Thief Zones: Not All Are Created Equal.
In conformance control, it’s often assumed that injected gelant will neatly find its way into the “thief zone” and solve the problem.
But here’s the reality many don’t expect—especially in multilayered, open-hole wells, or horizontal wells. When your thief zone is a matrix feature (high permeability channel for instance), and you inject 2,000 bbls of gelant, Darcy’s Law takes over.
The gelant, with its viscosity before gelation above 50cP, doesn’t go only into the thief zone—it enters all open zones, in proportion to their permeability. This is the basic principle behind polymer flooding where increasing the viscosity of the water helps improve sweep efficiency. Typical viscosities for a polymer flood: 5 to 50cP. Typical viscosities for gelants: 50 to 200cP… Why would the polymer sweep the low permeability zone and not the gelant?
So while you hoped all 2,000 bbls would treat the thief, maybe only 1,000 bbls actually do. The rest? They reduce injectivity in zones that didn’t need treatment—potentially harming oil productivity or limiting future injection efficiency.
In contrast, fracture-type thief zones (big thieves) act like highways. Gelant flows into them preferentially due to their high conductivity and large flow area. Placement is more efficient, more selective, and generally yields longer-lasting results.
Bottom line:
For fracture thief zones, gelant placement is more confined and effective.
For matrix thief zones, gelant distributes broadly—you lose selectivity.
Initial results in matrix-type thief zones can be misleadingly positive—but they often degrade as water eventually bypasses or breaks through the partially treated region.
That’s why accurate diagnosis and realistic expectations are vital in conformance work. And why bullheading delayed gels into anything but fractures is often doomed to fail.
I have attached a screenshot of a spreadsheet used to calculate how much gelant will enter 4 different zones.
You can download Randy’ Seright spreadsheet with important equations below.