The Design Of Casing String Based On Clay Swelling Formation

Casing string strength analysis and design is key technical of drilling design,which has bearing on the cost of drilling and continuous production of oil-gas well.Nowadays,with the development of the technical of oil-gas fields' exploration and exploitation,the increasing of length of casing and casing running leavel,the stress and deformation of casing is more and more complicated,which lead to higher requriment for the design of casing.This paper study about external load of casing string,triaxial strength design theory and finite element simulation about uneven load of casing combine with the special geological conditions of clay and the situation of casing damage in the Area of Tuo 142 in Shengli Oilfield.This paper first analyzes the casing string under the external load,calculated the effective internal pressure,effective external extrusion pressure and the effective axial force of casing based on summarizing calculation method,which made foundation to confirm the casing biaxial strength and triaxial strength to proofread the strength.And then deduced the biaxial strength and triaxial strength calculation formula of casing.During the design of casing string,firstly choose the model of casing according to collapsing strength of casing model,and then through the internal pressure strength and tensile strength of casing strength checking,if the internal pressure or tensile strength does not meet the design requirements,select casing internal pressure strength design,until the casing chosen to meet the requirements.Then using APDL language set up parametric model of casing,set related parameters of nonlinear,use of buckling analysis module of ANSYS finite element analysis software simulation carried out on carrying capacity of casing by changing the casing wall thickness,steel grade and loading length,in view of the different working condition of casing,get along with the change of casing deformation of radial bearing capacity curve and buckling load of casing,gain of the load bearing capacity to reduce the percentage of casing,analysis of carrying capacity of clay swell formation casing change rule.At last,derived the algorithm of casing string running length and designed the system of designing for casing string for clay swell formation by using VB software.The system has a friendly interface,and is easy to be operated,data can be management comprehensive,.What's more,it can comprehensive invoke ANSYS software,output the report of the design and strength the function of the curve.It can provide reliable theoretical basis and strong technical support for drilling engineers when design the casing string,and has great significance to reduction of casing design cycle.