Single-Pass Method | Oil Authority

The single-pass method in petroleum engineering refers to a production logging or completion diagnostic technique in which all required measurements — flow rate, phase holdup, temperature, pressure, and fluid identification — are acquired in a single tool run through the wellbore, using either an integrated multi-sensor tool string or a modular logging system designed to acquire the full suite of measurements simultaneously without requiring multiple passes at different speeds or with different tool configurations, thereby minimizing wellbore disturbance, reducing rig or coiled tubing time, and providing a spatially consistent dataset where all measurements are acquired under identical flow conditions at each depth.

Key Takeaways

Single-pass production logging acquisition addresses a fundamental challenge in flow measurement: the well's flow regime changes when the tool is stationary or moving at different speeds, meaning measurements made on different passes or at different times may represent different flow conditions at the same depth — the single-pass approach captures all parameters simultaneously under the same instantaneous flow state, eliminating the flow-state inconsistency that arises when, for example, the spinner flow meter pass is run at one cable speed and the holdup sensor pass is run at a different speed hours later after the well's flow rate or pressure has changed.
The most common implementation of single-pass production logging uses integrated tool strings where the spinner (or electromagnetic flow meter), pressure-temperature sensors, holdup probes, and fluid density sensors are all assembled in a single tool body conveyed on coiled tubing or e-line in a single run — SLB's Production Universe, Halliburton's MAPS, and Baker Hughes' Emerald platform are examples of integrated multi-physics tools designed for single-pass acquisition of the complete production logging measurement suite in horizontal and deviated wells where multiple passes would be impractical due to the tool's reduced mobility in deviated sections.
In horizontal well production logging, single-pass acquisition is particularly important because the flow regime in a horizontal wellbore is strongly influenced by tool position and movement — moving the tool creates turbulence that disturbs the naturally stratified flow of oil, water, and gas, potentially redistributing the phase distribution that the holdup sensors are trying to measure; a single smooth pass at a consistent speed through the horizontal section minimizes this disturbance compared to multiple passes at different speeds, and integrating the holdup and velocity sensors in the same tool eliminates the positional uncertainty that arises when sensors on separate tool strings pass the same depth at different times with different flow disturbances.
Single-pass cement evaluation (combining pulse-echo ultrasonic, flexural wave, and conventional CBL measurements in one tool run) is used in critical well integrity evaluations to reduce the number of logging runs required to fully characterize the cement quality in a casing string — multi-sensor cement evaluation tools (SLB Isolation Scanner, Halliburton CAST-V) acquire the azimuthal cement map, the radial cement thickness, and the cement acoustic impedance in a single pass, providing a complete 360-degree cement bond quality image without requiring separate CBL, USIT, and flexural wave tool runs that would each potentially disturb the wellbore and add rig time cost.
Single-pass method limitations include the requirement for a more complex and expensive tool string (combining multiple sensor types in one assembly adds engineering complexity, increases tool outside diameter, and can reduce tool reliability compared to simpler single-function tools) and the potential for inter-sensor interference where the electromagnetic or acoustic fields from one sensor affect the measurement of an adjacent sensor in the same tool string; logging service companies address these limitations through careful tool string design with appropriate sensor spacing, acoustic isolation, and electronic shielding, but single-pass integration always involves tradeoffs between measurement independence and operational efficiency.

Fast Facts

The single-pass production logging concept emerged as a response to the complexity of horizontal well production surveillance in the early 1990s, when the rapid adoption of horizontal completions in the North Sea, Gulf of Mexico, and WCSB created demand for production logging techniques that could characterize multiphase flow in wells where the conventional multiple-pass approach was impractical. SLB's Flow Scanner (1990s) and Production Universe platforms were among the first commercial implementations of integrated single-pass production logging for horizontal wells. Today, multi-sensor single-pass acquisition is the industry standard for production logging in horizontal and highly deviated wells, with coiled tubing conveyance enabling single-pass logging in wells with complex completions (packers, sliding sleeves) that prevent conventional wireline tool deployment.

What Is the Single-Pass Method?

Production logging in a vertical well is relatively straightforward — run the flowmeter, then run the holdup tool, then run the temperature and pressure sensors, and correlate the results by depth. If the well conditions are stable, three separate passes through the same depth interval give consistent results that can be combined into a complete production profile. This multi-pass approach works because vertical wells have approximately symmetric, time-invariant flow profiles that are reproducible from one pass to the next.

Horizontal wells break every assumption that makes multi-pass logging work. The flow is strongly stratified (gas on top, water on bottom), the tool disturbs the stratification as it moves, and the flow conditions at the wellbore are affected by the tool's presence and speed in ways that vary throughout the pass. Running the holdup tool an hour after the flowmeter, or at a different cable speed, can give holdup and velocity measurements that correspond to completely different flow states — making their combination into a flow rate profile unreliable.

