221 research outputs found
Analysis of Production Data in Shale Gas Reservoirs: Rigorous Corrections for Fluid and Flow Properties
No full textAbstract
Analysis of long-term linear flow periods associated with shale gas production has received much attention in recent literature as a means of obtaining information about stimulation efficiency. However, the most popular methods for analysis (ex. square-root of time plot) can lead to incorrect characterization. Nobakht and Clarkson (2011a) demonstrated that the square root-time plot may not be a straight line for constant gas rate production linear flow and the non-linear shape may lead to incorrect flow regime identification. The square root-time plot is however a straight line for constant flowing pressure (Nobakht and Clarkson, 2011b). Ibrahim and Wattenbarger (2005; 2006) and Nobakht and Clarkson (2011b) showed that using the slope of square root-time plot, for constant flowing pressure constraint, leads to an overestimation of fracture half-length. Additional important considerations for shale gas analysis are non-Darcy flow and non-static reservoir properties. Clarkson et al. (2011) demonstrated that ignoring gas slippage effects, thought to be important in ultra-low permeability reservoirs, can cause errors in reservoir characterization. They incorporated slippage into pseudo-variables for production data analysis, as has been done with non-static permeability (Thompson et al., 2010). Finally, Nobakht et al. (2011) extended the methodology proposed by Nobakht and Clarkson (2011b) to properly analyze linear flow in the presence of slippage and desorption.
The purpose of the current work is to evaluate the current methods for analyzing linear flow in shale gas reservoirs, and establish which method is the most accurate for reservoir characterization. First, recent studies addressing linear flow under constant flowing pressure and constant gas rate production are briefly reviewed. Then, a comparison among the above-mentioned methods for calculating fracture half-length or contacted matrix surface area is made. It is shown that Nobakht et al. (2011) method yields the fracture half-lengths that best match the expected values for constant flowing pressure. Finally, we present a method for analyzing linear flow for real production data, where neither flowing pressure nor gas rate is constant. The method is validated using three numerically-simulated cases. It is found that this method works well for the three cases provided.</jats:p
Facile enhancement of the active catalytic sites of N-doped graphene as a high performance metal-free electrocatalyst for oxygen reduction reaction
No full textA simple and facile N-doping process has been developed to prepare graphene nanosheets with a high loading of active catalytic sites through the combination of hydrothermal and microwave processes. High resolution transmission electron microscopy, X-ray photoelectron spectroscopy and Raman analysis have been used to characterize the morphology and composition of the prepared materials. Also, linear sweep voltammetry (LSV) was conducted to investigate the electrocatalytic performance of the N-doped specimens toward oxygen reduction reaction (ORR). It was revealed that post-treatment of hydrothermally-treated N-doped graphenes under microwave irradiation in the presence of nitrogen precursor can result in the formation of a large content of quaternary nitrogen functionalities. Also, the LSV analysis revealed that fabrication of the graphene nanosheets under the proposed N-doping strategy resulted in potent electrocatalytic activity of graphene nanosheets toward ORR through a four electron pathway. © 20181
Unitary unraveling for the dissipative continuous spontaneous localization model: Application to optomechanical experiments
No full textThe continuous spontaneous localization (CSL) model strives to describe the quantum-to-classical transition from the viewpoint of collapse models. However, its original formulation suffers from a fundamental inconsistency in that it is explicitly energy nonconserving. Fortunately, a dissipative extension to CSL has been recently formulated that solves such an energy-divergence problem. We compare the predictions of the dissipative and nondissipative CSL models when various optomechanical settings are used and contrast such predictions with available experimental data, thus building the corresponding exclusion plots
Hybrid Forecasting Methods for Multi-Fractured Horizontal Wells: EUR Sensitivities
