| Hot Dry Rock is an important geothermal resource,which has the characteristics of green,high efficiency and stability.Accelerating the exploration and development of dry hot rock is of great significance to improve the environment and optimize the energy structure.In Gonghe basin,Qinghai Province,China,the dry hot rock is widely distributed and rich in resources,but it is faced with such problems as high rock hardness,poor drillability of bit,frequent thermal fracture and so on.There are challenges in safe and efficient drilling,which restrict the exploration and development process of dry hot rock in China.In this paper,high temperature foam drilling fluid system is studied by means of field investigation and laboratory experiments.The lithological characteristics and mechanical properties of dry hot rock in Gonghe basin of Qinghai are systematically studied.Combined with rock drillability experiment,the best tool and process for rock breaking are selected.Field tests are carried out to provide scientific basis for efficient drilling of dry hot rock in this area.The field investigation in Gonghe basin,Qinghai Province shows that the maximum principal stress and tensile shear stress are NE-SW and NNW-SSE respectively;through the analysis of the core of the exploration well,it is determined that the dry hot rock mass in the block is gray white light flesh red granite,monzogranite and granodiorite,medium coarse grain and other grain structure,with highly developed fractures;it can provide important geological reference for the optimization of drilling tools and technology in the target area ?The research of high temperature foam drilling fluid technology has been carried out.The experimental results show that C-4 and wp-5 have high temperature resistance;the half-life of the system is obviously enhanced after adding liquid film reinforcement;the surface tension test shows that the system has stability;the interface rheological test shows that the system has good temperature resistance and meets the drilling requirements.Through the laboratory experiment of rock mechanics,the indentation hardness test(outcrop)was carried out,the hardness of outcrop rock was more than 5 grades,and the plasticity coefficient was 1.59 ? 2.00,belonging to the second grade plastic rock;the triaxial compression test was carried out,the compressive strength under confining pressure was 178 ? 430 mpa,Poisson's ratio was 0.23 ? 0.34,and the young's modulus was more than 36000mpa;the acoustic emission in-situ stress test was carried out,and the longitudinal wave velocity ratio was 1.79 ? 2.33 The deeper the formation is,the smaller the ratio is,the less the influence of confining pressure on the formation stress is,and the difference between the vertical stress and the horizontal maximum principal stress is small,even less than 0.7MPa;the rock tensile strength test results show that the rock tensile strength is 5.67 ? 10.80 mpa.The rock in Gonghe basin,Qinghai Province is hard,with high compressive strength and medium plasticity.The rock mechanical parameters of the same well section have no big fluctuation,and the porosity of deep formation is small.The experimental results provide important mechanical reference for optimizing drilling tools and technology.Based on the rock drillability experiment,it is found that the drillability of PDC bit and cone bit in the target formation is up to grade 10.Based on the rock mechanics parameters,the rock mechanics profile is established.Combined with the lithology characteristics of dry hot rock,two kinds of BHA are optimized: dry hot rock section and hard formation using metal sealed cone bit + hydraulic impactor,non dry hot rock section and soft formation using special impregnation Bit + turbine;further optimize the drilling technology,use the drilling program of high temperature while drilling measuring instrument of formation with temperature resistance up to 225 ? plus forced cooling technology of drilling fluid cooling device based on plate heat exchanger;carry out field drilling test,and the rock breaking efficiency of the optimized BHA in practical application has increased by 20%.Through the research of this project,the rock mechanics parameters of Gonghe Basin in Qinghai Province are obtained,the rock breaking tools and rock breaking technology are optimized,so as to further guarantee the smooth drilling of the target formation. |
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