Unconventional gas is predominantly methane and can exist in various forms. Given today’s technologies, the most commercially viable are coalbed methane (CBM) and shale gas.

CBM is methane gas that is locked within unmined coal seams. The International Energy Agency estimated that CBM made up 10 percent of the total gas production in the USA in 2008. In China, CBM was made one of the 16 priority projects in the 11th Five Year Plan.

Shale gas deposits are trapped within sedimentary (shale) rock, which has very low porosity and permeability. This presents challenges in extracting and producing the gas and stimulation is required to allow the gas to move freely from its tight pockets to the wellbore. Such gas is therefore extracted principally by horizontal drilling and hydraulic fracking techniques.

The majority of unconventional gas exploitation will target shale gas deposits and play an increasingly important role in the worldwide energy supply market. This is because the demand for a sustainable, cheap source of energy has never been more prevalent and natural gas is considered a cleaner resource, as methane combustion produces half as many CO2 emissions compared to coal or oil.

A report by NEL, supported by the UK’s National Measurement System, ‘Waste Water Metrology Challenges Related to Unconventional Gas Production in the UK’, predominantly focuses on CBM and shale gas exploration and production, and its findings are highlighted in this article.

The success of unconventional gas has been led by North American operators, and companies are preparing the ground for a similar economic boom in Europe. This has been attributed to a number of reasons including good infrastructure, vast reserves of unconventional basins, the political environment moving towards more energy self-sufficiency, and a well established upstream oil and gas industry.

Over the last ten years US shale gas production has increased 12-fold and now makes up about 25 percent of the country’s total gas production. In the coming years the USA is expected to move from being a net importer to a net exporter. Also, there are plans for the USA to exploit reserves of unconventional oil, which could see it becoming the world’s largest oil producer within the decade.

It has also been reported that almost 40 percent of global CBM methane reserves are located in Australia, China, India and Indonesia, with Australia currently leading the development and production. There is, however, huge potential for market growth in Asia, especially as China has been using significant amounts of coal for energy generation over the last two decades. Chinese energy companies are investing in shale gas exploration projects as the country seeks to boost investment in unconventional energy and replicate the success of the shale gas revolution in the USA.

In Europe, the European Commission’s Energy Roadmap 2050 has identified natural gas as a critical fuel for the transformation of energy supplies. Indeed, there is a strong argument for shale gas production in Europe as North Sea production continues to decline. In 2011, the EU recorded the largest decline in gas production on record (-11.4 percent), due to a combination of mature fields, maintenance and weak consumption. A European shale gas boom, similar to that experienced in the USA, could have the potential to offset the steady decline in domestic production of conventional gas. There are other positives as well. These include:

• Europe will not have to rely on foreign gas imports. For example, the Arab Spring and Russian gas disruptions have demonstrated that Europe should have less reliance on foreign imports

• Improved diversification of supplies could improve the European Union’s bargaining position as a gas consumer

• As shown previously, unconventional gas reserves are geographically dispersed. This distribution could reduce any nascent gas cartel’s power to control the scarcity, and hence monopolise the price of global natural gas supplies

In the UK a report published in May 2013 by the Institute of Directors showed that the UK has around 300 TCF (trillion cubic feet) of shale gas in place. To put this in perspective, the UK consumes 3 TCF of natural gas per year. The latest July 2013 report published by the BGS (British Geological Survey) estimates that reserves in central England alone amount to approximately 1,400 TCF. It should be noted that not all of the in place reserves can be extracted.

Unconventional gas is therefore an important prospect for the UK, and the industry is being encouraged by the government to explore and develop these unconventional fields. This includes recent government announcements to create a separate department, Office for Unconventional Gas and Oil (OUGO), which will oversee unconventional gas E&P (Exploration and Production) activities. It has also given the ‘green light’ to construct up to 30 gas fired power generation plants, as well as promising tax breaks to operators. As a result, unconventional gas reserves in the UK are expected to be explored and produced steadily in the years to come.

The USA is expected to overtake Russia as the world’s largest gas producer within the next two years as a result of the shale gas boom. In contrast, since 2004 the UK has been a net importer of gas as North Sea production steadily declines. Europe should be approaching the dawn of shale gas with a degree of caution as there are still a number of uncertainties as to whether the USA’s success story can be replicated.

While there is a huge appetite for operators and stakeholders to be involved in this new energy sector, companies interested in the exploration and production of shale gas must consider the environmental implications. Water management remains one of the biggest challenges they must plan for and carefully tackle.

Reducing risk

Hydraulic Fracturing (HF) or ‘fracking’ is a well proven technology that involves injecting large amounts of water, mixed with sand and small traces of chemicals at high pressures to break up the sedimentary rock to release the gas. This process induces small cracks which in turn allow gas to flow more freely. If full development is warranted, companies drill horizontal wells through the gas bearing rock, and fracture the shale play along the entire horizontal leg.

One of the key environmental challenges for regulators lies with the high volume of flowback water associated with the hydraulic fracturing processes and subsequent produced water related to production. This by-product of fracturing can also contain significant levels of contaminants and requires further treatment prior to disposal or re-use. The total volume of water required to fracture a typical well can be some 20,000m3 (equivalent to the volume of eight Olympic sized swimming pools), with up to 40 percent of the original HF volume being returned to surface within the first 30 days of fracturing.

The risks associated with hydraulic fracturing can be managed. This can be achieved through the implementation of appropriate and comprehensive regulation and legislation as well as industrial best practises, but the regulatory framework in Europe for water treatment and discharges shows some gaps, and there is now an onus on European regulators to have rules in place by which operators must abide to control the environmental impact of waste water (flowback and produced water).

