The Injection Above the Fracture Pressure (IAFP) has became one of the most important alternatives to guarantee high injection rates, even when the quality of the injected water is below the minimum requirements for not damaging the rockreservoir. For this reason IAFP has found a vast application in both, the discard or re-injection of oily water or water with high solid content and to maintain the injectivity index of injector wells.

In Campos Basin, an interesting application of IAFP to assure the injection rate has been done in a pair of parallel horizontal wells completed with HOHGP (horizontal open hole gravel pack) in a Maastrichtian reservoir, where the fracture growth has been monitored through Hall Plots. In the first group (IAFP for water discard) some new projects have been planned, such as an "ecological well" (so called because the reduction of discard) which plan to inject large amount of water in dolomites.

All these projects were preceded by a fracture growth analysis. Usually, these analyses are carried-out by using simulators which are based in Linear Elastic Fracture Model theory (LEFM) and consider a single planar fracture. However, in the case of IAFP in non-consolidated sandstones or soft carbonates, these assumptions can be quite unrealistic. Effects of plastic deformation in the fracture tip, compacting or fluidization of porous media, multiple fractures and pore-elastic effects can be predominant in these cases.

An example that ratifies this was the attempt to re-inject produced water above the fracture pressure in an unconsolidated Miocene reservoir. Even with injection pressure 800 psi above the fracturing pressure (measured through a previous minifrac), it was impossible to propagate the fracture. In another well, the IAFP was aborted when a completely unexpected fracture gradient greater than 0.83 psi/ft was attained (it was expected 0.52 psi/ft). This behavior can only be explained if we consider the occurrence of any different phenomena of those foreseen by LEFM.

This work details the IAPF projects here mentioned and depicts the deviations of LEFM observed in IAFP wells in Campos’ Basin.

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