ABSTRACT
Waterflooding chalk reservoirs with seawater is an attractive option that has the dual advantages of substantially increasing the amount of petroleum ultimately recovered from the reservoir while maintaining reservoir pressure, thereby mitigating reservoir compaction and reducing the potential for seafloor subsidence. However, Newman found that North Sea chalks remain strong when injected with oil or formation water, but are much weakened when injected with seawater or a 30,000-ppm NaCl brine. Waterfloods were simulated by flowing heated simulated seawater or Tor Formation water through the sample after the rock had equilibrated strain at a constant effective axial stress of 4,000 psi for at least 46 hours. Seawater and formation water injection tests were conducted on the water free plugs at an axial stress of 4,000 psi in the same manner as the simulated seawater floods. Strain was equilibrated at 6,000 psi axial stress for approximately 30 days for the water free injection tests.
