Research On Bearing Capacity Of Drilling Conduit Installed By Deep Water Jet Method

The jetting method for installing drilling conduits has the advantages of strong adaptability and high operation efficiency,and is currently one of the most commonly used methods for installing drilling conduits in deepwater operations.As the circulation channel and force-holding structure of deepwater drilling,the drilling conduit needs to bear the wellhead load and conduit string after running.If the standing time is designed to be too short,the bearing capacity of the drilling conduit will be insufficient,which may easily lead to risks such as wellhead subsidence and inclination;If the standing time is designed too long,the bearing capacity will be redundant and the operation cost will increase.In this thesis,through theoretical analysis,finite element simulation and experimental research,the relationship between the bearing capacity of the drilling pipe and the time change after the installation of the drilling pipe is analyzed,and it is used to optimize the design of the drilling pipe running depth and resting time.The purpose is to accurately calculate and make full use of the drilling pipe.Bearing capacity to ensure safe operation and improve drilling efficiency.In this thesis,the influencing factors of the real-time bearing capacity of the drilling conduit are analyzed,and the calculation model of the critical earth-breaking pressure and injection parameters is established by studying the pressure distribution under the action of the submerged water jet and the damage form of the soil.Based on the formation mechanism of the vertical bearing capacity of the drilling conduit,it is revealed that the formation and dissipation of excess pore water pressure is the main reason for the variation of the vertical bearing capacity of the drilling conduit with the resting time.The bearing capacity of the drilling conduit under different layered soil conditions was simulated by ABAQUS,and the indoor simulation experiment of the conduit friction resistance was carried out based on the similarity theory,and the variation law of the friction resistance of the drilling conduit under the layered soil condition was studied.It is found that the friction resistance of drilling conduit in sandy soil is greater than that of clay soil,a method for judging the position of the boundary between sand and clay layers is obtained,and a calculation model for vertical bearing capacity of layered soil drilling conduit is established.Through outdoor experiments,the relationship between the surface friction force of the drilling conduit and the injection displacement,the bit extension and the resting time was studied by using the control variable method,and the functions of the real-time surface friction recovery coefficient of the drilling conduit,the injection parameters and the resting time were constructed.A real-time bearing capacity calculation model for drilling conduits under layered soil conditions is established.The bearing capacity of the drilling conduit gradually recovers after it is put in place.The real-time bearing capacity of the recovery needs to ensure the stability of the drilling conduit under the two conditions of disengagement of the running tool and surface casing cementing.By studying the shallow drilling operation process of a well in the eastern South China Sea,analyzed the influence of different operating water depths and completion depths in the second opening on the design of the drilling conduit running depth and resting time.The calculation chart of the operation time under dangerous conditions provides an important basis for the accurate calculation and full utilization of the bearing capacity of the drilling conduit when designing the resting time of the subsequent drilling conduit.The research results were successfully applied in the jet installation of drilling conduits in a well in the eastern part of the South China Sea.Compared with the adjacent well operations,the design method reduced the running depth of the drilling conduits in the target well by 1m,and the standing time was reduced by 14.3%,which improved the drilling of deep water and shallow layers.The accuracy and timeliness of the operation design have better field application effect.