Analysis On The Safety Of Perforated And Curved Part Casing In Horizontal Fractured Well

Horizontal wells are widely applied in the development of general and special nature oil and gas reservoirs.Generally,in order to improve well production and ultimate recovery,fracturing stimulate technology is adopted in horizontal well.Horizontal wells has relatively complex well structure comparing with vertical well,perforated and curved part casing withstand a variety of loads due to the complex ground stress distribution.Therefore,it's necessary to analyze the safety of perforated and curved part casing in Fractured Horizontal well.For the safety analysis of perforated casing in horizontal well,stress distribution model of perforation tunnel surface was established and obtained perforation tunnel surface stress.Considering the stress concentration and fracture mechanics performance of perforated casing,simplified three-dimensional mechanical model of perforated casing as perforated plate model to analyze the residual strength of the perforated casing.Additional,build finite element model of formation cement sheath and perforated casing with ANSYS,study on the effect of cement,formation and casing's elastic modulus,poissons ratio and thickness on casing strength.And an example is given for optimizing the cement sheath parameters to ensure safety of casing strength.The analysis indicates cement sheath elastic modulus is the greatest impaction factor on the stress of perforated casing,while cement thickness is the minimal,the reasonable cement elastic modulus should range from 7.8-9.4GPa.Curved casing in horizontal well loaded on combination loading of bending,shear and extrusion loads,it may cause damage to the casing.According to the mechanical characteristics of curved casing in horizontal well,mechanical model of three-point bending casing was established.The formulas of bending moment at plastic zone and elastic zone were obtained based on the elastic-plastic theory,and the relationship between bending moment,extreme corner with elastoplastic boundary angle in the elastic-plastic deformation stage were derived.Combined with the actual situation of oil field,P110 and TP140 V casing with different wall thickness were analyzed.The results show that high-grade casing has obvious better performance in the working condition of larger bending loads.Considering the combined effects of bending,shear and extrusion,applying the fourth strength theory and Lame formula,collapse strength formula of curved casing in horizontal wells was derived.Using the formula,the collapse strength of ?139.7mm×10.54 mm,12.7mm P110 and ?114.3mm×8.56 mm,9.65 mm TP140V casing under different angles different curvature was calculated,and then ANSYS finite element analysis was used to verified the results.The results show that curvature has a significant impact on casing collapse strength,with increasing of the curvature,casing collapse strength decreasing significantly,this situation should be considered when designing wellbore structure.