| Cement sheath is mainly to support casing and sustain zonal isolation.Cement sheath integrity may be damaged during well operation,and failure,which is related to safety production and well life time.Research on cement mechanical properties in high pressure high temperature(HPHT)conditions and analyzing failure mechanism will help to insure cement sheath integrity in deep oil and gas wells.Aimed at cement sheath integrity under HPHT environment,this paper mainly focuses on the followings:1.In this paper,approximately 100 domestic and international documents have been investigated.From the following aspects,such as the research methods used in the cement sheath failure research,cement mechanics experiment,cement sheath failure form and failure factors etc.On the base of review,a summary about present condition and deficiency in cement sheath integrity studying is given.2.An experimental scheme is proposed,completed triaxial test and uniaxial test of cement,tensile strength test and cyclic loading in room temperature,besides triaxial test in high temperature and cyclic load test,then analyzed mechanical property and failure characteristics of cement.3.This paper evaluated cement mechanical property and failure by damage mechanics,and built an isotropic damage model of cement.4.Built casing-cement-formation model by FLAC 3D finite difference,and studied the influence of property of cement on cement sheath integrity by control variate method,in addition the damage model is used to evaluate cement sheath integrity when the well is during loading and unloading operation,with a conclusion that cement with lower Young's modulus and higher strength and tenacity is advantageous to maintain long-term cement sheath integrity.5.The mechanical property optimized analysis of the cement sheath of Well KES8-X showed that: lower elasticity modulus and higher Poisson's ratio,cohesion and internal friction angle would reduce the damage of the cement sheath. |
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