**6.1. Problem 1: fracturing the rock**

**Figure 9.** Annual precipitation in South Africa [22].

44 Aquifers - Matrix and Fluids

**Figure 10.** Location of shale gas basins in South Africa [14].

The main challenge of hydraulic fracturing is to create deep fractures in solid rock that is confined by the pressure associated with great depth. To accomplish this water is forced at high pressure through perforations in the well pipe. Pressures can be as high as 15,000 psi. In a horizontal well that is thousands of meters long, the fracking process is accomplished in multiple shorter sections.

This process uses vast quantities of water. In the USA it has been found that some wells use as little as 10,000 liters, but more typically wells are using in the range of 1 to 10 million liters, with some wells using more than 35 million liters. More important than the water use itself is the fact that the water use is consumptive, in that most of the water used to hydrofrack a well is lost within the fracked formation. The water that does return to the surface through the production well is too contaminated to be reused.

The water is only able to fracture rock if it is delivered at extremely high pressures. Pumps at the surface must not only pressurize the water but also deliver that pressure vertically and then horizontally through thousands of feet of pipe to the portion of the formation being fractured. This involves overcoming the frictional resistance to flow. This could not be accomplished without chemical friction reducers. Currently, organic polymers are most often used, but historically petroleum distillates were the friction reducer of choice.
