Solid Phase Residues Research Articles

Influence of reservoir physical properties on guar gum fracturing fluid damage in unconventional tight reservoirs

Solid phase residue, fracturing fluid filtration, and incomplete backflow during hydraulic fracturing can easily cause damage to tight sandstone reservoir. Thus, it is necessary to explore the relationship between the physical properties of tight reservoirs and damage caused by fracturing fluids. Based on the identification of reservoir physical properties, the relationship between reservoir physical properties and fracturing fluid damage was studied by core displacement, computerized tomography, and nuclear magnetic resonance (NMR). The results show that the higher the clay mineral content is, the denser the formed core is, and the corresponding core porosity and permeability are lower. When the permeability and porosity of the rock core are relatively high, the overall radius of the pore throat in the rock core shifts to the left under the action of the gel breaking fracturing fluid, showing a decreasing trend. However, when the permeability and porosity of the rock core are relatively low, the frequency peak of the smaller size of the pore throat in the rock core under the action of the gel breaking fracturing fluid increases upwards. The corresponding core permeability decline rate of the two types of tight sandstone reservoirs is 9.91%–8.78% and 15.85%–14.74%. The porosity decline rates are 5.53%–5.84% and 10.40%–9.94%. According to NMR results, it is speculated that under the action of gel breaking fracturing fluid, the small pore throats in the rock core are blocked or even disappear, while the proportion of smaller pore throats increases and the proportion of larger pore throats decreases. The results of this study provide theoretical reference for reservoir protection during the fracturing process of tight sandstone reservoirs.

Mechanism of sulfur migration and conversion in pyrolysis/combustion staged conversion process of high sulfur coal

To investigate the effects of circulating ash heat carriers and dolomite catalysts on sulfur migration in the coal pyrolysis/circulating fluidized bed combustion staged conversion process, five experiments of coal pyrolysis, ash/coal co-pyrolysis, coal pyrolysis catalyzed by dolomite, ash/coal co-pyrolysis catalyzed by dolomite and combustion of pyrolysis solid products were designed and carried out. By examining the effects of pyrolysis temperature, heating rate, coal-ash ratio and dolomite species on sulfur migration, the final distribution of sulfur-containing pollutants throughout the staged conversion process was systematically analyzed. The results showed that the separate mixing of ash heat carrier at final pyrolysis temperature of 600 °C increased the residual sulfur in solid phase from 79.29 % of raw coal pyrolysis to 90.00 %. When dolomite catalyst was added individually, the sulfur released into gas phase and tar was reduced from 18.28 % and 2.43 % of the raw coal to 13.14 % and 1.94 %, respectively. And Fe additive significantly improved sulfur resistance of the dolomite catalyst. The regeneration process has little effect on the sulfur fixation capacity of natural dolomite. When ash heat carrier and dolomite catalyst were simultaneously added to the system, the sulfur fixed in ash increased from 79.29 % of the raw coal to 91.27 %, and the sulfur fixed in natural dolomite and modified dolomite accounted for 4.32 % and 4.46 % of the total sulfur, respectively. In the combustion experiments of pyrolysis solid phase products, 43.57 %, 65.57 % and 61.44 % of sulfur was retained in the solid phase residue after combustion with circulating ash, circulating ash/natural dolomite and circulating ash/modified dolomite were added, respectively. Compared with direct combustion of coal, the staged conversion process resulted in a 55 % reduction of sulfur in the boiler flue gas. This study provides a theoretical basis for the purification of sulfur-containing pollutants in the staged conversion process.

Thermal De-Oxygenation to Form Condensable Aerosol From Reconstituted Tobacco without Auto-Ignition

Summary A novel concept is described here that utilizes externally applied heat to a solid rod of reconstituted tobacco biomass to form a stream of aerosol under progressively oxygen-deficient atmosphere. The boundary of auto-ignition was determined at oxygen concentrations of 0%, 5%, 10%, and 21% and then the effects of these different atmospheres on various parameters were studied. Experimental results indicated that the ignition temperature decreased with the increase of oxygen concentration and a negative temperature coefficient (NTC) for atmosphere with oxygen was observed at before but close to ignition temperature. Significant differences in the yields of CO and CO2 between oxygen and oxygen-free atmosphere were observed. The mass of aerosol produced under an inert atmosphere and reduced-oxygen atmosphere were characterized with selected volatile and semi-volatile components, phenols, aldehydes, and other organic compounds of interests. In addition, higher oxygen concentration resulted in higher bulk and surface oxygen content of solid-phase residue, the reduction of carbon and hydrogen element content and related functional groups, and the content of inorganic compounds also exhibited an increase with oxygen concentration. By systematically changing oxygen concentrations of the biomass bed with increasing temperatures, an aerosol stream of controlled chemical composition and yields could be formed without leading to ignition. Key chemical markers of inhalation harm were measured and compared to each other under different degrees close to combustion. Studying reconstituted tobacco or other biomass materials in such a way could provide alternative and useful information in the design heated biomass aerosol generators.