Europe can learn vital lessons from the USA shale gas experience, where natural gas production, including shale gas, is regulated by a complex set of federal, state and local laws that address every aspect of oil and gas exploration. In the USA there are regulations currently in place for pre-treatment discharge standards. These standards ultimately state the requirements of flowback water quality before it can be sent to waste water treatment or sewage plants, with new rules expected to be introduced in 2014.

According to current EU law, flowback water must be re-injected into underground wells or transported for further treatment at water treatment sites.

Dealing with waste water

The vast quantities of water required for fracturing operations presents many challenges as it must be sourced, monitored and transported to site with the returned flowback fluids disposed of or reused appropriately.

One vital consideration is that both water to be used for fracturing and the resulting waste water must be transported economically and sustainably. Typically, operations may require up to 300 truckloads of water to be transported to a well site. This alone presents a number of issues as truck emissions could undermine shale gas being considered a greener option in developing sustainable energy sources.

There are, however, a number of options including trucking, using existing pipelines, building new pipelines and above-ground temporary transfer.

Waste water treatment can be complex as it has wide and rapidly variable flowrates, contains varying concentrations of oils, salts and pH, and may have difficult to treat chemicals present – particularly gels and polymers. During the initial extraction high concentrations of sand will also be present in the flow.

In the USA, the Environmental Protection Agency has stated that “Currently wastewaters associated with shale gas extraction are prohibited from being directly discharged to waterways and other waters of the US. In order to meet this prohibition, some of the shale gas wastewater is reused or re-injected, but a significant amount still requires disposal. Some operators re-inject the wastewater into disposal wells.”

It is clear that waste water from fracturing operations cannot simply be discharged into watercourses. To allow for discharge, the waste water must be treated to an appropriate standard. This may be achieved by a specialised treatment facility onsite or trucking the water to a centralised waste water treatment plant. The plants themselves must be responsible for setting out guidelines regarding what the specification should be for any waste water arriving on their site.

As the European unconventional gas industry is still in its infancy, there has yet to be a standard set of regulations which are specifically designed to govern the management and measurement of flowback and produced water. Scotland, however, is already one step ahead as SEPA (Scottish Environmental Protection Agency) and has produced a set of guidelines for operators with unconventional gas interests.

As the unconventional gas industry matures in Europe, and regulations evolve, operators must therefore be prepared to manage flowback and produced water in a cost effective manner that complies with those regulatory requirements. The primary options for them will be to inject underground through a disposal well or to reuse for future fracturing jobs.

The re-use of flowback and produced water represents economic savings as the water does not need to be transported great distances for disposal. Indeed, it has been reported that there is a substantial increase in reusing the flowback water in Pennsylvania, from some 15% in 2009 to 76% in 2012. Such recycled water will, however, still have to meet certain specifications, with key treatment objectives including the removal of residual oil, friction reducers, polymer additives, salts, bacteria and Naturally Occurring Radioactive Material (NORM).

Two other options are also possible, but both present limitations due to issues with total dissolved solids (TDS) within the produced water. The first is to transport the water to a municipal waste water treatment plant but, depending on the contaminant within the water, the plant may not be able to accept it for treatment. A second option is to transport the produced water to a commercial industrial waste water treatment facility, but again the level of TDS and the specific compositions present may cause problems and result in violating surface water quality.

Future action

To meet regulations, any flowback and produced water from unconventional gas E&P will need to be measured by means of a flow meter prior to storage or transportation in trucks. Measurement of unconventional gas is believed to be not inherently different from that of conventional gas, with many operators adopting topside multiphase/wet gas flowmeters for process control and monitoring.

Electromagnetic meters, which measure volumetric flowrate, may be used for most aqueous solutions, but not for metering gases or oils. Such meters have the advantage of being unaffected by either fluid density or viscosity, and they are also non-intrusive.

While the quantity of produced water decanted into large vessels or storage tanks prior to further treatment and disposal is expected to be recorded for regulatory and operational purposes, the associated measurement uncertainty has yet to be defined. There is a need to establish some guidance regarding acceptable uncertainty requirements.

While the unconventional gas sector has proved to be hugely successful in the USA and Australia, a number of challenges with regard to water management exist in the UK and Europe. There is also a significant challenge in educating and convincing local communities and the general public that hydraulic fracturing is a well practised operation and that flowback and produced water from unconventional gas E&P can be managed with proper regulations and best practise.

In the UK underground water extraction and discharge of waste water is regulated by the Scottish Environment Protection Agency (SEPA) in Scotland, the Environment Agency (EA) in England and Wales, and the Northern Ireland Environment Agency (NIEA) in Northern Ireland. Specific regulations related to water use and waste water discharges associated with unconventional gas E&P are being established. Guidance on measurement and associated uncertainties should be considered.

While the regulators establish clear specifications for the discharge quality of waste water, it is critical that operators keep abreast with evolving local and national legislations. It is also important that the industry as a whole continues to encourage dialogue between all stakeholders, including academia, service companies and operators, so that challenges associated with the water management of unconventional gas can be discussed, experiences shared, and issues tackled.

To address some of the community issues and to establish a knowledge base as well as to provide transparency of the unconventional gas E&P operations, in particular regarding hydraulic fracturing and water management, NEL is currently in discussion with government bodies, operators and industrial associations to create a web-based technical forum.

The forum will cover topics such as water management, hydraulic fluids and fracturing, environmental and community issues. Its key objectives are to provide information, to keep abreast with technological and legislative developments, to promote best practise, and to bridge the various groups including operators, regulators, technology providers, local communities and the general public.

Published: 27th Feb 2014 in AWE International