Holdup Image | Oil Authority

A holdup image is a production logging measurement that provides a spatial cross-sectional or azimuthal display of the local phase fractions (holdup) of oil, water, and gas within a flowing wellbore at a specific depth, using an array of miniaturized sensors deployed at multiple radial positions across the borehole diameter to resolve the lateral distribution of multiphase flow — distinguishing stratified flow (where gas, oil, and water form distinct horizontal layers in deviated wellbores due to density differences) from bubbly, slug, or churn flow regimes, providing quantitative local holdup values for each phase at each sensor position that are integrated to compute the in-situ cross-sectional average holdup needed for accurate flow rate calculation.

Key Takeaways

Holdup (also written hold-up) is defined as the fraction of the wellbore cross-sectional area (or volume element) occupied by a specific phase at any instant — the oil holdup Yo is the fraction of the cross-section occupied by oil, the water holdup Yw by water, and the gas holdup Yg by gas, with the constraint that Yo + Yw + Yg = 1; holdup differs from in-situ volume fraction only in multiphase flow where phases travel at different velocities (slip velocity), making holdup different from the superficial velocity fraction (flow rate fraction) used in surface measurements.
The slippage between phases in multiphase wellbore flow — gas rising faster than liquid, oil floating above water in inclined flow — means that the local holdup measured at a sensor is not proportional to the surface-measured production split of oil, water, and gas; the production logging interpretation must account for slip by combining holdup measurements (from the image tool) with velocity measurements (from spinner flowmeters, turbine meters, or electromagnetic flow meters) using a multiphase flow model to calculate the actual volumetric flow rates of each phase, rather than multiplying the holdup fraction by the total flow velocity.
Full-bore holdup imaging tools use arrays of 6 to 12 miniaturized impedance probes or optical fiber sensors distributed across the borehole cross-section at different radial and azimuthal positions, sampling the local dielectric or refractive index properties that distinguish oil from water from gas with response times of milliseconds — each probe independently measures the local phase at its position as a function of time, and the time-averaged responses from all probes are combined to construct a spatial holdup image that shows the distribution of phases across the full borehole cross-section rather than a single centreline measurement that misrepresents stratified flow.
Holdup imaging is particularly critical for inclined and horizontal production wells where multiphase flow becomes strongly stratified by gravity — in a horizontal well with simultaneous oil and water production, water (denser) accumulates on the low side of the wellbore and oil on the high side, with the gas (least dense) occupying the top; a centralized single-sensor flowmeter would measure predominantly one phase depending on where in the borehole it was positioned, giving a completely misleading indication of the in-situ phase fractions; the holdup image resolves this by simultaneously sampling the entire cross-section, capturing both the high-side gas/oil and low-side water distributions that characterize stratified flow.
Holdup image data combined with velocity image data (from imaging spinner arrays or velocity cameras) provides the complete multiphase flow characterization needed to compute the zonal contribution of each production interval in a horizontal well — by integrating the product of local holdup and local velocity across the borehole cross-section at a series of depth stations in the production interval, the production logging analyst computes the volumetric flow rate of each phase entering from each perforation cluster or production zone, enabling the identification of water breakthrough zones, dry gas zones, and under-producing intervals that guide production optimization decisions.

Fast Facts

The need for holdup imaging in inclined and horizontal wells was recognized in the late 1980s as the industry began drilling significantly deviated production wells, and commercial holdup imaging tools entered the market in the early 1990s. Schlumberger's Electrical Micro-Imager (EMI) for near-wellbore imaging and the Flow Scanner tool for production logging were early commercial implementations of multi-sensor cross-sectional flow characterization. Today, SLB's Production Universe and Holdup Scanner, Halliburton's MAPS (Multiphase Advisor Production System), and Baker Hughes' Emerald production logging system each offer holdup imaging capabilities combined with velocity imaging in a single integrated production logging string, providing the complete multiphase flow characterization required for horizontal well production optimization in prolific deep water and unconventional reservoirs.

What Is a Holdup Image?

In a vertical producing well, oil, water, and gas flow upward together in a relatively uniform mixture — the wellbore cross-section is roughly symmetrical, and a centralized flow sensor provides a representative average of the in-situ phase fractions. In a horizontal or highly deviated production well, gravity separates the phases dramatically — gas rises to the high side, water sinks to the low side, and oil occupies the middle. A single centralized sensor in this stratified flow would tell you the phase at the exact center of the borehole, but this may be pure oil, pure gas, or pure water depending on the flow regime, bearing no relationship to the actual cross-sectional average phase fractions.

The holdup image solves this problem by replacing the single centralized sensor with an array of miniaturized sensors that sample the borehole cross-section simultaneously at multiple positions — some near the top (where gas accumulates), some near the center, some near the bottom (where water accumulates). Each sensor independently measures the local phase at its radial and azimuthal position, and the combination of all sensor responses constructs a spatial map of phase distribution across the full cross-section. This image shows the actual geometry of multiphase flow in the well — whether phases are uniformly distributed (turbulent, well-mixed flow), partially stratified (intermediate), or completely stratified (laminar, gravity-dominated flow) — and provides the local holdup values at each sensor position that are needed to compute the true cross-sectional average holdup for flow rate calculations.