Mechanism of fracture damage induced by fracturing fluid flowback in shale gas reservoirs

In this paper, the Lower Silurian Longmaxi shale samples and the backflow fracturing fluid in the Changning Block of the Sichuan Basin were selected to investigate the damage mechanism of retained fracturing fluid to fractures in shale gas reservoirs. Thus, experiments were conducted on fracturing fluid backflow and gas-driving fracturing fluids. The changes of liquid permeability of shale samples, solid particle size distribution and turbidity of the backflow fracturing fluid were monitored. The gas permeability before and after fracturing fluid gas drive was compared, and the damage degree and mechanism of the backflow fracturing fluid to the fractures in shale samples were analyzed. And the following research results were obtained. First, the damage rate of shale permeability after the fracturing fluid backflow is between 53.1% and 97.6%, and the range of the solid particle size of the flowback fluid is significantly reduced. The main reservoir damage modes include phase trapping damage caused by liquid phase retention, blockage caused by the solid phase residue, particle migration induced by gas-carrying liquid and salt precipitation. Second, in the stage of gas phase flow, the damage rate of permeability drops to 23.1–80.2%, and the damage caused by liquid phase retention is relieved, but the damage caused by the blockage of solid phase residue and the salt precipitation of flowback on the facture surface is inevitable. Third, based on the damage mechanism of fracturing fluid backflow in shale gas wells to fractures, considering the treatment difficulty of the flowback and its damage to reservoir fractures, it is recommended to give a full play to the fracturing capacity of fracturing fluid and optimize the properties and dosages of fracturing fluid so as to reduce the flowback of fracturing fluid as much as possible.

A new model for fracturing fluid leak-off in a single natural fracture

Hydraulic fractures can open or penetrate natural fractures when naturally fractured oil and gas reservoirs are hydraulically fractured. Meanwhile, fracturing fluids enter the natural fractures, significantly increasing the leak-off volume. This paper proposes a new model of fracturing fluid leak-off in a single activated natural fracture, taking the deposition of solid-phase residues into account. The impact of leak-off on the viscosity of the fracturing fluids, volume concentration of the solid-phase residues, and critical natural fracture width were analysed using example calculations. The leak-off in a natural fracture mainly occurred in the beginning when the fracturing fluids enter the fracture. Within a few minutes, the viscosity of the fracturing fluids, the particle size, and dosage of solid-phase residues reached an optimal value range. The model calculation results provide guidance for the control of fracturing fluid leak-off in a natural fracture. [Received: March 8, 2016; Accepted: January 28, 2017]

Assessment of Potassium Concentration in Biochar Before and After the After-burner of a Biomass Gasifier

Small scale biomass gasifiers are gaining continuously attention due to the renewability of the fuel, the high feed-in tariffs and the novel systems with high efficiency that are becoming available in the market. Gasification is a thermochemical conversion process which mainly produces a gaseous fuel, i.e. syngas, but also other by- products. The most important ones are the solid phase residues, i.e. char and ash which represent 2-5 % of the initial input by mass. The small scale of operation does not allow the operators to develop centralized efficient strategies for managing char and ash. Thus, onsite strategies have been developed like the after-burner which converts part of the char and the alkali and heavy metals from solid to gas in order to reduce the concentrations of specific substances within the environmental limit. Commercial software are not able to properly model the operation of an after-burner and, therefore, not all the product streams of interest can be calculated. This work introduces a three phase thermodynamic model that aims to assist the operation of commercial software in modelling an after-burner. The key aspect of this three-phase model is that it uses the yield of char as a control variable for modelling the concentration potassium and how it fluctuates among the different phases. Combustion of potassium has the characteristic of creating several intermediate oxides that distribute among the solid and the gaseous phase for a wide range of operating conditions contrary to the majority of heavy and alkali metals which concentrate completely in the solid phase until a tipping point when they completely convert to gaseous products. The model returns results consistent with the onsite measurements and also is able to provide all the additional data, i.e. the molar fractions of gases and the amount of reactive oxygen, which can assist the optimization of the after-burner.

