Research On The Evolution Mechanism Of Bearing Capacity Of Layered Soils During The Running Of Conduit

The running of deep-water drilling conduits is the first step in the construction process of deep-water oil and gas wells and the foundation of the subsequent process technology,which directly determines the success or failure of the well-building process.Instability of the surface conduit is the main risk faced by deep-water jet drilling.Therefore,in view of the problems of poor diagenesis,low stratum strength,low bearing capacity,and complex soil layering properties in shallow seafloor strata,it is urgent to develop bearing capacity based on engineering geological layering characteristics and soil disturbance mechanism during the process of pipe injection Research on evolution mechanism.The process of jetting down the conduit is a drilling process that uses submerged water jets to destroy the submarine soil to form a borehole,and the conduit and the drill bit go together.When the pipe is injected into the soil,the squeezing effect of the water jet on the soil will cause the excess pore water pressure between the soils.The calculation model of the excess pore water pressure is derived through theoretical derivation;two main stages for the disturbance of the soil Based on the study of the expansion and contraction disturbance model of soil,the process of layered soil formation into mixed soil under the dynamic disturbance of spraying was explored.Through the indoor experiment,the variation law of the frictional resistance of the conduit in the mixed soil with different sand-viscosity ratios and the sand-sticky layered soils with different depth proportions was studied;the simulation experiment on different proportions of sand-clay mixed soil revealed different According to the change law of the frictional resistance of the pipe in the sand and mud ratio soil,the research found that with the increase of the sand viscosity ratio,the change of the pipe frictional resistance increased nonlinearly,combined with the change law of the frictional resistance at the interface of the layered soil,the basis was obtained Method for judging the layering of soil by the frictional resistance change curve of the pipe.The method was verified by an outdoor simulated jet experiment and the law of frictional resistance recovery of disturbed soil was studied,and the frictional resistance recovery coefficient curve was obtained.The above research reveals the change law and evolution mechanism of the friction coefficient of the conduit under the coupling of the layering characteristics of the soil and the disturbance of the soil,and proposes an optimization method for the penetration depth of the conduit.According to this method,the penetration depth of an exploration well in the South China Sea Optimized,the effect is good.It provides a geological stratification situation identification method and an optimized scheme for the minimum mud entry depth of the jetting conduit for deepwater exploration and development.