Experimental study on reservoir sensitivity characteristics of tight sandstone after fracturing:Taking No.8 sand body of Shaximiao Formation in JQ area of Sichuan Basin as an example
With the expansion of hydrocarbon exploration into unconventional fields,the reservoir stimulation treatments such as fracturing are increasingly applied.For purposes of understanding reservoir properties,figuring out reservoir potential,predicting the changes in reser-voir sensitivity characteristics after stimulation,and then implementing appropriate reservoir protection,it is necessary to conduct sensitivity experiments on reservoir cores after simulated stimulation in order to identify how the stimulation affects the reservoir sensitivity character-istics.Through thin section identification,X-ray diffraction,scanning electron microscopy,and mercury injection test,flow experiments were carried out for drilled cores under different pressures,temperatures and fluid chemical properties to evaluate the reservoir sensitivity char-acteristics.The results of sensitivity experiments on cores before and after stimulation were compared to analyze the impacts of stimulation treatment on reservoir sensitivity characteristics.The results are shown as follows:(ⅰ)There appears netlike fractures in the cores drilled from No.8 sand body of the Middle Jurassic Shaximiao Formation in the JQ area of Sichuan Basin after stimulation,and the core permeability is 167%higher averagely than that before stimulation.(ⅱ)The cores are characterized by moderate to weak velocity sensitivity,strong water sensitivity,weak salt sensitivity,weak alkali sensitivity,and weak acid sensitivity.After stimulation,the characteristics of velocity sensitivity and salt sensitivity remain unchanged,while the strong water sensitivity changes to a weak level.Moreover,the proportion of core samples with strong water sensitivity reduces to 17%from 93%.(ⅲ)Comprehensive analysis indicates that the stimulated cores present a reduced level of water sensitivity,which manifests as weak or zero water sensitivity.Thus,the coverage of reservoir stimulation treatments needs to be expanded so as to improve the reservoir fluid flow capacity.
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