Abstract
In the process of CO2 enhanced oil recovery (CO2-EOR), CO2interacts with formation brine containing high concentrations of scale-forming ions to produce inorganic salt precipitation, which blocks the rock pore throats, changes the characteristics of the reservoir and thereby reduces the oil recovery rate. In this study, a series of experiments on the static reaction of CO2-formation brine were conducted. The amounts of precipitation formed from the interaction of CO2-formation brine under various conditions were tested. Using the PHREEQC software, the mathematical characterisation formulas between the precipitation amount and various environmental factors (e.g. temperature, pressure difference, scale-forming ion concentration and pH) were established. On this basis, a numerical simulation model of CO2 flooding in a typical area of Oilfield C was established. The distribution of inorganic salt precipitation during continuous gas flooding was predicted, and the effect of inorganic salt precipitation on oilfield recovery was analysed.
Highlights
As indicated by relevant studies on CO2 flooding for enhanced oil recovery (EOR), the injected CO2 is involved in strong chemical reactions with the formation brine, and the generated precipitates block the rock pore throats and reduce the porosity and the permeability of the reservoir
The Eclipse E300 module was used with the mathematical characterization formula to correct mathematical model parameters, optimize reservoir engineering parameters, simulate the distribution pattern of inorganic salt precipitation generated during the CO2 -EOR process in a block of oil field
The concentrations of Ca2+ in the initial formation brine and the liquid samples taken out of the system each time were determined by inductively coupled plasma emission spectrometry
Summary
As indicated by relevant studies on CO2 flooding for enhanced oil recovery (EOR), the injected CO2 is involved in strong chemical reactions with the formation brine, and the generated precipitates block the rock pore throats and reduce the porosity and the permeability of the reservoir. Based on previous research results, in this paper, the influences of various environmental factors (e.g., pressure difference, temperature, and scale-forming ion concentration) on precipitation formation from the reaction of CO2 and brine were investigated quantitatively. Using the PHREEQC software, the effect of pH values was simulated, and the corresponding exponential mathematical characterization formula was established via mathematical regression On this basis, the Eclipse E300 module was used with the mathematical characterization formula to correct mathematical model parameters, optimize reservoir engineering parameters, simulate the distribution pattern of inorganic salt precipitation generated during the CO2 -EOR process in a block of oil field.
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