Reduced well productivity or injectivity is often caused by near-wellbore formation damage in most of the existing oil and gas wells. The formation damage is caused by the invasion of fluids during the drilling and completion process and in a later stage by the deposition of particles (fines, scale, asphalthenes, etc) due to production. The conventional technique to remove these types of damage is the technique of hydraulic fracturing and matrix acidization. A promising new technique to remove the near-wellbore damage is high-frequency acoustic stimulation. It has the potential for being a relatively low-cost procedure for enhancing oil recovery in depleted fields, or returning some shut-in wells to production.
This paper reviews acoustic stimulation technology. Commercially available acoustic stimulation tools are comprehensively described along with their field testing and future research directions are proposed. Application of seismic stimulation for enhancing environmental remediation effect is also briefly discussed.
Near wellbore damage can arise due to many activities such as drilling, completion, production. This generally happens due to plugging of solid particles. For years industry is using well stimulation techniques to mitigate formation damage. The convention well stimulation techniques include two main classes -Matrix acidization and Hydraulic Fracturing. Although they have been applied successfully to many fields but they suffer from certain limitations.
Petroleum industry is now implementing a promising new acoustic stimulation technology to combat the effect of formation damage. Successful applications have also been found in improved, oil recovery. Acoustic stimulation technology has the potential for being a relatively low-cost procedure for enhancing oil recovery in depleted fields. Field tests of the technology, however, have yielded promising but mixed or inconclusive results.
Interest in acoustic or seismic stimulation started in the 1950s with observed correlations between water well level and seismic excitation produced from railroad trains and earthquakes. It was noticed that a rise in well fluid levels and an increase in fluid (pore) pressures were associated with earthquakes and cultural seismic noise. Similar effects were observed in producing oil fields where distant earthquakes caused increases in production, and wells close to operating machinery, highways or railroads appeared to produce more oil than wells in quieter areas. These anecdotal observations motivated Russian researchers to perform surface vibroseis stimulation tests in several producing oil fields. The results of these early field tests were mixed. In some fields, production increased after vibroseis stimulation, but in others the production actually declined. It became clear that a better understanding of the stimulation phenomenon was needed before it could be exploited reliably. This led to numerous research efforts beginning in the early 1970s and continuing today. Beresnev and Johnson (1994) provide a comprehensive review of over 100 Russian and U.S. technical articles and patents on the effects of seismic and acoustic stimulation on fluid flow in porous media, including laboratory investigations, theoretical studies and field tests. Documented work covers the use of a wide range of stimulation wave types and energy coupling modes, with frequencies spanning the range of one Hz to five MHz.
