射流作用对岩石局部孔隙压力的影响

在油气井钻进过程中，射流对井底的作用可大幅度提高钻速。而由于岩石材料的多样性和结构的复杂性，多年来有关射流破岩的机理还不明了。为此，提出了射流作用下岩石局部范围具有较高渗流压力的思路，并认为该渗流压力大小对射流的破岩作用有重大影响。通过对射流作用的岩石表面进行网格划分并绕网格节点取微面积，建立微面积上液流束作用的渗流压力计算模型，分别在地面条件和井底条件下，对射流作用于湿砂岩体作数值计算与分析，得出了在相同条件下，射流的喷射速度对岩石局部范围内的岩石孔隙压力有较大影响；井越深，井底射流对岩石孔隙压力的影响越小等规律，以及增大射流喷射速度可以较大地提高射流对井底的辅助破岩作用等结论，这对认识射流的辅助破岩作用机理有重要意义。

EFFECTS OF JET ON LOCAL PORE PRESSURE OF ROCKS

The jet action can largely improve ROP during oil/gas well drilling. While due to the variety of rock materials and the complicated rock structures, the rock-cutting mechanism of the jet is still not known after so many years. Therefore, it is put forward herein that high seepage pressure exists locally in the rocks when under jet action, and the magnitude of seepage pressure greatly affects the rock cutting results. Calculation model for seepage pressure of liquid flow streams is therefore established by taking elements of area around the grid nodes on rock surface. Numerical calculation and analysis are made regarding jet effects on wet sandstone body at surface and hole bottom. It is concluded that under the same conditions, the jet speed will highly affect the pore pressure of local rocks; the deeper the well, the smaller the influence; and to increase the jet speed can enhance the rock-cutting assisting effects of the jet, and etc. All these are significant for investigating the rock-cutting assisting mechanism of the jet.