Diversion (Stimulation) | Oil Authority

Diversion in well stimulation and cementing refers to any technique used to force treatment fluids — acid, fracturing fluid, or cement slurry — into lower-permeability or lower-injectivity zones that would otherwise be bypassed in favor of higher-permeability intervals that preferentially accept the treatment fluid, using mechanical or chemical means to temporarily or permanently reduce the injectivity of the high-permeability intervals so that subsequent fluid volumes are diverted into the less-permeable zones, achieving more uniform distribution of the treatment across the entire target interval and improving the overall effectiveness of the stimulation or isolation program.

Key Takeaways

The fundamental challenge that diversion solves is the natural heterogeneity of reservoir rock — in any interval with multiple pay zones or perforations, some zones will have higher permeability or higher existing fractures than others, and fluid pumped into the wellbore will follow the path of least resistance into these high-injectivity zones while the lower-injectivity zones receive little or none of the treatment; without diversion, a matrix acid job or fracture treatment in a multi-zone interval may effectively stimulate only the highest-permeability layer while leaving the remaining interval untreated, resulting in incomplete stimulation and suboptimal production improvement.
Mechanical diversion methods use physical tools to isolate zones during sequential treatment: bridge plugs (drillable or retrievable) set below a lower zone to seal it off while the upper zone is treated; ball sealers pumped with the treatment fluid that seat on perforations as the fluid exits, progressively blocking perforations that have accepted their treatment volume and diverting flow to unblocked perforations; coiled tubing-deployed packers that straddle individual perforation clusters in horizontal wells, allowing each cluster to be stimulated individually; and downhole flow control devices (sliding sleeves, inflow control valves) that can be selectively opened and closed to direct treatment to specific intervals.
Chemical diversion uses temporary blocking agents that dissolve or degrade after the treatment, restoring the original permeability: degradable fiber diversion (DFD) systems inject bundles of biodegradable polymer fibers with granular particles that form a temporary filter cake on high-injectivity perforations, redirecting subsequent acid or fracturing fluid to lower-injectivity zones; wax-coated benzoic acid flakes (used in matrix acid diversion) form temporary plugs at formation temperature that melt when the treatment fluid contact heats them; and viscoelastic surfactant (VES) divertors form viscous gels in the high-permeability zones that reduce injectivity, then break back to low viscosity on contact with hydrocarbon or temperature change.
Far-field diversion (fracture diversion) in multistage hydraulic fracturing extends the diversion concept to the fracture tips — by pumping diverter agents (particulate plugging agents, engineered particle blends) at the end of a fracture stage, the propped fractures near the wellbore are temporarily blocked, forcing the subsequent stage's fracture initiation to occur at a new location away from the existing fractures; this far-field diversion technique is used in refracturing operations to stimulate unstimulated rock matrix between existing fractures, as well as in initial completions to encourage more uniform coverage of the lateral length.
Cement diversion (squeeze cementing) uses diverter pills to force cement into specific behind-casing communication channels or perforations that are accepting cement preferentially, while ensuring that other target channels also receive cement; in high-volume perforated zones, a viscous pill or LCM treatment is placed across the high-injectivity perforations before squeezing cement to reduce their acceptance rate, diverting the cement slurry to the tighter communication paths that need sealing.

Fast Facts

The concept of diversion in well stimulation was recognized in the first matrix acid treatments of carbonate reservoirs in the 1930s, when it became apparent that acid injected without diversion preferentially dissolved the most permeable vugs and channels, leaving lower-permeability matrix unacidized. The first ball sealer diversion tools were patented in the 1950s and became widely used in multi-zone fracturing programs through the 1960s. Fiber-based chemical diversion, now the dominant chemical diverter technology for plug-and-perf horizontal well refracturing, was commercialized in the 2000s by Halliburton, SLB, and Baker Hughes. The development of degradable diversion technology has transformed refracturing economics — previously unprofitable in many basins because mechanical diversion required a costly workover rig, degradable chemical diversion allows refracturing from a standard pumping unit with no mechanical well access, reducing treatment cost by 40 to 60%.

What Is Diversion?

Imagine injecting acid into a carbonate reservoir through 20 perforations, with one perforation opening into a high-permeability natural fracture and the other 19 opening into tight matrix. Without any diversion, virtually all the acid will flow through the fracture perforation — the path of least resistance — dissolving a short finger of rock along the fracture face while the 19 matrix perforations receive almost nothing. The treatment pumped at great expense and effort stimulates only the zone that least needed it (the fracture was already high permeability) while leaving the matrix interval completely untouched.

Diversion is the engineering approach to this inequality problem — forcing the treatment to go where it is needed rather than where it wants to go. By temporarily reducing the injectivity of the high-permeability fracture perforation (whether by seating a ball sealer, placing a fiber-particle plug, or building up a VES gel in the fracture channel), the subsequent acid volume is redirected to the matrix perforations where it can generate new wormholes and permeability enhancement. The result is stimulation of the entire interval rather than just the most permeable path.

The economic importance of diversion is enormous in multi-zone reservoirs and in horizontal wells with multiple perforation clusters. Without effective diversion, a 10-cluster fracture treatment in a horizontal well may stimulate only 3 to 4 clusters while the others receive negligible fracturing fluid; the well is effectively a 3-to-4-cluster completion despite the cost of 10. With effective diversion, 8 to 9 clusters may be stimulated, dramatically increasing the well's contact with the reservoir and improving the production rate and ultimate recovery per dollar of completion cost.

