Sour Gas Plant Research Articles

CO2 Flooding Potential in West-Central Alberta: Generalized BusinessCase of a Medicine River/Gilby Area Mature Waterflooded Reservoir

Abstract There are several maturing waterfloods in the Medicine River/Gilby region of West-Central Alberta which are operating at high reservoir pressures, and are suitable candidates for enhanced oil recovery (EOR) by CO2 flooding. Potential CO2 supplies also exist in the region from various petrochemical, as well as sour gas and solution gas processing plants. A prototype reservoir was selected for a detailed "business case" study. CO2 flooding and geological storage were seen to be feasible in the prototype reservoir based on geological/ reservoir reviews, laboratory testing and reservoir simulation. Economic parameters (payout periods for the investment, rates of return) on risk-weighted basis were moderate in light of front-end capital requirements for extraction, recycle and transportation facilities. The situation would change for the better if regional infrastructure for CO2 capture, extraction and transport is developed. This, in turn, is dependent upon adequate assured demand. On the other hand, demand won't develop unless there is appropriate infrastructure in-place. Fragmented ownership of the resource and of CO2-rich waste gas streams, as well as inertia favouring status quo, are some of the other challenges. We present here a generalized "business case" for illustrating some of the issues of CO2-EOR implementation. Introduction CO2-EOR is receiving increasing attention mainly because of the following emerging trends:Increasing awareness of potential reserves addition by CO2 flooding in mature sedimentary basins such as the Western Canadian Sedimentary Basin (WCSB), based on performance of Weyburn and Joffre Viking CO2 flooding projects in WCSB, and also in various oil fields of West Texas Permian Basin.Growing recognition of the importance of Carbon Capture and Storage (CCS) and anticipated incentives for CCS projects in value-added mode such as EOR.Consensus that the main barrier to widespread implementation of CO2-EOR in Alberta is lack of supply and transportation infrastructure for CO2.

Sulfolane Attenuation by Surface and Subsurface Soil Matrices

This study was undertaken to evaluate sulfolane (tetrahydrothiophene-1, 1-dioxide) attenuation by soil and subsurface materials collected from a sour gas plant site using batch equilibration systems. The analyzed sample materials used in this study showed a wide range in terms of their selected physical and chemical properties. The reaction of sulfolane with the sample materials was fast initially and followed by slower rates at longer times. There was not much increase in the amount of sulfolane sorbed after about 5 hours of equilibration time irrespective of the temperature of the system. The rate of sorption of sulfolane followed a first-order reaction at both 25 and 8°C temperature conditions and not affected by the temperatures range considered in this study. It appears that the sorption data of sulfolane on the various sorbents could be best described mathematically by the Freundlich equation. Kd values derived at 25°C ranged from 0.05 to 0.88 L/kg and from 0.30 to 1.23 L/kg at 8°C. Furthermore, increasing the ionic strength of the solution didn't affect sulfolane sorption by the various sorbents, which indicates that sulfolane sorption is not consistent with an ion-exchange mechanism but rather occurs through dipole-dipole interactions. Desorption of sulfolane was relative high in all systems. Multiple regression analysis shows a high level of correlation between Kd and several soil parameters. No sulfolane biodegradation was detected under anerobic conditions in any of the microcosms systems after 45 days of incubation at 25 and 8°C, respectively. Sulfolane biodegradation data could be all fitted to zero-order kinetics. Biodegradation rates of sulfolane in the microcosms was the highest in sample depth 0–0.20 m, decreased with sample depth but significantly increased with the addition of nitrogen, and markedly decreased with temperature. At 25°C and no supplement of N, biodegradation rate ranged from 4.26 to 12.70 mg/kg/day but with addition of N, the range was from 9.41 to 16.50 mg/kg/day.

