Production Log: Definition, Techniques, and Well Performance Analysis

What Is a Production Log?

A production log records one or more in-situ measurements that describe the nature and behaviour of fluids in or around the wellbore during active production or injection, enabling engineers worldwide to quantify flow contributions by zone, diagnose underperforming intervals, confirm stimulation effectiveness, and allocate production accurately across multilayer or multi-lateral well completions.

How Production Logging Works

A production logging survey involves lowering a tool string into a live, producing or injecting well and making measurements while fluid is flowing. Unlike open-hole wireline logging, which is conducted in a static borehole before the well has been completed and put on production, production logging takes place with the well in its normal operating condition. The tool string is conveyed either on conventional wireline cable from a surface truck, on slickline if only mechanical tools are needed, or on coiled tubing in horizontal wells where gravity prevents wireline tools from reaching the lateral section. The tool is run in hole at a controlled speed and then pulled back at a series of different flow velocities to determine how the instrument response changes as a function of tool velocity, allowing the true fluid velocity to be separated from the tool's own motion through the fluid.

The most fundamental production logging measurement is the spinner flowmeter, which consists of a small rotating impeller whose spin rate is proportional to the fluid velocity past the tool. In a vertical well producing a single-phase fluid, the spinner reading directly converts to volumetric flow rate when multiplied by the pipe cross-sectional area. Measurements at multiple tool speeds, both up-passes and down-passes, allow the interpretation software to determine the cable-motion correction and produce a reliable velocity profile. Integrating the velocity profile over depth gives the contribution of each perforated interval to the total flow, expressed either as a flow profile (barrels per day or cubic metres per day per metre of perforated interval) or as a cumulative percentage contribution by zone.

Because most wells produce two or three fluid phases simultaneously, oil, water, and gas, a single spinner measurement is insufficient for complete flow characterisation. The fluid density log, recorded by a gamma-ray densitometer or a differential pressure sensor, measures the bulk density of the fluid mixture at the tool depth, which shifts between the density of water (approximately 1.0 grams per cubic centimetre, or 62.4 pounds per cubic foot) and the density of oil (typically 0.75 to 0.85 g/cc) as the water cut changes. The capacitance or water-holdup tool measures the dielectric properties of the fluid mixture, which change sharply between the high-dielectric water phase and the low-dielectric oil and gas phases, providing a direct estimate of the local water fraction, or water holdup, in the pipe cross-section. Temperature logs detect the Joule-Thomson cooling effect as gas expands through perforations or zones of high pressure drawdown, identifying gas entry points that may not be obvious from the spinner alone. Pressure gauges record the flowing bottomhole pressure and the pressure gradient, which confirms fluid density calculations and provides the data needed for inflow performance relationship (IPR) analysis and future well deliverability forecasting.

Production Logging Across International Jurisdictions

Canada: AER Production Reporting and Log Data Requirements

The Alberta Energy Regulator (AER) regulates production logging activities in Alberta under Directive 038, which covers well servicing operations, and Directive 083, which covers commingled production from multiple zones. When an operator produces oil or gas from two or more separate pools through the same wellbore, the AER requires production allocation between pools to be demonstrated, which is typically accomplished through either zonal testing with packers or through production logging surveys that quantify the fractional contribution of each zone. Log data submitted in support of commingled production applications must include interpretation reports demonstrating the basis for the proposed allocation percentages. The AER's Petrinex reporting system tracks monthly production volumes by pool, and production log data provides the technical justification when those allocations are challenged or reviewed.

In the Montney and Duvernay unconventional plays, multi-stage hydraulically fractured horizontal wells are almost universally commingled across dozens of perforation clusters. Production logging in these wells, conducted via coiled tubing-conveyed PLT suites, identifies which stages are contributing to production and which are not, informing refracturing decisions and completion design improvements in future wells on the same pad. The British Columbia Oil and Gas Commission (BCOGC) has similar reporting requirements for Montney wells in northeastern British Columbia, where the province's Petroleum and Natural Gas Act governs well servicing and production surveillance activities.

United States: BSEE and BOEM Production Monitoring Requirements

In U.S. offshore waters, the Bureau of Safety and Environmental Enforcement (BSEE) and the Bureau of Ocean Energy Management (BOEM) jointly regulate production operations on the Outer Continental Shelf under the authority of the Outer Continental Shelf Lands Act (OCSLA). BSEE's regulations at 30 CFR Part 250 require operators to maintain accurate production records and to conduct periodic well surveys to verify that production is being allocated correctly between zones, leases, and royalty-bearing intervals. Production log surveys are a standard means of demonstrating that zonal commingling is consistent with approved field development plans and that no undisclosed inter-zone communication is occurring through the wellbore or through the reservoir.

