Shaft Wall Stability Analysis Of Shale Complex Formation Based On Mg-C Criterion

The exploration and exploitation of shale gas has important strategic significance for my country's energy reserves.Therefore,our country is speeding up the efficient exploitation of shale gas.In the process of shale gas drilling and production,the most important technology is horizontal well drilling technology.In the process of horizontal well drilling,we often encounter the problems of wall collapse,rupture,leakage and other well wall instability.These problems lead to the occurrence of stuck and buried drills,which affect the construction cycle in severe cases and cause huge economic losses.Therefore,the research on the shale shaft lining in Block L is of great significance to the domestic shale gas exploitation.In this paper,combined with the reservoir characteristics of the shale formation in Block L,and considering the influence of the force-chemical coupling,a series of studies have been carried out on the mechanical characteristics of the surrounding rock of the shaft wall.Firstly,it starts from the physical and chemical properties of the rock,and describes the mechanical properties of the rock microscopically.Then,the mechanical properties of the rock are understood from a macroscopic point of view through the laboratory test of rock mechanics;on this basis,the study of the in-situ stress and the stability of the shaft wall is carried out and calculated A reasonable mud density window was obtained,and a reasonable borehole stability evaluation was made for the block.The conclusions are as follows:(1)A preliminary analysis of the physical and chemical properties of shale is carried out through whole-rock mineral composition analysis,scanning electron microscopy experiments and hydration performance experiments.The analysis shows that the internal brittle minerals in the shale are mostly,with well-developed cracks and bedding surfaces,and strong hydration.The characteristics of shale show the importance of physical and chemical properties to the stability analysis of shale boreholes,and provide theoretical explanations for the instability mechanism of boreholes.(2)Through the laboratory test of rock mechanics,the formation mechanics parameter profiles of two adjacent wells in this block are obtained.It is recognized that the reservoir in this block has a certain transverse isotropy,but according to the experimental data,this study will ignore the influence of anisotropy on wellbore stability.(3)Analyze the existing in-situ stress model,and use Huang's model according to the geological characteristics of the shale formation to establish the relationship between the in-situ stress and provide intermediate parameters for the calculation of collapse pressure and rupture pressure.(4)Considering the hydration performance of shale,and substituting the Mogi-Coulomb criterion hydration damage strength model according to the magnitude of the three-dimensional principal stress,the calculation model of collapse pressure and fracture pressure is established.Based on this,three pressure profiles are established to provide a basis for the evaluation of well bore stability.Based on the above understanding,the shale horizontal well in Block L is used as the industrial and mining research area,and the three pressure profiles of Well Lz1 and Well Lz2 are established based on the mechanical parameters of the area,and the drilling fluid density suitable for Block L is proposed.Evaluation of the stability of the well wall.