The Toutunhe Formation in Fukang Sag

Junggar Basin

is mainly characterized by low porosity and low permeability with many types of fillers and complex pore structures. But there is a serious contradiction between the potential acid sensitivity damage and the indoor evaluation

and the variability exists in the sensitivity of the reservoir. Therefore

the reservoir sensitivity evaluation and control factors are studied by the core experiments such as core displacement

casting thin section identification

nuclear magnetic resonance

scanning electron microscope

etc. The results show that in Toutunhe Formation

the velocity sensitivity is weak

the water sensitivity and salt sensitivity are both upper medium to strong

the alkali sensitivity is upper medium

and the acid sensitivity is weak to moderate weak. The difference of reservoir sensitivity is related to many types of interstitial fillers and complex pore structures. In the Toutunhe Formation reservoir enriched with the cement of authigenic quartz

whose diameter is less than 5 μm

the corrosion of the surface clay by the acid-base liquid lead to the exfoliation of the crystals such as the authigenic quartz. Then

these movable particles obstruct the pore throat. The mechanism of this kind of damage which shows a upper medium to strong acid sensitivity is different from that of the other traditional damage such as the secondary precipitation. The sensitivity damage mechanism shows that all kinds of sensitivities have superposition effects.