| High pressure water jet technology plays an important role in petroleum engineering,especially in the field of drilling and completion,has outstanding advantages.An in-depth understanding of the relativity of the characteristic of acoustic emission signal and the process of rock fragmentation by high pressure water jet can provide a theoretical basis to dynamical assessment of the efficiency of rock fragmentation by high pressure water jet.Rock fragmentation experiments is conducted by submerged water jet on shale,sand stones,coal rocks,limestone and concrete blocks.By locating AE sensors on the surface of cylindrical rocks,we can collect continuous AE signals.We analyze these signals by using the method of waveform analysis,such as FFT and wavelet analysis.The main conclusions are as follows: Different rocks have different forms of damage,Shale and Limestone are mainly due to particle erosion,while others are due to the micro-cracks.Main frequency changes from single to double as standoff distance decreaing,meanwhile,the difference of main frequency band is obvious;After wavelet decomposition,signal energy of shale is concentrated in the frequency band of 0~93.75 KHz,93.75KHz~187.5KHz,281.25KHz~375KHz,while the signal energy of Limestone and concrete are concentrated in the frequency band of 0~93.75KHz93.75KHz~187.5KHz,and sand is concentrated in the frequency band of 0~93.75 KHz.With the increase of rock fragmentation time,the acoustic emission energy of different rock(shale,sand stone,Limestone,concrete)is reduced by 65.0%,44.6%,27.8%,62.3% respectively.With the same depth of the hole,the acoustic emission energy of shale is the minimal,which means that it is the most difficult to break shale.Specific energy for rock breaking of shale is greatest,and after the depth of the hole to 5mm,specific energy for rock breaking of shale raise rapidly,which means that the depth of the hole exert a great influence on the shale's breaking. |
PDF Full Text Request