Yongjin Shen
Engineer
China University of Petroleum (East China)
Yongjin Shen is a student pursuing doctor’s degree in China Uinversity of Petroleum(East China). His major is well logging. He studies sonic logging. He received Master’s degree in South China University of Technology. His major is signal processing. He received Bachelor’s degree in Yunnan University. His major is math.
Participates in
TECHNICAL PROGRAMME | Energy Leadership
Financing the Future Energy Supply
Forum 27 | Digital Poster Plaza 5
28
April
12:30
14:30
UTC+3
Objectives
With an axisymmetric connected fracture model, this paper discovers that the resonance of acoustic waves within the connected fractures yields reflected Stoneley waves of many oscillation cycles. The inherent frequency of the resonant waves changes with the extension length of the fracture and with the depth of mud invasion for gas layer. Stemming from these discoveries, this paper proposes a method for identifying connected fractures and gas layers using the attenuation coefficient of Stoneley waves.
Methodology
Using the axisymmetric connected fracture model to study the Stoneley waves that enter the fracture, it is found that the waves propagate radially within the fracture invasion zone and are totally reflected at the liquid-gas boundary. The reflected waves propagate continuously towards the opposite opening of the same fracture system. Upon reaching the liquid-gas interface again, they are reflected once more. The consecutively reflected waves superimpose, resulting in a resonance with the inherent frequency of the fracture. This specific cross-borehole resonance exhibits as a barrier against the Stoneley waves of the same inherent frequency.
Conclusion
This barrier produces total reflection for the Stoneley wave of the inherent frequency. The reflection spectrum peaks at the inherent frequency, while the transmission Stoneley waves lack the inherent frequency components. The inherent frequency components are severely attenuated when passing through the connected fractures, and the attenuation coefficient of the transmitted Stoneley waves peaks at the inherent frequency, and it is referred to as an anomaly. When the extension length of the fracture or invasion length of gas zone is limited, the abnormal values of the attenuation coefficient are evenly distributed with frequency. Therefore, the distribution of abnormal values can be used to determine the presence of fractures and the invasion depth of the fracture zone.Using the improved matrix method to process the waveform of array acoustic logging to obtain the image of the Stoneley wave attenuation coefficient varying with frequency. From the image, it can be seen that at some depth intervals, the value of the Stoneley wave attenuation coefficient is significantly larger, showing an anomaly with red areas. The anomalous values indicate the presence of connected fractures and gas layer.
Additive Information
The figure shows an example of fracture in dolomite, with the far right being the image of the Stoneley wave attenuation coefficient. There are many densely distributed red areas on the image, indicating that there are connected fractures here.
With an axisymmetric connected fracture model, this paper discovers that the resonance of acoustic waves within the connected fractures yields reflected Stoneley waves of many oscillation cycles. The inherent frequency of the resonant waves changes with the extension length of the fracture and with the depth of mud invasion for gas layer. Stemming from these discoveries, this paper proposes a method for identifying connected fractures and gas layers using the attenuation coefficient of Stoneley waves.
Methodology
Using the axisymmetric connected fracture model to study the Stoneley waves that enter the fracture, it is found that the waves propagate radially within the fracture invasion zone and are totally reflected at the liquid-gas boundary. The reflected waves propagate continuously towards the opposite opening of the same fracture system. Upon reaching the liquid-gas interface again, they are reflected once more. The consecutively reflected waves superimpose, resulting in a resonance with the inherent frequency of the fracture. This specific cross-borehole resonance exhibits as a barrier against the Stoneley waves of the same inherent frequency.
Conclusion
This barrier produces total reflection for the Stoneley wave of the inherent frequency. The reflection spectrum peaks at the inherent frequency, while the transmission Stoneley waves lack the inherent frequency components. The inherent frequency components are severely attenuated when passing through the connected fractures, and the attenuation coefficient of the transmitted Stoneley waves peaks at the inherent frequency, and it is referred to as an anomaly. When the extension length of the fracture or invasion length of gas zone is limited, the abnormal values of the attenuation coefficient are evenly distributed with frequency. Therefore, the distribution of abnormal values can be used to determine the presence of fractures and the invasion depth of the fracture zone.Using the improved matrix method to process the waveform of array acoustic logging to obtain the image of the Stoneley wave attenuation coefficient varying with frequency. From the image, it can be seen that at some depth intervals, the value of the Stoneley wave attenuation coefficient is significantly larger, showing an anomaly with red areas. The anomalous values indicate the presence of connected fractures and gas layer.
Additive Information
The figure shows an example of fracture in dolomite, with the far right being the image of the Stoneley wave attenuation coefficient. There are many densely distributed red areas on the image, indicating that there are connected fractures here.
