| The sky、the earth、the sea and the polar were the four human dreams that humanconquer the nature.From the20th century,our understanding of the space、the oceanand the polar have reached a certain height. Conversely we knew too little about theearth. It was difficult to gain the information of the earth, Drilling engineering wasthe best way of gain information of deep earth.Deep continental scientific drilling was regard as a telescope penetrating into theinterior earth, which was a significant measure to explore the underground mysteriesand resources. The deep continental scientific drilling of the Soviet Union foundbiological under extreme conditions, deep oil and gas and mineralization, which brokethrough the traditional theory of hydrocarbon accumulation, expanded the space ofresources, and deepened the understanding of the evolution of life.However, deep continental scientific drilling project involved multipledisciplines and fields, such as geoscience、 mechanics、 machinery、electronics、material、 physics、 chemistry and bionics. Technology level of the drilling, in acertain sense, reflected the scientific and technological level and economic strength ofa country. Up to now, the scientific drilling program was carried out by only a fewcountries in the world. According to the different geographical position, scientificdrilling can be divided into continental scientific drilling, ocean scientific drilling andpolar scientific drilling. The research in this paper was based on the continentalscientific drilling.In order to meet the requirement of the diamond drilling in the continentalscientific drilling, the weight on bit was controlled accurately. If the weight on bit wastoo small, it would shorten the footage per run; If the weight on bit was too big, itwould accelerated the wear of the bit, and shorten bit service life.In the process of drilling，the traditional way of bit feed was the manual bit feed,which would be easy to cause discontinuous when the drill pipes were down, and uneven pressure on the drill bit. Especially in the complex geological conditions, theundulation swing of the weight on bit would lead drilling accidents, such as bitbouncing. In addition, due to difference of the technical level of the operator orfailures, the weight on bit would fluctuate severely. And then the auto-drillingtechnology arises because of the disadvantages of manual bit feed. Auto-drillingtechnology was an advanced drilling method, which doesn’t adjust the parameters ofthe drilling relying on the drillers, but according to the requirements of drilling. Whendrilling using the auto-drilling technology, the weight on bit will be adjustedautomatically by the control system to realize automatic feed drilling tools.The auto-drilling system with constant drilling pressure, as the weight on bitcontrol system of drilling, was mainly responsible for automatic drilling with constantdrilling pressure when tripping or drilling, without the need for manual control. Whendrilling in homogeneous formations, automatic drilling system can guarantee the bit toget a smooth weight on bit, so that the bit jumping would be reduced in drillingprocess.This paper was based on the continental scientific drilling equipmentdevelopment project. Aiming at the current situation of the auto-drilling technology,dynamic simulation of small motor auto-drilling system was made on AMESim.Experimental investigation of the disc brake auto-drilling system was carried on inthe paper. Comparison and analysis of two structure scheme were carried out. Theconclusions were made as follow.(1)In the first instance the analysis of pressure transmission process in theborehole was made especially the friction. The calculation of the friction wasconverted into contact-impact research between the beam and the rigid beam.According to the technical requirements of deep continental scientific drillingproject, Comprehensive analysis of the weight on bit、rotational speed and thepumping capacity was made for the technical requirements which was penetrationrate、bit service life、footage per run、core recovery and borehole deviation. Throughthe formation conditions and drilling requirement, the optimal weight on bit was estimated. The analysis of pressure transmission process in the borehole was madeespecially the friction. The calculation of the friction was converted intocontact-impact research between the beam and the rigid beam.(2) Secondly the theory equation of constant weight on bit drilling system wasdeduced and the structure scheme was proposed.The vertical stress of drill pipe system was analyzed in this paper based on theexisting theory equation with constant drilling pressure, And the theory equation ofconstant weight on bit drilling system was deduced, which was gained bysummarizing the conventional calculation of drilling pipes weight、 buoyancy ofdrilling fluid、 lifting force and friction. Based on the spot investigation andtheoretical research, combined with the project requirements, two auto-drillingsystems were proposed: small motor auto-drilling system and disc brake auto-drillingsystem.(3) For the second time dynamic simulation of small motor auto-drilling systemwas made on AMESim, and results show that the fluctuation range of the weight onbit can be up to±3kN.The pressure which applied on the bit was divided into two types. It was staticload (drilling pipes weight)and dynamic load (buoyancy of drilling fluid andfriction),which was very complex.In this paper, the static load was represented by theweight of a mass at the bottom of the block and tackle, and the dynamic load wassimulated by a load function of periodical or random changing. The simulation ofconstant weight on bit drilling was conducted in the software of AMESim, and resultsshow that the control precision of the weight on bit can be up to±3kN.(4) Finally this paper analyzed control effect of disc brake auto-drilling systemin experimental investigation, the fluctuation range of the weight on bit can be up to±5kN.In order to validate the control effect, the disc brake auto-drilling experiment wascarried out in Sichuan province. According to the formation conditions of gravel.Thecontrol scheme and detection scheme were designed. PID control algorithm was used in the test. The instrument needed to be debugged successfully after installation. Twoexperients were conducted and the weight on bit was tested. In one of the test, theweight on bit was set to140kN, and the weight on bit measured at the bottom of thebore was about130kN, the fluctuation range was greater than5kN and less than10kN.Sometimes the weight on bit would be100kN or160kN, which has been far morethan the designed control requirement of the weight on bit (fluctuation range shouldnot be more than5kN). In the other test, the weight on bit was set to90kN, and theresult showed that the measured weight on bit curve coincided the given drillingpressure curve very well, the fluctuation range of the weight on bit can be up to±5kN.and the fluctuation range of the weight on bit met the requirements. |
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