The development of holdup imaging represented a fundamental advance in production logging technology because it acknowledged a physical reality that single-sensor tools deliberately avoided: in most real horizontal and deviated production wells, the flow is not uniform across the borehole cross-section, and measuring it as if it were produces systematically incorrect phase holdup and flow rate estimates that lead to incorrect production allocation, missed zonal contributions, and poor optimization decisions.

Holdup Image Tool Designs and Measurement Principles

The most common holdup image measurement uses miniaturized electrical impedance or capacitance probes — small sensors that measure the local dielectric properties of the fluid in contact with the probe tip. Oil has a dielectric constant of approximately 2, water has a dielectric constant of approximately 80, and gas has a dielectric constant of approximately 1 (near vacuum). An impedance probe in contact with oil reads differently from one in contact with water or gas, allowing each probe to determine the local phase (or mixture of phases for an intermediate dielectric reading when the probe is at a phase boundary) from its electrical response.

Tool configurations vary between manufacturers: some use linear arrays of 6 to 12 probes arranged radially (measuring a profile from top to bottom of the borehole); others use a full cross-sectional array with probes at multiple radial distances and azimuthal positions (providing a true 2D phase distribution map). The tools are run on a centralized carrier that holds the sensor array in the center of the wellbore, or on an eccentric carrier that hugs one side of the borehole in horizontal wells to sample near the high side where gas accumulates — the eccentric configuration provides better characterization of the gas layer thickness in stratified flow than a centralized configuration that may miss the thin gas layer at the borehole top.

Optical fiber sensors offer an alternative measurement principle — the refractive index contrast between oil, water, and gas causes total internal reflection at the fiber tip surface to occur in gas (low refractive index) but not in liquid (higher refractive index), giving a binary oil/water versus gas discrimination at each probe tip with sub-millisecond response time. Optical holdup probes are widely used in gas-liquid flow characterization where the binary gas/liquid distinction is the primary measurement needed.

Holdup Image Applications Across International Jurisdictions

Canada (AER / WCSB): WCSB horizontal Montney and Cardium production wells use holdup image production logging to diagnose water breakthrough zones and gas-oil contact movement in horizontal producers where the long laterals (2,000 to 4,000 meters) make it economically impractical to run multiple individual flowmeters at each production cluster — a single holdup-velocity imaging pass provides the spatial distribution of production contributions from all clusters simultaneously. AER Directive 065 (Resources Applications for Conventional Oil and Gas Reservoirs) implicitly requires production allocation to individual zones for multi-zone completions, and holdup image production logging is the primary diagnostic method for verifying that allocated production reflects actual zonal contributions rather than reservoir engineering assumptions.

United States (API / BSEE): Gulf of Mexico deepwater horizontal and sub-horizontal completions (Paleogene Wilcox, Miocene turbidites) routinely use holdup image production logging for early production surveillance to detect early water breakthrough from the aquifer contact and to verify that all perforation clusters are contributing production as designed in the completion model. BSEE production reporting requirements for OCS wells implicitly require accurate phase measurement, which in horizontal wells requires holdup imaging rather than conventional single-sensor flowmeter logs. The Permian Basin horizontal development program uses holdup-velocity imaging passes on diagnostic wells to calibrate production models used to forecast performance of the full development well inventory without requiring expensive production logging on every well.

Norway (Sodir / NORSOK): Equinor's Gullfaks and Statfjord field horizontal producers use holdup image production logging for annual production surveillance that tracks the water-oil contact movement and gas cap expansion in the mature Brent Group reservoirs, providing the input data for reservoir simulation history matching that underpins production plateau planning and infill drilling decisions. NORSOK D-010 well integrity requirements for production logging specify that production surveillance programs must provide quantitative phase holdup data adequate for zonal production allocation, and holdup image tools are specified in Equinor and Aker BP production logging programs for horizontal well surveys as the minimum adequate instrumentation for inclined wellbore phase measurement.

Middle East (Saudi Aramco): Saudi Aramco's Arab Formation horizontal maximum reservoir contact (MRC) wells — some with up to 7 to 12 lateral branches extending from a single main wellbore — use holdup image production logging to identify which lateral branches are producing water from the underlying aquifer and which are producing dry oil from the oil column, enabling selective water shutoff using mechanical or chemical conformance control at the underperforming laterals while maintaining production from the oil-producing branches. Aramco has published extensively on holdup-velocity imaging in MRC wells in SPE papers from the Dhahran SPE conference, documenting the combination of holdup image and Doppler velocity tools that provides the most accurate phase flow rate calculation in the complex multiphase flow regimes of multi-lateral Arab Formation wells.