ANALYSIS OF EFFECT FACTOR IN SHALE WELLBORE STABILITY
WANG Qian1，2，ZHOU Yingcao2，TANG Yulin3，JIANG Zhibo1，2
(1. PetroChina Research Institute of Petroleum Exploration and Development，Beijing 100083，China；
2. Drilling Research Institute，China National Petroleum Corporation，Beijing 100195，China；3. PetroChina Yumen Oilfield Refining and Chemical Complex，Yumen，Gansu 735200，China)
Abstract：A new shale wellbore stability model considering fluid flow and ion transmission induced by shale-drilling fluid system electrochemical potential osmosis，and solid deformation resulted by solute diffusion，ion transmission and hydrate expansion is proposed. Pore pressure and stress field around the wellbore wall is computed by finite element method，and the effect of shale and drilling fluid parameters on collapse index and caving pressure is analyzed. The research results demonstrate that large shale permeability，large solute diffusion coefficient and small shale per unit surface charge are favour of shale stability. Drilling fluid with high concentration and reflection coefficient is beneficial for shale stability. High mud weight can sometimes result in instability for shale formation. While the swelling coefficient of shale-drilling fluid system decreases，the shale hydration can be alleviated. Especially for the case that the drilling fluid concentration is larger than the shale pore fluid，the chemical reverse osmosis may cause shale dehydration. The collapse index of small shale wellbore altered with time is more obvious than large wellbore.
2012, Vol. 31 
