Study On The Mechanism And Prevention And Control Technology Of Casing Failure In Guan 104 Reservoir

There is a serious casing failure in our country’s oilfield.According to the statistics in 2002,the average casing failure is 20.37%in our country,and the numbers is creasing.According to the statistics in 2016 of Guan104 block in Dagang oilfield,its’ casing failure is very serious that the casing failure accounts for 57.44%.The casing failure has a heavy influence for production of oil and gas,which results in well network destroyed,cut or stop production even abandon the well.It causes a heavy loss of economics.To solve this problem,112 casing failure materials were analyzed to know the critical reasons of casing failure in Guan104 block.Then,this paper established the finite element model(FEM)accordingly based on FEM and mechanics theories.The mechanism of casing damage was researched by the numerical simulation method.At last,the paper put forward to the controlling measures of casing failure and repairing scheme based on the repaired tools and type of casing failure in Guan104 block.The main innovation and results of this dissertation are as follows:(1)It is clear that sandstone-shale interface,mudstone hydrated and corrosion are the main reasons of casing failure after statistical analysis of 112 casing failure materials of Guan104 block.(2)According to the critical reasons of casing failure in Guan104 block,this paper accordingly established axisymmetric finite element model for sandstone-shale-sandstone three-layer section,the plane strain finite element model for mudstone hydrated section and 3D finite element model for casing with one and two corrosion pit based on the viscoelastic and elastic-plastic mechanics,string mechanics and rock mechanics to reaserch the mechanics of casing failure in sandstone-shale-sandstone,mudstone hydrated section and casing with corrosion pits.(3)The mechanism of casing failure in the interlayer of sandstone and mudstone indicated that the Von Mises stress inside the casing was the highest at sandstone-shale interface and shale interval,and it occured a strong shear effect in this position,which made casing failed.And it is shown that the casing failure in shale interval can’t be controlled effectively by thickening the casing wall if the steel grade is kept the same,and the effective way is to increase the steel grade.(4)The results that the mechanism of casing failure and the law of casing’s stress in mudstone hydration showed that the maximum stress of casing rises with the increase of mudstone hydration,and it had different influence on different cementing quality and the degree of mudstone hydration.So it is important to avoid the water into mudstone,thicken the casing wall and have a good cementing quality for controlling the casing failure in mudstone hydration.(5)Strength is assessed of casing with the defect of corrosion pits,and the study found that casing strength can be assessed with the model of one corrosion pit defect when the distance of corrosion pits more than a certain value.Furthermore,The results show that it occurred the stress concentration in the corrosion pit,and the stress concentration factor rises with the increase of pit’s depth.Besides,it woud accelerate the casing failure when the corrosion casing was in the condition of mudstone hydration.So it was necessary to use the casing with a good corrosion resistance or use preservative.Secondly,use the coating casing and increase the steel grade to prolong casing’s life.(6)The paper analyzed structural characteristics of repaired technology and tools to repaire the damaged casing.At last,According to characteristics of repaired tools and the type of casing damage,the repaired scheme is put forward.