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John Crane - A part of Smiths Group

Water treatment and injection system specification

A prerequisite for any successful and cost-effective water injection or water disposal process, is a thorough understanding of the chemical and physical composition of the water (or waters) involved, together with a rigorously defined water injection specification, such that sustained injection/disposal, without undue injectivity issues, can be achieved. Only once these parameters have been defined can the most appropriate water treatment system be specified.

Flooding with poor quality water can lead to plugging of the reservoir and loss of injectivity, which in turn necessitates the use of higher than anticipated injection pressures (and possible, inadvertent hydraulic fracturing of the reservoir), expensive well work-overs, and in the most extreme cases, total loss of affected injection wells. Despite this, it is not always necessary to improve water quality, some source waters are naturally clean (e.g. most aquifer waters) and some (high permeability) reservoirs will accept poor water quality without suffering injectivity losses. 

Any water injection specification must be realistic with respect to capital and operating costs of the water treatment design required to achieve sustained injection, and is unique to each reservoir. The specification should consider untreated water quality, porosity/permeability characteristics, fracturing potential, treatment constraints, the injection philosophy of the operator, life of the project, and the compatibility of the injection water with reservoir rock and the formation water.

John Crane’s Oil Plus team has developed an approach to defining a water quality specification to assist those who are looking to set the parameters for a water treatment plant.

Source waters

Produced water is widely used as a source water for injection to maintain pressure in, or water flooding, the reservoir. Re-injection of produced water is one option that offers a solution to the problem of disposal, however availability of produced water is often insufficient for waterflood requirements and often needs to be commingled with another type of source water e.g. aquifer, lake/river, or sea water. When undertaking characterization studies of source waters a number of physical and chemical characteristics must be established.

Our team can assist with on-site sampling and laboratory analysis studies, providing recommendations on the ‘ideal’ injection specification for the water treatment plant.

Scaling and water compatibility

Scale formation can be a costly issue, both in terms of production down-time and equipment replacement, therefore the compatibility of the various waters that are used within a water injection system needs to be carefully considered.

Our team has the capability to determine the scaling tendency and potential volume of scale production under a variety of operating conditions which are matched to actual field observations. This data can be used to provide a mitigation strategy for the water treatment system.

Reservoir Souring

When selecting a water source for use in pressure maintenance or sweep, the microbially mediated generation of hydrogen sulphide (H2S) should be considered. Options to prevent reservoir souring range from the conventional use of biocides through to modification of the microbial population by, for example, nitrate treatment, or even sulphate removal.

Our team can provide souring predictions for production facilities in the early design stage as part of an overall field development plan, as well as recommending a remedial strategy for existing fields to improve reservoir conditions, increase production and more importantly, improve health and safety conditions for personnel running the water treatment system.

Environmental Analysis

The composition of oilfield produced water is often very complex and many of the components are toxic and detrimental to the environment at large.

Whether it’s being treated for surface disposal or re-injection, a full and thorough understanding is essential for any successful treatment design in terms of minimizing the effects of dissolved or dispersed contaminants on water quality.

Troubleshooting

Poor performance of process systems can lead to bottlenecks, non-compliance with environmental legislation and a risk of creating a local environmental incident. The root cause of these is frequently poor system operation or quite simply producing at rates in excess of the original design capacity.

Maintaining or improving the performance of existing water injection systems can help sustain - or in some cases - improve current production. Our team has all the required expertise and experience supported by all the necessary laboratory facilities, specialist on-site equipment and process simulation software to develop and achieve the most cost-effective solution for your operational issues.