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Working with water

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Oilfield Technology,

Gareth Digges La Touche, Golder Associates, UK, shows why responsible access to shale resources begins with comprehensive water management strategies.

Getting water management right is one of the absolute essentials for shale operations. Only through an end-to-end approach can companies secure the permits and social licence to operate needed for responsible access to shale resources. Everything from identifying water sources, through to transport, storage, stimulation, flowback, treatment, reuse and disposal has to be done with the bigger picture in mind. Having worked with many of the major North American and European operators, it has become clear just how important operational best practice across the entire water supply chain is. On the way to best practice, however, operators have to beware of a whole range of issues.

Figure 1. The water lifecycle.

The scale of water use

To start with, it is important that the industry recognises the correct scale of water use in shale operations. A persistent myth is that hydraulic fracturing uses large amounts of water. To realise that this is incorrect, it is necessary to understand the broader context of industrial water use. This can easily be illustrated from a UK perspective.

Typical hydraulic fracture stimulation will use approximately 1000 - 5000 m3 of water – somewhere between a half and two Olympic swimming pools. As an example, if one assumes operators drill 20 wells a year and stimulate 20 stages in each well, they will use around 2 000 000 m3 per year, by way of comparison this is less than 0.01% of the total amount of water abstracted in England and Wales each year. This is unlikely to be a large pressure on the overall demand for water supply.

Water use in shale extraction is thus not an issue of companies exhausting large quantities of water. Instead, the important thing to focus on is how operators can take an integrated approach that allows everyone involved in an project to be aware of the effects of water use on their operations, and vice versa.

The water supply chain

The most proactive way to handle water management is thus through the project supply chain (Figure 1). Different teams traditionally work with different aspects of water management; but if operators are able to develop an integrated approach, they can better identify potential weak links, explore alternatives and develop practical mitigation solutions. Water management should also be approached with a cautionary attitude. Operators must consider any potential scenario and protect against the risks involved with appropriate measures – as with any standard risk assessment procedures.

To this end, using a dynamic simulation model to calculate the current and future water demands of a project will let operators compare different scenarios for water management. Golder develops dynamic system simulation models that represent and integrate all stages of water supply, use, and treatment over the full lifecycle of a project. This gives operators the complete view of water management, helps them adapt to changing conditions and aligns them with industry best practice for water management, such as that published by the IPIECA.

Importantly, every potential water source has to be assessed thoroughly for each project. There is no ‘one-size-fits-all’ solution. Water management must instead be tailored to local conditions. These will always vary, but competition with other industries and local residents for water is a common concern – securing a supply at the expense of local farmers’ irrigation sources is hardly a viable solution. It is also important to be aware of local and national regulations on water use and disposal in the operating area.

Transportation becomes a further concern if nearby surface and ground water resources are not sufficient, which is often the case. Water will then have to be supplied via pipelines or by road, depending on accessibility and infrastructure. Local water storage must also be developed. During initial stages of operations, transport vehicles will normally be the means of choice for supplying water to a site; but as extraction continues, pipelines may become more suitable, even though this will increase capital expenditure.

Flowback and produced water

An integral part of water management is the treatment, reuse and disposal of flowback and produced water recurring after stimulation. On average, 25% to 75% of injected water flows back within one to five weeks. Flowback is then replaced by produced water, which comes from the rock formation itself. Both flowback and produced water can, in many situations, be reused several times for subsequent hydraulic fracturing operations before it has to be subject to intensive treatment; this is a good way of decreasing competition with other water users. Produced water, however, may not suitable for other uses without significant treatment, as it comes from hydrocarbon bearing formations.

Figure 2. Golder Associates’ personnel undertaking water management activities at an unconventionals site.

Flowback and produced water also create environmental risks that must be considered as part of all hydraulic fracturing. This is an area where operators can allay many local stakeholder concerns by demonstrating best practice. The early flowback and later produced water must be kept in lined reservoirs or tanks, depending on the local regulatory regime, with leak control systems, on site or in a centralised location. The storage space must not only have sufficient capacity for storing all the water while allowing for precipitation, but also be able to withstand storm events. It is essential to have detailed engineering controls during the construction process of the water facilities to verify its structural integrity and ensure the highest quality assurance.