Principal Component Analyses of Groundwater Chemistry Data During Enhanced Bioremediation

A bioremediation project has been monitored for two years at a former sour gas plant site that had ethanolamine, glycol and their degradation products in the subsurface. The active enhanced bioremediation program consisted of dewatering and bioventing. An extensive groundwater monitoring program mapped the distribution of chemical species. Principal component analysis was used to help organize and interpret the chemical analysis. Three principal components accounted for 75% of the variability in the data. The first component separated contaminated waters from background. The second component indicated aerobic versus anaerobic conditions and the third component was indicative of the accumulation of nitrogen compounds. The site is extremely heterogeneous with preferential pathways due to fractures, sand lenses and a fractured horizontal well. In addition the source and contaminated areas are very heterogeneous. The PCA shows drastically different geochemical conditions residing within relatively small areas. The study site can be conceptualized as a series of small, meter-scale sized reactors that interact and mix due to preferential flow paths and diffusion. The evolution of the chemistry shows that the bioremediation process is successfully removing acetic acid, and it is becoming more aerobic. Enhanced infiltration in the process area is slowly removing the source and degradation products.

Protecting the Public Interest-The Evolution of Sulphur Recovery and Solution Gas Conservation in Alberta

Abstract Alberta has used two different approaches in developing new requirements for sulphur recovery and for managing solution gas flaring in Alberta. Both processes have used multi-stakeholder input and have demonstrated measurable success. The new sulphur recovery guidelines include clear requirements with both an incentive and enforcement component. The policy developed for solution gas management combines a voluntary approach with a regulatory backstop. The involvement of diverse stakeholders contributed to the success of using novel approaches to find solutions. Introduction As the petroleum industry and concerns with development evolve, a regulator cannot expect to regulate in the same manner as it always has. Even the approach taken for developing regulatory requirements must grow and adapt. In this paper, two examples are explored where a regulator employed different approaches for developing requirements which are in place today and working successively. These novel approaches have resulted in measurable successes, including a 70% reduction in solution gas flaring and a 30% reduction in sulphur emissions from larger, older sour gas plants. Details are provided on the resulting requirements and the paths taken to get there. Key elements that contributed to the successes are highlighted. The Alberta Energy and Utilities Board (EUB) is a government agency charged with regulating the oil and gas industry in Alberta. In doing so, it must protect the public interest as it relates to the discovery, development, and delivery of oil and gas resources. Regulation is needed so that non-renewable resources are produced in a responsible, efficient, and fiscally sound manner. History of Sulphur Recovery Requirements in Alberta Currently, Alberta has approximately 50 sulphur recovery gas plants producing about 15,000 tonnes of sulphur per day. The average sulphur recovery efficiency for these plants in 2004 was 99.0% Sulphur recovery guidelines in Alberta were set for all plants in 1971. At that time, requirements were in place for recoveries that the technology of that time could not yet achieve. Industry rose to the challenge, drove research, and developed the technology required to meet the new requirements, which became more stringent during a number of upgrades through the 1970s and 1980s. Revisions to the requirements dating from 1988 grandfathered existing facilities unless significant new gas was added. In 2001, the sulphur recovery guidelines were revised to provide clarity regarding when upgrading of grandfathered plants (plants not meeting the requirements of new plants) was required as a means to improve regulatory certainty, consistency, and fairness in interpretation. Consultation that preceded Alberta's current sulphur recovery requirements included a discussion paper issued to solicit broad input, plus recommendations from a multi-stakeholder advisory group consisting of the public, environmental organizations, industry, and academic stakeholders. This group advised the EUB in several areas, one of the most difficult being when the requirements for new plants should be applied to grandfathered plants. The advice of this group formed the basis for the current requirements. Current Requirements The requirements set out in August 2001 in EUB Interim Directive 2001–03 have three components that contribute to their success:

Two‐ and three‐dimensional electrical resistivity imaging at a heterogeneous remediation site

Geometrically complex heterogeneities at a decommissioned sour gas plant could not be adequately characterized with drilling and 2D electrical resistivity surveys alone. In addition, 2D electrical resistivity imaging profiles produced misleading images as a result of out‐of‐plane resistivity anomalies and violation of the 2D assumption. Accurate amplitude and positioning of electrical conductivity anomalies associated with the subsurface geochemical distribution were required to effectively analyze remediation alternatives. Forward and inverse modeling and field examples demonstrated that 3D resistivity images were needed to properly reconstruct the amplitude and geometry of the complex resistivity anomalies. Problematic 3D artifacts in 2D images led to poor inversion fits and spurious conductivity values in the images at depths close to the horizontal offset of the off‐line anomaly. Three‐dimensional surveys were conducted with orthogonal sets of Wenner and dipole–dipole 2D resistivity survey lines. The 3D inversions were used to locate source zones and zones of elevated ammonium. Thus, conducting 3D electrical resistivity imaging (ERI) surveys early in the site characterization process will improve cost effectiveness at many remediation sites.

