A discussion about the method to study the effect of ambient pressure on hydraulic jetting

- The method widely used to generate ambient pressure may be not suitable to the research of the hydraulic jet.
- The jet pressure is found that it hardly changes until the ambient pressure exceeds a threshold.
- The ambient pressure at the bottom of oil wells may have no influence on hydraulic jet.

Hydraulic jetting techniques are widely used to improve the rate of penetration (ROP) and enhance oil recovery (EOR) in the oil and gas field. However, a high ambient pressure could significantly weaken the performance of hydraulic jetting at the bottom of wells, especially in the case of deep (>4500 m) and ultra-deep (>6000 m) wells. Hence, many excellent studies have been conducted to study the effect of the ambient pressure on a hydraulic jetting. A method to generate ambient pressure by changing the diameter of the outlet valve is widely used. However, in our study, it is proved that the method cannot simulate the real ambient pressure environment for a hydraulic jetting. In our study, an outlet valve is used to maintain the pressure in the pressure vessel. Jet pressure and impact pressure with different ambient pressures at different standoff distances are measured. The jet pressure remains unchangeable until the ambient pressure exceeds a threshold and then increases linearly with the ambient pressure. The threshold is approximately equal to the product of the pressure drop of the nozzle and the square of the nozzle discharge coefficient. The hydrostatic pressure is not evenly distributed in the pressure vessel under the generated ambient pressure. According to Bernoulli's equation, the process to generate ambient pressure by this method is the conversion process between the hydrostatic pressure and the dynamic pressure. Given that the ambient pressure is evenly distributed at the bottom of oil wells, it may not have an influence on the hydraulic jetting. Performing an experiment to measure the effect of the ambient pressure on hydraulic jetting at the bottom of oil wells is strongly recommended. The results in our study are helpful for the application of hydraulic jetting in oil and gas industry.