深井高应力砂岩压裂裂缝扩展规律研究

Study on Fracture Propagation Law of High-Stress Sandstone in Deep Well

针对深井高应力条件下,煤矿顶板坚硬难以垮落带来的冲击灾害问题,提出高应力条件下压裂方案并进行试验研究,采用大尺寸真三轴压裂渗流模拟装置进行水力压裂物理模拟试验,研究不同注液速率、不同黏度压裂液介质对裂缝起裂扩展规律的影响。结果表明:注液速率的提升可以明显缩短高应力条件下砂岩的起裂时间;注液速率的改变对高应力条件下砂岩的起裂压力影响不明显;压裂液黏度的增加对裂缝宽度具有一定的影响;通过对注液速率和压裂液黏度的合理调控,在一定的试验条件范围内可实现对砂岩起裂压力和起裂时间的预测;高地应力条件是影响裂缝发育的主要因素,由于高水平地应力差的存在,裂缝基本不会发生偏转,形成一条垂直于最小主应力的主裂缝。研究结果对深井高应力致裂顶板具有一定的参考价值。

The difficulty of caving due to hard roof of coal will lead to the impact disasters under the condition of deep mines with high stress.Aiming at this problem,fracturing scheme and experimental research under the condition of high confining pressure were proposed.The large true triaxial fracture seepage simulation device was used for hydraulic fracturing physical simulation experiment,and the influences of the different liquid injection rates,different fracturing fluid medias with different viscosities on the laws of crack initiation and propagation were studied.The results are concluded as follows.The increase of liquid injection rate can obviously shorten the initiation time of sandstone under high stress condition.The change of liquid injection rate has little obvious effect on the initiation pressure of sandstone under high stress.The increase of fracturing fluid viscosity has a certain influence on the fracture width,and the initiation pressure and initiation time of sandstone could be predicted within a certain range of test conditions by reasonable adjustment of injection rate and fracturing fluid viscosity.High in-situ stress condition is the main factor affecting fracture development.Because of the existence of high horizontal in-situ stress difference,the fracture basically would not deflect and can form a main fracture perpendicular to the minimum principal stress.The research results has a certain reference value for high-stress fracturing roof in deep well.