Toxicity Screening of Benzene, Toluene, Ethylbenzene and Xylene (BTEX) Hydrocarbons in Groundwater at Sour-Gas Plants

In this paper a toxicity-based approach was used to assess the quality of groundwater samples collected from gas plants in western Canada. The gas plants selected were typical of plants currently in operation and represent a cross-section of hydrogeological conditions and of the sweetening processes in use. The focus was on the levels of benzene, toluene, ethylbenzene and xylene (BTEX) group of hydrocarbons as indicator compounds for monitoring the degree of bioremediation and bioventing at the sites. Toxicity tests included bacterial luminescence (Microtox®), daphnia mortality, fathead minnow mortality and lettuce seedling emergence. In general, the concentration of BTEX was a good indicator of the toxicity of the groundwater. However, approximately 5% of the samples were observed to be toxic although the concentrations of BTEX were low (< 1 μg/L). Based on the laboratory results, the remediation of BTEX in groundwater at the sour-gas plants is expected to correlate well with the removal of acute toxicity to selected aquatic organisms.

Pulmonary Symptoms and Spirometric Values in Kangan Sour Gas Refinery Workers

In this study, the author measured the frequency of symptoms and/or alterations in respiratory functions in workers of the sour gas refining industry. All workers (n = 62) were employed in the most-exposed units of the Kangan Sour Gas Refinery. The refinery is approximately 250 km east of Bushehr Port along the Persian Gulf. This cross-sectional study involved a comprehensive health questionnaire, standardized clinical examinations by physicians blinded to subjects' symptoms and concerns, and multiple spirometric values. Although gas refinery workers experienced more respiratory symptoms than the 30 controls (i.e., 37.7% vs. 23.3%, respectively), who were matched for age and smoking status, pulmonary function data were not statistically different (p > .05) between the groups. The authors concluded, therefore, that in Kangan Sour Gas Refinery workers there were no respiratory or spirometric values associated with chronic low-dose exposure to sour gas plant emissions, including hydrogen sulfide.

Cosolvency Effects of Monoethanolamine and Triethanolamine: Implications for the Remediation of Benzene in Groundwater at Sour-Gas Plants

Studies were conducted to measure the cosolvency effect of monoethanolamine (MEA) and triethanolamine (TEA) on the aqueous solubility of benzene in support of the remediation of contaminated subsurface environments at gas plants in western Canada. Experiments utilized sodium chloride solutions of the amines in the concentration range of 0–0.065 volume fractions, and non-saline waters in the range 0–1 volume fractions. The measured values of the cosolvency power σ for MEA and TEA, based on the log-linear model, were 1.86 ± 0.05 and 2.21 ± 0.04, respectively. The corresponding values for the semi-cosolvency power σ0.5 were 1.22 ± 0.005 and 1.19 ± 0.005, respectively. It is postulated that the difference in the values of σ and σ0.5 may be linked to cosolvent polarity of the amines in water. In 0.2 Mol/L NaCl saline water, the solubility of benzene increased linearly from 1660 mg/L to 2170 mg/L and 1960 mg/L for cosolvents MEA and TEA (0–0.065 volume fractions), respectively. As evidenced by the measured 30% increase in the solubility of benzene, remediation strategies of groundwater at sour-gas plants should therefore take into account the levels of these amines and their effects on the transport of hydrocarbon contaminants.