In onshore U.S. operations, the Railroad Commission of Texas (RRC) requires production reporting by lease and by field, and the formation-specific allocation data that underpins those reports is often derived from production log surveys. In the Gulf of Mexico deepwater environment, where horizontal subsea wells produce from multiple reservoir sands in a single completion, production logging surveys are conducted periodically to verify that the flow allocation model used in the reservoir simulation history match is consistent with actual in-situ measurements. BSEE's inspection and enforcement division reviews production log data as part of its metering verification programme for offshore royalty payment purposes.

Australia: NOPSEMA Production Facility Requirements

The National Offshore Petroleum Safety and Environmental Management Authority (NOPSEMA) regulates offshore petroleum production facilities in Australian Commonwealth waters under the Offshore Petroleum and Greenhouse Gas Storage Act (OPGGSA). NOPSEMA's Safety Case framework requires operators to demonstrate that production operations are conducted within specified safety parameters, and production logging data contributes to the well integrity evidence base by confirming that produced fluids are flowing through intended perforations and not through annular channels or compromised casing. The West Australian Department of Mines, Industry Regulation and Safety (DMIRS) governs onshore and state-water petroleum activities in Western Australia, where the Carnarvon Basin offshore and the onshore Perth Basin and Cooper Basin extension into South Australia require similar production allocation documentation.

Australian operators such as Woodside Energy and Santos conduct regular production logging surveys in their North West Shelf and Timor Sea facilities to manage water breakthrough in high-rate gas condensate wells and to identify gas cap expansion in oil rim reservoirs. The challenging wellbore environments on Australia's North West Shelf, with high bottomhole temperatures exceeding 150 degrees Celsius (302 degrees Fahrenheit) and pressures above 70 megapascals (about 10,000 psi), require high-temperature, high-pressure (HTHP) rated production logging tool strings, which add cost but are essential for reliable data acquisition.

Middle East: Saudi Aramco Ghawar Horizontal Well Production Logging

Saudi Aramco operates one of the world's most sophisticated production logging programmes in the Ghawar field, where hundreds of horizontal oil producers and water injectors require regular surveillance to manage the advancing water drive and to maintain oil production rates that underpin global energy markets. In Ghawar's Arab-D carbonate reservoir, horizontal wells may extend 2,000 metres (6,560 feet) or more through the reservoir, and the production log confirms whether the entire lateral length is contributing uniformly or whether certain sections have watered out, are experiencing near-wellbore damage, or are producing from below the oil-water contact. Saudi Aramco has developed proprietary interpretation protocols for production log data in carbonate horizontal wells, incorporating advanced multiphase flow modelling that accounts for the irregular fracture and vug network that characterises Arab-D reservoir heterogeneity.

The Ministry of Energy of the Kingdom of Saudi Arabia sets national production targets under Saudi Aramco's concession agreement, and accurate production allocation data from production logs is integral to the reservoir management strategy that supports those targets. Saudi Aramco's production logging programme includes permanent downhole gauges in many Ghawar producers that transmit pressure and temperature data continuously to surface, complementing periodic PLT runs to provide a continuous surveillance record over the producing life of each well.

Norway: Sodir Production Allocation Requirements

The Norwegian Offshore Directorate (Sodir, formerly Oljedirektoratet) requires all operators on the Norwegian Continental Shelf to maintain accurate production allocation documentation in accordance with the Resource Management Regulations issued under the Petroleum Act. Where multiple reservoirs are produced commingled through a single wellbore, operators must demonstrate allocation accuracy to within agreed tolerances, typically five to ten percent, using approved metering systems or alternative techniques such as production logging surveys. Sodir's DISKOS national petroleum data repository holds production data for all Norwegian fields, and production log data submitted in support of allocation documentation is archived in DISKOS for the field's producing life.

Equinor, Aker BP, and ConocoPhillips Norway conduct production logging in subsea horizontal wells on fields such as Johan Sverdrup, Snorre, and Ekofisk using either wireline-deployed tractor-conveyed tool strings (which use motorised wheels to pull the tool string through the horizontal section against gravity and friction) or coiled tubing-conveyed PLT suites, depending on the completion configuration and the available intervention vessel. The North Sea's challenging well environment, with high H2S and CO2 concentrations in some fields and bottomhole pressures exceeding 50 megapascals (about 7,250 psi) in Ekofisk chalk, requires tool strings with enhanced materials specifications and downhole electronics rated for sour-service environments.