commingled flow, Oil & Gas Glossary

What Is Commingled Flow?

Commingled flow (also called commingled production) is the simultaneous production of reservoir fluids from two or more distinct geological intervals, formations, or zones through a single wellbore without physical isolation between the contributing intervals, such that fluids from different reservoirs mix within the wellbore before reaching the surface facility. It differs from selective production, where packers or sliding sleeves allow each zone to be produced and measured independently, and from a simple perforated completion targeting only one formation.

Key Takeaways

Commingled production requires regulatory approval in most jurisdictions, including a Permit to Commingle from the Alberta Energy Regulator (AER) under Directive 065 and analogous applications in British Columbia, Saskatchewan, and US state agencies.
Wellbore crossflow, where reservoir pressure differentials drive fluid from a higher-pressure zone into a lower-pressure zone behind casing, is an unintended and often damaging form of commingling that can cause one zone to deplete another without producing to surface.
Production allocation between commingled zones is determined using pressure-transient testing, production logging runs, chemical tracers, or material balance calculations, since surface meters record only a combined stream.
Water coning or gas coning from a water- or gas-bearing zone can migrate to an adjacent oil-producing zone under commingled conditions, accelerating unwanted fluid breakthrough.
Commingling is economically attractive when individual zones are too thin or low-pressure to produce independently at commercial rates, allowing marginal reserves to be recovered through a shared wellbore.

Intentional Commingling vs. Unintended Crossflow

Intentional commingled completions are designed from the outset to produce multiple reservoir intervals simultaneously. Operators pursue commingling when individual zones lack sufficient deliverability to justify separate wellbores, when the formations are owned by the same working interest owners and can be legally combined, and when the produced fluids are compatible (similar chemistry, no precipitation risk when mixed). A commingled completion typically uses a single tubing string with perforations across multiple intervals, relying on reservoir pressure alone to apportion flow between zones. The apportionment changes dynamically as individual zone pressures decline at different rates, making ongoing surveillance essential to track which zone is contributing what fraction of the combined stream.

Unintended crossflow is a different and more problematic condition. When a wellbore intersects two zones with different reservoir pressures, the higher-pressure zone can inject fluid into the lower-pressure zone through the open wellbore rather than producing to surface. This is particularly common during shut-in periods but can occur during production if one zone's flowing bottomhole pressure falls below the static pressure of an adjacent zone. Crossflow wastes reservoir energy, can damage the receiving formation (especially if the crossflowing fluid is water injecting into a gas sand), and prevents accurate material balance for either zone. Cement integrity failures behind casing can also create communication channels that mimic crossflow even when individual intervals are separately perforated.

Regulatory frameworks distinguish sharply between these two scenarios. Intentional commingling requires advance approval with supporting documentation that the zones share a common fluid contact or that commingling will not impair correlative rights of other mineral owners. Unintended crossflow, if discovered during a production logging survey, typically triggers a remediation requirement: squeezing the offending perforations, setting a bridge plug, or installing a downhole check valve to prevent backflow. In Alberta, the AER's Directive 065 (Resources Applications for Conventional Oil and Gas Reservoirs) governs both commingling approvals and the remediation of unauthorized zone communication.

Fast Facts: Commingled Flow

Alberta regulatory authority: AER Directive 065, requires Permit to Commingle before production from multiple zones
BC regulatory authority: BC Energy Regulator (BCER), Oil and Gas Activities Act; commingling application required
Allocation methods: production logging (spinner surveys), pressure-transient tests, chemical/radioactive tracers, material balance
Crossflow detection: production logging with flow meter and temperature log during shut-in reveals crossflow direction and rate
Common commingled formations: multiple Viking, Cardium, or Montney intervals in Alberta; Bakken and Three Forks in North Dakota
Metering requirement: most jurisdictions require separate wellhead measurement or an approved allocation plan before commingling approval is granted
Economic threshold: commingling is typically pursued when individual zone IP rates are below 30-50 bbl/d oil equivalent and combined rate exceeds economic minimum
Risk factor: pressure depletion interference can cause one zone to inadvertently support pressure maintenance in another, complicating reserves calculations