Reduced Productivity Impairment For Fracture Stimulated Gas Condensate Wells

Abstract Development of a retrograde condensate reservoir requires accurate well productivity predictions for a capital commitment to gas processing facilities. Historically, Fussell(1) identified that liquids condensing in the reservoir will result in a substantial productivity impairment. A single well model, which included a hydraulic fracture as part of the grid system, was developed to perform sensitivities for well test interpretation and to predict long term performance. Interesting results were obtained. The productivity of fractured wells was not impaired to the degree expected. Radial modelling confirmed the results obtained by Fussell. Current simulation technique allows for direct modelling of a hydraulic fracture instead of using an equivalent well bore radius. The distribution of pressure drawdown and condensate dropout around a hydraulic fracture results in limited productivity impairment. The methodology used and the results obtained are described. Introduction This work was originally completed to forecast production from wells in a new field, which was being developed in the Deep Basin area of Alberta, Canada. This study was comprised of geological review, PVT characterization, numerous well test sensitivities, as well as simulating the effects of condensate dropout on well productivity. The ultimate objective of this work was to make a nomination for a sour gas plant. This paper concentrates on the most important technical point which is that the productivity of wells, which are hydraulically fractured, may not be as adversely affected by condensate precipitation as was previously reported. However, in any actual study, there are a significant number of factors which are derived from different disciplines within petroleum engineering, which must be integrated. We have therefore placed our main results within an abbreviated outline of the process used in solving an actual field problem. In the authors' opinion, this is more valuable to practicing engineers. As much as possible, the material is presented chronologically so as to follow the development of the technical work. Material is presented under the following major headings: Geological Review, PVT Characterization, Model Construction, Well Test Modelling, Effects of Condensate Dropout, and Conclusions. Originally this work was completed for a single well, which was later expanded to include other wells in other pools. Only the work done on the first well analysed is presented and does not apply universally to the area. Geological Review The main objective of this phase of the study was to develop a quantitative reservoir description. This included porosity, permeability, water saturation and layering (heterogeneity). Since this was a new play, relatively little information was available on this zone. The lithology of the sandstone in this well was derived from a core description. Overall, the sand comprises interbedded dark grey-black shaley siltstones and light grey dolomitic sandstones. The shaley siltstones occur in beds that range in thickness from centimetres (inch) to metres (3 to 6 ft.). The sandstone occurs in beds 1/10 of a metre (4 in.) to metres (3 to 6 ft.) thick. Layering can be a major consideration in the design of a simulation, particularly for secondary recovery.

Key Factors Affecting Subsurface Contamination of Natural Waters near Sour-gas Plants

Hydrocarbon contamination of lakes and rivers from subsurface discharge of ground-water is a common environmental problem in many countries. This source of contamination, particularly dissolved phase hydrocarbons, can significantly reduce the quality of natural waters. Laboratory results show that the aqueous solubility of benzene can be predicted by Raoul's Law for BTEX mixtures and for gas condensate. In contrast, the solubility of total xylenes was up to three times higher than the calculated results using Raoul's Law. A comparison of these finding with the composition of BTEX in groundwater at a sour-gas plant, indicated that the mole fraction and groundwater flow velocity were two principle factors affecting the discharge concentration of benzene and xylenes to natural waters.;Hydrocarbon contamination of lakes and rivers from subsurface discharge of ground-water is a common environmental problem in many countries. This source of contamination, particularly dissolved phase hydrocarbons, can significantly reduce the quality of natural waters. Laboratory results show that the aqueous solubility of benzene can be predicted by Raoul's Law for BTEX mixtures and for gas condensate. In contrast, the solubility of total xylenes was up to three times higher than the calculated results using Raoul's Law. A comparison of these finding with the composition of BTEX in groundwater at a sour-gas plant, indicated that the mole fraction and groundwater flow velocity were two principle factors affecting the discharge concentration of benzene and xylenes to natural waters.

Options for Small-Scale Sulfur Recovery

Summary With the issuance by the Alberta Energy Resources Conservation Board and Alberta Environment of their report entitled Sulphur Recovery Guidelines for Sour Gas Plants in Alberta in August of 1988, the requirement in Alberta to recover sulfur was broadened to a sulfur content of 1 tonne/D or greater in the inlet gas to a new sour-gas treating plant. This paper reviews the processes in use for recovering sulfur from sour-natural-gas streams that have a total sulfur content of 5 tonne/D or less. These processes are the modified Claus process, the recycle Selectox process, and the reduction/oxidation processes LO-CAT and SulFerox. While the modified Claus process is used in large sulfur-recovery plants, the other processes may be more economical for sulfur recovery on a small scale. A description of the sour-gas treating and sulfur-recovery processes is given, and a comparison of estimated capital and operating costs for typical sour-gas streams is provided. All of the above processes are in operation in North America. Operating experiences with these processes in Alberta are discussed. The quality of the end-product sulfur varies among these processes, and the options for sulfur disposal are reviewed.

