Hamidreza Shahverdi

Enhanced oil recovery from carbonate reservoirs by spontaneous imbibition of low salinity water

An experimental study was performed to investigate the impact of low salinity water on wettability alteration in carbonate core samples from southern Iranian reservoirs by spontaneous imbibition. In this paper, the effect of temperature, salinity, permeability and connate water were investigated by comparing the produced hydrocarbon curves. Contact angle measurements were taken to confirm the alteration of surface wettability of porous media. Oil recovery was enhanced by increasing the dilution ratio of sea water, and there existed an optimum dilution ratio at which the highest oil recovery was achieved. In addition, temperature had a very significant impact on oil recovery from carbonate rocks. Furthermore, oil recovery from a spontaneous imbibition process was directly proportional to the permeability of the core samples. The presence of connate water saturation inside the porous media facilitated oil production significantly. Also, the oil recovery from porous media was highly dependent on ion repulsion/attraction activity of the rock surface which directly impacts on the wettability conditions. Finally, the highest ion attraction percentage was measured for sodium while there was no significant change in pH for all experiments.

Impact of water saturation and cation concentrations on wettability alteration and oil recovery of carbonate rocks using low-salinity water

In this study, the effect of initial water saturation on the oil recovery for carbonate rocks is investigated using spontaneous imbibition experiments. The experiments are performed using 20 times diluted sea water as imbibing fluid and the sea water as initial water. In addition, the impact of pH and Ca2+, Mg2+, Na+, and K+ cations concentration change of imbibing fluid are investigated during tests. These results help to identify the active cations in the wettability alteration process of carbonate rocks during the low-salinity water injection. A mechanism is proposed to describe the effect of initial water saturation on the oil recovery by low-salinity water injection. The impact of initial water saturation on the wettability alteration might be positive or negative depending on its value and the rock permeability. The comparison of divalent cations concentrations shows that the minimum adsorption of Ca2+ and maximum desorption of Mg2+ lead to maximum oil recovery of spontaneous imbibition. The results confirm that three cations of Ca2+, Mg2+, and Na+ are active for wettability alteration of carbonate rocks in the presence of sea water as initial water and diluted sea as imbibing fluid, whilst the amounts of potassium remain constant.

Co-estimation of saturation functions (kr and Pc) from unsteady-state core-flood experiment in tight carbonate rocks

Abstract The production from oil and gas reservoirs is greatly affected by rock and fluid properties of the porous rock. Capillary pressure (Pc) and relative permeability (kr) are two important properties employed in the mathematical simulation reservoirs for predicting oil recovery from underground hydrocarbon resources. In this study, various core-flood experiments were performed using different tight carbonate rock samples for oil–water and oil–gas systems. The objective of this research is to investigate the multi-phase flow functions (kr and Pc) in tight formations. The kr curves of each sample were obtained by two different mathematical methods: the history-matching (ant colony optimization) technique and analytical method (JBN). The comparison between the relative permeability of the history-matching technique with that of the JBN method revealed a significant discrepancy between them. The modeling of an experiment using kr of JBN revealed a significant difference between experimental and simulation oil production, whereas the relative permeability of history matching accurately reproduced the experimental oil recovery. This observation highlights the inadequacy of the JBN technique for determination of relative permeability in particular in the tight rock where capillary forces are important. In addition to the relative permeability, the capillary pressure values as a function of saturation were estimated from core-flood tests using a history-matching technique. The comparison between oil–water capillary pressures obtained from centrifuge tests with those of core-flood experiments depicted good agreement, whereas the capillary pressure of oil–gas system measured from core-flood tests was considerably different from centrifuge experiment results. This outcome demonstrated that the capillary pressure obtained from centrifuge experiments in some cases may not be representative of dynamic capillary pressure governing the multi-phase flow in porous media.

Investigation of three-phase relative permeabilities and hysteresis effects applicable to water alternating gas injection

Large quantities of oil usually remain in oil reservoirs after conventional water floods. A significant part of this remaining oil can still be recovered economically by Water-Alternating-Gas (WAG) injection. Accurate numerical simulation of complex three