Freeze services are used to place a temporary pressure barrier (ice) in a well casing, annular space, tubing, drill pipe, spool, valve, or other pressure-containing components when the use of conventional barrier options is not possible. In its simplest form, a freeze involves bringing a wellhead component to a very low temperature to transform the existing fluid within the wellbore component into ice, and this ice is utilized as a testable pressure barrier.
The most important steps before any freeze are understanding the current well condition, reviewing the surface equipment (well casing, wellhead, and tree), and determining the current fluid (including cement, gas, or void) in each annulus of the well. It is important to ensure surface components can safely withstand the cryogenic temperatures that will occur during the expected duration of the freeze operation. The specific surface equipment of the well will help guide the most effective and safe method to produce the freeze plug. Of equal importance is ensuring the best freezable medium is present in the well to achieve the highest quality ice plug.
Using liquid N2, in combination with integral temperature monitors, ensures a competent freeze plug can be safely and efficiently set. Once the freeze plug is established, a positive and negative pressure test can be completed to confirm the temporary barrier is in place, allowing surface operations to begin.
Within certain parameters, cryogenic freezes can be set across multiple strings of casing resulting in an effective temporary barrier in the innermost tubular.
In order to establish a freeze barrier, there must be a freezable medium (brine, water, water-based mud, etc.) in the ID of the component. If there is flow, any void, gas, or hydrocarbon-based fluid present in the freeze area, a freezable medium must be injected into the ID of the component. This can be established through existing wellhead/tree valves or through a Hot Tap operation if required. When liquid hydrocarbons are present, Wild Well’s FreezeLITE product, a special water-based fluid, can be injected into the freeze zone. FreezeLITE can be spotted on hydrocarbon-based fluids and stay suspended in the freeze zone above the hydrocarbon-based fluid. This allows a freeze to be put into effect when unable to fully remove the hydrocarbon-based fluids in the well. FreezeLITE is non-hazardous and safe for onshore and offshore applications. Cryogenic Freezing is proven to be a safe solution when a temporary barrier in the wellbore/component is needed for completing remedial work at the surface.