Some Applications of Fractal Mathematics In the Evaluation of Environmental Problems

Abstract Recent advances in the development of the techniques of fractal mathematics permit applications to environmental problems commonly encountered in the petroleum industry and other industries. Examples are given whereby the use of Turcotte's theory of renormalization groups leads, to simple equations for 'use in the interpretation of data sets and in practical decision making. Specifically; the applications are illustrated, by examples. Mercury contamination data at a gas plant are interpreted and the optimal volume of soil excavation is determined at a contaminated site. Introduction The relatively new theories of fractal mathematics were introduced as recently as 1967 by Manctelbrot(1). He noticed that the apparent or measured length of a complex coastline increased with the decreasing length, of the measuring rod, in accordance with a power law Equation (Available in full paper) where P is the length of the coastline, and r is the length of the measuring rod. The term D in the exponent is referred to as the fractal dimension. Since Mandelbrot's initial work, many natural phenomena have been shown to have fractal properties. Applications have been published in petroleum engineering by: Hewett in investigating the effect of reservoir heterogeneities on a water flood(2), by Tang et al., as a means of forecasting the performance of carbon dioxide and water floods(3), and by the present authors in reserve estimation of hydrocarbon(4). Maloy et al., have analysed the viscous fingers in two-dimensional fluid flow in porous media and have demonstrated fractal properties(5). In heterogeneous catalysis, it was realized that the molecular accessibility of a rough catalyst surface is dependent of molecular size, and an equation of the type Equation (Available in full paper) is obeyed, where N is the number of molecules needed for monolayer coverage, S is the molecular size, and Da is the fractal dimension of the surface available for coverage. A short review of this subject has recently been published by Avnir(6). In addition to the practical engineering applications, Turcotte has applied the theory to geology and geophysics(7), and it is these applications which are considered here for the solution to environmental problems. Turcotte shows that the cumulative average weight grade of an ore, Equation(1)(Available in full paper) Equation(2) (Available in full paper) Equation(3) (Available in full paper) The derivations may be found in Reference (6). Turcotte illustrated these equations by considering the total tonnage and grades of mercury ore mined in the United States. He obtained a fractal dimension of D =2.01. On extrapolation, by setting Mo equal to the tonnage of soil in the United States and arbitrarily choosing a data pair from the line, he obtained a value of Co = 80 ppb. This value is the same as the generally accepted mean concentration of mercury in U.S. soils, as required. Applications Case 1: Mercury Contamination at a Gas Plant At a sour gas plant in Southern Alberta, which is currently being decommissioned, a limited number of soil samples were analysed for the presence of mercury.

Biodegradation of Sulfolane in Soil and Groundwater Samplesfrom a Sour Gas Plant Site

Sulfolane is used as a solvent in processes for the removal of H2S from sour gas. Because of its high water-solubility, soil contamination by sulfolane quickly leads to groundwater contamination. To assess the possibility of using bioremediation to remove this compound, samples of soils, groundwaters, and sandstone from a contaminated aquifer at a gas plant were used in laboratory studies to determine if they contained sulfolane-degrading microbial populations. Aerobic shake-flask slurry cultures were incubated at 26° and 8°C, and solid phase soil bioreactors, approximating bioventing, were incubated at 8°C to test sulfolane biodegradability. Each environmental sample yielded microbial populations that degraded sulfolane. Supplementation with N and P stimulated degradation. The most rapid rates of degradation in slurry cultures incubated at 26°C and 8°C were 8 and 4 mg L−1 d−1, respectively. In the soil column bioreactors supplemented with N and P, the rates of sulfolane biodegradation were between 0.5 and 0.7 mg kg−1 d−1.

