No abstract

No abstract

No abstract

No abstract

Successful development of shale gas in North America triggered great enthusiasm of developing shale gas in China. Experiments for hydraulic fracturing shale Outcrops sample in 762ϫ762ϫ914mm(height) were performed by using large-scale true tri-axial testing system to study what kind of hydraulic fracture will be for South China marine shale and how the formation condition or the human-controllable parameter influence the fracture complexity. Investigations of fracture geometry and fracture complexity are conducted with different natural fracture distribution, different main stress difference, different fracturing fluid viscosity, different injection rate, using methods such as acoustic emission monitoring and cutting the rock sample into pieces. The testing results show the hydraulic fracturing in shale generates more complex fractures than that of in sandstone, where both tensile and shear cracks are observed. Natural fractures, shale bedding and small principal stress differences are in helping to form complex fractures. When a low viscosity fluid is used, complex fractures are easier achieved than that with high viscosity fluid. This work explores a way of conducting hydraulic fracturing large-scale shale test. The testing results provide important basis for numerical simulation of fracture propagation, pre-frac layer or stage choosing and fracturing design optimization for hydraulic fracturing in shale.

Organic cathode materials are attractive for rechargeable lithium-ion batteries due to their advantages in sustainability and designability of molecular structure as well as the high upper limit of theoretical capacity....

Hydraulic fracture simulation based on hydro-mechanical coupled element partition method SCIENTIA SINICA Technologica 49, 716 (2019); Several key problems of modern mechanics in shale gas exploitation

The optimal design of hydraulic fracturing parameters is the key to commercial exploitation of unconventional reservoirs. Hydraulic fracturing test is one of the main methods for optimizing fracturing parameters. It is known that scale effect exists between laboratory experiments and field treatments of hydraulic fracturing. However, studies on how to eliminate the scale effect are rarely reported. In this work, we conduct sensitivity analysis on rock mechanical parameters and fracturing parameters at different scales by using the dimensionless analysis method. The initiation and propagation process of field hydraulic fracturing is reproduced through laboratory tests, and fracturing parameters are analyzed by using numerical simulation. Our results show that the fracture propagation in the laboratory is inconsistent with that in the field fracturing. The fracture initiation and propagation in the field can be reproduced in experiments by using samples with high modulus and low toughness as well as high-viscosity fracturing fluid. Microcracks are created before the breakdown pressure is reached, and hydraulic fractures extend perpendicular to the direction of the minimum principal stress. The Carter’s leak-off coefficient has little effect on breakdown pressure and propagation pressure, but the injection rate and the horizontal principal stress have significant effects on breakdown pressure. This study provides a theoretical basis and guidance for the design of fracturing parameters both in the laboratory and in the field.