On the contrary of the polymer flood application consisting in viscosifying injection water, the principle of Water Shut-Off (WSO – production well treatment by polymers) is to solve production problems caused by early water breakthrough or reservoir fractures linked to water drive. The main purpose of WSO is thus to reduce water influx from the water producing zones in order to stimulate production from oil-bearing zones.
In a similar way, Conformance Control (CC- injection well treatment by polymers) consists in injecting polymer/gel formulations to solve water channeling problems in the reservoir (high-permeability streaks, reservoir fractures, etc.). Therefore, the main purpose of CC is to improve reservoir conformance by a deep treatment of the thief zones from the injection well. CC is also called “Profile Control”.
In the case below, a production well is represented producing from two layers: one low-permeability oil layer and one high-permeability water layer.
Due to higher mobility and permeability, water production overtakes oil production from the low-permeability zone, resulting in high-water-cut production, poor sweep efficiency and poor economics. Well performance becomes strongly affected by water influx, and early shut-in may be expected with such a poor economics. WSO polymer treatment enables reducing water influx from the high-permeability layer with little impact on oil permeability. The net result is a reduction of the water cut of the well sometimes along with an increase in oil production rate, if the total fluid production of the well can be maintained.
Range of polymers for WSO & CC
A broad range of chemicals called Powelgel™️ was created to perform WSO and CC in most of the formations including those high salinity and high temperature. Some of these products may be used in North Sea.
Powelgel™️ products descriptions :
- Size-controlled microgel species (adapted to large range of permeabilities)
- Delayed gels environmentally-friendly (free of toxic cross linkers)
Powelgel™️ products specificities:
- Temperature stability: from 30°C up to 165°C,
- Salinity up to 200 g/L TDS,
- Withstanding the presence of H2S, Acids,
- Excellent mechanical stability at high shear rate (up to 1,000,000 sec-1)
- High efficiency in heterogeneous/Multi-layer formations
Proven track records have been obtained in a wide variety of field situations (i.e. gas wells, water-flooded wells, heavy-oil horizontal wells, offshore gravel-pack wells…). The design of Poweltec WSO and CC’ treatments combines near-wellbore reservoir simulations and laboratory core-flood experiments.
Payout of WSO treatments is often achieved within 1 month. Plots of Cumulative oil vs. Cumulative water production enables a good evaluation of additional oil produced after the treatment.