Performance Investigation of Organic Acids on Carbonate Rocks

Acidizing involves a wide range of stimulation treatments that can yield impressive production increase if properly applied. Acidizing treatments can be divided into two categories; matrix acidizing and fracture acidizing.In sandstone matrix acidizing the intend is to dissolve and/or disperse materials that impair well production by blocking or bridging the pore throats in matrix, thus ideally recovering the original reservoir permeability. Carbonate acidizing dissolves the formation minerals around the damage therefore creating new flow channels between the wellbore and the formation without fracturing the producing formation. Increase in permeability will decrease pressure drop associated with production or injection of fluids. Not all damages are acid-soluble.In most carbonate-stimulation treatments, HCl is pumped as the main stimulation fluid. HCl is cheap and has a high rock-dissolving power, and the reaction products are usually soluble. However, the HCl/carbonate reaction is also fast, especially at the higher downhole temperatures. The rapid HCl spending prevents deep penetration of acid into the formation. This results in only short wormholes or even compact dissolution with only a marginal skin decrease. There are several options to lower the HCl-spending rate. Of them using polymers and emulsified acid can be stated.An alternative approach is to switch to other, less aggressive acid types, such as acetic or formic acid. These organic acids are good alternatives to HCl and find more applications as cleanup and stimulation fluids, especially in high-temperature wells. Compared to HCl, organic acids spend slower on carbonate rock (retarded reaction rate), providing deeper penetration into formation and improved stimulation through providing more conductive length. Additional benefits of organic acids vs. HCl are lower corrosivity and a reduced tendency to form acid/oil sludge in asphaltene-rich crudes.

Keywords:

carbonate acidizing , organic acids , spending rate , acid penetration , incomplete spending