Research and application of ultimate mechanical behavior law of drilling under impact fracturing
In order to study the mechanical characteristics of hole walls under impact load fracturing,theoretical analysis and experimental methods were used to study the mechanical behavior of hole walls under different impact loads.The volumetric strain equation of fracture was derived,and the changing laws of hole wall strength,strain and permeability under different impact loads were ob-tained.Through the site pumping practice,the influence of different impact loads on drilling and pum-ping was studied.The results show that:compared with the test curve of p<1.0 MPa,when 1.0 MPa≤p<10.0 MPa,the maximum strength of the specimen decreases by 38.5%,the maximum strain increases by 19.5%,and the maximum strain rate increases by 43.4%.Transverse and longitudi-nal cracks of the specimen develop,forming radial and circumferential fracture networks,and the per-meability increases linearly with the increase of penetration channels and number.When p≥10.0 MPa,impact fracture occurs,impact load is released,crack development is stable,and permeability tends to be stable.When p=5.0 MPa borehole gas extraction timeliness is 2.0 times and 3.0 times of p=0.5 MPa and p=15.0 MPa,the initial extraction volume is 1.2 times and 2.4 times of the other two kinds of gas extraction.Under the impact load between the ultimate tensile load and the ultimate com-pressive load,the borehole has higher permeability and better stability.It shows the extraction char-acteristics of high permeability and high timeliness.
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