Diversion Methods: Mechanical and Chemical Approaches

Mechanical diversion methods are the oldest and most reliable in terms of confirmed zonal isolation — a bridge plug set below a zone definitively prevents fluid from reaching that zone during treatment. The plug-and-perf completion method for horizontal wells uses mechanical diversion as its fundamental operating principle: the deepest cluster is perforated and fracture-treated, then a bridge plug is set above the cluster, the next cluster is perforated above the plug, fracture-treated, and the cycle repeats up the lateral. Each stage is mechanically isolated from all others, ensuring that 100% of the fracturing fluid for each stage goes into that stage's perforations. The trade-off is cost and time — setting bridge plugs and perforating each cluster requires a coiled tubing or workover rig run between stages, adding $50,000 to $200,000 per well in service costs.

Chemical diversion methods sacrifice some isolation certainty for a significant reduction in cost and operational complexity — degradable fiber and particle systems are pumped directly in the fluid stream without requiring a separate tool run, allowing multiple diversion events within a single continuous pumping operation. The most widely used chemical diverter for horizontal well completion is a blend of degradable polymer fibers (polyglycolic acid or polylactic acid fibers that dissolve in formation temperature within 24 to 72 hours) with sized particulates (calcium carbonate or salt crystals that dissolve in formation water or acid) that form a temporary filter cake on perforations that have accepted fracturing fluid. The fiber cake reduces the injectivity of treated perforations, diverting subsequent fluid to untreated clusters; after the treatment, the fibers and particles dissolve, restoring full perforation injectivity for production.

Acid diversion in matrix stimulation uses chemical diverters specifically matched to the treatment chemistry — for carbonate matrix acid jobs, wax-coated benzoic acid flakes are suspended in the treatment acid and preferentially deposit at perforations accepting high flow rates (where particle velocity-driven deposition is greatest), progressively blocking high-injectivity perforations and diverting acid to tighter perforations. Viscoelastic surfactant (VES) diverter systems form viscous gels in the contact zone between the VES solution and the acid-dissolved carbonate rock surface (forming a wormhole face), then break when contacted by hydrocarbon during production flowback — this self-diverting acid technology achieves diversion automatically as a function of wormhole development rather than requiring a separately pumped diverter slug.

Diversion Applications Across International Jurisdictions

Canada (AER / WCSB): Alberta Montney and Duvernay horizontal well completions use chemical diversion (degradable fiber and particulate systems) as the standard practice for stimulation of wells where mechanical bridge plug operations are not economically justified for all clusters. Plug-and-perf completions remain the dominant method for premium wells in the core of the Montney play (Tourmaline, Paramount Resources) where the additional completion cost of mechanical diversion is justified by the higher expected ultimate recovery. AER Directive 083 (Hydraulic Fracturing) requires operators to report diversion method used in each completion stage, building a provincial database of diversion technology adoption that correlates with production performance data. CNRL's heavy oil thermal operations in Cold Lake and Peace River use cement squeeze diversion for re-cementing operations on producing wells with behind-casing communication, placing diverter pills in high-injectivity gas migration paths before squeezing cement to seal them.

United States (API / BSEE): Permian Basin Wolfcamp and Bone Spring horizontal completions routinely use 30 to 50+ perforation cluster designs with chemical diversion to achieve more uniform distribution of fracturing fluid across the long laterals (2,000 to 4,000 meters) typical of Midland and Delaware Basin development. The diversion efficiency debate — whether chemical diverters achieve the same cluster-by-cluster stimulation coverage as mechanical bridge plugs — is a major topic in Permian Basin completion engineering research, with operators including Pioneer Natural Resources, ConocoPhillips, and Chevron publishing completion diagnostics studies comparing tracer-tagged diversion stages with DFIT and microseismic data to quantify actual cluster participation rates. BSEE regulations for offshore stimulation require documented treatment design including diversion strategy for Gulf of Mexico wellbore stimulation programs.

Norway (Sodir / NORSOK): NCS horizontal well matrix acid stimulation in Brent Group sandstones and Ekofisk chalk uses mechanical straddle packer diversion (deployed on coiled tubing) to isolate individual intervals during bullhead acid treatments, ensuring that each target zone receives adequate acid volume for wormhole penetration. Equinor and Aker BP employ targeted acid stimulation with coiled tubing-deployed packer systems rather than the chemical diversion methods used in North American unconventional plays, reflecting the different geology (conventional, multi-layer reservoirs versus unconventional tight rock requiring massive hydraulic fracturing) and well economics of the NCS. NORSOK D-010 well integrity requirements include treatment pressure monitoring and injection profiling data from stimulation operations to document zonal coverage and diversion effectiveness.

Middle East (Saudi Aramco): Saudi Aramco's Arab Formation matrix acid stimulation programs use chemical diversion extensively in the multi-layer Arab A, B, C, and D carbonate reservoirs that are often commingled in production wells — diversion ensures that acid treatments benefit the tighter Arab A and B intervals rather than concentrating in the more permeable Arab D that already provides most of the production. Aramco's EXPEC Advanced Research Center has developed proprietary viscoelastic diverter formulations matched to Arab Formation temperature and brine chemistry, including temperature-activated VES systems that build viscosity at Arab Formation bottomhole temperature (80°C to 100°C) to provide diversion in the high-temperature intervals without requiring the cooler surface-temperature gellation that is characteristic of conventional VES diverter products.