Using Compound-Specific Isotope Analysis to Assess Biodegradation of Nitroaromatic Explosives in the Subsurface

Assessing the fate of nitroaromatic explosives in the subsurface is challenging because contaminants are present in different phases (e.g., bound to soil or sediment matrix or as solid-phase residues) and transformation takes place via several potentially competing pathways over time-scales of decades. We developed a procedure for compound-specific analysis of stable C, N, and H isotopes in nitroaromatic compounds (NACs) and characterized biodegradation of 2,4,6-trinitrotoluene (TNT) and two dinitrotoluene isomers (2,4-DNT and 2,6-DNT) in subsurface material of a contaminated site. The type and relative contribution of reductive and oxidative pathways to the degradation of the three contaminants was inferred from the combined evaluation of C, N, and H isotope fractionation. Indicative trends of Δδ(15)N vs Δδ(13)C and Δδ(2)H vs Δδ(13)C were obtained from laboratory model systems for biodegradation pathways initiated via (i) dioxygenation, (ii) reduction, and (iii) CH3-group oxidation. The combined evaluation of NAC isotope fractionation in subsurface materials and in laboratory experiments suggests that in the field, 86-89% of 2,4-DNT transformation was due to dioxygenation while TNT was mostly reduced and 2,6-DNT reacted via a combination of reduction and CH3-group oxidation. Based on historic information on site operation, our data imply biodegradation of 2,4-DNT with half-lives of up to 9-17 years compared to 18-34 years for cometabolic transformation of TNT and 2,6-DNT.

Seasonal sensitivity of weathering processes: Hints from magnesium isotopes in a glacial stream

Seasonal changes in river chemistry offer the potential to assess how weathering processes respond to changing meteorological parameters and ultimately how chemical weathering might respond to climatic parameters. Systematic seasonal variations in magnesium isotope ratios (the 26Mg/24Mg ratio expressed as δ26Mg in per mil units) are reported in stream waters from a mono-lithological granitic, weathering-limited, first order catchment from the Swiss Alps (Damma glacier). Rain, ground, and pore-waters, in addition to plants, rocks, mineral separates and soil are also reported. The concentration response of the river waters is attenuated compared to the large changes in discharge. However, the systematic trends in the isotope data imply that either the source of the Mg changes in a systematic manner, or that the process by which Mg is released into solution changes as a function of discharge. The two first order observations in the data that need to be explained are 1) the systematic enrichment in 24Mg in the stream waters compared to the granitic rocks they drain and 2) a systematic increase in δ26Mg in the waters during the summer melt season. Both observations (which are similar to many other rivers draining silicate rock) can either be accounted for by 1) conservative mixing between at least two different sources of Mg (in addition to precipitation inputs), or 2) process related fractionation. If the stream water compositions can be rationalised by multi-component mixing, there is at least one unidentified component with a δ26Mg < − 1.2‰. This is considered unlikely. Multiple physicochemical processes could fractionate Mg isotope ratios such as 1) preferential leaching of 24Mg, 2) exchange of Mg onto (or from) mineral surfaces and into interlayer sites of clays, 3) uptake by plants, and 4) 26Mg could be preferentially retained during the formation of secondary phases, such as clays, amorphous phases or oxides. These processes are not mutually exclusive and distinguishing between them at a field scale is not trivial, but significant biological uptake is improbable at this site. Unless there is a non-identified external input of Mg, 26Mg must be accumulating in solid phase residues in the catchment because of at least one physicochemical process. Such processes are likely well described, at least in the first order by a Rayleigh distillation model. Simple calculations illustrate how much 26Mg would accumulate in the catchment per unit time. In the first order, the isotopic enrichments in the solids are so small that they would not be detectable for the time-scales that are relevant to this field site, in spite of the marked impact on the water chemistry. The seasonal signal detected by Mg isotope ratios is promising for using them (with a better understanding of fractionation mechanisms) to quantify how specific weathering processes impact upon both export fluxes, and retention of elements within catchments.

