Enhanced oil recovery through integration of ultrasound and polymer flooding

Hassan, KJ

Abstract

Initially, when an oil well is drilled the oil gushes to the surface at high pressure. However, with time the pressure declines leaving more than 50% of the oil trapped in the reservoir. Even with the introduction of current technologies, more than 40% of the oil remains unrecoverable. Enhanced oil recovery from these mature and declining oilfields is receiving extensive research attention. Cost effectiveness and environmental impact are vital factors for consideration. Ultrasound application, as a cheap and environmentally friendly recovery method, is independently being investigated, to a limited extent, in enhanced oil recovery. Other forms of enhanced oil recovery that employ chemical injection including polymer flooding are being studied separately, but full potentials and mechanisms involved are yet to be fully understood. It is in view of this, that this experimental investigative research combined both ultrasound and polymer flooding, as a novel and innovative approach for increasing the overall recovery from carbonate and sandstone reservoirs at petroleum reservoir conditions.
The methodology involved petrophysical and geophysical analysis. The petrophysical analysis included interfacial tension measurements and characterisation of hydrolysed polymer acrylamide polymer solutions. The geophysical analysis characterised the pore properties of sandstones and carbonates. The other components of the methodology entailed the investigation of oil recovery from polymer flooding without ultrasound, and polymer flooding with ultrasound as well as the evaluation of enhanced oil recovery (EOR).
Hydrolysed polyacrylamide (HPAM) polymer solutions of varying molecular weight ranging from 6 million Daltons to 23 million Daltons were characterised through analysis of the viscosity and viscoelastic properties at different concentrations. HPAM polymer solution concentrations were 400ppm, 800ppm, 1200ppm, 1600ppm and 2000ppm. The viscosity, viscoelasticity as well as hysteresis behaviour increased with increased concentration.
Sandstone and carbonate reservoir rocks were subjected to computed tomography scans to determine and confirm pore size and pore distribution. The scan images obtained were reconstructed with VG MAX 2.2 Volume graphics to determine pore properties. The sandstone core samples were Berea upper and Berea lower, and the carbonates were Guleph dolostone, Indiana Limestone and Edward brown. The scans indicated the confirmation of the presence of interconnected pores. Sandstones showed greater pore uniformity than carbonates.
An acoustic core holder and signal power amplifier were used to generate ultrasound waves. The frequency of the waves ranged from 20 to 100KHz. Preliminary core flooding indicated highest power, intensity and fluid displacement occurred at a frequency of 20±0.5 KHz. Thus, subsequent core floods were conducted at 20±0.5 KHz.
Two displacement positions were considered with UFS-200 core flooding equipment: horizontal displacement and vertical displacement. In both displacement scenarios, the highest oil recovery was obtained from the sandstone cores irrespective of the pore volume injected when compared with carbonate core oil recovery. The highest recovery for sandstones was 80% and 68% for carbonates. High differential pressures were obtained in all the carbonate core samples with the application of 400ppm HPAM and lower differential pressure in sandstones. This was attributed to the anionic charge of HPAM and the cationic charge of carbonates leading to blockage of the interconnected pores and potential for formation damage. The utilisation of 400ppm HPAM solution during core flooding enhanced safety and minimised the potential for pore blockage as well as reduced potentials for excessive pressure generation.
The application of ultrasound and polymer flooding simultaneously showed improved oil recovery in sandstone and carbonates. The acoustic coupling potential of HPAM was confirmed as wave transmission improvement was observed. However, the use of anionic HPAM for carbonate reservoirs was deemed unfavourable in oil recovery.

Citation

Hassan, K. Enhanced oil recovery through integration of ultrasound and polymer flooding. (Thesis). University of Salford

• Thesis Type: Thesis
• Deposit Date: Feb 5, 2021
• Publicly Available Date: Feb 5, 2021
• Award Date: Dec 1, 2020