DEVELOPMENT OF AN IN-SITU WATERJETS SYSTEM FOR PERFORATION

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To develop an in-situ perforation system for increasing natural gas production by using high pressure waterjets, laboratory perforation tests on a vinyl chloride casing pipe and measurements of impact pressure were carried out in a pressure vessel. Based upon the test results, an in-situ perforation system was then designed and preliminary in-situ tests were carried out for an injection well in the South Kanto natural gas field.The main results were summarized as follows :1. The perforated area becomes maximum at an ambient pressure of 2 to 3% of the driving pressure. When the standoff distance is increased, the maximum ambient pressure where no perforation occurred decreases and the perforated area increases at low ambient pressures. Horn nozzles are more effective than a conventional straight nozzle. A horn angle of 15ﾟ performs best both in perforated area and in the maximum ambient pressure.2. Dynamic components of impact pressure play a decisive and direct role in cutting materials under ambient pressure. Under the conditions where waterjets show high performance, the power spectral density of impact pressure has a peak, the frequency of which varies from a few kHz at low ambient pressures to about 23 kHz at high ambient pressures. The dynamic components seems to be related to effective cavitations for cutting materials under ambient pressure. The dynamic characteristic of noises is similar to that of impact pressure, which enables us to detect dynamic impact force during cutting materials by measuring noises outside a pressure vessel.3. Preliminary in-situ tests were conducted successfully. The injectivity of a poor injection well was recovered drastically by perforating the casing pipe with an in-situ waterjets system, which was designed according to the results in this study.