Research related to weak elastic wave stimulation of oil reservoirs started in the late 1950's. Activity peaked in the 1970's and 1980's in the US and in the Soviet Union. However in recent years there has been a resurgent interest and research. This interest derives form observations made in some fields near areas affected by earthquakes and, even heavy traffic, where changes in water level and oil production have been observed. For example, some variations in oil production were noticed in Kern County during the Southern California earthquake of July 1952. However, mechanism associated with earthquakes are very complex and variations in oil production or water level could be consequences not only of seismic vibrations, but also of rock fracturing and other effects associated with earthquakes.
Two different types of waves are usually distinguished: high power frequency (around 20 kHz) and low power frequency waves (e.g. 40 Hz).
High power frequency waves have a local effect in the reservoir and are mainly applied for wellbore stimulation. Their effects are limited to a region close to source due to higher sound absorption in the porous medium at higher frequencies.
Low frequency acoustic waves effects can cover a larger region and are consequently used for reservoir, rather than well stimulation. They are generally applied by using surface vibrators, but there are also example of downhole applications.
This paper is primarily focused on waves used for reservoir stimulation, as opposed to well stimulation. It aimed at understanding the main mechanisms associated with the application of vibrational energy in porous media, and assessing laboratory and field studies.
In this paper, together with potential mechanisms, laboratory and field trials are discussed.