Numerical Simulation of Breathing Effect Induced by Drilling in Deep-Water Shallow Formations

It is easy to misjudge the breathing effect as kick and take killing measures to cause malignant loss, which will increase the risk and cost of deep-water operation and seriously harm the safety and efficiency of deep-water drilling. In this paper, the mechanism of breathing effect induced by drilling in deep-water shallow formations was studied, and the COMSOL was used to simulate the whole process of breathing effect during drilling in deep-water shallow formations, so as to study the influence of formation characteristics, mud properties and pressure difference on breathing effect. The simulation results show that the breathing effect observed during drilling in deep-water shallow formations belongs to the transient permeability-induced breathing effect. Which is very easy to occur in formations with low elastic modulus, low Poisson’s ratio, and high porosity and permeability. However, through using the mud with high viscosity and high yield stress and balanced or near-balanced drilling mode (achieved by reducing displacement and mud density, etc.) is conducive to suppressing the breathing effect. When drilling in formations with low elastic modulus, low Poisson’s ratio, high porosity and high permeability, measures should be taken in advance, such as adding filtrate reducer and reducing pump rate, to reduce the impact of breathing effect. The study results can provide some references for the identification, prevention and control the breathing effect during drilling in deep-water shallow formations.