| Most of China's untapped oil and gas resources are mainly buried in unconventional strata and complex and difficult to drill formations.When using traditional drilling tools to mine such formation oil and gas resources,problems such as low rock breaking efficiency and serious bit damage are often encountered.Therefore,the research on new methods,new theories and new technologies for efficient rock breaking is the primary problem that needs to be solved in current oil and gas drilling.At present,scholars at home and abroad have carried out research on various new technologies for rock breaking.Among them,one of the representative and development prospects is the combined laser rock breaking technology.However,in the current research on laser rock breaking,the shape of the laser spot used is mostly circular,the spot diameter is generally 5-10 mm,and the rock acts in a static form.Compared with the actual drilling size of the laser-mechanical combined rock breaking,the damage area of the laser to the rock is limited,and the laser-assisted rock breaking effect is not good.In this paper,different shapes of moving laser spot are used to scan rocks in order to increase the damage area of rocks,and related simulation and experimental studies are carried out.Specific research contents and results are as follows:(1)Establish the mathematical models of the intensity and density distribution of rectangular spot and the temperature distribution of moving rectangular and circular spot,which obey the Gauss distribution,and provide the theoretical basis for the follow-up simulation analysis.(2)Using COMSOL Multiphysics simulation software,the thermal-mechanical coupling finite element simulation calculation of two kinds of moving spot theoretical models is carried out.The temperature field distribution on the rock surface after two kinds of moving spot irradiating granite and sandstone is obtained,and the results are compared with the experimental data to verify the accuracy of the simulation model.(3)Taking Mohr-Coulomb strength criterion as the criterion for determining the failure of rock,the topography of rock surface fragmentation area after scanning with two kinds of moving spot is simulated and analyzed,and compared with the experimental data,the damage range of rock surface caused by moving spot is determined to be consistent with the irradiation area of the spot.The effects of two kinds of moving spot on rock mechanical properties and drillability are obtained through experiments.(4)The effects of two moving spots on rock strength and drillability were obtained through experiments.The results show that the uniaxial compressive strength of the granite and sandstone after the rectangular scanning of the rectangular spot is reduced by 24%and 20%,respectively,and the tensile strength is reduced by 20%and 17%,respectively.Drilling grade values decreased by 16%and 38%,respectively.The granite uniaxial compressive strength decreased by 27%and 29%,respectively,and the tensile strength decreased by 26%and 20%,respectively,in the granite and sandstone after scanning the circular spot.The sex value decreased by 20%and 53%,respectively.(5)Taking the rectangular spot irradiation area as the evaluation area of two kinds of movable spot rock breaking effect,by comparing the influence degree of two kinds of movable spot on rock strength and drillability in this area,the quality of two kinds of movable spot rock breaking effect is evaluated.The results show that in the range of the rectangular spot irradiation area,the rectangular spot has better ability to improve the uniaxial compressive strength,tensile strength and drillability of the two rocks than the circular spot. |
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