Water Journal : Water Journal April 2014
WATER APRIL 2014 88 Feature Article The development of unconventional natural gas resources is in the news. In the United States shale gas dominates, whereas in Australia it is coal seam gas -- commonly referred to as CSG. Whether we are talking about shale gas or CSG, the bene ts of tapping such a valuable energy source are often overshadowed by public concerns about hydraulic fracturing and the disposal of water resulting from natural gas well development and production. Water issues pertaining to the various types of unconventional gas are common and share many similarities. Solving this part of the water- energy nexus is the key to success in this segment of the upstream energy sector in the US, Australia, China and any other part of the world. Figure 1. 2011 PADEP data. It is not surprising that gas producers and water treatment service providers have made signi cant progress in managing the water and acquiring a good understanding of the issues that have an actual or perceived impact on the industry, regulatory agencies, academia and the general public. Sizeable research dollars are being directed at nding better treatment methods, and the industry has become more proactive in reaching out to various stakeholders. As a result of all this activity, the unconventional water treatment industry is itself in the limelight. Media events and unconventional water treatment conferences are plentiful, and seemingly limitless related content can be found on the Internet (although one must be careful about the accuracy of online sources). A lot has been accomplished, yet much remains to be done. Areas of impact include water management infrastructure, government regulation and water treatment technology solutions. Even though CSG is the current focus in Australia, shale gas is also gaining interest. A simple comparison between shale gas and CSG will help explain the differences in wastewater management approaches. First, the shale wastewater volumes are signi cantly lower than those produced in a CSG operation. Hydraulic fracturing of shale requires approximately 15 megalitres of water per well, with 10% to 15% coming back to the surface after completion of fracturing. In addition, shale gas generates wastewater for a shorter duration -- one time per well from drilling and hydraulic fracturing. In comparison, CSG has insigni cant volumes during drilling, but peak volumes last months as the well is put into gas production. A typical CSG well may generate up to 300ML of wastewater over 18 months. Thus, in essence, shale gas fracturing is a water-negative operation compared to CSG, which is a net water producer. THE THREE 'R'S (OR AT LEAST TWO) All differences aside, the basics of water treatment and its management don't change. We were taught the value of the "Three Rs" in school; when it comes to unconventional gas water treatment, the Three Rs stand for Reduce, Recycle and Reuse. "Reducing" is often more challenging than the other two Rs. As a rule, Recycle/Reuse remains the cheapest -- and by far the most effective -- form of water management in the unconventional gas industry. The approach bene ts several gas well development cost accounts and is environmentally bene cial. Since shale gas is water- negative, recycle/reuse at a multi-well pad or another nearby well pad, by moving water via piped network to reduce trucking is a cost- effective, environmentally conscious and public-friendly approach to solving the waste disposal. The data points to industry making efforts to maximise reuse and save cost. On a standalone basis, it sounds like a bottom-line driven effort. However, it is not that simple. Recycle/reuse takes a conscious effort and requires development costs in creating the appropriate infrastructure and setting relevant goals for the operating team. On the upside, recycle/reuse reduces the cost of sourcing water for well development and for disposing of the water. LESSONS LEARNED IN UNCONVENTIONAL GAS MINING WATER MANAGEMENT Devesh Mittal discusses the interplay of infrastructure, regulation and technology in better managing the unconventional natural gas wastewaters in Marcellus Shale.
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