Experimental Study On Key Evaluation Parameters Of Ice Hole Wall Instability Under Brittle Behavior

With the acceleration of industrialization and the continuous development of the world economy,resources are more and more important for human beings.At present,oil,natural gas,and other resources are in short supply in the world,so we need to find new resources to meet the needs of human sustainable development.According to the survey,there are many kinds of mineral resources with huge reserves under the Antarctic ice,such as coal and oil.It will be very beneficial to the sustainable development of mankind if these resources can be reasonably exploited and utilized.Meanwhile,the study of polar glaciers is also significant to other disciplines,such as the formation of the Antarctic continent and the law of global climate change,and these studies all need bedrock core under the ice.The stability of ice hole wall seriously affects the progress of polar drilling engineering,and the instability of ice hole wall brings a series of problems in the process of drilling the ice core.Generally,the instability of ice hole wall may be caused by two cases.One case is the hole wall shrinkage,collapse,block falling and so on,leading to sticking.And the other is the hole wall enlargement,making the hole wall rupture,which can result in drilling fluid loss and environmental pollution.Therefore,in order to ensure the safety of ice drilling,it is necessary to keep ice hole wall stable,and the key to solve this problem is to obtain the critical pressure condition.This paper focuses on the brittle stability of the ice hole wall in the deep ice-breaking zone.According to the previous research,it can be known that the friction coefficient between ice bodies and the fracture toughness of ice are the key parameters to determine the stability of ice hole wall.In this paper,the friction coefficient between ice bodies is studied by electric test bench and digital display tensile machine.The influences of rate,loading pressure,contact area,roughness,temperature,and drilling fluid on the friction coefficient between ice bodies are analyzed.The findings are as follows:(1)When the sliding rate increases from 40 to 180mm/min,the friction coefficient decreases firstly and then increases,and finally tends to a constant value,and the value of the friction coefficient ranges from 0.27 to 0.46;(2)When the loading pressure increases from 2.80to 8.80N,the friction coefficient decreases firstly and then increases,and the value of the friction coefficient ranges from 0.20 to 0.33;(3)When the contact area is changed from 68.61 to 130.15cm²,the variation of friction coefficient with contact area is also different when the loading pressure and sliding rate are different,and the value of the friction coefficient ranges from 0.16 to 0.39;(4)When the contact surface roughness of the upper ice sample increases from 0.383 to 2.426?m,the friction coefficient keeps increasing,and the value of friction coefficient ranges from 0.28 to 0.48.In this paper,the influences of temperature and drilling fluid on the friction coefficient between ice bodies are studied by an orthogonal experiment.It is found that the friction coefficient increases with the reduction of temperature when the temperature ranges from-5 to-20?and the filling drilling fluid is zero,ethyl butyrate and butyl butyrate respectively.When KF-96-2CS silicone oil is used as drilling fluid,the variation of friction coefficient is just the opposite.When the temperature ranges from-5 to-15?,the three kinds of drilling fluids all play the role of lubrication and drag reduction,and the friction coefficient decreases with the increase of rate under three kinds of drilling fluid filling state and no medium state.When the temperature is-20?,KF-96-2CS silicone oil can prevent the ice body from sliding,and the friction coefficient decreases firstly and then increases with the increase of rate.Under the experimental conditions,the value of the friction coefficient ranges from 0.18 to 0.41.Next,the fracture toughness of ice is studied by the Brazilian disc method.The influences of temperature,loading rate,and drilling fluid on the fracture toughness of ice are analyzed.It is found that the fracture toughness of ice decreases with the reduction of temperature and the increase of loading rate under the experimental conditions of temperature ranging from-5 to-20?and drilling rate ranging from 60to 240mm/min.The influences of KF-96-2CS silicone oil,ethyl butyrate,and butyl butyrate on the fracture toughness of ice can be ignored.Under the experimental conditions,the value of the fracture toughness ranges from 3.3 to 27.2KPa.m^0.5.Finally,according to the existing brittle stability theory of ice hole wall,the tested friction coefficient between ice bodies,the fracture toughness of ice,and the critical pressure conditions for the brittle instability of ice hole wall are analyzed under the hole wall stress states of??and??in the deep ice-breaking zone.The influence laws of temperature,drilling rate and drilling fluid on the critical pressure condition for the brittle instability of ice hole wall are obtained.The results shows that the friction coefficient between ice bodies plays an important role in determining the critical pressure condition for the brittle instability of ice hole wall under the experimental conditions of temperature ranging from-5 to-20?and drilling rate ranging from 60 to 180mm/min and drilling fluid being KF-96-2CS silicone oil,ethyl butyrate,and butyl butyrate.Meanwhile,the critical pressure for the brittle instability of ice hole wall ranges from 4.1 to 4.9MPa when the stress state of ice hole wall is??;The critical pressure for the brittle instability of ice hole wall ranges from 3.4 to 4.5MPa when the stress state of ice hole wall is??.In addition,the critical pressure condition for the brittle instability of ice hole wall under specific conditions is verified by hydraulic pressure simulation experiment.In this paper,the key parameters affecting the stability of ice hole wall,such as friction coefficient and fracture toughness,are systematically studied.Moreover,according to the critical conditions for the brittle failure of ice hole wall,the brittle stability law and critical pressure of ice hole wall instability under different conditions are given,and the results are expected to provide a theoretical basis for the brittle stability study of ice hole wall in the deep ice-breaking zone.