Clarifications on Oil/Heavy Oil Recovery Under Ultrasonic Radiation Through Core and 2D Visualization Experiments
Authors: Naderi K. , Babadagli T. 
Published: March 2010

Abstract
Our previous research on the effects of ultrasonic waves on oil recovery conducted at the University of Alberta had shown that capillarity and interfacial tension (IFT) might be responsible for the observed improvements in incremental oil recovery. Although the results seem encouraging, questions about the mechanism and effective parameters causing additional recovery still remain.
To analyze the influence of parameters other than IFT and capillary forces, we conducted capillary imbibition experiments on cylindrical Berea sandstone core samples under ultrasonic radiation, and the results are presented in this paper. Through this experimental scheme, we focused on:the effect of initial water saturation for rocks with different wettability;oil viscosity; andmatrix wettability. The cores were placed into imbibition cells where they were contacted with an aqueous phase. Every experiment was conducted with and without ultrasonic radiation for comparison. Different intensities of ultrasonic waves were tested as well.
To investigate the acoustic interaction between rock and fluid, we performed certain visualization experiments. We used 2D glass bead models to clarify the effects of ultrasonic waves on the oil displacement process for different oil viscosities and matrix wettability through comparative analysis.
The qualitative and quantitative observations and analyses presented are expected to provide additional understanding regarding investigations in the use of in situ recovery of oil/heavy oil, as well as surface extraction.

Introduction
Acoustic energy was considered as one of the unconventional EOR methods to replace or to be applied with conventional ones. Studies have been conducted to understand the effects of acoustic energy on oil recovery over the last four decades. Duhon and Campbell(1) performed waterflood tests of cores with ultrasonic energy and showed that the ultrasonic energy improved the oil recovery and displacement efficiency in the cores.
Beresnev and Johnson(2) performed a critical analysis of the work done in this area up to the early 1990s and provided a comprehensive review of the seismic and ultrasonic stimulation studies. They concluded that the elastic wave and seismic excitations of porous media affect permeability and production rates in most cases
Kuznetsov et al.(3) reviewed seismic techniques for enhanced oil recovery and observed an increase in oil/water relative permeabilities and also oil recovery after elastic vibration. They concluded that this increase is due to fines removal by vibration.
Roberts et al.(4) applied mechanical stresses to rock samples which were placed inside a core holder and observed changes in permeability and an increase in wettability in the non-wetting phase.
There also exists field-scale applications of sound waves of different characteristics. Spanos et al.(5) observed improvements in waterflooding and injectivity when pressure pulses were applied by a hydraulically-operated tool. Westermark et al.(6) applied a complex system of vibration tools in the field and observed an improvement in permeability at certain intensities and up to a 20% increase in the oil production rate. Zhu et al.(7) documented the results of the application of a special downhole vibration tool in several oil fields in China, pointing out that sand content, water content, viscosity and density of oil decreased after treatment.