Study For Stability Mechanism Of Deepwater RMR Drilling Pipe

With the development of offshore oil in deep water,drilling engineering is facing great difficulties and challenges in operating environment and construction technology.Riserless Mud Recovery(RMR)drilling technology is a double gradient drilling technology,which can overcome a series of difficulties in deepwater drilling and has a strong application and development prospect.The field application has not been carried out in China.In RMR drilling operations,the coupling between shallow string and soil under composite loads and the complex mechanical behavior of drilling string in Marine environments can affect the safety and efficiency of production and construction.Therefore,the stability of deepwater RMR drilling string is studied in this paper.The coupling test of tube and soil in shallow deep water under composite static load was carried out.According to the pile structure test,the similarity ratio of the test model is calculated based on π theorem.A shear soil box which can reduce soil boundary effect was designed and made.The composite static load of bending moment and shear force is applied to the wellhead and the soil layer is changed.The distributed strain of the string model is measured by strain gauge,and the influence of the composite static load on the string strain is analyzed.Based on the Duncan static model and the Hardin-Drnevich dynamic model,a planar quadrilateral eight-node element of soil was constructed.The traditional Euler beam element was used as the pipe string model and the modified Goodman contact element was used as the tube-soil contact model.The planar finite element model of tube-soil coupling in shallow deep water was jointly constructed.The mechanical response characteristics and parameter sensitivity of shallow pipe string under the combined action of dynamic and static loads were analyzed by python programming.Based on Hamilton theorem and considering the structural characteristics of single pipe string(drill pipe or mud return line)in deepwater RMR drilling,the partial differential equation of transverse bending of deepwater RMR drilling string is derived,and the finite element equation of deepwater RMR drilling string is established by using the weighted margin method for finite element discretization.A finite element model for stability analysis of deep-water RMR drilling string was established based on the pipe-soil coupling finite element model in shallow deep water.The quasi-static mechanical response of single pipe string in deep-water RMR drilling was analyzed by python programming and the influence law was discussed.Based on the quasi static stability analysis model of a single pipe string in deepwater RMR drilling and combined with the riser interference effect,the calculation method of the clearance between drill pipe and mud return line under quasi static conditions is established.Genetic algorithm is introduced to optimize the mooring and positioning scheme of deep-water RMR mud return line under the non-collision criterion,and the specific method and process are formed.The mechanical response law of tube-soil coupling and pipe string quasi-static stability under deepwater RMR drilling conditions are obtained,which has certain guiding significance for pipe design and reasonable positioning of mud return line in deepwater RMR drilling operations.