Vinyl chloride casing pipes were perforated with high pressure water jet in a pressure vessel to develop an in-situ perforation system. The casing pipes, 73mm in inner diameter and 8mm in thickness, are those used in Chiba Prefecture for natural gas production. Driving pressure of water jet was up to 98.1MPa, and ambient pressure was up to 10MPa which corresponds to the depth of 1, 000m. In addition to a so-called straight nozzle, various horn type nozzles were used to clarify the effects of shape on the performance.
The main conclusions obtained in this study are summarized as follows:
(1) The vinyl chloride casing pipes can be perforated with high pressure water jet up to the depth of 1, 000m if driving pressure is sufficiently high (98.1MPa).
(2) The perforated area becomes maximum at the ambient pressure of 2-3% of the driving pressure.
(3) The maximum ambient pressure under which the pipe can be perforated decreases with standoff distance while the perforated area under low ambient pressure increases with standoff distance.
(4) The horn type nozzle whose half horn angle is from 15°to 35°is much more effective than the straight nozzle. The half horn angle of 15°is the most effective for the perforation of the casing pipe.
(5) The length of horn can be reduced to about four times nozzle diameter without lowering the performance.
(6) The perforated area per unit area of nozzle exit increases with nozzle diameter.
(7) Cavitation is one of the main mechanisms for perforation of the vinyl chloride pipe under high ambient pressure.
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