Enhancing Produced Water Quality in Kuwait Oil Company
Authors: Al-Kandari Ali Hussain , Rochford David B. 
Published: December 2007

This paper describes the strategy adopted to identify produced water processing options at oil production facilities throughout Kuwait. These facilities are located in three main regions, the South East, North and West. This paper also addresses the results from one month of trials at GC7 in SEK and covers nearly two years of operational experience at GC15 in NK, where desalter effluent water was recycled to wet tanks (Wet Tank Recycle Scheme) and clean water was produced. In Kuwait the water cut is relatively low, however in future produced water rates are expected to increase. Produced water will be injected into producing reservoirs and, as dirty water can reduce well injectivity, good water quality must be maintained. More stringent water control coupled with cost reduction targets requires a dramatic increase in water treatment performance to take KOC into the next century. The wet tank recycle scheme was trialed to establish if it could meet these new tough requirements.

A broad technical and cost comparison with conventional produced water processing systems is presented to emphasize the merits of the scheme. These benefits are potentially wide ranging and include reduced Capex and Opex. Deployment of the recycle scheme requires the resolution of issues covering plant integration, corrosion, chemicals, and solids loading which will are also discussed.

In conclusion, the wet tank recycle trial was a success and is viewed as a potential alternative to conventional oily water polishing plant with the additional benefit of being fully integrated with oil production facilities.

The scheme demonstrates the value of a small trial team approach which maximizes the use of proven technology in a cost effective manner, and is a robust solution for all but the tightest emulsions.

The scheme has potential applications in a Middle East environment, either as a plant retrofit if tankage already exists, or as a new integrated water handling facility.

Introduction

In KOC there are eighteen existing oil production facilities (gathering centres): fourteen of these process wet crude with a handling capacity of up to 25% formation water cut. These gathering centres are designed for oil throughputs ranging from 80 to 250 mbopd and approximately half of the production at each gathering centre is wet crude. Gathering centres process water rates ranging from 10 mbwpd up to 25 mbwpd. There are plans to install a further three new large gathering centres, each with wet crude handling facilities designed to process up to 50% formation water cut. Existing water processing facilities feature free water removal from both wet tanks and from the wet crude desalting system (Fig. 1). The wet tanks remove the majority of the formation water and the desalting system removes the balance of 1 to 5%. The wet crude oil is mixed with low salinity aquifer water in the desalter vessels to reduce the salt content. This combined water stream is known as the desalter effluent stream.

The low salinity brackish water is pumped from underground aquifers to a two stage electrostatic desalting system. Salt removal is achieved by physical dilution with aquifer water and by coalescence to remove the last traces of the high salinity formation water. The removal of this high salinity formation water, which approaches 250 gm/l (87,000 ptb), is key to achieving an oil export specification of 0.1% BS&W with a 5 ptb salt concentration.

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