Produced Water Management and Beneficial Use

Large quantities of water are associated with the production of coalbed methane (CBM) in the Powder River Basin (PRB) of Wyoming. The chemistry of co-produced water often makes it unsuitable for subsequent uses such as irrigated agriculture. However, co-produced waters have substantial potential for a variety of beneficial uses. Achieving this potential requires the development of appropriate water management strategies. There are several unique characteristics of co-produced water that make development of such management strategies a challenge. The production of CBM water follows an inverse pattern compared to traditional wells. CBM wells need to maintain low reservoir pressures to promote gas production. This need renders the reinjection of co-produced waters counterproductive. The unique water chemistry of co-produced water can reduce soil permeability, making surface disposal difficult. Unlike traditional petroleum operations where co-produced water is an undesirable by-product, co-produced water in the PRB often is potable, making it a highly valued resource in arid western states. This research project developed and evaluated a number of water management options potentially available to CBM operators. These options, which focus on cost-effective and environmentally-sound practices, fall into five topic areas: Minimization of Produced Water, Surface Disposal, Beneficial Use, Disposal by Injection and Water Treatment. The research project was managed by the Colorado Energy Research Institute (CERI) at the Colorado School of Mines (CSM) and involved personnel located at CERI, CSM, Stanford University, Pennsylvania State University, the University of Wyoming, the Argonne National Laboratory, the Gas Technology Institute, the Montana Bureau of Mining and Geology and PVES Inc., a private firm

Quantifying PCE and TCE in DNAPL Source Zones: Effects of Sampling Methods Used for Intact Cores at Varied Contaminant Levels and Media Temperatures

An experimental study was completed to assess the impact of sampling methods, contaminant levels, and subsurface temperatures on the quantification of tetrachloroethylene (PCE) and trichloroethylene (TCE) in source zones contaminated by dense non-aqueous phase liquids (DNAPLs). Intact cores of clean aquifer solids (fine-grained uniform sand with low foc) from a DNAPL site in Florida were spiked with neat PCE and TCE to yield concentrations such that DNAPL-phase contamination would be absent or present. Three methods characterized by different levels of media disaggregation and atmospheric exposure (MDE) were used to obtain samples from intact cores, which were at temperatures of 2°C, 20°C, and 38°C. The results of this study demonstrated that sampling of intact cores can yield negative bias, ranging from 0% to 98% or more, in the concentrations of PCE and TCE measured. Larger negative bias was correlated with higher MDE methods, presumably due to elevated volatilization losses during sample collection and containerization. Larger negative bias was also correlated with higher temperatures but only during sampling using higher MDE methods. The results of this study suggest that intact core sampling procedures may or may not lead to erroneous conclusions about a DNAPL source zone. For example, sampling data may lead to a conclusion that a potential source zone has no DNAPL-phase contamination present when in fact it is present, or that remediation has achieved source zone cleanup to a residual concentration goal, when in fact the goal was not met. Conversely, if a remediation goal is to achieve a specified mass depletion level (e.g., 90%), measurement bias may not result in an erroneous conclusion. Further research is planned to examine a wider range of aquifer properties and sampling conditions and to assess the impacts of measurement errors on DNAPL source zone characterization and assessment of remediation performance

The effect of NaOH pretreatment on coal structure and biomethane production.

Biogenic CBM is an important component of detected CBM, which is formed by coal biodegradation and can be regenerated by anaerobic microorganisms. One of the rate-limiting factors for microbial degradation is the bioavailability of coal molecules, especially for anthracite which is more condense and has higher aromaticity compared with low-rank coal. In this paper, NaOH solution with different concentrations and treating time was employed to pretreat anthracite from Qinshui Basin to alter the coal structure and facilitate the biodegradation. The results showed that the optimal pretreatment conditions were 1.5 M NaOH treating for 12 h, under which the biomethane production was increased by 17.65% compared with untreated coal. The results of FTIR and XRD showed that NaOH pretreatment mainly reduced the multi-substituted aromatics, increased the C-O in alcohols and aromatic ethers and the branching degree of aliphatic chain, and decreased the aromatic ring structure, resulting in the improvement of coal bioavailability and enhancement of biomethane yield. And some organics with potential to generate methane were released to filtrate as revealed by GC-MS. Our results suggested that NaOH was an effective solution for pretreating coal to enhance biogenic methane production, and anthracite after treating with NaOH could be the better substrate for methanogenesis

Speciation, Fate and Transport, and Ecological Risks of Cu, Pb, and Zn in Tailings from Huogeqi Copper Mine, Inner Mongolia, China

Tailings collected from the tailing reservoir at Huogeqi Copper Mine, located in Inner Mongolia, China, were used in a leachate study to evaluate the acid potential, neutralization potential, and possibility for producing acid mine drainage (AMD) from the site. The speciation of Cu, Pb, and Zn contained in the tailings was also determined during the leachate study to further access the potential migration abilities of these metals. The results showed that the tailings did not produce significant AMD as the pH of the leachate ranged from 7 to 9 and decreased with time. The Cu, Pb, and Zn concentrations were high, ranging from 439.1 to 4527 mg/kg in the tailings and from 0.162 to 7.964 mg/L in the leachate, respectively. Concentrations of metals in the leachate and tailings were positively correlated. Over 60% of the Cu in the tailing samples existed in an oxidizable form. Most of the Pb also existed in its oxidized form, as did the silicate and Zn. Metals usually have higher mobility in their exchangeable and oxidizable forms and as such represent a higher potential risk to the environment. Results of risk assessment code also revealed that metals in tailings exerted medium to high risks to the environment

Enhanced production of secondary biogenic coalbed natural gas from a subbituminous coal treated by hydrogen peroxide and its geochemical and microbiological analyses

Unmineable coal accounts for over 90% of the world's fossil fuel resources. Fortunately, many coal seams contain indigenous microorganisms capable of utilizing the coal as a carbon source to produce secondary biogenic coalbed natural gas. However, coal bioavailability has been shown to be a significant factor that limits the extent of bioconversion. In this study, we have analyzed the rate and yield of the biogas production and assessed the gas potential, carbon balance, stable carbon isotopes, microbial communities, and microbial pathways changes resulting from the hydrogen peroxide pretreatment with the Wyoming's Powder River Basin subbituminous coal. The results showed that coal pretreated with hydrogen peroxide can significantly enhance the bioavailability of coal for enhancing the biogas production, with a peak yield of 552.6 mu mol/g coal (437.1 Scf/ton coal) at the day 184. The stable carbon isotopic analysis indicated that the delta C-13 values of the methane and carbon dioxide were much less negative than the published field data. This suggested that the enrichment or depletion of the precursor C-13 could contribute to the shift of the carbon isotopic composition in the subsequence processes. Therefore, the data should be used with cautions for interpreting genesis of the thermogenic/biogenic methane and the methanogenic pathways. The methanogenic pathways were also investigated with re-fed experiment and microbial community analysis. The results indicated that the hydrogenotrophic pathway was not active in the original inoculum became activated after the gas production. The microbial community analysis demonstrated that the obligate hydrogenotrophic methanobacterium was the most dominant methanogens in the microcosms after the gas production. This suggested that the chemical treatment of coal has impacts on the microbial structure during the subsequent methane production phase