油水含量对疏松砂岩断裂韧性的影响

Effects of Water-Oil Contents on Fracture Toughness of Soft Sandstone

为研究油水含量对砂岩断裂韧性的影响,提出了一种新的砂岩试件油水饱和方法,并通过三点弯实验测试了不同油水含量下砂岩的断裂韧性。研究发现:当砂岩孔隙中仅含有一种饱和流体时,饱和油砂岩的断裂韧性比饱和水砂岩的断裂韧性大;当试件中含有两种饱和流体时,油水混合试件的断裂韧性介于饱和油、饱和水试件的断裂韧性之间;饱和油、饱和水及油水混合砂岩试件的断裂韧性比干燥试件断裂韧性低10%~50%。微观角度上,从吸附作用、水化作用、黏土膨胀和毛细管力等方面分析了油水含量对砂岩断裂韧性的影响;水化作用比毛细管力对砂岩断裂韧性的影响显著。宏观角度上,基于应力-应变曲线对砂岩断裂过程进行了能量耗散分析;所有试件均有能量耗散,耗散能量比为5%~30%;干燥试件的能量耗散比低于油水混合试件的能量耗散比,平均低约10%。

In order to study the effects of water-oil saturation on fracture toughness of rock,a new method for saturating rock specimen was proposed.The fracture toughness of sandstone with different water-oil saturations were measured by three-point bending tests.The experiment results show that-when only one kind of saturated fluid is present,the fracture toughness of oil-saturated sandstone is higher than that of water-saturated sandstone;when two kinds of saturated fluids are present,the fracture toughness of water-oil saturated sandstone is between the fracture toughness of oil-saturated and water-saturated;the fracture toughness of specimens which are water-saturated and oil-saturated decrease by 10-50 percent compared with the dry specimens.From the micro perspective,the effects of water-oil contents on the fracture toughness of sandstone were analyzed from the adsorption,hydration,clay expansion and capillary pressure;the effect of water reaction is more obvious than that of capillary pressure on fracture toughness of sandstone.From the macro perspective,the energy dissipation analyses of the sandstone fracture process were carried out based on the load-displacement curve.Both dry specimens and water/oil saturated specimens were accompanied with energy dissipation,and the value of the energy dissipation are nearly 5-30 percent.The mean value of energy dissipation for the dry specimen is 10 percent less than that for the water/oil saturated specimen.