Study On Prediction Methods Of Downhole Casing Wear Under Complicated Well Conditions

In the complex well-drilling engineering,such as horizontal wells,extended-reach wells(ERWs)and ultra-deep wells(UDWs),it is inevitable to encounter complicated well conditions and downhole accidents,especially serious casing wear,which can lead to the problem of wellbore integrity.In addition,the casing bearing capacity after casing wear will be reduced,which has a crucial impact on subsequent operations such as drilling,completion,production,workover and so on.Serious casing wear will also lead to casing collapse,deformation,leakage and other wellbore integrity failure,and even make the whole well scrapped,resulting in huge economic losses and environmental damage.Therefore,it is of great practical significance for safe operation and wellbore integrity of complex oil and gas well-drilling engineering to accurately predict casing wear under complicated well conditions.Aiming at the wear mechanism of casing metal material and energy dissipation,the wear mechanism of casing metal material is studied by experiments,and the casing wear efficiency model built by white and Dawson is modified.Besides,the specific casing wear efficiency model equations based on conventional drill string,sinusoidal and helical buckled drill string,whirling drill string are given respectively.For the aspect of the prediction of casing wear depth,the prediction of casing wear depth in complicated well conditions can be divided into two categories: complicated well conditions based on casing and based on drill string.For the former,both the prediction models of casing wear depth based on the internal eccentricity and the ovality of casing are established;for the latter,the prediction models of casing wear depth based on sinusoidal buckled,helical buckled and whirling drill string are also established.Composite prediction models of casing wear depth are built,and the relevant parameters are discussed as well.Combined with the data provided by the oilfield,different models are used to evaluate the wear depth of casing.On the problem of casing wear location prediction,based on the three-dimensional downhole curved surface,the prediction model of casing wear measured depth location considering the sinusoidal and helical buckled drill string is developed.Moreover,considering the influence of casing ovality on the contact angle of casing wear tool surface in a certain casing wear measured depth position,the corresponding prediction model established by the predecessor is modified,and a novel modified prediction model is developed.For the casing with internal eccentricity,the prediction model of the risk range of the contact angle of the casing wear tool surface is studied,and the expression of the ?safe zone? and ?dangerous zone? under this situation are given.In view of the prediction of residual strength of worn casing,based on the finite element method(FEM)of ABAQUS,the finite element models of casing residual strength against collapsing and internal pressure under complicated well conditions are built.Additionly,the corresponding influence parameters and their influence rules are discussed.Results can be used to provide reference for the evaluation of casing residual strength under complicated well conditions.