International Journal of Earth Sciences and Engineering

Ni Yafei , Li Zhonghui , Lou Yishan

Abstract

It changed obviously about rock mechanics parameters and in-situ stress after formation pressure depletion. A new model was determined for predicting the stress change s after pressure depletion by considering the change of rock mechanics parameters and using generalized Hooke's law. At the same time, a new method was established about using log data to interpret the rock mechanics parameters of pressure depletion formation. Foremost, we gain the interval transit time of pressure depletion formation by using effective stress principle and the positive correlation between effective stress and acoustic velocity and mathematical iteration method. It shows: original stress state, pore pressure and rock mechanical parameters all play an important role in the change of stress of pressure depletion formation. The original vertical stress and the pore pressure will weaken the change of stress, and the one direction horizontal stress will weaken the change of the other direction stress. In addition, the stress difference will increase after pressure depletion. It will increase the shear stress of rock, so the probability of destroyed rock by shear stress will increase. It is the mechanical reason that the formation of pressure depletion is easy to leak, well collapse and produce cracks or faults. After pressure depletion, the cohesion of rock, uniaxial compressive strength and elastic modulus increased obviously, the tensile strength increased slightly, and the internal friction angle and Poisson's ratio decreased significantly.

Keywords

Mathematical Iteration, Pressure Depletion Formation, Mechanical Parameters, Stress Calculation Model.

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