Distribution, Gas, Markets, Projects, Technology

Managing water for unconventional gas developments

The most relevant experience for Australian projects originates from the USA, where many operators have learned the hard way.

Some operators in the Marcellus shale region of the USA delayed water management planning and were forced to pay upwards of $US500,000 per well to dispose of spent hydraulic fracturing (HF) fluids.

When decisions are not made early, or are not implemented in a timely manner, the number of possible water management options may decrease, and the costs can escalate by an order of magnitude.

A Decision Framework can be used to define the variables that impact HF water management options, and identify the best strategy, such as recycling, reusing or disposal.

Decision Framework

The Decision Framework consists of five key drivers:

  • Hydrology of the field (or region) – is fresh water available?
  • Regulatory requirements and community concerns – is injection disposal an option?
  • Fracture fluid quality required – can saline water be used for HF fluid make-up?
  • Flow-back fluid characteristics – is the flow-back fluid saline?
  • Stage of field development – what kind of equipment is appropriate?

The first two questions define whether the reuse or recycling of flow-back fluids is needed at all.

In some regions where shale and coal seam gas resources are found, there is plentiful fresh water available.

In other locations, water is scarce and can be sourced from brackish or saline aquifers using reverse osmosis.

Regulations, often developed at a regional government level, set strict constraints on the disposal of flow-back, produced water and any waste generated from flow-back treatment.

Community concerns are as important because regulations, as public pressure can delay, limit or prevent certain disposal options or even stop development.

The next two questions define whether desalination is required.

The optimal HF fluid type may or may not require fresh water makeup.

If low-salinity water is required for fracture fluid makeup and if the flow-back water has high salinity, then desalination is required.

In addition, the type of fluid used will dictate the level of pre-treatment required.

The cost model

The final step in selecting the most appropriate water management strategy is to develop a detailed cost model and systematically analyse the options.

The cost of water management options for any given field depends on the location.

Factors that can influence the cost of water treatment include remoteness, regulatory practices, and availability of staff and materials.

The cost model starts with an understanding of the local regulations and hydrogeology.

The hydrogeology will define water availability for use in drilling and completion.

Regulations define the constraints for disposal.

Within these two constraints, more precise options are developed by considering the fluid types, and the stage of field development.

In addition to fluid types pumped into the well, the characteristics of the flow-back fluid must be considered.

Salinity (TDS), the composition of dissolved components and the presence of particular contaminants such as iron, boron, and scaling components must be known.

The pumped and flow-back fluids have important effects on the type of water treatment technology that will be required, and the likelihood that the fluids will need to be reused or recycled.

Once the regulatory, hydrogeological and fluid-type constraints are known, early water management options can be evaluated.

Early options will be different from later options.

Water treatment at the beginning of development must deliver water – using appropriate technology – to the well site without the benefit of a water pipeline or gathering system afforded to a centralised treatment system.

There are four water treatment categories: minimal, mobile, modular, and centralised.

The cost drivers for each type are significantly different.

Minimal treatment includes course filtration and chemical treatment for biological control and scale inhibition.

This treatment is used for disposal well injection.

Mobile technologies are required at an early stage of development when limited infrastructure is available for transporting water.

This category covers a range of treatment technologies.

The capital cost of the equipment is rarely a factor in determining the overall of cost of treatment.

Instead, the cost depends on the number of staff required to operate the equipment and the water processing rate.

Modular technologies can be used when clusters of wells are developed.

Water from one well can be treated and used on the next well in the cluster.

This involves skid-mounted equipment loaded on one or more trucks, which is delivered to site and constructed in a timely manner.

The cost of a mobile system depends on the required mobilisation and demobilisation.

Centralised facilities offer the greatest number of treatment options and the lowest per barrel costs.

These facilities employ traditional industrial water treatment technologies (primary, secondary, tertiary) and result in brackish or potable water quality.

An extensive gathering network is required to transport the water to the centralised treatment plant and dispense the treated water to environment or further treatment systems.

The cost model must be developed before field development commences.

Initially, it will be based on data from other regions, tailored to the local regulations and hydrogeology.

Once field development commences, the model can be updated with actual field data.

The model must be updated periodically as additional wells are drilled and the field develops.

During field development, the number and type of water treatment options will change and opportunities may emerge to reduce costs further.

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