Evaluation Of Mechanical Properties Of Shale Based On Micro-scale Indentation Experiments

As a clean and unconventional natural gas resource,shale gas has become the new darling of global oil and gas exploration and development.Due to the large differences between shale gas reservoirs and conventional reservoirs,conventional technologies cannot be used for efficient development,and breakthroughs in key technologies are urgently needed.The progress of horizontal well drilling technology plays an important role in promoting the development of shale gas.The rock mechanics of shale reservoirs is an important parameter for horizontal well drilling.At present,researchers generally use the combination of indoor test core and logging data interpretation to obtain shale mechanical parameters.For shale gas horizontal well drilling,due to the cost of shale drilling,few engineering issues such as borehole wall stability are determined,and mechanical parameters are obtained by indoor core testing.The logging data interpretation method is generally used to establish parameters of mechanical parameters such as acoustic logging,density logging,etc.,and then predict the effective data,but the logging cost is relatively expensive,and the logging times are few.For this reason,this paper hopes to use microindentation experiments to analyze easily accessible shale cuttings and study the relationship between micromechanical properties and macromechanical properties,to bridge the mechanical properties of the two and provide a new acquisition.The research method of real mechanical properties of shale achieves the purpose of guiding drilling construction in real time on site.This study has obtained the following results:1)Research on the preparation of shale granular samples.Collect 470 shale particles from the Longmaxi Formation shale in the three blocks of Changning,Weiyuan and Jiaoshiba,including 60 debris and 410 outcrop debris.Due to the anisotropy of shale,vertical and parallel layers are After distinguishing the two,and determining the cement preparation plan,the cementation of the particles was carried out,and the shale granules were prepared by cutting,rough grinding,fine grinding,and fine grinding of the rock sample surface.Finally,the cementing of the shale granule system was clearly clarified.In the preparation scheme,a total of 47 experimental samples were prepared.And mathematically determine the minimum number of indentations required for analysis normalization.2)Conduct micron indentation test of rock samples.Based on the characteristics of the load-displacement curve of the indentation test,the output conditions of the best mechanical parameters of the shale cuttings were determined:the loading force was 50 N and the loading rate was 15 N/min.Taking into account the boundary effects,the size specifications of the debris particles are clarified.Three phenomena that analyze the special curve of the indentation of shale:"Pop-out","Pop-in",and "Bending",and the reason for this depends on the state of energy transition.3)The fracture toughness formula was modified by means of the actual measurement of the energy area,and it was found through the calculation law of the fracture toughness that when the fitted value of the loading curve is less than 1,the fracture toughness value may not be obtained.The indentation modulus(IM)was normalized to the parameters and a fitting relationship between the intensities(UCS)was established.Analyze the calculation method of the uniaxial strength indentation test of shale.4)Evaluate mechanical parameters of shale outcrop in three blocks.As the indentation point mathematical statistics can approximately represent the macroscopic characteristics,based on the elasto-plastic characteristics of shale,the elastic modulus,hardness,elastic modulus,and elasticity of the debris in the Changning block,Weiyuan block,and Jiaoshiba block are implemented.Evaluate the accuracy of elastic modulus,hardness,elastic modulus,brittleness index,and strength.