井下低频脉动水力压裂技术参数优化及现场应用

对于地层压力高、岩石破裂压力大的储层,水力压裂施工面临井口泵压大、设备要求高的难题。井下低频脉动水力压裂技术通过在井底产生低频脉动,可以显著降低岩石起裂压力和延伸压力,提高压裂增产效果。通过室内实验以及理论计算,对低频脉动水力压裂技术的脉动频率及脉动压力幅值两个关键参数进行了优化。结果表明:当脉动频率为20 Hz时,岩石的破坏最为严重; 脉动频率越高,振幅衰减越快; 岩石的抗压强度与脉动压力幅值成反比,幅值越大,岩石的抗压强度越低。最后,在陕北地区低渗透油田进行了3口井的低频脉动水力压裂现场试验。试验结果表明,低频脉动水力压裂后的试验井与相邻常规压裂井相比,砂堵问题明显减少,且在降低施工压力方面具有显著效果。

Parameter Optimization and Field Application of Downhole Low Frequency Pulsation Hydraulic Fracturing Technology

For the reservoir with high formation pressure and rock fracture pressure, the hydraulic fracturing is faced with the difficult problems of high wellhead pump pressure and high equipment requirements. By producing low frequency pulsation at the bottom of the well, the downhole low frequency pulsation hydraulic fracturing technology can significantly reduce rock initiation pressure and extension pressure, and improve the stimulation effect of fracturing. Through laboratory experiment and theoretical calculation, two key parameters of low frequency pulsation hydraulic fracturing technology, including pulsation frequency and pulsating pressure amplitude were optimized. The results show that when the pulsation frequency is 20 Hz, the rock damage is the most serious; the higher the pulsation frequency, the faster the pulsating pressure amplitude decays; the compressive strength of rock is inversely proportional to pulsating pressure amplitude; the greater the pulsating pressure amplitude, the lower the compressive strength of rock. Field tests of low frequency pulsation hydraulic fracturing technology were carried out on three wells in low permeability oilfield of northern Shaanxi. The test results show that compared with the adjacent conventional fracturing wells, the sand plugging problem of the test wells after low frequency pulsation hydraulic fracturing is significantly reduced, so downhole low frequency pulsation hydraulic fracturing technology has a significant effect in reducing the construction pressure.