考虑岩石抗拉强度受围压影响的地层破裂压模型

预测地层破裂压力是地下流体注入工程中的关键问题，关系到工程的稳定性和安全性。根据地测资料，岩石的抗拉强度会随着围压产生变化，然而目前常见的地层破裂压预测模型均未考虑该因素。基于厚壁圆筒法，针对2种砂岩开展不同围压条件下的砂岩致裂试验，根据试验数据，计算各组试验中试样的抗拉强度，并拟合围压与岩石抗拉强度的关系函数。研究岩石抗拉强度随围压变化的规律，提出能在实际地层中表征该规律的参数，基于该参数对现有的地层破裂压模型进行修正，并结合实测数据验证修正模型的可靠性。研究结果表明:岩石的抗拉强度随着围压的增加呈现明显的线性正相关关系，低围压下，新模型的预测结果与实测数据较为接近。随着围压增加，二者的差异逐渐增大，说明选取的特征参数在低围压下能较好地描述抗拉强度受围压的影响效应，而高围压下参数的取值需进一步研究。

Model of formation fracture pressure considering influence of confining pressure on tensile strength of rock

Predicting the formation fracture pressure is a key problem in the underground fluid injection engineering,which is related to the stability and safety of engineering.According to the geodetic data,the tensile strength of rock will change with the confining pressure,but this factor has not been taken into account in the common prediction models of formation fracture pressure.Based on the thick walled cylinder method,the sandstone fracturing tests under different confining pressures were carried out for two kinds of sandstones.According to the test data,the tensile strength of samples in each group of test was calculated,and the relationship function between the confining pressure and the rock tensile strength was fitted.The variation law of rock tensile strength with the confining pressure was studied,and the parameters which could characterize the law in the actual formation were proposed.Based on these parameters,the existing model of formation fracture pressure was modified,and the reliability of the modified model was verified by the measured data.The results showed that the tensile strength of rock presented an obvious linear positive correlation with the increase of confining pressure,and the predicted results of the new model were close to the measured data under low confining pressure.With the increase of confining pressure,the difference between them increased gradually,which indicated that the selected characteristic parameters could better describe the influence effect of confining pressure on the tensile strength under low confining pressure,while the value of parameters under high confining pressure needs further study.