Literature Review of Hydraulic Fracturing in Tight Gas Reservoirs and the Formation Damage Induced by it and How can They be Eliminated
Engineering Honours Degree 2010
University of Adelaide
Because tight gas reservoirs cannot produce at economical rate, they need to be simulated. One way to do that is by injecting fluid at high pressure which is known as hydraulic fracturing. The choice of the fracturing fluid is so critical.
The report will be divided in to three different parts. The first part talks about different type of fracturing fluid. It will be shown that the industry mostly used guar derivatives fluid- linear gel- and they are water based but because the industry is moving toward tighter formation, the use of unconventional fluid such as 100% liquid CO2 is suggested because they result in less damage. However, due to its high treatment cost, most of the fracturing companies are using the water based fluids.
The second part talks about formation damage induced by hydraulic fracturing. The damage can be classified to hydraulic damage and mechanism damage. Hydraulic damage is caused due to water saturation increment near fracture vicinity while mechanical damage occurs as injected fracture fluids come in contact with the formation. Clay swelling is one type of mechanical damage and it can be avoided by designing the fracture fluid with enough salinity. Failing to do so, it will be impossible to restore the initial permeability hence the production rate. Hydraulic damage does not highly impact the productivity of the well compared with the mechanical damage in which even slight damage might highly impair the productivity.
The last part talks about some ways to remove the damage. One of the methods to facilitate the flowback of trapped gas is by using energized fluids. Fracturing fluids can be energized by N2, CO2, or CO2 with methanol. CO2 will always outperformed N2 due to the solubility of CO2 while CO2 will give similar results to CO2 with methanol. Therefore, if energizing is considered, CO2 should be the first choice. The second method is by using alcohol. The addition of methanol does not improve the return permeability unless it is occupied by high drawdown pressure. The effect of vaporization to decrease the water saturation- trapping issue- was investigated. If alcohol is used with vaporization, cleanup will be reached quickly. The last experiment was conducted to investigate the success of adding enzymes to overcome the polymeric damage. Two case studies will be presented that shows the special enzyme treatment is capable to enhance the production rate giving that the production rate after the hydraulic fracturing treatment is more than the production rate. Otherwise, the enzyme treatment will not be able to result in a production rate that is higher than the initial rate.