Mobilization of Colloidal Particles by Low-Frequency Dynamic Stress Stimulation

Abstract

Naturally occurring seismic events and artificially generated low-frequency (1 to 500 Hz) elastic waves have been observed to alter the production rates of oil and water wells, sometimes increasing and sometimes decreasing production, and to influence the turbidity of surface and well water. The decreases in production are of particular concern, especially when artificially generated elastic waves are applied as a method for enhanced oil recovery. The exact conditions that result in a decrease in production remain unknown. Although the underlying environment is certainly complex, the observed increase in water well turbidity after natural seismic events suggests the existence of a mechanism that can affect both the subsurface flow paths and the mobilization of in situ colloidal particles. This article explores the macroscopic and microscopic effects of low-frequency dynamic stress stimulations on the release of colloidal particles from an analog core representing an infinitesimal section along the propagation paths of an elastic wave. Experiments on a column packed with 1 mm borosilicate beads and loaded with polystyrene microparticles demonstrate that axial mechanical stress oscillations enhance the mobilization of captured microparticles. Increasing the amplitude of the oscillations increases the number of microparticles released and can also result in cyclical spikes in effluent microparticle concentration during stimulation. Under a prolonged period of stimulation, the cyclical effluent spikes coincided with fluctuations in the column pressure data and continued at a diminished level after stimulation. This behavior can be attributed to rearrangements of the beads in the column, resulting in possible changes in the void space and/or tortuosity of the packing. Optical microscopy observations of the beads during low-frequency oscillations reveal that individual beads rotate, thereby rubbing against each other and scraping away portions of the adsorbed microparticles. These results support the theory that mechanical interactions between porous matrix grains are important mechanisms in flow path alteration and the mobilization of naturally occurring colloidal particles during elastic wave stimulation. These results also point to both continuous and discrete en masse releases of colloidal particles, perhaps because of circulation cells within the packing material.

Frequency dependence of mud volcano response to earthquakes

“…Thus long period waves with a given amplitude should be more effective at mobilizing trapped bubbles and particles that may be limiting permeability and the otherwise free flow of fluids and gas. Laboratory experiments confirm that oscillatory flows mobilize particles [e.g., Beckham et al, 2010] and trapped droplets [e.g., Beresnev et al, 2011].…”

An extended model for ultrasonic-based enhanced oil recovery with experimental validation

“…In addition, the ultrasonic energy is usually dissipated at the location of cracks & defects causing temperature distributions at these locations which in turn significantly contribute in oil recovery. Furthermore, it has been demonstrated that small oil droplets, which usually are found in the reservoir after primary recovery, may coalesce to form larger ones leading to the flow of oil which results in oil recovery [17,18]. In terms of ultrasonic frequencies, some practical experiments done in [19] showed that high ultrasonic frequency is better as compared to low ultrasonic frequency as long as the velocity of waves and their thermo sonic effects are concerned.…”

Maximization of wave motion within a hydrocarbon reservoir for wave-based enhanced oil recovery

“…It has also been suggested that the movement of the pore walls could also mobilize oil droplets trapped in pore spaces (Averbakh et al (2000); Beckham et al (2010); Beresnev and Johnson (1994); Beresnev (2006); Hilpert et al (2000)). That is, the vibration of pore walls can dislodge the trapped droplets and coalesce them into larger ones, allowing them to be mobilized and flow, as illustrated in Figure 2.…”

“…However, since waves at such high frequencies attenuate rapidly with distance, techniques relying on ultrasound waves are not viable for mobilizing oil droplets at the reservoir scale (Roberts and Abdel-Fattah (2009);Roberts et al (2001)). On the other hand, a number of laboratory tests have demonstrated dislodging of oil droplets by using elastic or acoustic wave sources at low frequency ranges: Beckham et al (2010), Roberts and Abdel-Fattah (2009), and Roberts et al (2001 showed that dynamic stress, exerted on a solid rock matrix of a sandstone core at low frequencies (10Hz -100Hz), can release trapped oil droplets; Vogler and Chrysikopoulos (2004), Thomas and Chrysikopoulos (2007) also showed that acoustic waves of frequencies up to 300Hz can remove the non-aqueous phase liquid (NAPL) from porous permeable core samples; Spanos et al (2003) conducted experiments demonstrating that fluid-pressure pulsing at frequencies ranging from 30Hz to 60Hz can increase the oil recovery rate from confined sand packs;…”