Reservoir Management Tip:

Before approving a commingled completion, run a sensitivity analysis on the pressure interference between the target zones using simple material balance or reservoir simulation. If one zone has a significantly higher initial reservoir pressure (more than 500 psi difference), it will dominate early production and potentially damage the lower-pressure zone through fluid invasion during shut-ins. Installing a downhole check valve on the lower-pressure interval costs approximately $15,000-30,000 per well but prevents irreversible reservoir damage and is far cheaper than a remediation workover after the fact.

Commingled flow is also referred to as:

Commingled production — the most common operational term, used interchangeably in regulatory filings and well completion reports
Multi-zone production — a broader term that includes both commingled and selectively produced multi-interval wells
Pooled production — sometimes used loosely in field operations, though pooling more precisely refers to the land tenure arrangement rather than the wellbore flow regime
Blended production — occasionally used in facilities engineering contexts when describing the combined stream at the separator or sales meter

Frequently Asked Questions About Commingled Flow

How are individual zone production rates determined from a commingled well?

Because surface meters record the combined stream from all producing zones, operators use several indirect methods to allocate production back to individual formations. Production logging tools run on wireline or coiled tubing measure flow rate at multiple depths within the wellbore, allowing the contribution from each perforated interval to be identified from the incremental flow increase. Spinner-based production logs can resolve zone contributions as small as 5% of the total stream. Chemical tracers injected separately into each zone allow surface sampling to identify which tracer (and thus which zone) is producing at any given time. Pressure-transient analysis during individual zone shut-ins provides permeability-thickness products that can be used to partition production historically using a deliverability-weighted allocation formula.

What happens to lease expiry under a commingled completion?

In most North American jurisdictions, production from a commingled well is legally attributed to every zone included in the commingling permit. This means that a lease covering a zone that is producing only minimal volumes (or even zero volumes) as part of a commingled completion is typically held by the commingled production from the dominant zone, as long as the regulatory permit designates all zones as contributing. Operators must be careful to include all target formations in the initial commingling application; adding a new zone later requires an amendment and, in some cases, the lease over that zone may have already expired if the amendment is not filed in time.

Can commingled production be used in offshore wells?

Yes, commingled production is used in offshore wells, though the regulatory and metering requirements are typically more stringent than for onshore operations. In Canadian offshore waters regulated by the Canada-Nova Scotia Offshore Petroleum Board (CNSOPB) or the Canada-Newfoundland and Labrador Offshore Petroleum Board (CNLOPB), commingling applications must demonstrate that royalty allocation between zones can be determined by an approved method, since different zones may have different royalty rates or ownership interests. In US federal waters (Gulf of Mexico), the Bureau of Safety and Environmental Enforcement (BSEE) requires individual zone allocation plans as part of the production safety systems permit. Subsea completions often avoid commingling because production logging access is limited without costly intervention vessels.

Why Commingled Flow Matters in Oil and Gas

Commingled production is a practical and widely used tool for maximizing economic recovery from wells that penetrate multiple productive intervals, particularly in mature basins where individual zones are too thin or depleted to sustain standalone production. By combining zone contributions into a single producing stream, operators can achieve commercial flow rates from reservoirs that would otherwise be sub-economic, extending field life and improving overall recovery factors. However, commingling introduces complexity into every downstream workflow: reserves estimation must account for the interaction between zones, royalty calculations require a defensible allocation methodology, and production optimization cannot be performed on individual zones without intrusive wellbore surveys. Operators who invest in regular production logging and pressure surveillance of commingled wells consistently achieve better ultimate recovery and fewer regulatory compliance problems than those who treat commingled wells as black boxes.

Commingled Flow: Multi-Zone Production Through a Single Wellbore