Research On Sealing Integrity Of Offshore Abandoned Well

Offshore wellbore abandonment is the last operation of the oil and gas well life cycle,involving the integrity of the wellbore seal,and the sustainable and healthy development of the marine environment and marine ecology.With the development of the economy and society,the requirements for marine environmental protection at home and abroad are becoming more and more stringent,and the importance of marine environmental safety is increasing.Therefore,it is especially important to ensure the long-term safety after the wellbore is disposed by optimizing the construction design method of the abandoned operation and improving the evaluation method of the abandoned wellbore sealability.In view of the above background,this paper mainly carries out the following research work: Firstly,based on the engineering practice of offshore wellbore abandonment construction design,the development status of offshore wellbore abandonment cementing technology at home and abroad is deeply investigated,and the technical difficulties and key problems to be solved in offshore wellbore abandonment technology are analyzed.Secondly,the mechanical behavior characteristics of cement stone under different stress conditions are reflected.The mechanical parameters,strength parameters and permeability of cement paste were tested,and the parameters describing the mechanical behavior of cement paste were obtained.Based on the grouting bolt theory in civil engineering,considering the influence of mechanical parameters and geometric parameters of cement paste material,the mechanical model of the barrier of abandoned wellbore was established,and the mechanical parameters and geometric parameters of cement paste under different material mechanical parameters and geometric parameters were studied.Finally,based on the theory of thermal-solid coupling,a finite element numerical model of wellbore barrier for offshore abandoned wells is established,and the influence of mechanical parameters,geometric parameters and working conditions of adjacent wells on the failure length of cement plug interface is studied.Taking JZ20-2-9D well as an example,the sealing integrity of abandoned wellbore is analyzed.Through the above research work,the following conclusions can be drawn: properly reducing the elastic modulus of cement plug will reduce the compressive stress at the interface between cement plug and casing,thereby reducing the risk of mechanical failure of the interface;the influence of Poisson's ratio on the failure length of cement plug is not obvious;with the increase of cement plug cementation strength,the failure length of the interface between cement plug and casing decreases significantly;with the increase of cement plug cementation strength,the failure length of cement plug-casing interface decreases The failure length of cement plug-casing interface increases significantly with the increase of cement plug bottom pressure;the failure length of cement plug-casing interface increases significantly with the increase of cement plug bottom pressure;the temperature change caused by water injection or thermal recovery in adjacent wells has little effect on the failure length of cement plug-casing interface;after the abandonment of JZ20-2-9D wells,the integrity of the interface of 4# cement plug and 6# cement plug is very high and the interface is dense.The risk of seal failure is small.The above research can provide some theoretical reference for offshore wellbore abandonment construction design and promote safe and efficient abandonment of offshore wellbore.