In order to study the distribution of fractures controlled by layer curvature, fold and fault-related folds in East Kuqa, including one anticline (Biyoulebaoguzi Anticline profile), one fault-bent fold (Kezilenuergou Faultbent Fold profile) and one drag fold (Yangxia Coal-mine Drag-fold profile), are selected as investigating profile, and density of their structural factures and the layer curvature of middle-lower Jurassic and Triassic are measured. The result shows that the layer curvature has an effect on the fracture density; structural fractures are easier to be developed in the layers with larger curvature compared with those with smaller one within the same stratum. Besides, there is a positive linear relationship between fracture density and layer curvature. The mechanics of layer curvature’s effect on structural fracture from angle of solid mechanics is discussed: fracture density is tightly related to stress distribution, and stress is proportional to curvature in bent beam model; hence, a positive linear relationship exists between the fracture density and layer curvature, which is applied to both elastic and plastic folds.

In order to study the distribution of fracture controlled by layer thickness and lithology, clastic rock of 6-7th Member, Yanchang Formation in Longdong area is selected as investigated subject, and the areal density of their structural fractures is meassured. Measured fracture densities show that the layer thickness of clastic sequence has an effect on fracture density. Compared with thicker layer, it is easier for thinner layer to develop structural fracture, which is related to the different stress concentration near fracture tip in different layer thickness. Within a certain thickness range, fracture density has an exponential relationship with layer thickness, while the fracture density remains mostly unchanged when thickness exceeds 250 cm. Under the condition of same layer thickness and different lithology, the value of fracture densities from small to large follow the order of medium sandstone, fine sandstone, siltstone and mudstone, which means that in the same tectonic setting and layer thickness, the smaller the size range is, the larger the fracture density will be. Besides, there is an exponential relationship
between fracture density and grain size, which may be caused by the different stress between grains of different size. By multivariate statistics and mechanism analysis, layer thickness is the key factor in controlling fractures’ development compared with lithology.