Use of optimization modelling to evaluate industrial waste reduction options: Application to a sour gas plant

This note reports on a study of waste reduction options for the upstream oil and gas industry and involves the application of a waste reduction optimization model to a generic sour gas plant. The waste reduction optimization model is meant as an aid for decision-making relating to the implementation of waste reduction options. The generic facility was developed from process knowledge provided by industry members of a project steering committee, as well as waste management information from industry manuals and represents a facility of average capacity and typical configuration. Several waste minimization options were modelled for selected waste streams. The selected streams were chosen based upon waste flows and disposal costs and their potential for waste reduction. The results of the modelling for the generic sour gas plant have shown that a set of cost-effective waste reduction options exist, there is significant potential for reducing the total quantity of waste to be managed and disposed of, and that implementation of the options would lead to considerable cost savings. The value and usefulness of the modelling approach lie not only in the generated results, but also in the fact that to construct the model, relevant waste flows and every possible manner that these waste flows can be minimized or processed are systematically identified. Once modelled, the parameters can be readily manipulated to determine various possible waste management strategies. To effectively use the modelling approach, the waste reduction team should have knowledge of the plant processes, existing waste management practices and costs, information on potential waste reduction options and technologies, as well as experience in mathematical modelling and analysis.

Estimation Of The Acid Sensitivity Of A Soil

Abstract Current regulations For environmental monitoring in the sour gas industry require annual reporting of soil pH. It is well known that this procedure may produce results with wide scatter, and without a clear trend over time. An alternative method, which overcomes this problem, is proposed.Rather than relying on soil monitoring to indicate the beginning of an irreversible pH drop, the new method allows the time of this occurrence to be calculated if the mean SO2 or sulphur deposition rate is known or can be estimated. It is also possible, in at least some cases, to identify the minerals that govern initial pH control of the soil. The method rests on kinetic measurements of soil pH change with time after acidification in the laboratory. It is recommended for monitoring, and especially for environmental impact assessment submissions to regulatory authorities. Introduction The acidification of soil, as a potential consequence of sour gas processing operations, has been of concern to industry and government in Alberta for some 20 years. While fears of regional groundwater pollution from trace elements, thought to be released from acidified soils and free to leach into aquifers, appear not to be a serious threat in the part of Alberta overlain by glacial till soils(1, 2) there is residual concern about yield reductions of acid sensitivie crops over the long term. During this period, there have been a number of strategies to monitor or control potential acidification effects. Prior to 1980, mere were continuing efforts by government and the private sector to ncrease sulphur recovery at sour gas plants, measure stack emissions directly and continuously, and to improve mathematical predictions of sulphur dioxide deposition; sulphur dusting was monitored by normal dustfall monitoring techniques. With the increase in the price of sulphur around 1980, there was an incentive to rapidly break up sulphur blocks by mechanical means. The attendant problem of sulphur dusting, as well as the analysis of several years of monitoring data by Alberta Environment, showed that the true sulphur dusting near these plants was seriously underestimated by dustfall methods. In some cases the discrepancies were more than an order of magnitude. In 1980, dustfall methods were abandoned in favour of regular soil pH measurement at predetermined sampling sites. In addition to these measurements, the requirement of the determination of a "buffering curve" was introduced(3). The buffering curves were dropped after a few years, when it became apparent that they underestimated the assimilative capacity of most soils for sulphur and sulphur gases. The reason for this may be the finding of Thimm and Weleschuk(1) that, after an initial acid addition, the equilibration of the soil sample requires some 15 to 30 days, instead of the days specified in the prescribed method. At present, the pH monitoring requirement still stands, but the details of it have been expanded on significantly to include the analysis of soil sulphur, and of carbonate in some cases. Details are given in the Alberta Environment Reference Method (AERM)(4).

Acidification adjacent to an elemental sulfur stockpile: I. Mineral weathering

Soil pH values below 3.0 are measured in soil material located adjacent to stockpiles of elemental sulfur on sour gas plant sites. The objective of this study was to examine the influence of extreme acidity on the changes and redistribution of major chemical and mineralogical components in soil along the side of a 25-year-old elemental sulfur block. Soil samples, obtained from pits located 2 m from the side of the sulfur block, were analyzed for total content of Al, Fe, Ca, Mg, Na, K, and Ti. Sand and clay separates were analyzed by X-ray diffraction, and physical and chemical methods to identify and quantify mineral phases. Carbonate, Fe-containing primary minerals, chlorite, smectite, and plagioclase feldspars were either partially or completely dissolved in soil having pH values of about 2.1. Clay-sized mica and kaolinite were apparently not affected by the acidity. Calcium carbonate and Ca-feldspars dissolved in the presence of H2SO4 to form gypsum. Iron dissolved from minerals in the acidified surface layer was deposited primarily as oxyhydroxides at the interface of acidic and calcareous materials to form an indurated layer about 10–15 cm thick. Jarosite precipitated within the acidic material just above the indurated layer. Key words: Elemental sulfur, anthropogenic acidification, mineral weathering, acid soils