Direct Chemical Speciation of P in Sequential Chemical Extraction Residues Using P K-Edge X-Ray Absorption Near-Edge Structure Spectroscopy

Sequential chemical extraction is a common analytical approach used to separate soil P into operationally defined fractions based on solubility in increasingly strong extractants. However, there are some concerns that the relationship between these operationally defined pools and the true chemical speciation of P may not always be correct. This study was conducted to compare the speciation of P in soils amended with either biosolids or an inorganic fertilizer as using a combination of sequential chemical extraction and synchrotron X-ray absorption near-edge structure (XANES) spectroscopy on the solid-phase residues after each extraction step. The combined results from sequential chemical extraction and XANES analysis indicate that although sequential extraction steps may remove the same broad class of P from soil, the solubility and precise chemical speciation of that P may be quite different. For example, P K-edge XANES analysis determined that calcium phosphates are removed by the HCl extraction step, but this takes the form of a poorly crystalline dicalcium phosphate in biosolid-amended plots and apatite-type calcium phosphate in the commercially fertilized plots.

Characterization of the curing process from high-solids anaerobic digestion

A laboratory-scale study was completed to simulate aerobic curing of solid-phase residue (digestate) from an anaerobic reactor fed a mixture of food and landscape wastes. The degree of organic stabilization was determined through routine analysis of oxygen uptake rates, percent O 2, temperature, volatile solids, and Solvita Maturity Index; measurements of ammonia and volatile fatty acid (VFA) concentrations served as indicators of phytotoxicity. Results suggest that stabilization of organics and elimination of phytotoxic compounds from anaerobic digestate preceded significant reduction of each volatile sulfur compound (VSC) detected (hydrogen sulfide, methanethiol, and dimethyl sulfide). Within 10–15 days of curing, stabilization of organics was achieved and phytotoxic compounds were eliminated, whereas reduction of VSCs to low levels required 15–20 days of curing. Based on these results, incomplete curing and anaerobic microenvironments within a curing facility may increase odor potential via formation of VSCs, whereas sufficiently cured digestate will resist VSC formation, despite the onset of anaerobic conditions.

Modeling Fate of RDX at Demolition Area 2 of the Massachusetts Military Reservation

The movement of explosive RDX residue from soil to groundwater at Demolition Area 2 of the Massachusetts Military Reservation was studied with mathematical models to assess its utility and limitations and to determine requisite model improvements and data needs. The Munitions Residue Characterization and Fate model, which is based on the MEPAS source term model for soil modified for solid phase residue with dissolution, the MEPAS vadose zone model, and the MEPAS aquifer model were used in this study. All three models were applied within ARAMS™ to facilitate model-to-model connectivity for computing movement of RDX from soil to vadose zone, and from vadose zone to groundwater. Model parameters and a hypothetical RDX residue loading rate were adjusted to match model results to measured RDX concentrations in surface soil and in groundwater. Through an iterative process, a loading rate of 1 kg/yr for RDX residues applied for 10 years starting in 1978 was found to fit measured conditions 20 years later. Model results were sensitive to the C4-RDX dissolution flux rate and the aqueous RDX degradation rate. Results indicate that dissolution of C4 and degradation of RDX in soil and groundwater could be quite slow, and such processes warrant further study. Mechanistic models such as those presented will be useful for estimating fate of constituent residue in soil and transport to receiving waters for evaluating range residue carrying capacity and compliance issues.

Fate of prions in soil: Interaction of a recombinant ovine prion protein with synthetic humic-like mineral complexes

Prion proteins are regarded as the main agents of transmissible spongiform encephalopathies. Understanding their fate in soil may be crucial to elucidate the dissemination of the prion in the environment, associated with a possible transmission of infectivity. Studies were performed with simplified model systems, derived by the birnessite-mediated oxidative polymerization of catechol, which simulate processes naturally occurring in soil. A benign full-length recombinant purified ovine protein (PrP) (residues 23–234), as well as a truncated-form ovPrP (tPrP) (103–234) were utilized. Catechol and prion protein interacted under experimental conditions that reproduced the interaction of PrP with soluble organic matter or with insoluble organic matter during or after formation of catechol polymers. PrP stability in all buffers and chemicals was preliminarily monitored by circular dicroism (CD) measurements. The disappearance of protein molecules from the solution, the decrease of UV–Visible absorbance of supernatants, and the FT-IR spectra and the elemental analyses of solid-phase residues indicated that both PrP and tPrP were involved in catechol polymerization by birnessite. Furthermore, a clear flocculation of soluble catechol–protein polymeric products in solid aggregates was observed when PrP was added to the supernatants. Different kinds of extracting agents were not able to desorb/extract PrP as well as tPrP from the formed solid aggregates, thereby highlighting the high stability of protein–organic and –organo-mineral complexes.