Water contamination from fracking fluids must also be considered. While there have been few independently verified examples of aquifer contamination from fracking fluid in the United States to date, there has been some evidence of change in methane content in some shallow aquifers. This can be attributed to poor well construction or legacy contamination, where operations have ceased, but management has grown negligent. Strong regulatory processes in the UK and Europe significantly reduce the chances of such containment from fluid storage facilities – but these cases also demonstrate the importance of having proper well engineering.

Well design and reservoir analysis

Designing wells for unconventional gas exploration and extraction should, in fact, not be underestimated as an engineering challenge. No shales are the same and hydraulic stimulation will inevitably create different reactions even within the same shale play. Without an accurate analysis of a reservoir, this process is difficult to predict and can become a major headache for operators.

Using discrete fracture network (DFN) modelling to analyse the reservoir goes a long way in minimising risks. Figure 2 shows an example of how FracMan – a comprehensive DFN-technology – assesses a reservoir this way. A 3D simulation approach based on input of geomechanical data, seismic attributes and other local features provides a visualisation of the drilling process revealing the presence of any critically stressed fractures and the simulation and design of induced hydraulic fractures. This technology has been developed over the past 25 years and has featured collaborative thinking and insight from both clients and Golder Associates’ geoscientists and reservoir engineers.

Figure 3. FracMan naturally fractured reservoir model.

The analyses generated are subsequently compared to measured seismic data to calibrate the models and make sure they are representative. With this analysis, operators can identify the structural characteristics of the reservoir before drilling and stimulation, as well as defining the extent of the induced fractures within the formation, providing a means not only to demonstrate to local stakeholders how the fracturing process is managed, but also to enable the optimisation of development and production. With some local stakeholders being concerned about the impact of shale extraction on ground water, such communication is an important part of the broader water management strategy.

Once the reservoir has been analysed, the next step is constructing a well to the highest standard. This is crucial because without good cementing and casing, even exceptional designs are worthless. Not only will correct well completion help prevent the migration of natural gas into water-bearing formations, it is also in the best interests of the investor from a technical and economical point of view, since any escape of the gas flow outside of the wellbore will result in significant economical loses and could even cause abandonment of the well.

Figure 4. Learning from those who have successfully worked on unconventional oil and gas operations in the past is essential for effective and responsible water management.

Water reuse and disposal

As for the treatment, reuse and disposal of water, operators need to shape their approaches based on their overall water strategy. Meticulous planning of the supply chain can save money, minimise risk and secure sustainability. There is a growing emphasis in the industry on the recycling and reuse of water, leading to advances in technology, which can only be a good thing.

Specialised plants capable of cleaning flowback and produced water already exist, but not necessarily in the same locations where operators extract gas. A mobile treatment plant is then typically used. An issue that is becoming increasingly scrutinised by the industry is the fact that existing water laws in Europe, the Water Framework Directive and its daughter directives, pre-date the ‘shale boom’. In some new instances the implementation of these laws can be unclear and will possibly change as hydraulic fracturing becomes more prominent in Europe.

Finally, some disposal of water will always be necessary. Currently, the most feasible way is to transport water off site in vehicles or through a pipeline for disposal in special facilities, although using pipelines is not yet common in Europe. Other possibilities are evaporation ponds or direct disposal on site following extensive treatment; however, local communities are likely to resist this vehemently, and Northern and Eastern Europe do not have the appropriate climate for evaporation ponds. It is also important to have a back-up solution, such as emergency storage facilities, in case the chosen disposal method becomes temporarily unavailable. By establishing plans for this early, and understanding the water lifecycle, hydraulic fracturing is far more likely to satisfy social, environmental and regulatory demands.

Watertight strategies

Although the shale industry is still comparatively new in Europe in general, in the UK in particular onshore oil and gas exploration and development is not. While there are similarities there are also differences and companies across Europe should look to shale projects in other jurisdictions for lessons as to how to economically and responsibly extract unconventional hydrocarbon resources. Learning from those who have successfully worked on unconventional oil and gas operations in the past is essential. This is certainly also true for water management. Being aware of all the pitfalls takes time, but not being aware of them will be costly.

By adopting best practice water management, operators will not only establish a better reputation and significantly increase business opportunities, but could, over time, also begin to change the perception of the broader unconventional industry as a whole. From analysing with DFN-technology to creating watertight water management strategies, every part of shale projects has to be of the highest standard and planned well in advance. With a comprehensive water management strategy in place, operators will be one step closer to responsible shale gas development.

Adapted by David Bizley

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