Abstract
Casing deformation (CD) is a major challenge for shale gas development in Weiyuan gasfield, natural fracture (NF) slippage is one of the main causes of CD in Weiyuan gas filed. In order to study the mechanism and regularity of NF slippage induced CD, a wellbore shear stress calculation model and a CD degree prediction model are established. And results show that, the approach angle and ground principal stress difference have significant influence on wellbore shear stress, high wellbore shear stress occurs when wellbore orientation is perpendicular to the NF trend. Wellbore shear stress increases with the increase of fracture fluid pressure and NF area, improving casing strength or cementing quality has limited effect on reducing the risk of CD. The smaller the young's modulus, the higher the CD degree, Poisson's ratio has limited effect on CD degree. NF approach and fracture fluid pressure determines the value of CD degree. Field case shows that reasonable fracturing technology to control fracture net pressure and wellbore position arrangement are helpful for reducing CD risk, and the model proposed in this paper can be used to predict CD risk and calculate the CD degree.
