Shale Gas and Groundwater Quality A literature review on fate and effects of added chemicals Alette Langenhoff 1202141-008 © Deltares, 2011 1202141-008-ZWS-0001, 28 December 2011, final Contents 1 Introduction 1 2 The process of fracturing or fracking 5 3 The use of chemicals 7 4 Polyacrylamide 8 4.1 Aerobic degradation of polyacrylamide 8 4.2 Anaerobic degradation 10 4.3 Chemical or physical removal 10 4.4 Conclusion on removal of polyacrylamide 10 5 Glutaraldehyde 12 5.1 Biocide 12 5.2 Biodegradation 12 5.3 Chemical inactivation of glutaraldehyde 13 6 Conclusions 14 7 References 15 Appendices 17 Appendices A Chemicals identified in hydraulic fracturing fluid and flowback/produced water (EPA, 2011). A-1 B Fracturing fluid ingredients and common uses (Europe Unconventional Gas 2011) B-1 C Properties of Polyacrylamide (source: Wikipedia) C-1 D Properties of Glutaraldehyde (source: Wikipedia) D-1 Shale Gas and Groundwater Quality i 1202141-008-ZWS-0001, 28 December 2011, final 1 Introduction Shale gas is a so-called unconventional sources of natural gas, and is one of the most rapidly expanding trends in onshore domestic oil and gas exploration and production today (Fig. 1 and 2). Shale gas is present in hydrocarbon rich shale formations. Shallow gas is commonly defined as gas occurrences in unconsolidated sediments of Tertiary age (often down to depths of 1000 m below surface). The occurrences are positively associated with thick Neogene sediments and are often trapped in anticlinal structures associated with rising salt domes (Muntendam-Bos et al, 2009). Shale has low matrix permeability, so gas production in commercial quantities requires fractures to provide permeability. Hydraulic fracturing (fracking) creates extensive artificial fractures around well bores, making gas exploration possible. Figure 1 Conventional gas and shale gas exploration (source DTE Energy) Shale Gas and Groundwater Quality 1 1202141-008-ZWS-0001, 28 December 2011, final Figure 2 Detail of onconventional gas and shale gas exploration (Time, april 2011)) Shale gas has become an increasingly important source of natural gas in the United States over the past decade (Fig. 3), and interest has spread to potential gas shales in the rest of the world. It is believed that also Canada and Europe (e.g. in the Netherlands and Poland) will have large supplies of shale gas (Muntendam-Bos et al, 2009). Other advantages are the reduced CO2 emissions compared to charcoal or oil, and the independency of foreign supplies. Shale Gas and Groundwater Quality 2 1202141-008-ZWS-0001, 28 December 2011, final Figure 3 Expected natural gas supplies in the US, including shale gas. Europe’s dependency on natural gas is already considerable, with conventional gas accounting for 25% of the primary energy need. Half of this natural gas comes from intercontinental imports (pipeline and shipments). Off-setting the decline of Europe’s indigenous gas production from conventional fields by the development of indigenous unconventional gas fields could lower its dependency on imports from abroad. The unlocking of Europe’s unconventional gas resources therefore would increase the security of gas supply (Weijermars et al, 2011). Shale gas development requires significant amounts of water (hydraulic fracturing) and is often conducted near valuable surface and ground water. Hydraulic fracturing is a well stimulation technique used to maximize production of oil and natural gas in unconventional reservoirs, such as shale. During hydraulic fracturing, specially engineered fluids containing chemical additives and proppant1 are pumped under high pressure into the well to create and hold open fractures in the formation. These fractures increase the exposed surface area of the rock in the formation and, in turn, stimulate the flow of natural gas or oil to the well bore. As the use of hydraulic fracturing has increased, so have concerns about its potential environmental and human health impacts. In the US, many concerns about hydraulic fracturing focus on potential risks to drinking water resources (EPA, 2011). Questions on the impact of such activities arise, e.g. the nature of shale gas development, the potential environmental impacts, and the ability of the current regulatory structure to deal with this development. 1. Proppant; Suspended particles in the fracturing fluid that are used to hold fractures open after a hydraulic fracturing treatment, thus producing a conductive pathway that fluids can easily flow along. Naturally occurring sand grains or artificial ceramic material are common proppants used (source; Wikipedia). Shale Gas and Groundwater Quality 3 1202141-008-ZWS-0001, 28 December 2011, final In the Netherlands, the British company Cuadrilla had successfully applied for a permission for a shale gas test drilling in Boxtel, in the province of Brabant. This has caused a lot of commotion in the Netherlands. In response to this public concern about announced test drillings in the Netherlands, the ministry of Economic Affairs, Agriculture and Innovation (EL&I) has announced