Tube Wave: Definition, Borehole Acoustics, and Permeability Estimation

What Is a Tube Wave?

A tube wave (also called a Stoneley wave) is a low-frequency guided acoustic wave that propagates along the borehole-fluid column as a coupled fluid pressure and formation shear deformation wave, travelling at velocities slightly below the borehole fluid P-wave velocity, and whose attenuation and velocity dispersion provide information about formation permeability, fracture presence, and fluid mobility in the near-wellbore zone.

How Tube Waves Propagate in Boreholes

The tube wave is a borehole-guided acoustic mode in which the acoustic energy is primarily confined to the borehole fluid column with a relatively small penetration into the formation. Unlike formation head waves (P and S waves) that travel predominantly through the formation rock, the tube wave energy is concentrated in the fluid and the near-wellbore interface. The wave is axisymmetric — it propagates as a pressure pulse in the fluid accompanied by a radial stress coupling into the formation wall — and travels at a velocity slightly below the borehole fluid velocity that depends on the fluid bulk modulus and the formation shear stiffness.

When the tube wave encounters a zone of formation permeability (either matrix permeability or an open fracture), the oscillating borehole pressure drives fluid in and out of the formation in response to the wave's pressure cycle. This fluid exchange dissipates acoustic energy from the tube wave and reflects a portion of the wave energy back toward the source. The higher the formation permeability, the greater the energy exchange per unit time, the greater the attenuation of the transmitted tube wave, and the stronger the reflected tube wave at the permeable interface. Measuring these attenuation and reflection characteristics from the full waveform sonic log provides qualitative and, with appropriate models, quantitative information about formation permeability.

Tube Wave Applications Across International Jurisdictions

In Canada, tube wave analysis from full-waveform sonic logs is used in WCSB wells to identify open natural fractures intersecting the wellbore, particularly in the Devonian carbonate reservoirs of the Rainbow and Zama Lake areas and in the Pre-Cambrian basement that serves as a fractured reservoir in some Alberta basin edge wells. AER pool establishment submissions for naturally fractured carbonates benefit from tube wave fracture identification that corroborates borehole image log fracture observations with permeability-sensitive acoustic data. Montney tight gas wells that rely on natural fracture networks for gas drainage use tube wave analysis as an independent permeability indicator where conventional methods are ambiguous.

In the United States, tube wave analysis complements borehole image log fracture mapping in Gulf of Mexico carbonate reservoirs and in Permian Basin naturally fractured carbonate plays where open fractures control productivity. BSEE well completion technical submissions for fractured reservoirs may include tube wave fracture analysis as supporting evidence for open fracture characterisation. In Norway, Equinor's chalk reservoir characterisation at Ekofisk uses full-waveform sonic data including tube wave analysis to identify open fractures in the chalk matrix that enhance well productivity beyond that expected from the matrix permeability alone. In the Middle East, Saudi Aramco's EXPEC ARC research group has published on the application of Stoneley wave analysis to characterise near-wellbore permeability and open fracture distribution in Arab Formation carbonate producers at Ghawar.

Tube Wave Reflection for Fracture Mapping

When a tube wave encounters a permeable feature in the wellbore — an open fracture, a permeable bed boundary, or a zone of high matrix permeability — part of the wave energy is reflected back toward the source and part is transmitted past the feature with reduced amplitude. The reflected tube wave travels back up the wellbore toward the transmitter, where it may be recorded by an uphole receiver. By analysing the two-way travel time of these reflections, the depths of permeable reflectors within a range of several metres above and below the transmitter can be located. In a swept frequency or broadband tube wave acquisition, the spectrum of the reflected wave provides information about the physical properties (aperture, extent) of the reflecting fracture. This tube wave reflection technique extends the depth-of-investigation of acoustic fracture imaging beyond what is achievable with borehole image tools that measure only the surface of the borehole wall.

Tube Wave Synonyms and Related Terminology

Tube wave is also referenced as:

• Stoneley wave — the seismological name for the guided interface wave that is the same physical phenomenon as the tube wave in borehole acoustics; Stoneley wave is preferred in geophysical and seismological literature while tube wave is used more in well logging contexts
• Borehole Stoneley wave — used specifically to distinguish the borehole-guided Stoneley wave from surface Stoneley waves; the "borehole" qualifier is important because Stoneley waves can occur at any solid-fluid interface
• Guided fluid wave — the descriptive term used in some acoustic modelling papers to indicate that the wave is guided by the fluid-filled cylindrical borehole rather than being a bulk wave in the formation

Related terms: sonic log, leaky mode, permeability, natural fracture, borehole image log

Frequently Asked Questions

How does a tube wave indicate formation permeability?

At a permeable formation boundary, the oscillating pressure of the passing tube wave drives fluid into and out of the formation through the Darcy flow mechanism. The energy required to force fluid in and out of the formation pores is dissipated as heat in the viscous flow process, removing that energy from the tube wave. Higher permeability means more fluid exchange per pressure cycle, more energy dissipation per unit length of wave propagation, and therefore greater attenuation of the tube wave amplitude per unit distance. This attenuation is measured as the ratio of tube wave amplitude in the permeable zone versus adjacent impermeable zones. Models relating tube wave attenuation to formation permeability (Rosenbaum 1974, Tang and Cheng 1996) allow quantitative permeability estimation from the attenuation data, though calibration against core or test permeability is required for accurate quantitative results.

What is the difference between a tube wave and a Stoneley wave in the context of oilfield logging?

In oilfield logging, the terms are used interchangeably to refer to the same wave type — the low-frequency borehole-guided mode that travels at near-fluid velocity. The term "tube wave" is more common in production logging and borehole seismic literature; "Stoneley wave" is more common in open-hole sonic logging and academic geophysics literature. Both terms refer to the axisymmetric, dispersive guided wave whose attenuation and reflection provide permeability and fracture information. The distinction matters more in seismology, where Stoneley waves at non-borehole interfaces have different properties, but in oilfield acoustics the two terms are synonymous.

Why Tube Waves Matter in Oil and Gas

In naturally fractured carbonate reservoirs — which host some of the world's largest oil and gas accumulations, from the Arab Formation at Ghawar to the Ekofisk chalk to the Cantarell complex in Mexico — the productivity of any well is dominated not by matrix permeability (which is typically below 1 millidarcy) but by the network of open natural fractures that provides the connected pore volume and high-permeability pathways for fluid flow to the wellbore. Identifying which fractures are open and permeable versus healed (cemented) and non-contributing is the critical question for completion design, well placement, and production forecast in fractured reservoirs. Tube wave analysis from full-waveform sonic logs provides a permeability-sensitive acoustic measurement that distinguishes open from sealed fractures, complementing borehole image logs that identify all fractures but cannot distinguish permeable from cemented ones, and together providing a more complete characterisation of the productive fracture network than either tool can provide alone.