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中文核心期刊

不同温度条件下含流体砂岩裂隙摩擦特性的试验研究

EXPERIMENTAL STUDY ON FRICTIONAL PROPERTIES OF FLUID-BEARING SANDSTONE FRACTURES AT DIFFERENT TEMPERATURES

  • 摘要: 砂岩储层中由流体注入导致的地震活动与砂岩断层(裂隙)的摩擦行为有关. 为了揭示不同温度条件下含流体砂岩裂隙的摩擦特性, 在温度范围为25 °C ~ 140 °C和有效法向应力范围为4 ~ 12 MPa的试验条件下, 本文分别对干燥、水饱和以及注CO2锯切砂岩裂隙进行了速度分级加载试验. 试验结果表明: (1)对于干燥砂岩裂隙, 增大有效法向应力和升高温度均能增大裂隙的初始摩擦系数, 而改变有效法向应力对裂隙摩擦稳定性影响不明显, 仅升高温度会略微降低其摩擦稳定性; (2)对于水饱和砂岩裂隙, 裂隙的初始摩擦系数同样会随着有效法向应力的增大而增大, 但会受到升温的弱化作用, 而增大有效法向应力和升高温度均能降低裂隙的摩擦稳定性; (3)对于注CO2砂岩裂隙, 裂隙的初始摩擦系数受有效法向应力和温度变化的影响与水饱和砂岩裂隙相反, 但裂隙的摩擦稳定性仅会随着温度的升高而降低, 受有效法向应力的影响不明显. 因此, 砂岩裂隙的摩擦特性受有效法向应力、温度和注入流体类型的共同影响. 该试验结果对理解流体注入诱发地震有一定的指示作用.

     

    Abstract: Seismic activity caused by fluid injection in sandstone reservoirs has been associated with the frictional properties of embedded faults or fractures. In order to study the frictional characteristics of fluid-bearing sandstone fractures under different temperature conditions, velocity stepping tests were carried out at varying temperature and pressure conditions (a temperature range of 25 °C ~ 140 °C and an effective normal stress range of 4 ~ 12 MPa) on dry, water saturated and CO2 injected sandstone fractures (obtained by saw cutting), respectively. The experimental results show that: (1) For dry sandstone fractures, increasing effective normal stress and increasing temperature can both increase the initial friction coefficient of fractures, while varying effective normal stress has no obvious effect on the frictional stability of fractures. An increase in temperature is found to enhance the frictional stability of fractures. (2) For sandstone fractures saturated by water, the initial friction coefficients of fractures also increase with the effective normal stresses, but they can be weakened by the rising temperatures, and increasing effective normal stress and temperature can both favor the frictional instability of fractures; (3) For the CO2 injected sandstone fractures, the initial friction coefficients of fractures are affected by the change in effective normal stress and temperature, which is opposite to that of water-saturated sandstone fractures. The frictional stability of fractures is affected by the ambient temperature, seemingly independent of the effective normal stress. To sum up, these experimental results suggest that the frictional characteristics of sandstone fractures are jointly controlled by the effective normal stress, temperature and the injected fluid type. These experimental results may provide a better understanding of earthquakes induced by fluid injection.

     

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