Fracture structures are widely present in fractured strata,and its borehole stability analysis is always a difficult point in research.In this paper,the fluid-solid coupling method is used to study the borehole stability of fractured formation,and the unsteady seepage model derived.Combined with rock mechanics experiments,the in-fluence of seepage on rock mechanics parameters is determined,and the collapse pressure calculation model based on fluid-solid coupling is established and verified.The results show that the initial stage of seepage is dominated by unstable seepage.When the seepage time exceeds 6 min,the seepage flow increases almost linearly with the seepage time,indicating that the unstable seepage has changed into stable seepage.Under the action of seepage,the internal friction angle of coal rock changes greatly,and the change of cohesion is relatively small.The seepage effect has little influence on the axial stress,but has great influence on the radial and circumferential stress.After considering the seepage effect,the equivalent density of collapse pressure increases by about 0.3 g/cm3.By com-paring and analyzing the prediction results of borehole stability in coal seam section of X01 well and X04 well,the fluid-solid coupling prediction model of borehole stability established in this paper is more accurate to calculate the collapse pressure of coal strata.The research results are helpful to ensure the borehole stability of fractured for-mations and provide a theoretical basis for reasonably reducing drilling fluid density.
关键词
破碎性地层/流固耦合/坍塌压力/非稳定渗流/煤岩力学参数
Key words
fractured strata/fluid-solid coupling/collapse pressure/unsteady seepage/coal rock mechanics parameters
维普
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