Research On The Risk Of Jack-up Platform In Penetrating In Clay

The Jack-up platform is the most commonly used drilling platform for oil and gas exploitation.However,due to the complex seabed environment,some accidents are often encountered in the penetration process.Among them,the risk of punch-through and “step in footprint” are the most common.Punch-through mainly occurs in the layered soil which is hard at the top and soft at the bottom.At present,the research on it is mainly concentrated in multilayer soil.However,it was found that the phenomenon of punch-through also occurred when the spudcan penetrated in the clay in actual operation.After the completion of the operation,the jack-up platform will leave obvious holes on the seabed,which are called hole of the leg or "footprint" and "step in footprint" means that the platform will conduct secondary penetration near these "footprints".At present,the research on "step in footprint" of jack-up platform is mainly the experiment and finite element calculation of single leg's penetration,There are few studies on the overall platform for step in footprint.Based on this phenomenon,this paper conducted a punch-through experiment and a "step in footprint" slide experiment.The punch-through experiment adopts the non-continuous loading method,the loading process of jack-up platform was simulated by means of force loading,and the mechanism and elimination method of punch-through in clay were studied.The simulation study was conducted by ABAQUS,a large software.In the "step in foot" experiment,the three-leg platform model is adopted to study the influence of footprint on the three legs,and the experimental model is verified by finite element calculation.The main research contents of this paper are as follows:(1)A set of experimental models for single-leg model instrumentation with discontinuous loading was established,the loading process of the jack-up platform' penetration was simulated by force loading and the paper analyzes the punch-through phenomenon of penetration in clay and the effect of jetting operation on eliminating punch-through risk.(2)Based on the finite element software ABAQUS,the consolidation analysis model and the CEL(Coupled Eulerian-Lagrange)model were established.Firstly,the consolidation analysis method is used to analyze the drainage consolidation in the static loading stage during the test loading process.The pore pressure at different depths and the consolidation degree at different times are calculated,and the thickness and strength of the consolidated hard layer which at the bottom of the spudcan during the stationary stage of discontinuous loading is obtained.Then importing the hard layer information into the CEL model,calculating the bearing capacity of the penetration in the clay with solid hard layer by CEL finite element method,and realize the simulation of penetrating in the clay with punch-through.(3)The "step in footprint" experiment of the three legs was carried out and the bending moment,horizontal force and the inclination angle of the platform were studied.The influence of the different offset of footprint and spudcan on the force of the legs was analyzed.(4)Using the CEL method to establish a “step in footprint” model based on the experiment,and comparing with the experiment data,the internal force changes of the legs during the penetration process was studied.Overall,the experiment and simulation have good fitting.