Literature Study on the Current State of Cold-Frac Technology
The production of gas from Tight Gas Reservoirs requires the creation of high permeable flow paths in the surroundings of the borehole by fracturing the reservoir formation.
For the frac processes several frac fluids were presented, described by their properties and behaviour in the reservoir formation and the practical experiences in using. Energized fluids such as CO2-foam or commingled CO2 fluids are predominantly used for the optimization of the backflow and the aimed proppant transport.
Cold fracturing fluids have strong cooling effect in fracturing process mainly in rock-stress reduction, however these kinds of fluids should be investigated precisely, in terms of thermal stress effect, cleanup process and proppant movement. Cold water fluid has been tested successfully in geothermal reservoirs. This stimulation technique is successful in this field but not in Tight Gas Reservoirs. The use of liquid CO2 as a fracturing fluid offers a viable method of stimulation. The successful application of these fluids to a variety of formations in USA was shown. The process has proven to be an economical alternative to conventional stimulation fluids. Liquid N2 has also been used in limited cases.
From these results it can be concluded, that liquid CO2 seems to be the most efficient frac fluid for future Tight Gas stimulations. The increase of fluid volume and decrease of injecting temperature and the proppant transport should be the direction for further optimization.