Abstract

As a large number of on- and offshore oil fields continue to mature there has been an increasing focus on the use of innovative technologies and methods to optimise production and to extend the life of existing reservoirs. One such method that is being increasingly implemented is the use of drag reducing agents to increase the rate of water injection and produced water re-injection.

Water injection is the most common secondary recovery method used to maintain reservoir pressure and enhance oil recovery. Drag reducing agents are high molecular weight polymers that can be injected into water injection systems to reduce the frictional pressure loss. Thus the water injection rate can be increased resulting in maintenance of reservoir pressure and an increase in oil recovery rate.

The aim of this paper is to evaluate the economic viability using drag reducing agents while also considering the potential positive and negative side effects.

When considering how to increase water injection into a reservoir there are three main alternatives: the installation of more or larger pumps, increasing the number of water injection wells or the use of drag reducing agents. Considering capital expenditure and time for implementation, it is clear that the application of drag reducing agents is the most attractive option. For example, the use of drag reducing agents in the Galley field, offshore UK, resulted in a 45% increase in water injection rate and an extension of three years to the life of the reservoir. The recoverable reserves increased from 28 million barrels to 29.5 million barrels, equating to an NPV of $16.5 million (USD) over the anticipated production life of the field.

Through their continued application, it has been shown that drag reducing agents have no negative side effects and can further provide several other benefits. These include minimising the number of water injection wells needed, reducing the energy required to drive a water injection system and hence reduce the CO₂ and NO_x emissions, increasing the amount of produced water that can be re-injected, providing optimal distribution of water in the reservoir and reducing the effect of corrosion by up to 30%.

It is clear from this technical and economic evaluation that the use of water-soluble drag reducing agents in water injection systems is the most cost effective and timely method that can be employed to optimise production in maturing oil fields.