The single-pass method addresses this by acquiring all measurements simultaneously in one tool string during one pass through the wellbore. Every sensor is at a known position relative to every other sensor, every measurement is acquired at the same time under the same flow conditions, and the dataset is spatially and temporally coherent in a way that multi-pass data never can be. The result is a production profile in which the holdup and velocity data truly correspond to the same flow state at the same depth, enabling the accurate flow rate computation that justifies the investment in production logging.

Single-Pass Method Applications in Production Logging

Zonal contribution analysis in horizontal wells is the primary application — by acquiring velocity, holdup, and pressure gradient simultaneously at multiple depths along the horizontal section, a single-pass production log provides the complete dataset needed to compute the volumetric flow rate of oil, water, and gas entering from each perforation cluster or completion interval. The spatial consistency of the simultaneous measurements means that the production profile from a single pass is self-consistent, unlike profiles assembled from multiple passes where inconsistencies between non-simultaneous measurements can mask real production variations or create apparent anomalies that are artifacts of the measurement timing rather than real production heterogeneity.

Water breakthrough zone identification uses the single-pass holdup and temperature profile to locate the specific perforation clusters or natural fractures that are contributing water to the wellbore — the holdup sensor detects the sudden increase in water fraction above the single-pass baseline at the water entry depth, while the temperature anomaly (from cooler water entering the warmer formation fluid) at the same depth confirms the entry location. The simultaneous temperature and holdup data from a single pass provides a more reliable water entry location than either measurement alone because each measurement has different sensitivities to the same flow perturbation, and their spatial coincidence in a single pass confirms the entry depth without the ambiguity of trying to correlate non-simultaneous measurements that may have detected the same entry at slightly different apparent depths.

Single-pass cement evaluation during workover operations allows the operator to assess cement quality in a specific casing string in a single wireline run before deciding whether to proceed with a planned perforation or workover operation — if the cement evaluation reveals poor isolation behind the casing at the target interval, the workover plan can be modified to include remedial cement before perforating, saving the cost of an unsuccessful perforation job followed by emergency remediation. The single-pass cement image provides the complete radial and azimuthal cement quality map needed for this decision in the time it takes to make one logging run, rather than the two or three runs required with separate CBL, USIT, and flexural wave tools.

Single-Pass Method Across International Jurisdictions

Canada (AER / WCSB): Montney and Cardium horizontal wells in the WCSB routinely use single-pass production logging on coiled tubing to evaluate completion efficiency and identify underperforming perforation clusters without requiring a workover rig — the coiled tubing conveyance allows the integrated multi-sensor tool string to access the full horizontal section (2,000 to 4,000 meters) in a single CT run lasting 4 to 8 hours, providing the production profile needed for completion optimization decisions at a cost substantially below what a wireline or drillstring-conveyed multi-pass program would require. AER production surveillance requirements for multi-zone completions implicitly require the zonal flow allocation data that single-pass production logging provides, and several WCSB operators (Tourmaline, ARC Resources, Canadian Natural) have published SPE papers documenting the use of single-pass coiled tubing production logging for Montney completion optimization.

United States (API / BSEE): Gulf of Mexico deepwater horizontal and sub-horizontal completions use single-pass production logging for early production surveillance to verify that all perforation clusters are contributing to production as designed, with the integrated tool string deployed on coiled tubing through the completion tubing to the horizontal section. BSEE production reporting requirements for deepwater OCS wells require accurate phase flow rate measurements, and single-pass integrated production logging is the method specified in several major operator's internal production surveillance standards for horizontal deepwater wells where accurate water cut and GOR determination is needed for production allocation and reservoir management. Permian Basin unconventional horizontal wells increasingly use single-pass diagnostics combining production logging with distributed temperature sensing (DTS) fiber optic data to provide spatially continuous flow profiling along the entire lateral.

Norway (Sodir / NORSOK): NCS horizontal producers in the Brent Group, Statfjord, and Oseberg fields use single-pass production logging as part of annual well surveillance programs that track the evolution of water breakthrough and gas cap expansion along the horizontal sections over the field's producing life. Equinor and Aker BP production logging programs specify integrated multi-sensor tool strings for horizontal well surveys as the minimum acceptable approach for production surveillance in horizontal completions, per internal engineering standards that reference NORSOK D-010 well integrity requirements for quantitative production allocation to individual completion zones. Norwegian regulatory frameworks require that production from multi-zone NCS completions be allocated to individual zones for resource booking purposes, and single-pass production logging provides the quantitative flow data needed for this zonal allocation.

Middle East (Saudi Aramco): Saudi Aramco's MRC horizontal wells with multiple lateral branches use single-pass production logging to evaluate the production contribution of each lateral and to identify water breakthrough from the underlying Arab Formation aquifer in individual branches — the integrated tool string is deployed on coiled tubing through the main horizontal wellbore and into each lateral branch in sequence, providing a consistent measurement set for each branch under similar wellbore flow conditions. Aramco has published extensively on single-pass production logging methodology for MRC wells in SPE papers from the Dhahran SPE conference, documenting the combination of holdup, velocity, temperature, and pressure measurements in integrated tool strings that provide the complete multiphase flow characterization needed for MRC well production optimization.