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Plugging upper and lower tips of hydraulic fracture by forming artificial barrier with diverting agent is as an effective method to prevent hydraulic fracture height from extending excessively. This work, obtained the transient analytical solutions of both fluid pressure decrement generated by artificial barrier (Δp) and equivalent permeability between artificial barrier and reservoir (K) at different positions of hydraulic fracture tips, clarifies parameters that affect the plugging effect of diverting agent on the tips. Seepage velocity that changes with plugging time (t) and maximum seepage distance were acquired by plugging experiments and were used to calculated Δp − t curves and K − t curves. It indicates that the variation rate of Δp and K changes from fast to slow until reaching a balance. However, for different positions of the tips, the time taken by Δp and K to reach balance is different. The diverting agent is suitable for hydraulic fracture beginning plugging when its floating or sinking effect appears relatively obvious and its horizontal migration effect is relatively weak. But if on the contrary, the agent is suitable for the ending plugging. When diverting agent concentration (λ) is lower, the effect of shortening time to complete plugging is more obvious by increasing λ, but the effect is weak when λ is higher because of the excessive accretion. This work has been successfully applied to an oilfield, which increased the production by 68.5% in a month and achieved directional plugging in hydraulic fracture.

The study of rock damage evolution is of great significance in the field of underground engineering. In this paper, the damage development of deep formation rock was quantitatively evaluated by acoustic emission (AE) test. The Young’s modulus of the test rock specimens under ideal intact state was obtained by assuming a linear relationship between the AE rate parameter and the damage variation based on the rate process theory. Through the multi-stage cyclic loading test, the damage parameters corresponding to the peak stress of the previous stage were calculated by using the tangent modulus at the initial moment. The results showed that there was abrupt transition stage of damage development with the linear increase of stress. The damage parameter curves of rock specimens during loading process were obtained by using the method of cumulative AE energy, and the development trend of the curves was analyzed simply by combining the concepts of crack initiation stress and crack damage stress. Comparing the two methods of obtaining damage parameters by using cyclic loading test and cumulative AE energy, the results of them were highly consistent except for some deviation in the initial and final stages.

This paper studies the pile foundation of shield tunnel in soft soil stratum, establishes the mechanical model of shield tunneling process, analyzes the displacement vector field of shield passing through bridge pile foundation process, and calculates the bridge pile foundation and surface settlement. According to the calculation results, the parameters of shield tunneling (speed, propulsion, earth pressure, synchronous grouting, etc.) are selected. the follow-up monitoring shows that the model simulation analysis is reasonable, the calculation results are reliable, and the disturbance of the pile foundation is reduced, and the construction is effectively guided.This paper studies the pile foundation of shield tunnel in soft soil stratum, establishes the mechanical model of shield tunneling process, analyzes the displacement vector field of shield passing through bridge pile foundation process, and calculates the bridge pile foundation and surface settlement. According to the calculation results, the parameters of shield tunneling (speed, propulsion, earth pressure, synchronous grouting, etc.) are selected. the follow-up monitoring shows that the model simulation analysis is reasonable, the calculation results are reliable, and the disturbance of the pile foundation is reduced, and the construction is effectively guided.

Nowadays, China is not experienced in the research and practice of the abandonment approaches to oil and gas pipelines retirement. Using the experience of the North America for reference in abandonment of onshore pipelines, including retired pipeline safety environmental disposal scheme choice, waste disposal technology and retired environmental impact assessment of the key problems were discussed. The comparatively complete construction technology was put forward to dismantle pipelines. Besides, the construction technology of filling the controlled low strength material to the decommissioning oil pipelines was put up. Based on the case of Dong-Huang pipeline abandonment, the selection disposal scheme was optimized, key construction practices such as the cleaning of pipeline residues and low strength controlled material filling pipeline were expounded, potential environmental influence of different disposal scheme was analyzed, besides, some measures were represented to prevent and relieve the pollution corresponding to the construction technology. Research results have guiding significance for perfecting safe abandonment research of domestic retired oil and gas pipelines.