The Measurement Of Trace Element Concentrations In Sour Gas Plant Process Streams

Abstract The design of an all- Teflon impinge train, suitable for the sampling of trace elements from high-pressure gas process streams, is described. The method was used to sample streams that might be diverted to flare slacks at two sour gas plants in southern Alberta. The results from this study suggest that most of the detected trace elements have an affinity for streams with high hydrogen sulphide contents. Introduction While the trace element contents of Alberta's crude oils and bitumens are reasonably well known from a number of studies into maturation and migration of oil(1–5), the same is not true for Alberta's natural gases. The limited work with gases appears to have been motivated primarily by specific environmental questions. In a study of mercury concentrations in gases, condensates and formation waters by the Energy Resources Conservation Board, Shaw et al.(6) reported an inability to detect mercury in most samples, with a detection limit of 0.1 ppb (w/w) for natural gases. Where the presence of mercury was indicated, results were sufficiently close to the limit or detection (LOD) to be doubtful. In only one case a concentration of 1.5 ppb was found in a gas from the Mississippian age Shunda formation. In condensates and formation waters, mercury was similar difficult to find, with no result greater than 4.5 times the LOD for these fluids. Because no concentrations that might give rise to environmental concerns could be found, this work was abandoned after a survey of eighteen gas fields. Hsu and Hodgson(7) have reported a depletion of selenium in stack gases compared to the acid gases at sour gas processing plants. Their findings suggest the possibility of retention of this element in the elemental sulphur product. In another paper(8), the authors have described a technique for estimating levels of twenty-nine trace elements in the gases exhausted from sour gas plant incinerator stacks. Sampling Requirements and Method In the previous work, representative samples were collected from two-phase flows in large diameter ducts at low pressures and very high temperatures. The isokinetic sampling technique employed in that study, however, is not applicable to natural gas streams flowing in ducts, typically of small diameters, at lower temperatures, and at pressures approaching 6900 kPa (1000 psig). In addition, the gas streams to be sampled might contain more than 70% hydrogen sulphide. A schematic of the sampling process developed for this study is shown in Figure 1. As far as was possible, all parts of the train ahead of the impingers were constructed or Teflon at the University of Windsor, Department or Chemical Engineering Workshop. The sampling line consisted of 9.5 mm (1/8,-in.) I.D. Teflon tubing with 1.6 mm (1/6-in.) wall thickness. A filter holder, also made of Teflon, provided support for the filter material used in the previous study. However, filter use was discontinued because filter deterioration could not be prevented at the sampling pressures encountered in the initial tests.

