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

Mohammad Reza Zaeri,Mohsen Mohammadi,Hamidreza Shahverdi,Rohallah Hashemi

doi:10.1007/s13202-018-0552-2

Abstract

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.

Highlights

The development of technology in the recent century has increased the consumption of the fossil fuels in the world, since the oil production from many reservoirs have been declined, the oil companies are interested to invest for the technologies that enhance the oil recovery (EOR technology)
The matrices have low permeability, and the capillary forces are dominant in the matrix region of carbonate rocks, so that the oil recovery from these rocks is lower than the sandstone reservoirs
The results showed that the initial water saturation in a certain range (15–25%) positively affected the wettability towards the water-wet condition, whereas the oil recovery from water-flooding tests decreased with increase in water-wetness of the rock (Zhou et al 2000)

Summary

Introduction

The development of technology in the recent century has increased the consumption of the fossil fuels in the world, since the oil production from many reservoirs have been declined, the oil companies are interested to invest for the technologies that enhance the oil recovery (EOR technology). Wettability alteration of pore surfaces towards water-wetness by imbibing fluid would be one of the main mechanisms that lead to the oil production from core plug during imbibition test.

Results

Conclusion