| Aiming at the instability of the borehole wall in the fault zone,the method of theoretical and experimental research is used to study the time delay of the wall failure in Wenchuan earthquake fault zone as an example.Firstly,the characteristics of the strata drilling project,the stratigraphic characteristics and the distribution of the geostress stress and the influence of the coal shale are analyzed in detail in the Wenchuan earthquake fault zone.Then,the material composition and microstructure of the rock mass in the fault zone are obtained by microscopic experiment.The hydration stress and the compressive strength of the rock mass in the fault zone are obtained with the hydration time.Then,based on the research results of the rock mass in the fault zone,the establishment and analysis of the mathematical model of the stability of the pore wall in the fault zone are carried out,and the stability characteristics of the hole wall in the fault zone are studied deeply.The main results are reflected in the following aspects:(1)The ground stress of the formation of the rock specimen is obtained by field data collection and differential strain analysis,and the formula of the change of the geo-stress with depth is deduced: ?H=0.098×H-2.92(R2=0.605).The calculation of the ground stress has A certain reference value;(2)A series of laboratory experiments were carried out on the rock samples.Among them,X-ray diffraction experiments and infrared scanning experiments were carried out for the rock samples in the fault zone.The main mineral components of the rock samples were illite,quartz and green Debris,etc.,in which the clay minerals in the form of degradation,easy to absorb water swelling caused by wall failure;by scanning electron microscopy observation and analysis,obtained rock microstructure: flaky structure and the existence of a large number of small gaps and pore throat,The Internal Structural Factors of Wall.(3)According to the strain experiment,the change curve of hydration stress with hydration time was obtained,and the maximum hydration stress and maximum hydration stress time in different solutions were obtained.The drilling and hydration process was simulated by FLAC3 D software.The results show that the change of rock mechanics intensity is basically completed within 15 h under slurry soaking.After 15 h,the curve is smooth and the trend is slow.(4)According to the strength test,the compressive and shear strength of rock samples under different hydration time and different slurry types were obtained.It is found that the compressive strength and elastic modulus of the rock are decreased with the prolongation of the hydration time,and the compressive strength of the rock is especially affected by the soaking time.The compressive strength of the rock is different after the different slurry types: The compressive strength of the rock specimen after 2 # and 3 # drilling fluid is the smallest,and the compressive strength is still up to 36 MPa.(5)Through the expansion experiment,the relationship between the hydration strain and the hydration time was obtained.The swelling amount and the ultimate failure mode of the rock samples in different solutions were intuitively understood,and the expansion amount was the largest in the clear water.In the expansion of the amount of varying degrees of inhibition;(6)Based on the above series of experiments,this paper analyzes the changes of pore wall morphology and the distribution and variation of the corresponding stress in the process of analyzing the instability.The project analyzes the stress,,The pore pressure and the stress caused by hydration stress are applied to the surrounding rock of the pore wall,and the stress distribution equation of the surrounding rock of the deep coring hole is obtained and the Mohr-Coulomb criterion is selected as the fault zone Criteria for Judging the Instability of Wall Rock.(7)Based on the COMSOL Multiphysics platform,the mathematical model of the stability of the hole in the fault zone is obtained by using the geotechnical module,the porous elastic module and the custom equation module.The variation law of axial stress and radial stress distribution in the surrounding rock of the fault zone is obtained,and the pressure distribution of the surrounding wall is obtained at different time points.(8)A modified sulfonated drilling fluid system with high density,low water loss,low permeability,strong lubrication and so on was developed with the drilling of WFSD-1 hole water and strong creep fractured strata as an example.The basic formula is: 4%swelling + 0.2%soda ash + 0.5%high viscosity sodium carboxymethyl cellulose(HV-CMC)+ 2%loss agent(S-1)+ 5%film-forming agent(X-1)+ 3%sulfonated pitch(SAS)+ 1%chromium-free sulfonated coal(SMC)+ barite powder.The system successfully solved the aging problem of the fracture wall. |
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