An Experimental and Modelling Study to Evaluate the Potential of Low-salinity Waterflooding in a Tight Carbonate Reservoir
Creators: name: Singh, Navpreet
Publisher: name: Graduate Studies
Year: 2023
Subjects: subject: Low salinity waterflooding
subject: Zeta Potential
subject: Smart waterflooding
subject: Smart brines
subject: diluted sea water
subject: Engineering--Chemical
subject: Engineering--Petroleum

description: Over the years, the low-salinity water flooding (LSWF) process has received a lot of attention as a promising enhanced oil recovery (EOR) method due to its superior performance over conventional water flooding. It has been an area of great interest for the researchers for almost last three decades for its cost effectiveness and the potential benefit over other enhanced oil recovery (EOR) techniques. Conventional waterflooding is not as effective especially in carbonate reservoirs as they tend to be more oil wet. The objective of this study is to modify the ionic composition of the injection brine in a way that leads to higher incremental oil recovery for a specific carbonate reservoir. Before doing any of the experimental studies to study the rock-brine-oil interactions in a LSWF process, we characterized the physical and chemical properties of rock and fluid to understand the reservoir. Experimental components of this study included reservoir-condition high-pressure high-temperature (HPHT) displacement tests in composite cores using brines of different salinities and specially designed ionic compositions, investigation of wettability alteration in a unique and specifically designed HPHT imbibition cell, interfacial tension (IFT) studies and Zeta potential studies using a Zeta potentiometer that provided a more representative evaluation in brine-saturated whole cores rather than with pulverized samples. These studies gave us an insight to the rock-brine-oil interactions. Simulation studies involved flow simulation using geochemical reactions during LSWF, incorporating oil/brine/rock interactions, and linking laboratory data to simulation data from the given candidate reservoir. Findings of the coreflooding experiments conclusively showed that LSWF with certain specific ionic compositions yielded a higher oil recovery. HPHT imbibition tests provided visual and quantitative estimations and monitoring of how wettability alteration took place during LSWF and how it was impacted by the degree and magnitude of temperature and pressure. Zeta potentiometric studies enabled an investigation of the charging behavior at the rock-water interface at various salinities using a whole reservoir core rather than pulverized samples. A new method to estimate Zeta potential in a high-salinity environment was developed and validated, and it conclusively proved that rock-surface charge played a vital role in the LSWF process. Results of various experiments conducted indicated that lower ionic strength brine can yield higher oil recovery. Coreflooding experiments revealed that low ionic strength brine, particularly 1% diluted seawater (1% dSW) flooding, had the highest incremental recovery factor due to increased repulsive forces between the oil-brine and rock-brine surface. Zeta potential measurements showed that the addition of divalent anions, such as SO42-, to smart brine could generate more negative values than 1%dSW, but this must be weighed against the potential for sulfate ions to cause scaling on the porous formation and reduce fluid permeability. Divalent cations like Ca/Mg ions did not help in increasing oil recovery. Wettability alteration was observed as the dominant mechanism for improving oil recovery in LSWF experiments. IFT, Hele-shaw model and Zeta potential measurements indicated that rock-water interactions were more dominant than oil-water interactions. A statistical model was developed to predict the zeta potential for a given brine based on the comprehensive analysis of the various experiments. At the end, the simulation studies involved history matching of coreflooding displacement tests to predict the performance of various diluted brines, and incorporate various geochemical reactions occurring during a LSWF process. Developing a proper geochemical reservoir model requires the measurement of effluent concentration and history matching of effluent concentration. We used the geochemical reactions published in the literature to simulate LSWF process.