| Hot Dry Rock(HDR)is a rock body that contains no or only a small amount of fluid,with a temperature higher than 180°C.Its thermal energy can be developed and utilized under current technical and economic conditions,and has the advantages of large energy,wide distribution,renewable,safe,clean and pollution-free,and not limited by seasons and day and night compared with traditional hydrothermal geothermal systems,and is an important target for future geothermal energy development.The related findings and main research of the thesis are as follows.(1)The reasons for the decrease in drilling speed in high-temperature hard rock drilling were discovered.In this thesis,we summarize a number of successful cases of granite HDR formations drilled at home and abroad,and analyze and test the physical and mechanical properties of the reservoir rocks,and find that as the drilling depth of HDR increases,the temperature and stress changes in the reservoir also increase,making the rocks harder,more plastic,more abrasive,more difficult to drill,and the volume of rock broken by each rock-breaking action of the drilling teeth becomes smaller,causing the drilling speed to decrease.Combining the above characteristics,we have developed key technologies for drilling in high-temperature hard rock conditions and innovative process combinations to achieve efficient and rapid drilling in HDR.(2)A new structure of torsional impactor was designed and a research on the composite drilling process of "turntable + screw drilling tool + torsional impactor" was carried out in hard rock drilling.In view of the problems of short life span and low drilling efficiency of HDR drilling tools and the mechanical characteristics of HDR,we designed and patented a new structure of torsional impact drilling tools to fully utilize the advantages of torsional impact vibration composite drilling process in the drilling process.The innovative "turntable + screw drilling tool + torsional impactor" composite drilling process is applied in the coaxial heat transfer drilling of granite HDR formation,and the "screw drilling tool + torsional impactor short section" drives the drill bit to rotate at high speed and cut the rock and the torsional impactor drives the drill bit to impact the rock at high frequency,and the two modes of impact and cutting are coupled in thedrilling process.The drilling speed is increased by 29.59% under the coupling effect of both impact and cutting modes,which eases the abrasion of high temperature hard rock on the drill bit,protects the drill bit,prolongs the service life and increases the drilling speed.(3)A water-based film-forming drilling fluid with a temperature resistance up to220°C was developed.A water-based film-forming drilling fluid system with a temperature resistance up to 220°C has been developed to address the performance failure of drilling fluids caused by high temperatures in HDR wells and the core loss caused by loose fracture of the formation during the construction of the GR1 well.This drilling fluid system introduces organosilicate on the basis of traditional inorganic silicate,which can form a dense film-like structure on the surface of rock chips(a film can be formed in the well wall or formation pore space during drilling),which can significantly reduce the hydration dispersion of rock chips and has strong inhibition,and is conducive to well wall stability.Using the high temperature of the formation in the well,the film-forming reaction of the composite silicate film-forming system occurs at a temperature higher than150°C,forming a crystalline silica film with a dense structure,which is temperaturedependent;the formulation of the higher temperature-resistant water-based drilling fluid containing the composite silicate treatment agent obtained is: 2% bentonite base slurry +3% SPNH + 0.1% DSP-1 + 0.2% Driscal-D + 2% SO-1+3% FT-99+2% potassium methylsilicate+0.5% potassium silicate+0.5% KOH+3% triethanolamine.The formulation has stable rheological properties after aging at high temperatures of 150°C,180°C and 220°C,significant filtration loss reduction effect and high mud cake quality,and can be used as a drilling fluid candidate for high temperature drilling of HDR.(4)The research on the application of "rotary(top drive)+ screw drilling tool" composite drilling process in the high-temperature hard rock formation of HDR was carried out.According to the environment of the tool under the HDR drilling,the rubber material of the screw drilling tool was selected and improved in terms of high temperature resistance,fatigue resistance and abrasion resistance,and the design of the wall thickness of the screw drilling tool was optimized,and the fit gap between the stator and rotor was adjusted,so that the screw drilling tool could resist high temperature and extend its service life.When the "rotary(top drive)+ screw drilling tool" composite drilling process is applied to the high-temperature hard rock formation of HDR,the drilling speed of the composite drilling process is much higher than that of the conventional drilling process driven by rotary,and the average drilling speed is increased by 43%,which significantly improves the drilling speed of hard rock,indicating that the "rotary(top drive)+ screw drilling tool" composite drilling process is much faster than that of the conventional drilling process driven by rotary.This shows that the "rotary(top drive)+ screw drilling tool" composite drilling process is feasible for drilling in HDR hard rock formations,which shortens the drilling cycle and realizes efficient and fast drilling.(5)The newly developed turbo core drilling tools were tested in the drilling of high temperature hard rock wells in HDR.The newly developed domestic turbo drilling tools and KT140 core drilling tools and bits have withstood the test of high temperature hard rock in the bottom of the well over 220℃,and the "turntable + turbo drilling tools" composite core drilling process has achieved a complete success.Compared with the conventional turntable-driven core drilling process,the average drilling speed of the "turntable+turbine drilling tool" composite core drilling process has increased by 53.5%,achieving high quality and rapid core drilling of HDR. |
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