缝长,尺度对水压致裂应力测量结果的影响规律

本文从弹性力学、断裂力学的基本理论出发,结合室内实验和野外观测结果研究了尺度、缝长对水压致裂应力测量结果的影响规律。研究结果表明,室内实验样品的孔径比不应大于四分之一,最好小于十分之一,较大的绝对尺度可以使实验结果变得稳定。野外实际测量除了满足上述要求外,裂缝单翼长度不应小于十倍的钻孔半径,否则测不到可靠的封闭压力。据此,进行大尺度水压致裂室内模拟实验对于提高压裂技术,完善水压致裂应力测量理论是非常必要的。

REGULARITIES OF INFLUENCE ON THE OBSERVATIONALRESULT OF HYDROFRACTURING STRESSMEASUREMENTS EXERTED BY THEFISSURE LENGTH ANDSPECIMEN SIZE

Starting from the theories of elastic mechanics and fracturing machanics and incorporating the observational results respectively achieved in the laboratory and field experiments, this paper studies the regularities of influence on the observational result of hydrofracturing stress measurements exerted by the fissure length and scale. The result of the study shows the f ollowing: a) For laboratory tests, the aperture ratio should not be greater than 1/4, whreas the aperture ratio should be kept within 1/10. b) Greater absolute scale is helpful to stabilize the result of the experiments. In the case of practical field experiments, it is not only necessary to satisfy the above listed requirements, but also to keep the single-wing length of the fissure within 1/10 of the borehole diameter if reliable closed pressure is to be measured. Therefore, it is of vital importance to conduct laboratory simulation tests using larger-sized specimen in order to enhance our technology of hydrofracturing experiments as well as to improve our theory related with hydrofracturing stress measurement.