摘要
In this paper, the expression of teeth invasion depth was developed, and rock failure model for teeth invasion was established according to Morh-Coulomb principle. Using the ratio of error function and depth x as the reference parameters for underbalanced drilling application, invasion depths under all kinds of differential pressures and β/x were calculated, and the variation law was analyzed. The results show that the expression of teeth invasion depth can clearly demonstrate respective effect of pressures and fluid on rock failure. This model can explain the mechanism of enhanced rate of penetration in underbalanced drilling, and it can depict the scope of application for dc index method correctly.