Study On Key Parameters Determining Methods Of Conductor Jets Drilling In Deepwater

Many countries have been exploiting oil and gas resources in deepwater for that the land and shallow sea resources cannot meet the needs of the world's economy.However,the shallow and surface drilling has always been the stumbling block in deepwater drilling.The safety of shallow and surface drilling relates directly to the projects' success or failure.Focused on the determination methods of key parameters of shallow and surface drilling,the following work has been done through theoretical analysis,numerical simulation and experimental research in this paper.The determination methods of vertical and horizontal bearing capacity of conductor,the conductor setting depth in mud,the determination of pumpage and bit stick-out in jet drilling and hydraulic parameters optimization in surface drilling have been studied.The results can provide certain theoretical references for the design and construction of the shallow and surface drilling in deep water.Aiming at determining the variation of vertical bearing capacity with time,jet drilling experiment has been done based on the rock mechanics and pile foundation theory,combined with the characteristics of jetting conductor.On the basis of data analysis,the vertical bearing capacity of conductor calculation model is established considering time effect.The equation of the conductor bearing capacity increasing with time in sand soil and in clay is obtained.The real time bearing capacity of conductor of a deepwater well in the South China Sea is calculated and analyzed with the equation.The results show that the recovery rat of bearing capacity is faster in sand soil than in clay.A theoretical model is established to calculate the lateral bearing capacity of conductor structure of shallow and surface drilling in deepwater,considering the characteristics of the drilling.In the model,the transverse force from upper riser system is equivalent to a transverse force and a bending moment loading on the conductor.The effect of the transverse force,the bending moment and the ground reaction force to the conductor are considered as well.Based on the theoretical derivation,the calculation model of the lateral bearing capacity of conductor structure is solved by the method of Glesser.A calculation procedure is given to calculate it.Certain key parameters,the diameter and the wall thickness of the conductor,the equivalent transverse force and bending moment,and the setting depth,which influencing the lateral bearing capacity of conductor structure,are analyzed on the basis of the model.The method of determining the minimum setting depth is presented based on the time effect experiment of the conductor vertical bearing capacity.The method of determining the minimum setting depth by the transverse force of conductor structure is given,taking the maximum allowable rotation angle as the standard.The method considering the vertical force and transverse force to determine the minimum setting depth,gives more security in designing conductor in the harsh environment with large wave current could be ensured.In order to determine the pumpage and bit stick-out in jetting drilling,a finite element model of soil breaking is established based on the theory of pipeline and soil interaction.The stress field of soil is simulated under the condition of different jetting pumpage and bit stuckout.Then,a method determining jetting pumpage is proposed considering the stress characteristics of rock and soil,which reduces the dependence on exploratory wells and reference wells by adding some field experiments.Aiming at the determination of hydraulic parameters in surface casing drilling,the experimental study of the rock compressive strength under the condition of simulating the drilling formation is done first.The changing law of rock compression strength under different temperature,pressure and soaking time is obtained by analyzing experimental data.The varying coefficient of rock compressive strength is introduced and its systhetic equation is acquired by fitting experimental data.Based on that,a method to calculate “the safe mud weight window of surface drilling” is proposed considering time effect in surface casing drilling.Finally,the optimizing method of key hydraulic parameters of surface casing drilling is established considering the influence of “the safe mud weight window of surface drilling”.And the pumpage of surface casing drilling is optimized with the method.