Smart waterflooding (SWF) is the science of injecting water of reduced salinity or modified potential determining ions (PDI) concentration in petroleum reservoirs for a specific brine/oil/rock system to obtain higher oil recovery efficiency. The study validates the surface interactions by zeta potentiometric measurements, estimates oil recovery, and generates relative permeability by core flood simulation through laboratory inputs, using in-situ samples of oil, water, and rock samples from one of the Giant offshore fields of India.

The main emphasis of this paper is on 1) Varying the ionic composition of the injection water and reducing salinity for injection purposes; 2) Tuning the concentration of PDI (Ca+2, Mg+2 & SO4-2) ions after fixing a reduced salinity, the surface ionic chemistry between carbonates and water results in altering the rock wettability; 3) Surface charge of oil-saturated whole core samples of rock in the presence of various diluted and smart brines were estimated by zeta potential measurements;4) Smart water flood for incremental recoveries; 5) Single porosity simulation model to match oil recovery and pressure profiles obtained from smart water floods.

The main conclusions of the study are 1) Wettability alteration in the carbonate rock tested to a more water-wet state by tuning the ionic concentrations of injection brine; 2) Zeta potentiometric studies with low-salinity waterflood (LSWF) in carbonate reservoirs can achieve positive results by:

  • Increasing the concentration of sulfate ion to increase the zeta potential of the rock surface to an optimum level above which the deposition of calcium sulfate will not become a problem;

  • Tuning the concentration of divalent cations, preferably calcium, such that the value of zeta potential is close to zero. At this stage, a weak bond exists between the oil and the rock surface due to a weak negative charge on the oil and a weak positive charge on the rock surface;

  • Increasing the hydrophobicity of oil by dilution of injected brine which seems to be responsible for increasing the zeta potential and detaching the oil from the rock surface. This is due to electrical double-layer expansion which is principally caused by reduced ionic strength.

3) Smart flooding experiments indicated an increase in the overall recovery factor; 4) A positive shift in the oil relative permeability curve towards the right.

The novelty of the paper is manifested by the following findings:

  • Potential of PDI for carbonate reservoirs at a high-temperature range and an optimum concentration of PDI, at which maximum oil recovery is possible.

  • Confirmation of Smart water flood effect in offshore carbonate reservoir through wettability alteration.

  • A more efficient method as compared to sequential dilution.

  • Underlying mechanisms of waterflooding involving the chemistry of injection brine in a carbonate system are investigated.

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