The spatial distance of fractures in over-stimulation zone is relatively short and fracture networks are dense, so the pressure of this zone reaches an abandonment pressure in a very short time. In contrast, the spatial distance of fractures in the uncompleted stimulation zone is relatively long and fracture networks are sparse, so this zone contains a relative large amount of residual gas even though the pressure of this zone reaches an abandonment pressure.
Fig. 6. Schematic diagram of partitions corresponding to the appropriate-stimulation degree in Case ②
To further improve the appropriate-stimulation degree, the well azimuth, perforation location, fracturing parameters should be adjusted to achieve a better fracture distribution. In this way, the proportion of over-stimulation zone and the uncompleted stimulation zone will decline and fracturing performance will be improved.
Factors influencing the appropriate-stimulation degree of fracture networks
Analysis indicates that factors influencing shale gas production will also influence the appropriate-stimulation degree of fracture networks. These factors can be divided into two categories. One category refers to the final morphology parameters of fracture networks, including the orientation, length, conductivity, height and relative spatial location of artificial fractures and natural fractures. The other category refers to matrix porosity, permeability, pressure coefficient, gas saturation and the relative permeability of water and gas within the fracture networks.
1) The concept of appropriate-stimulation degree of fracture networks in a shale gas reservoir was proposed. It is recognized that relatively appropriate stimulation zone, transitional stimulation zone and uncompleted stimulation zone exist in target zones after fracturing treatment.
2) A more complex fracture network does not mean a better network. Swept volume is also a key factor influencing the fracturing performance, thus the fracturing performance cannot be demonstrated only by the complexity of a fracture network to avoid wrong cognition and conclusions.
3) The orientation, length, height, conductivity, height, and spatial location of artificial fractures are main factors influencing the appropriate-stimulation degree of fracture networks of a specific gas reservoir with a given well trajectory.
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* Corresponding author.
E-mail address: [email protected] (Yang LF.).
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