Trace element partitioning in Earth’s lower mantle and implications for geochemical consequences of partial melting at the core–mantle boundary

Trace element partitioning data between CaSiO 3-perovskite (CaPv), MgSiO 3-perovskite (MgPv), calcium–aluminum silicate (CAS-phase), and coexisting melts in peridotite and mid-ocean ridge basalt (MORB) compositions were obtained at 25–27 GPa and 2400–2530 °C using multi-anvil apparatus and ion microprobe. Results clearly show that CaPv is the predominant host for large ion lithophile elements (LILE) in the lower mantle. Because of the overwhelmingly high CaPv/melt partition coefficients (>10 for many of the LILE), partial melting in the lower mantle causes strong enrichment of LILE in the CaPv-bearing solid phase residue. CaPv has the following partitioning characteristics: (1) uniformly high partition coefficients for heavy rare earth elements (HREE) (e.g. 15 for Yb), decreasing toward light REE (e.g. 7 for La), (2) systematically lower partition coefficients for high field strength elements (Nb, Zr, Ti) and Sr relative to neighboring REE, (3) high Th and U, and systematically low Pb partition coefficients. Previous high-pressure studies have shown that the stability field of CaPv above solidus temperature is much wider in basaltic composition than in peridotite, indicating that melting of subducted oceanic crust in the lower mantle could produce significant geochemical CaPv signatures. Strong enrichment in Th and U relative to Pb in CaPv would result in radiogenic Pb isotopic compositions of the CaPv-bearing solid residue. Some clinopyroxenes in plume mantle peridotite xenoliths possess trace element patterns closely resembling those of natural CaPv found in diamonds and CaPv from the present experiments, suggesting that they were inherited from the CaPv-bearing precursor. In contrast, CaPv is the first phase to disappear during partial melting of peridotite above 24 GPa, and its geochemical signature may not be observable in nature. (MgPv + CaPv) fractional crystallization from a magma ocean has previously been put forward as a mechanism for Si depletion of the upper mantle. However, our data show that the magma ocean Sm/Ba ratio would deviate significantly from observed chondritic values when fractionation exceeds only 6%, if the crystallizing mixture were 10% CaPv and 90% MgPv. A significant hidden perovskite reservoir in the lower mantle can therefore be excluded.

Evolution of the rheological properties and structure of a system during copolycondensation of ethylene terephthalate with p-hydroxybenzoic acid

The changes in rheological properties during the formation of a copolymer of ethylene terephthalate with p-hydroxybenzoic acid are analysed. Two important features of the reaction are stressed: the appearance of the liquid crystal phase in the melt (and the visco-plastic behaviour of the system) and transformation of this phase in the continuous matrix. The plots of the dynamic modulus against time have maxima and minima corresponding to these characteristic times. The effects of temperature on the plots of the modulus and the flow plots for the product as a function of frequency are discussed. Below 250°C the flow activation energy attains a value of 400kJ/mole, and >250°C it does not exceed 70 kJ/mole. This, together with the low angular coefficient of the plots of the modulus against frequency and the low (<1) values of the tangent of the mechanical loss angle in the low temperature region indicate structuring of the melt. Such structuring can be due to the retention of solid phase residues above the softening point or the presence of elements of layer packing in the copolyesters.

Sulphur Neutralization by Lignite Ash: Pilot-Scale Combustion Experiments

A pilot-scale research boiler (750 kg steam/hr) has been used to study the degree of sulphur neutralization during combustion experiments with three lignites. A series of four closely controlled experiments showed that sulphur balances close to 100 percent could be achieved in the pilot-scale system burning Gascoyne lignite; in these experiments the sulphur retained in solid phase residues varied between 21 and 24 percent of the input sulphur. It was also demonstrated with Utility lignite that external recirculation of flue-gas was moderately effective in reducing nitric oxide emissions at the expense of major increased in the carry-over of unburnt carbon. However, sulphur dioxide neutralization by the coal-ash cations remained essentially unchanged as the recirculation ratio increased. Enhancement of sulphur neutralization by dry lime addition to Poplar River lignite was only found to be effective at addition rates above 1/2 percent lime by weight. The effectiveness of the lime was found to increase as the excess-air level increased.