Sonic gravel packing method and tool for downhole oil wells

Abstract

Gravel is packed around a casing in an oil well to prevent sand from entering into the casing, to loosen the sand around the gravel and facilitate the flow of oil into the casing. The gravel is vibrated around the periphery of the casing at a particular harmonic between approximately 1100 Hertz and 1700 Hertz. The transducer may be slotted to facilitate the production of a considerable amount of energy at the particular harmonic without breaking the transducer. When slotted, the transducer may be disposed within a slotted ring to facilitate the production of a considerable amount of energy at the particular harmonic without breaking the transducer. The transducer and the slotted ring may be disposed within a sleeve which may be filled with oil. At least one of the anti-nodes of the transducer may be clamped to produce vibrations at the particular harmonic without producing vibrations at the fundamental frequency. The transducer may be tuned so that the frequency of the particular harmonic such as the fifth harmonic is at the lowest possible value. This may be accomplished by partially slotting the metal ring at a position displaced from the slot in the ring or by adding mass to the ends of the transducer. The module described above may be depended from the bottom of the casing in a plurality of similar modules whose slots may be annularly staggered to facilitate the packing of the gravel without voids.