that independent research has to be carried out before any further activities are allowed. We have discussed shale gas exploration and possible impacts with various stakeholders, e.g. the Ministry of Infrastructure and the Environment (I&M), the Ministry of Economic Affairs Agriculture and Innovation (EL&I), DG Environment EU Brussels, Nicole (Network for Industrially Contaminated Land in Europe), TNO, KWR, RIVM, and Shell. It became obvious that stakeholders need an objective source of information on the impact of shale gas development. During a brainstorm session on shale gas by Deltares and TNO, the following research questions were identified: • Risk analyses, including leaking of well-casings; • Groundwater management; • Water cycle; • Monitoring. An integrated approach of these topics is foreseen and we have further discussed the formation of a consortium of TNO, Deltares, RIVM and KWR, to work on these topics. This report gives a literature review on one of the environmental impacts of shale gas exploration: the effects of the chemicals used in the fracturing process. A short description of the fracturing process is given, followed by the chemicals that are used, the degradability of the chemicals, followed by a conclusion on the environmental impact of these chemicals. Shale gas exploration uses fracturing fluids of different volumes and compositions. Chapter 3 describes the numerous chemicals that are mentioned to be used in the US and Canada. Cuadrilla, the company that is planning the first bore drilling in the Netherlands, has mentioned to use only two chemicals, polyacrylamide and glutaraldehyde. Therefore, this report will be limited to those chemicals reported to be used in the Netherlands. Other effects on groundwater quality are the release of salt, metals, methane and radioactive compounds from deeper layers. These topics are beyond the scope of the current literature review and will not be discussed in this report. Shale Gas and Groundwater Quality 4 1202141-008-ZWS-0001, 28 December 2011, final 2 The process of fracturing or fracking Hydraulic fracturing is the propagation of fractures in a rock layer caused by the presence of a pressurized fluid, in order to release the poresent natural gas (Fig. 4). The energy from the injection of a highly-pressurized fracking fluid, creates new channels in the rock which can increase the extraction rates and ultimate recovery of the natural gas. The fracture width is typically maintained after the injection by introducing a proppant into the injected fluid. Proppant is a material, such as grains of sand, ceramic, or other particulates, that prevent the fractures from closing when the injection is stopped. Figure 4 The process of hydraulic fracturing (EPA, 2011) The fracturing process consists of a series of injections using different volumes and compositions of fracturing fluids (GWPC & ALL-Consulting, 2009). Sometimes a small amount of fluid is pumped into the well before the actual fracturing begins. This “mini-frac” may be used to help determine reservoir properties and to enable better fracture design (API 2009). Shale Gas and Groundwater Quality 5 1202141-008-ZWS-0001, 28 December 2011, final In the first stage of the fracture job, fracturing fluid2 (typically without proppant) is pumped down the well at high pressures to initiate the fracture. The fracture initiation pressure will depend on the depth and the mechanical properties of the formation. A combination of fracturing fluid and proppant is then pumped into the well in varying amounts and concentrations. After the combination is pumped in, a water flush is used to begin flushing out the fracturing fluid (Arthur et al., 2008). 2 Fracturing fluid; The fluid used during a hydraulic fracture treatment of oil, gas or water wells. The fracturing fluid has two major functions: (1) Open and extend the fracture, (2) Transport the proppant along the fracture length (source; Wikipedia). Shale Gas and Groundwater Quality 6 1202141-008-ZWS-0001, 28 December 2011, final 3 The use of chemicals The make-up of fracturing fluid varies from one geologic basin or formation to another. Evaluating the relative volumes of the components of a fracturing fluid reveals the relatively small volume of additives that are present. Overall the concentration of additives in most fracturing fluids is relatively consistent, 0.5% to 2%, with water making up 98% to 99.5% (GWPC & ALL-Consulting, 2009). In 2009, a review of chemical use in fracking operations by the New York State Department of Environmental Conservation’s Division of Mineral Resources listed 257 additives that may be mixed with the water injected into shale formations during the fracking process. They provided a breakdown of the known chemicals that stretched 10 pages long, including carcinogenic chemicals (Parfitt, 2011). In 2011, the EPA has compiled a list of chemicals that are publicly known to be used in hydraulic fracturing (Table A). However, the chemicals in this table do not represent the entire set of chemicals used in hydraulic fracturing activities.