Remediation of groundwater contamination at Alberta sour gas plants

Remediation of groundwater contamination at Alberta sour gas plants

Lanthanide Fingerprinting And Acidification Of A Glacial Till Soil

Abstract A glacial till soil from southwestern Alberta was examined in terms of its lanthanide, Th and Sc content in order to establish a lanthanide labelling technique or soil type. It is shown that this technique may also be applicable in acidic soils. The acidification of the soils tested showed that the soils were capable of at least partial, natural pH recovery. This behaviour was found to be due to the presence of two minerals, one of which war confirmed as monazite, a tertiary rare earth phosphate; calcite, dolomite or albite (feldspar) contributions to this pH control were not important. Some implications of this result with respect to environmental monitoring at sour gas plants are discussed. Introduction In a previous paper(1), we reported on the use of lanthanide (rare earth) element abundances as an investigative tool for estimating the degree of pollution of pond sediments at a sour gas plant. The original intent in that work was to use the lanthanides as markers for trace element migration in soils subject to the deposition of sulphuric acid precursors. Instead, the hypothetical migration could not be detected, and the lanthanide abundance data implied that even where there is a high acidification potential due to sulphur dusting, the elements may serve better as a fingerprint for the identification of soil strata. The ability to label soils and sediments by lanthanide abundance might have numerous applications, apart from the utility in environmental assessment during decommissioning of gas plants which we have already reported(1). The present work deals with the examination of soil data from the Pincher Creek area of southwest Alberta to confirm both the soil labelling ability and the implied lack of sensitivity to deposition of acids. Because it is known from the previous work that the metals in question are easily stripped off the soil with 2.5 M sulphuric acid, it is also necessary to know the soil pH range in which the lack of acid sensitivity can no longer be assumed. Finally, it is of interest to compare the ease of metal removal from glacial till soils with data from the acid precipitation work at Hubbard Brooks, New Hampsttire(2,3) and others(4,5). There have been reports of groundwater pollution by metals released from acidified soils(6). In Alberta, the occasional deficiency of copper in livestock feed has been speculatively linked to the deposition of acidic gases to soil(7). Study Area The area chosen for study (Fig. 1) is located in the extreme southwestern comer of Alberta. Two sour gas processing plants had been operating in this area for over 25 years at the time of soil sampling (1983). Emissions for both plants typically totalled 40 t/d SO2 with particulates at 200 kg/day. Prior to 1972, SO2 emissions were substantially higher, near 130 t/d. The area shown in Figure 1 may be divided into two major soil Types(8). Soils developed from glacial lake bottom material extend to the southeast of Pincher Creek townsite, and then south to the Waterton Reservoir.

Interference Of Some Sulphur Compounds In The Analysis Of Aqueous Effluents For Cyanide

Abstract The unexpected and sporadic detection of cyanide in sour gas plant wastewaters and stack test scrubber solutions is investigated. It is shown that hydrogen sulphide and other reduced sulphur compounds are capable of producing a false positive in the standard method for cyanide analysis. The interference is unusual in that the response declines with increasing concentration of interferant. Introduction The pyridine-barbituric acid method for cyanide analysis in industrial wastewaters(1) is used widely, and is often a method recommended by statutory authorities where the wastewater is discharged to a natural watercourse. The limit of detection is commonly cited as 1 μg.dm−3. We have frequently seen reports of positive tests for cyanide by this method in sour gas plant wastewaters or stack test scrubber solutions. Such results are usually difficult to explain in terms of the processes involved, especially in the case of incinerator stack gases, where high temperatures (of the order of 500?C) prevail in the presence of excess oxygen. In the following, data are presented which suggest that the method may be limited to determining concentrations of CN-well above 40 μg.dm−3 in the presence of certain sulphur compounds, even when steps to remove interference from inorganic sulphides have been taken(1). A schematic of the reaction sequence is shown in Figure 1; accordingly, no positive interference is expected unless the interfering substance is capable of producing a compound analogous to the quaternized pyridine ring [A], which must also cleave to give the dye [C] with barbituric acid. In spite of this, the apparent detection of cyanidein sour gas plant incinerator stack gases led to the suspicion hat some sulphur compounds might give rise to an interference. Experimental In the present experiments, solutions of 5% and 10% w/v NaOH (ACS Reagent Grade, American Scientific &amp; Chemical Co.) were prepared in deionized water and were spiked in two or more replicates with COS, H2S, CS, and ethyl methyl sulphide. In the case of gases, the material was added slowly by means of a syringe, such that no visible gas bubbles escaped the solution. The liquids were added to the agitated aqueous solution by means of a microsyringe. No phase separation was to be expected at the concentrations used, and none was observed. The composition of CO2, H2S (Matheson Gas Products, 99.5%) CS2 (J.T. Baker Analyzed Reagent, 99+ %) and methyl ethyl sulphide (Canadian Western Natural Gas Co. Ltd., 98%) were known to be essentially free of HCN, such that a 1 μg.dm−3 concentration of CN− in solution could not be reached in this experiment. All solutions were stored in acid washed, deionized water rinsed amber glass bottles, and together with NaOH blanks, numbered at random. The numbering sequence was withheld from the analyst, who followed the "Standard Methods"(1) pyridine-barbituric acid procedure for cyanide; the method was amended in accordance with EPA method 335.3(2), to permit the use of a Technicon auto-analyzer. The V.V. lamp was shut off, and a distillation device described by Conetta et al. (3) was incorporated into the circuit.