Abstract: The Toutunhe Formation of the Middle Jurassic is the main exploration layer in Fudong slope area in Junggar Basin,where reservoirs are greatly influenced by sensitivity to clay minerals.Contents and types of clay minerals of the reservoirs are the major factors that influence sensitivity,thus were studied through cast thin section,rock thin section,X-ray diffraction and SEM.The result shows that ①various types of clay minerals can be observed and the thickness of clay membrane is related to some extent with productivity;②components of the clay minerals were determined by provenance,and sedimentary setting,climate change and later faulting helped transformation and preservation of the clay minerals;③abnormal pressure affects the distribution of the clay minerals;④the reservoirs are mostly water-sensitive and also acid-and speed-sensitive to some extent.The degree of sensitivity depends on the content of different types of clay minerals.The above understanding has been used as geologic basis for reservoir protection and modification during drilling,injection and production operation in the Formation.

Key words: reservoir sensitivity, clay mineral, Toutunhe Formation, Fudong slope area, Juggar Basin