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To study the mechanical damage characteristics of layered composite rocks, sandstones, and mudstones of deep tight reservoirs were used as the research objects, and layered composite class rocks were prepared by similar material model tests. Uniaxial compression tests were conducted and supplemented with AE (Acoustic Emission) system and DIC (Digital Image Correlation) system to obtain the physical and mechanical parameters such as strength and elastic modulus of the layered composite rocks. The corresponding law of AE ringing count and rock damage evolution was studied and the damage process of layered composite rock under uniaxial loading was divided into three stages: initial damage, stable damage development, and damage acceleration. Analysis of strain cloud diagrams of the DIC system revealed that the deformation characteristics of the layered composite rock under uniaxial were mainly tensile-shear-slip damage. Based on the internal damage evolution characteristics of AE and the surface damage evolution characteristics of DIC, a damage constitutive model of layered composite rocks based on the dual damage factor characterization was established, which reasonably revealed the damage evolution mechanism of internal structure development and external crack germination, extension and penetration of layered composite rocks under uniaxial compression.

Highly deviated well is widely applied in thin interbedded reservoirs fracturing in changqing oilfield. the oil production data shows that highly deviated fracturing well can increase the oil production compared with horizontal well fracturing, which suggests that highly deviated well fracturing is more efficient. However, it still needs deeper understanding for the mechanism of highly deviated well increase oil production, to study this problem, True-axial hydraulic fracturing physical simulation test is carried out on two kinds of cement specimen with interlayers, the results show that cement specimen for highly deviated well is more productive because fractures are more likely to cross the interbedded layers and connect oil reservoirs that separated by interlayers. Further research on the mechanism of highly deviated well fracture crossing interbedded layers is conducted via numerical simulation. Cohesive zone model is adopted to simulate the propagation of fracture in highly deviated well and horizontal well to compare the difference of thin interbedded layers stress. the results show that due to the deflection of highly deviated well fracture during propagation, the reservoir mass is divided into two parts, which causes relative displacement of rock mass on both sides of the fracture under the effect of vertical principal stress, thin interlayer eventually got broken under the action of tensile and shear stress. Both laboratory tests and numerical simulation results show that highly deviated wells have stronger interlayer penetration capability, which can improve the fracturing effect of thin interbedded reservoirs.