Abstract
The tight heterogeneous glutenites are typically characterized by highly variable lithology, low/ultra-low permeability, significant heterogeneity, and a less-developed natural fracture system. It is of great significance for economic development to improve hydraulic fracture complexity and stimulated reservoir volume. To better understand the hydraulic fracturing mechanism, a large-scale experimental test on glutenite specimens was conducted and the hydraulic fracture propagation behaviors and focal mechanism were analyzed. A three-dimensional numerical model was developed to reproduce the hydraulic fracture evolution process and investigate the effects of operating procedures on hydraulic fracture geometry and stimulated reservoir volume. A simultaneous variable injection rate and fluid viscosity technology was proposed to increase the hydraulic fracture complexity and stimulated reservoir volume. The results indicate that four fracturing behaviors can be observed, namely, penetration, deflection, termination, and bifurcating, in the laboratory experiment. Tensile events tend to appear during the initiation stage of hydraulic fracture growth, while shear events and compressive events tend to appear during the non-planar propagation stage. The shear and compressive mechanisms dominate with an increase in the hydraulic fracture complexity. The variable injection rate technology and simultaneous variable injection rate and fluid viscosity technology are effective techniques for fracture geometry control and stimulated reservoir volume enhancement. The key to improve hydraulic fracture complexity is to increase the net pressure in hydraulic fractures, cause evident pressure fluctuations, and activate or communicate a wide range of natural discontinuities. The results can provide a better understanding of the fracture geometry control mechanism in tight heterogeneous glutenites, and offer a guideline for treatment design and optimization of well performance.
Highlights
Glutenite reservoirs are widely distributed throughout the world, including the Los Angeles Basin in North America, the Argentine Basin in South America, and the Bohai Bay Basin in Eastern China
Rui et al (2018) conducted 2D numerical simulations to investigate the influence of rock mechanical parameters and gravel property on the hydraulic fractures (HFs) propagation, and indicated that the HF geometry is controlled by reservoir physical and mechanical parameters, in-situ stress, and operational parameters
According to the formation mechanisms of complex HFs obtained from the laboratory experiment, the tensile events tend to appear during the initiation stage of HF growth, most are located around the wellbore, while shear events and compressive events appear primarily around the branch fractures and non-planar extension fractures, most are located in the area away from the fracturing well
Summary
Glutenite reservoirs are widely distributed throughout the world, including the Los Angeles Basin in North America, the Argentine Basin in South America, and the Bohai Bay Basin in Eastern China. The geomechanical conditions such as in-situ stress, volume content of gravels, and mechanical properties of glutenite cannot be possibly changed, but we can improve fracture complexity and maximize SRV by optimizing the operating procedures and corresponding treatment parameters, such as injection rate and fluid viscosity.
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