الملخص الإنجليزي
ABSTRACT
Lekhawair field is a carbonate formation located in the north of Oman and characterized by high temperature (70 °C), high salinity and hardness (salinity: 165 g/L, Ca2+: 10 g/L, and Mg*: 1.8 g/L). This study focused on the formulation and optimization low tension polymer water flood (LTPWF) in the Lekhawair field. Clear and stable surfactant slug at reservoir conditions (salinity and temperature) was obtained by mixing an anionic surfactant (Alkyl Ether Sulfonate (iC17E07S) with a polyethoxyethylenated (iC13E010) nonionic surfactant. Surfactant system (iC17E07S/ iC13E010)-brine-crude oil phase behavior at 70 °C was used as the primary screening method to identify oil-in-water microemulsion (Winsor type I) with high oil solubilzation parameter ratio (0.=125) at very low surfactant concentration (0.01 wt%). The promising formulations were validated by interfacial tension (IFT) measurements between the surfactant solution and crude oil. Ultralow IFTs as low as 10-9 mNmwere generated with the surfactant formulation. The selected polymer (AN-105) showed good compatibility with the surfactant solution and increased the brine's viscosity to oil viscosity at 70 °C (~ 5 CP) at relatively low concentration (2000 ppm) and high shear speed. Efficiency of the selected low tension polymer slug in terms of oil recovery was investigated in reservoir conditions. The surfactant (0.5PV) slug was injected into fully water flooded core samples resulting in tertiary oil recovery of 68.03% of OOIP. In additional oil recovery was obtained (71.91% of OOIP) when the core was aged overnight after surfactant flooding. In another experiment, surfactant-modified water injection (0.5 PV) was performed as a secondary recovery and resulted in an oil recovery of 75.33%. Finally, surfactant/polymer slug (0.5PV as SP mixture or as sequences of 0.25PV surfactant followed by 0.25PV polymer) was injected into a fully water flooded core, resulting in higher oil recoveries of 79.03% and 74.81% of OOIP respectively.
