Other Special Situations and Methods

Certain other circumstances may be exploited to improve gel placement if zone isolation cannot be used. For example, before a gel treatment, the productive interval in a well might be plugged with debris, while a watered-out zone is open. If crossflow does not occur, the gel treatment could be applied with a reduced risk of gel entering productive zones. After the gel treatment, acid could be spotted on the productive intervals to remove near-wellbore damage and increase injectivity.1

In some cases, watered-out zones may contain natural, hydraulic, or thermally induced fractures while oil-productive zones do not.97 In certain circumstances, selective plugging of the water zones could occur without the use of zone isolation. Alternatively, the various zones in a reservoir may contain fractures, but since the fractures do not contain proppants, they remain closed unless the injection pressure is sufficiently high. Also, the pressure at which a fracture opens varies from one zone to the next. If at a given pressure, the fractures are open in the watered-out zones but are closed in the hydrocarbon-productive zones, a blocking agent can be placed primarily in the most offensive fractures. Hopefully, after the gel has been placed, damage to the oil zones (either fractured or unfractured) will be minimum. For this concept to work, a given fracture must not cut through most or all zones. Fractures that cut through multiple zones will allow vertical fluid movement throughout their heights.

In another case, a watered-out channel may be located some distance above a less-permeable, productive interval. If the tubing between the two zones contains enough buffer fluid (e.g., water) and the permeability contrast is high enough, gelants can be placed in the watered-out channel without contacting the productive interval. In contrast, if a watered-out channel is located below a productive zone, the need for zone isolation during gel placement is accentuated. Considering typical casing or tubing volumes, this approach generally will require very small gelant volumes or very large distances between zones. Perhaps, a more practical idea involves the use of coiled tubing.98 By locating the end of the coiled tubing at the interval to be plugged, one may minimize gelant injection into hydrocarbon zones (if the injection volume is sufficiently small).

In other cases,99 hydrocarbon-productive zones have been protected during gelant injection by simultaneously injecting gelant down the tubing and oil down the tubing annulus (or vice versa). If the pressures, injection rates, and tubing location are balanced properly, gelant enters the water zones while oil enters the oil zones.