in a frontier area, stands only one chance in forty of success. The odds are much better for a development or extension well, but nothing is a sure bet in the oil business. Thus, even though explorationists (oil and gas prospectors) of today have better tools than their ancient predecessors, luck remains a significant factor in the search for oil and gas. The reality is that most wildcats turn out to be dry holes, in fact about 82% of those drilled. Also, not every development well becomes a producer, which demonstrates that nothing is a “sure bet” in the oil industry.

Courtesy: http://www.sjvgeology.org

Posted By

Mahesh.P

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