Abstract

The current, late life production on the Miller field is characterised by high water cut wells that need frequent scale inhibitor squeezes to manage the production of scale. In addition, the wells are often choked back due to plant water constraints. The key to managing the decline in oil production is therefore to reduce water production. This allows the wells to flow un-choked and also lightens the fluid column, increasing drawdown and oil rate in the well. Other advantages include increased scale inhibitor squeeze (SISQ) life, reduced OPEX costs and reduced environmental impact of overboard discharge of produced water and production chemicals. However, the presence of scale in the wells means that intrusive surveillance and mechanical water shut off would require costly milling to gain access. The field is therefore ideal for the use of chemical selective water shut off (SWSO) treatments, which can be deployed without access to production logging data. BP Miller and Clariant have progressively applied SWSO treatments on a range of wells. A dilute solution of cross-linkable polymer is bullheaded down the wells and reacts with added cross-linker in situ. After cross-linking, the web of polymer is inflated in the presence of water, effectively blocking the flow path, whilst deflating in the presence of oil. Since the whole producing zone is treated, water will be retarded without the need to know where it is coming from. Providing due precautions are taken, this can be highly successful. For example, in May 2005 on Slot 32, oil production increased from 800 bopd to 2,800 bopd, whilst water cut reduced from 92% to 77%. The most likely explanation for this is a combined effect of the treatment stimulating production from the J-sand region while limiting water flow potential from wetter areas.

Introduction to Water Shut Off Techniques

Water production is a world wide challenge, with an average of three barrels of water being produced for every barrel of oil [1]. Economic and environmental issues are created due to lifting, separation and disposal of unwanted water. Water production can also lead directly to loss of hydrocarbon production due to gross fluid processing constraints or simply the inability to lift a well back to production due to very high water cut. The major environmental impacts of high water production are discharge of oil and entrained production chemicals in overboard water. Reducing the volume of disposed water is clearly the best way to reduce these types of discharge. Reducing water production also has the potential to reduce the requirement for some types of production chemicals associated with water production, e.g. scale inhibitors. Frequent scale squeezes also involve excessive down-time leading to significant production loss.

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