The Research Of Cement Sheath Packing Integrity For Deep-sea Shallow Weekly Consolidated Formations

With the exploration of oil from land to sea,deep ocean water has become an important oil and gas exploration area.However,in the process of deep water oil and gas exploration and development,due to the special geology and temperature environment of shallow deep strata,the problems of poor cementing quality and high operation risk are common,and the research on deep well cementing failure has gradually become the focus of research.Therefore,this paper studies the integrity of the cement sheath packing integrity in deep-sea shallow weekly consolidated formations.In this paper,by investigating the elasto-plastic mechanical model adapted to different geological conditions and combining the characteristics of deep-weak weakly cemented formations,the finite element model of the homogeneous formation and the finite element model of the solid-liquid two-phase medium are systematically analyzed to establish a geomechanical model conforming to the weak cemented formation.Through the evaluation of the ground stress balance,the mechanical model is in accordance with the actual cementing conditions.It is the theoretical basis and prerequisite for the study of the factors affecting the annular seal integrity of the weak cemented formation.In this paper,when the crack is completely penetrated from the interface to the second interface,it is used as the judgment criterion for cement sheath insulation failure.Using the extended finite element(XFEM)as a research method,based on the failure criterion of damage mechanics evolution,the failure criterion of maximum principal stress is taken as the criterion of damage initiation.The energy evolution-based,linearly softened,mixed-mode exponential damage is selected for the damage evolution.The law of evolution has studied the effect of factors such as the internal pressure of the casing,the mechanical properties of the cement stone,and the mechanical properties of the formation on the failure of the cement stone.In this paper,the self-designed cementation interface cementation force measuring device was used to test the effect of temperature on the cementation strength of the cementing interface,and the finite-element software of ABAQUS was used to calculate the static cement column pressure of cementing slurry for weak cementation.The consolidation law of the strata and the experimental verification of the relationship between the degree of compaction of the weak cemented formation and the cementation strength of the secondary interface.According to the stress state of the casing annulus sealing system during the construction of wells in deep-sea weakly cemented formations and the failure mechanism of the annulus sealing system of weak cemented formations,the combination of numerical simulation and laboratory tests is based on the weak cemented strata-cement sheath.Based on the judging criteria of the failure of the casing assembly seal,the law of factors affecting the integrity of the casing's annular seal during the construction of wells in weakly cemented formations is studied.According to the actual conditions of the deep-sea drilling project,the improvement of the weakly cemented formation casing annulus is proposed.Seal integrity measures are recommended.