Abstract
Active cavitation is novel, powerful, coiled tubing or workstring conveyed technology. Cavitation is the process of creating transient vapor filled cavities in a fluid at ambient fluid pressures exceeding the vapour pressure in the cavities. Implosions of such cavities are known to cause damage to ships propellers and pump impellors, however the effects can also be usefully applied for many purposes, including applications in the well construction and well servicing disciplines.
Commonly known cavitation occurs in low-pressure areas when a fluid flows around an obstruction or past the surface of an oscillating body; this type of cavitation is referred to as passive cavitation.
The particular technology described in this paper is referred to as ‘active’ cavitation. This is a method using liquid hammer enhancement to create vapor bubbles at much higher ambient pressures than previously possible. The vapor cavities at low pressure points created at high ambient pressure implode violently and decay into smaller bubbles thus significantly extending the life and extent of the low-pressure zone or ‘cavitation flare’ and enhancing the action of the jetstream flowing from the cavitator. A particular value of cavitation is that it produces a twofold effect, i.e. a combination of suction effects in the decaying cavitation flare and shock wave effects that reach much further away from the cavitation generating tool.
Active cavitation can for instance be employed to improve the hole making process, clean reservoir rock or remove scale and deposits from well completion equipment. Thus, use of cavitators allows intensifying rock fragmentation and bit cleaning. During field trials in Russia it was demonstrated that drill rates can be increased by up to 40% and bit life can be extended by up to 25% compared to the performance of previously applied bits. When using cavitators for fraccing and decolmatation (removal of fine plugging material) production or injection improvement of 1.5 – 3 times are commonly being observed. Cavitation is also very effective in cleaning tubes or plugged screens in water, oil or gas wells because it effects most commonly occurring deposits, including deposits that are insoluble in acid.
