Search

For hydrocarbon exploitation in tight glutenite, glutenite brittleness plays an important role in fracturing efficiency, but the detailed effect is not entirely clear. In this study, considering rock heterogeneity, RFPA (Rock Failure Process Analysis) was applied to establish the three-dimension computational model. An improved rock brittleness index considering post-peak properties in rock uniaxial compression test was proposed to quantify the glutenite brittleness. Results show that brittle glutenite can generate multiple failure surfaces under the exterior loadings, which can be a mirror to reveal the denser development of natural fractures in the brittle reservoir, while the ductile glutenite is prone to generate a simple shear failure. Hydraulic fractures propagate faster in more brittle glutenite and can generate short branches, which is beneficial to connect the reservoir natural fractures and form complex hydraulic fractures. Brittle glutenite requires a lower treatment pressure than the ductile glutenite, which can provide convenience for ground pumping operation. Hydraulic fractures prefer to propagate in brittle glutenite, rather than the ductile glutenite. The obtained conclusions can provide a reference for the similar practice.

Tight oil reservoirs are complex geological materials composed of solid matrix, pore structure, and mixed multiple phases of fluids, particularly for oil reservoirs suffering from high content of in situ pressurized water found in China. In this regard, a coupled model considering two-phase flow of oil and water, as well as deformation and damage evolution of porous media, is proposed and validated using associated results, including the oil depletion process, analytical solution of stress shadow effect, and physical experiments on multi-fracture interactions and fracture propagation in unsaturated seepage fields. Then, the proposed model is used to study the behavior of multi-fracture interactions in an unsaturated reservoir in presence of water and oil. The results show that conspicuous interactions exist among multiple induced fractures. Interaction behavior varies from extracted geological profiles of the reservoir due to in situ stress anisotropy. The differential pressures of water and that of oil in different regions of reservoir affect interactions and trajectories of multi-fractures to a considerable degree. The absolute value of reservoir average pressure is a dominant factor affecting fracture interactions and in favor of enhancing fracture network complexity. In addition, difference of reservoir average pressures in different regions of reservoir would promote the fracturing effectiveness. Factors affecting fracture interactions and reservoir treatment effectiveness are quantitatively estimated through stimulated reservoir area. This study confirms the significance of incorporating the two-phase flow process in analyses of multi-fracture interactions and fracture trajectory predictions during tight sandstone oil reservoir developments.

For high-steep slopes in hydropower engineering, damage can be induced or accumulated due to a series of human or natural activities, including excavation, dam construction, earthquake, rainstorm, rapid rise or drop of water level in the service lifetime of slopes. According to the concept that the progressive damage (microseismicity) of rock slope is the essence of the precursor of slope instability, a microseismic monitoring system for high-steep rock slopes is established. Positioning accuracy of the monitoring system is tested by fixed-position blasting method. Based on waveform and cluster analyses of microseismic events recorded during test, the tempo-spatial distribution of microseismic events is analyzed. The deformation zone in the deep rock masses induced by the microseismic events is preliminarily delimited. Based on the physical information measured by in situ microseismic monitoring, an evaluation method for the dynamic stability of rock slopes is proposed and preliminarily implemented by combining microseismic monitoring and numerical modeling. Based on the rock mass damage model obtained by back analysis of microseismic information, the rock mass elements within the microseismic damage zone are automatically searched by finite element program. Then the stiffness and strength reductions are performed on these damaged elements accordingly. Attempts are made to establish the correlation between microseismic event, strength deterioration and slope dynamic instability, so as to quantitatively evaluate the dynamic stability of slope. The case studies about two practical slopes indicate that the proposed method can reflect the factor of safety of rock slope more objectively. Numerical analysis can help to understand the characteristics and modes of the monitored microseismic events in rock slopes. Microseismic monitoring data and simulation results can be used to mutually modify the sensitive rock parameters and calibrate the model. Combination of microseismic monitoring and numerical simulation provides a more objective basis for the numerical model and parameters and a solid mechanical foundation for the microseismic monitoring.