| Drilling speed in petroleum engineering is a vital and the most important limiting factor influencing economical profit. It is of great significance to overcome the low penetration rate problem in deep well drilling operations. Negative pulsed jet is an effective method to improve the penetration rate in common drilling conditions because it can diminish the chip hold down effect and reduce the strength of cutting layer.Based on the mechanism of negative pulse jet assisted drilling and working theory of the self-vibration valve type generator, a negative pulsed generator was developed for drilling 8.5 inch borehole. During the experiments, the generator worked stably, and produced negative pressure pulses periodically. The hydraulic power in the bottom hole scarcely reduces because the pressure drop across the modulator is very small. Under conventional drilling conditions, the negative pulse generated characterizes with 20-40Hz in frequency and 5-6.5MPa in amplitude. It has been obtained that when bit pressure drop increases, the corresponding pulse frequency and amplitude will approximately increase proportionally. The results prove that the promising jet can increase the rate of penetration in lab drilling tests, which guarantee its effective field applications. When ambient pressure is kept 5MPa and pulse amplitude 5MPa, the drilling rate with negative pulsed jetting will bring out remarkably 1.4-2 times increase. The net increment in rate of penetration is greater at a higher weight on bit. Through three-well field tests, the operating rules and regulations are established, and a 41%-58% increase in penetration rate has been obtained compared with conventional drilling.
|
PDF Full Text Request