Study On Water Adsorption And Water Saturation Characteristics Of Carboniferous Shale In Qaidam Basin

Shale is a complex sedimentary rock with a variety of properties,characterized by mineral composition and structure,cation exchange capacity,specific surface area and water saturation to characterize.Shale contains potential hydrocarbon resources,which has long been the focus of energy and environmental research.According to the experimental principle,four shale samples taken from Shixi 1 and ZK1-1 wells in the eastern Qaidam Basin were used to study the water saturation characteristics of the shale samples from the experimental laboratory.The water content of each rock sample under different saturated water pressure is calculated by the experiment.The relationship between water absorption and saturation of shale with time and pressure is studied,and therefore the water measurement porosity is obtained.The results show that the water content of the shale gradually increases and after rising to the highest value tends to be smooth in the process of saturating water.The time required to reach the saturation is decreasing with the increase of the pressure of saturated water.Water adsorption rate is reducing with time required to reach the saturation;absolute saturated water absorption is gradually increasing with the rising of pressure of saturated water.The water measurement porosity of the shale gradually increases with the increasing pressure of saturated water.Shale water absorption capacity has many influencing factors,including pressure,pore size,specific surface area,organic carbon content,clay content,thermal maturity and burial depth and other various affected factors.The experimental researches find that the pressure has a significant effect on the capability of water absorption and water saturation of the shale,and the water absorption rate of the shale increases with the rise of the pressure of saturated water,and then gradually decreases after the approach of the highest level of pressure of saturated water.The shale water absorption increases with increasing pressure,but has its limit after reach some quantities,so the shale water absorption capacity is enhancing with higher pressure,but is also restricted by it;The pore size distribution of shale range is very large,under the conditions of pressurized water saturation,the volume of water absorption is positively correlated with the tiny pore volume,and under the conditions of no pressure water absorption,the water absorption volume is positively correlated with the total pore volume;The total specific surface area of shale is positively correlated with its absolute saturated water absorption,the lager the total specific surface area is,the more shale water absorption increases;There is a significant positive correlation between the clay mineral content and the saturated water absorption of the shale,clay minerals are one of the main factors affecting the water absorption of shale,the greater the content of shale clay mineral,the more water saturated by shale;The amount of organic matter content is another vital factor influencing the water adsorption of shale,shale water absorption is positively correlated with the organic carbon content,the correlation coefficient is more than 98%,shale water absorption increases with organic carbon content and the specific relationship is y=0.03x-0.01,the greater the shale TOC value,the lager the water absorption of shale;Shale water absorption rises with increase of its vitrinite reflectance(Ro),the higher the thermal maturity of organic matter,the greater the water absorption;And the water absorption of shale rock samples decreases with the increase of shale burial depth,and the water absorption of shale is negatively correlated with shale depth,and shallow shale with stronger water absorption capacity.