The injectivity index defines the flow conductance of the fluids from the injection well through the formation. From an operational point of view, it is important to maintain a sufficiently high injection rate for the SWAG mixture. Two main factors affect the injection rate-available injection power and injectivity index of the formation. Although hydraulic fracturing was not originally planned for the Siri injectors, it proved unavoidable because of unexpected low permeability in the water zone. The bottomhole pressure, and whether this exceeds the fracture-opening pressure, dictates the fractures' contribution to the injectivity.
Fractures enable injection of the desired volumes of water.
In Injector I-4, a dramatic increase in the injectivity index occurs at pressures close to the fracturing pressure. Injector I-1 shows a similar behavior, but the injectivity index increases less sharply above the fracturing pressure. For injector I-4, operation above the fracturing pressure improved the injectivity index by a factor of up to 4. As the GF increases, the injectivity index reaches a maximum, then declines rapidly toward the value without fractures. For this injector, the increase in injectivity index gained by fracturing the formation is completely lost if the GF becomes too large.