Stability analysis of a slope containing water-sensitive mudstone considering different rainfall conditions at an open-pit mine

Mudstone, as a typical soft rock with wide distribution, has been endangering the slopes containing mudstone by its watersensitivity of swelling and weakening strength when encountering water. To comprehensively understand the water-sensitivity of mudstone and reveal its infuence on slope stability, we took the working slope containing water-sensitive mudstone of Shengli No.1 open-pit coal mine in Xilinhot, Inner Mongolia, China, as an example. Mudstone samples taken from the working slope were remodeled and saturated, and then triaxial tested to obtain the efective cohesion and efective internal friction angle. The flter paper method was used to obtain the soil–water characteristic curve of unsaturated mudstone. The pore structure of mudstone samples with diferent water contents were analyzed using the mercury intrusion porosimetry tests combined with the fractal dimension. The total pore content of the mudstone sample with lower water content is greater than that of the mudstone sample with higher water content. The mesopores are more in the mudstone sample with lower water content, while the small pores are more in the mudstone sample with higher water content. The variation of water content will change the complexity of mudstone pore structure. The higher the water content, the simpler the mudstone pore structure and the smoother the pore surface. Numerical calculations were conducted on the stability of the working slope under diferent rainfall conditions. The efective saturation on the mudstone layer surface changed and the plastic strain all occurred on the mudstone steps under diferent rainfall conditions. The key to preventing landslide of the slope containing water-sensitive mudstone in Shengli No.1 open-pit coal mine is to control the deformation and sliding of the mudstone layer.

Water-sensitive damage mechanism and the injection water source optimization of low permeability sandy conglomerate reservoirs

The global mobility theory was used to evaluate the experimental results of oil displacement with water of different salinities.The results of scanning electron microscopy,X diffraction of clay minerals,nonlinear seepage and nuclear magnetic resonance experiments and particle migration inhibition experiments before and after water flooding were compared to determine the mechanisms of water sensitive damage and enhanced water flooding mechanism of low permeability sandy conglomerate reservoirs in Wushi region of Beibuwan Basin,China.A production equation of the oil-water two phase flow well considering low-speed non-Darcy seepage and reservoir stress sensitivity was established to evaluate the effect of changes in reservoir properties and oil-water two-phase seepage capacity on reservoir productivity quantitatively,and injection water source suitable for the low permeability sandy conglomerate reservoirs in Wushi region was selected according to dynamic compatibility experimental results of different types of injected water.The seepage capacity of reservoir is the strongest when the injected water is formation water of 2 times salinity.The water-sensitive damage mechanisms of the reservoirs in Wushi region include hydration of clay minerals and particle migration.By increasing the content of cations(especially K+and Mg2+)in the injected water,the water-sensitive damage of the reservoir can be effectively inhibited.The formation water of Weizhou Formation can be used as the injection water source of low permeability sandy conglomerate reservoirs in the Wushi region.

Water-sensitive characterization and its controlling factors in clastic reservoir:A case study of Jurassic Ahe Formation in Northern tectonic zone of Kuqa depression

Water-sensitivity is a factor that must be paid attention to in the reservoir development stage of oil and gas fields.As a clastic reservoir,the water effect of Ahe formation in the northern structural belt of Kuqa is strong as a whole,but the mechanism analysis of medium and strong water-sensitivity effect is restricted by the evaluation method with permeability damage rate as the main parameter.Taking the shape of water-sensitivity test curve as the starting point,combined with the analysis of microscopic pore throat and clay minerals,the difference of permeability change rate measured by samples is characterized.The strong to medium water-sensitivity effects in the study layer are divided into three types:The permeability gradually decreases in the early stage-the rapid decrease in the late stage,the continuous decrease in the permeability,and the rapid decrease in the early stage-the slow decrease in the later stage.As awidely developed reservoir space in the study section,the micropore not only has the characteristics of fine pore size and easy blockage,but also serves as the occurrence space of the main water-sensitive mineral illite-smectite mixed layer.Therefore,the change types of the above different water sensitivity test curves are mainly controlled by the difference of micropore content.When the micropore content is low,the permeability decreases slowly in the early stage and decreases rapidly in the later stage(type Ⅰ),while when the micropore content is high,the permeability decreases rapidly in the early stage and slowly decreases in the later stage(type Ⅱ),while when the micropore content is medium,the permeability decreases continuously,and there is no obvious rate change(type Ⅲ)before and after the micropore content.The results show that the structural characteristics and relative content differences of micropores in the samples are the internal mechanism of the difference of water sensitivity effect types.