Geology And Geophysics

An Overview on Hydraulic Fracturing



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Hydraulic fracturing is a technique used to propagate cracks through geologic stratas in clay and rock formations underground. It is primarily used in oil and gas extraction industries but has uses in several other human endeavors such as mining and increasing bore water yields for agriculture. In the industries where it is used it is commonly abbreviated to fracing or hydrofac.

The power of water and its impacts on the solid surface of the Earth can be seen anywhere on the planet, we call it erosion when it impacts our farmlands. One of the most potently visible examples of this is the Grand Canyon in the United States of America. The water flow of rivers does not only rub away the surface of the rock it flows across. The pressure of the water forces it into cracks and fissures within the rock, expanding them and eventually breaking off portions. The broken off bits get carried and tumbled downstream to become the smooth, rounded pebbles we find in many places.

As a method of facilitating the extraction of desired resources from underground, hydraulic fracturing was initially experimented with in 1948 in the US and then used commercially from 1949 through to the present. While predominantly using water under pressure, it is not limited to that fluid only. Other liquid substances being more useful on occasion for specific strata compositions.

The liquids used normally contain suspended proppants (propping agents), such as small particles of sand or gravel. The pressurized liquid creates cracks in the weaker aspects of the geological formations it interacts with and the proppants lodge within these cracks, thus holding them open to a degree after the liquid has been removed. This has the effect of making the strata more porous, allowing the desired resource, whether water, oil or gas, to more easily flow into the main body of the well from the surrounding strata and therefore easing its extraction.

This is not, however, as easy as it may sound. It requires careful calculation and study of the strata this process will be enacted upon. Improper use and application of this process can produce more problems than it solves. The hydraulic fracturing not only needs to provide fracturing that is functional under the circumstances where it is applied, but needs to not result in a fracture face skin that blocks permeability. The applied pressure of the liquid will only travel so far through the strata creating cracks or fissures. The endpoint of that spread is referred to as the fracture face skin (FFS). If the methodology used is inappropriate to the specific circumstances, the FFS may block permeability beyond it. So that the desired mineral resource in the strata outside that fissured by the fracing may be blocked from easily flowing into the drilled well.

Because of this, hydraulic fracturing could well be considered as much an art as a science. While anyone with the appropriate aptitude, desire and skill set can do it, only those with the instinctive artistry can consistently do it well, and are therefore in high demand.

In mining, hydraulic fracturing can be used as a way to cause desired cave-ins, an alternative to explosives that has a higher likelihood of providing the desired result. In groundwater extraction for agricultural purposes, it is a method for increasing seepage into a bore well without the risk of contaminating the water supply.

Hydraulic fracturing is a very useful tool utilized in a number of industries involved in extracting resources from below the Earth's surface. In most usages it has the advantage of not leaving a waste or polluting component behind afterwards. Making it vastly preferable to many of the techniques used in mineral extraction around the world.

Sources:

Guangqing, Z., & Mian, C. (2009) Complex fracture shapes in hydraulic fracturing with orientated perforartions. Petroleum Exploration and Development 36(1): p103-107.

Hossain, M. & Rahman, M. (2008) Numerical simulation of complex fracture growth during tight reservoir stimulation by hydraulic fracturing. Journal of Petroleum Science and Engineering 60(2): p86-104.

Reinicke, A., Rybacki, E., Stanchits, S., Huenges, E. & Dresen, G. (2010) Hydraulic fracturing stimulation techniques and formation damage mechanisms – implications from laboratory testing of tight sandstone-proppant systems. Chemie der Erde – Geochemistry 70 Supplement 3: p107-117.


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