Paper: Scale Removal With Downhole Shock Waves

Wellbore flow barriers, such as scale deposits, can be pulverized by a new technique that utilizes high-intensity sonic shock waves of microsecond duration. Improvements in well productivity have been realized in field tests at costs substantially below those of conventional remedial services. The Sonic Shock Tool is lowered in the well on a wireline. It is powered by a high-voltage arc whose shock waves in well fluids hammer the casing walls and openings with a high-intensity impact of microsecond duration. Mineral deposits, such as barium sulfate, gypsum and calcite (alone or mixed with each other or with oily residues), are susceptible to these high-intensity shock treatments. The tool can operate in acid or organic solvents if special conditions warrant their use. The rarification following the shock wave causes a large part of the scale in the casing perforations to fall down inside the casing. These pulverized deposits are bailed out of the well. Due to reductions in pressure and temperature as reservoir fluids enter a producing well, solid deposits of minerals and/ or asphaltic or waxy materials tend to build up in the openings into the wellbore and inside the well. Serious interference with well productivity often results. About five years ago, Sonics started working on a downhole tool aimed at breaking up these deposits and restoring productivity with shock waves produced under liquid opposite the perforations. First efforts were with a high-power ultrasonic transducer which produced a strong cavitation and shock waves. This did successfully break up the scale. However, it had two fatal shortcomings: ambient pressures above about 200 psi stopped the cavitation - and the shock waves - and the cleaning. Also, when the power was increased, it began tearing up the surface of the transducer. Efforts were then changed to the use of repetitive high-voltage shocks to break up the wellbore restrictions.