Tube or Stoneley waves are known to interact strongly at low frequencies with poroelastic formations provided that flow is not restricted at the borehole-formation interface. Increased permeability leads to increased attenuation and decreased velocity of the tube wave. Such mechanism has been explored previously for characterizing fractures and permeable formations in open-hole acoustic logging. In this study we focus on the reflection response of low-frequency tube waves from various finite-size poroelastic structures. First, we examine a model of a thin reservoir and demonstrate good applicability of the approximate 1D effective wavenumber approach to describe the interaction of tube waves with porous formations. We confirm that higher permeability leads to higher reflection coefficient. Then we analyze a model of idealized (disk-shaped) perforations inside a poroelastic layer and show that it has higher reflectivity compared to washout zones of the same geometry but with no-flow conditions at the interface.

Tube-wave monitoring is a fit-for-purpose downhole imaging and monitoring technique. It aims to detect and characterize time-lapse changes in a cross-well space. In contrast to conventional cross-well seismic it does not require production interruption or reduces it to a minimum. Monitoring relies on tube waves in a well fluid column to carry the seismic signals to and from the reservoir. We present a simple modeling to support the concept and validate experimental data acquired at Stratton and Mallik fields.

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Cross-well seismic with direct, reflected and tube waves is often used for imaging and monitoring of oil and gas reservoirs. Even though downhole sources are usually located in the borehole fluid, at low frequencies their radiation is modified by the presence of poroelastic formations surrounding the well. Permeable formations also enhance the conversion of borehole tube waves into body or other formation waves, which is an important foundation for a tube-wave monitoring. To capture the influence of porous and permeable formation on radiation of formation waves, we derive analytic expressions for a far-field radiation of compressional and shear waves from a point pressure source located inside a fluid-filled borehole. We demonstrate how various attributes of this radiation are controlled by permeability and viscosity of the pore fluid and other parameters at low seismic frequencies. We show that radiation patterns in formations with good permeability can be distinguished from the radiation patterns in an equivalent elastic impermeable media. To verify obtained results we compare analytical far-field radiation with a finite-difference computations and observe good agreement between the two approaches.

Tube or Stoneley wave is known to strongly interact at low frequencies with poroelastic formations provided that flow is not restricted at the borehole-formation interface. Increased permeability leads to increased attenuation and decreased velocity of the tube wave. In this study we focus on reflection of low-frequency tube waves from various finite-size poroelastic structures. First, we examine a model of a thin reservoir and demonstrate good applicability of the approximate 1D effective wavenumber approach to describe interaction of tube waves with porous formations. We confirm that higher permeability leads to higher reflection coefficient. Then we analyze model of an idealized (disk-shaped) perforation inside a poroelastic layer and show that it has higher reflectivity compared to washout zone of the same geometry but with no-flow conditions at the face.