Safety Analysis Of Flattened Casing Of Horizontal Well Bending Section

In the horizontal well process of drilling,the change of lithology and drilling pressure causes the wellbore to bend,The casing is bent into the curved section and the casing is bent and flattened due to the increasing curvature of the wellbore.After the flattening,the casing collapse strength is further reduced which causes the casing to bend and deform,In order to clarify the bearing capacity of the casing before and after the flattening of the bending section,Considering continuous contact between the casing wall and the borehole wall,the traditional three-point bending model is improved into a uniform load bending beam model.Considering the tube bending causes flattening deformation,the collapse strength of the casing before and after deformation of the casing,The rule of the collapse strength of the casing before and after the flattening varying with borehole curvature.Specifically include the following research content:The mechanical model of the casing of the uniformly distributed bending beam is established based on the theory of material mechanical bending deformation.Using the Elastic mechanics Lame thick-walled cylinder theory are deriving the relationship between the three-direction stress and the severity under the uniform load.Using Von Mises stress standard gained the formula of the collapse strength of the curved casing under the uniform load and examined by finite element.With the increase of the curvature of the wellbore,Considering the flattening rate of the section,the flattening mechanical model of the unit length is established by using strain energy theory the strain energy theory.Using Von Mises stress standard gained the formula of the collapse strength of the flattened casing under the uniform load and examined by finite element.Taking the 5 1/2 " P110 and 4 1/2" TP140 V bushings commonly used as an example,the collapse strength of the unflattened casing was simulated and analyzed,According to the calculation results of the flattening strength before and after the flattening of the wall thickness of the two specifications,the flattening strength of the casing before and after the flattening is changed with the curvature of the wellbore.In order to understand the safety of the casing strength under injection conditions,the safety coefficient of equivalent stress strength,tensile strength and internal pressure strength of the cementing section before and after casing flattening was analyzed.The results show that the flattening strength of the curved section decreases with the increase of the curvature of the wellbore before and after the flattening of the casing,and decreases more greatly after flattening than before;the equivalent stress intensity before and after the casing is flattened under the injection condition,The safety factor of axial tensile force increases with the increase of well depth.The safety factor of casing internal pressure resistance decreases with the increase of well depth;the safety factor of equivalent stress strength after casing flattening is less than that before flattening.It can provide basis for analyzing the flattening strength after deformation of the curved section casing and controlling the production pressure difference parameter of the injection condition.