Water production from hydrocarbon reservoirs is a serious problem in the oil industry. High water cut reduces the economic life of producing wells and costs the industry billions of dollars each year (Curtice and Dalrymple 2004). Throughout the years, several techniques and chemicals have been developed to control undesired water production.

The industry has developed and applied a variety of chemical systems to reduce or shut off unwanted water production. However, most of these chemical systems are often quickly categorized as environmentally damaging according to the environmental laws and regulations, particularly in the North Sea area. This means that service companies must keep pushing technology development in a more environmentally acceptable direction. The recent development of a "green," environmentally acceptable colloidal silica-based sealant system is an example of this process. This sealant system is a two-component system containing a liquid silica and an activator. The system is easy to mix and easy to pump because of its low viscosity. Once it is placed into the water-bearing zone, the system forms a stiff gel to block the flow of water. Any underdisplaced gel left in the tubing can also be easily washed out using coiled tubing (CT). The system can also be viscosified or slurried with polymer or particulates, respectively, if diversion is required in longer intervals with high permeability and pressure contrast. In addition to water and gas shutoff, this new system shows potential in other areas, such as formation consolidation, temporary gel plugs, annular barrier re-establishment, as well as stopping severe losses while drilling and recompleting.

The gel-setting time can be tailored for a wide temperature range from 20 to 150°C by varying the concentration of the activator. Extensive laboratory research has been performed to develop and qualify this sealant system. Simple, static-sealed tube tests were first run to qualitatively evaluate the gel strength and gelation time. Then, gradually, the formulation was refined and rheological data was measured and collected using a Brookfield viscometer. Further, core-flooding tests were conducted both in sandpack and carbonate cores to determine the effectiveness of the system in blocking water flow.

This paper describes the development of this environmentally acceptable sealant system and the qualification process including laboratory test methods and results.

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