Increasing pump pressures to achieve improved injectivity in a water injection well had our client concerned about the potential for extensive fracturing in the reservoir. While part of the concern was that the fracture may extend to nearby production wells creating a shortcut for water to pass through the reservoir, the main concern was that the fracturing would extend vertically resulting in OOZI (Out Of Zone Injection).
55 and North utilised Baker Hughes MPwri software to analyse a number of potential scenarios around uncertainty in the field stresses, the reservoir permeability and the injection rates that might result from the increase in topsides pump pressure.
The results showed that for the majority of the cases run, OOZI was not likely to occur. Furthermore, that in those instances where the scenario showed a small level of OOZI these were extreme cases and unlikely to occur in reality.
The figure below shows the extent and width of the fractures following a 5 year injection period. Note that fracture lengths varied from layer to layer over time as re-pressurisation of different layers caused the poor-elastic effects to change the predominant fracture horizon.
The results of this work should give our client confidence to go ahead with their water injection plans, helping to maintain reservoir pressure and continued production.