No full textIn this paper, the sensitivity of expected ultimate recovery (EUR) for horizontal wells with multiple fractures to decline exponent is studied using the simplified forecasting method introduced by Nobakht et al.[1]. This is very important from the reserves evaluation perspective due to uncertainty in decline exponent, b. This uncertainty is caused by many factors like desorption and reservoir/ completion heterogeneity. It is found that in case of timebased forecast (duration of forecast is specified), the ratio of EURs for two different specified values of decline exponent depends on the ratio of economic life time of a well to the duration of linear flow. On the other hand, this EUR ratio depends on the ratio of rate at the end of linear flow to economic rate limit for economic limit-based forecast (economic rate limit is specified).Key words: EUR sensitivities; Multi-fractured horizontal wells; Hybrid forecasting method
Self-assembly of three cationic silver(I) coordination networks with flexible bis(pyrazolyl)-based linkers
No full textThree new cationic silver(I) coordination polymers, {[Ag(mu-bpmb)](SO3CF3)}n (1), {[Ag(mu-bdb)1.5] (SO3CF3)}n (2) and {[Ag(mu-bpb)2](NO3)}n (3), with flexible 1,4-bis[(pyrazolyl)methyl]benzene (bpmb), 1,4-bis[(3,5-dimethylpyrazolyl)methyl]benzene (bdb), and 1,4-bis(pyrazolyl)butane (bpb) have been prepared at room temperature by the solvent layering method. The three compounds were characterized by FT-IR spectroscopy, PXRD, elemental analyses and single-crystal X-ray diffraction. Compound 1 is a highly undulated polymeric 1D chain in which the silver ions adopt a linear geometry, coordinating two bpmb linkers. Compounds 2 and 3 are both 2D coordination polymers with their silver atoms being three and four coordinated, and resulting in 6^3-hcb and 4^4-sql underlying net topologies, respectively. The flexible bispyrazolyl ligands display various conformations in the solid state, causing the formation of different Ag. . .Ag separations in the polymeric structures
Anion-directed assembly of three cationic silver(I) coordination polymers with bis(imidazolyl)-based linker: Structural characterization and anion exchange study
No full textThree cationic silver(I) coordination polymers, namely [Ag2(μ-bib)3](SO3CF3)2·(CH3CN)n (1), [Ag(μ-bib)](NO3)·(H2O)n (2), and [Ag(μ-bib)]BF4n (3), have been prepared using flexible bis(imidazolyl)butane (bib) ligand and silver salts of different anions. All compounds are characterized by FT-IR, PXRD, elemental analysis, and single-crystal X-ray diffraction. Compound 1, containing triflate (SO3CF3−) anions, exhibits a two dimensional 63-hcb network with an amazing ABCDEF packing mode of the single hexagonal layers. Compound 2, containing nitrate ions, forms a simple one dimensional wavy chain, while compound 3 with BF4− anions, shows a double helix DNA-shaped structure stabilized by Ag⋯Ag interactions between the two strands. The anions in the structures 1–3 are non-coordinating and participate in weak H-bonding, while imidazolyl rings are involved in π⋯π stacking interactions. Anion exchange experiments in aqueous solution, monitored by FT-IR and PXRD analyses, reveal interesting structural transformations
Capture of volatile iodine by newly prepared and characterized non-porous [CuI]n-based coordination polymers
No full textFour new non-porous CuI-coordination polymers [Cu-2(mu(3)-I)(2)(mu-bpb)](n) (1a), [Cu(mu(2)-I)(mu-bpb)](n) (1b), [Cu-4(mu(2)-I)(4)(mu-bpmb)(4)](n) (2), and [CuI(mu-bdb)](n) (3) (bpb = 1,4-bis(pyrazolyl) butane; bpmb = 1,4-bis[(pyrazolyl)methyl]benzene; bdb = 1,4-bis[(3,5-dimethylpyrazolyl)methyl] benzene) have been successfully prepared and their structures fully characterized by single-crystal X-ray diffraction, FT-IR spectroscopy, PXRD and elemental analysis. Crystallographic investigation revealed that 1a, 1b, and 2 exhibit two-dimensional (2D) structures; in 1a parallel [Cu2I2](n) staircase motifs are cross-linked into two-dimensional sheets by bpb linkers with a fully extended conformation, while in the structures of 1b and 2 Cu2I2 rhomboid dimers are linked by bpb and pbmb ligands, respectively, into two-dimensional sheets with a 4(4)-sql net. Differently, compound 3 shows a one-dimensional (1D) zigzag chain structure with monomeric CuI units. All the four non-porous coordination polymers show the ability to capture volatile iodine in the gas phase. The solid-state photoluminescence properties of 1a, 1b, and 2 have also been investigated. The iodine-adsorbed samples 1a-I-2, 1b-I-2, and 2-I-2 show no fluorescence behavior
Three Cationic: Nonporous CuI-Coordination Polymers: Structural Investigation and Vapor Iodine Capture
No full textThree cationic nonporous copper(I) coordination polymers containing bis-pyrazolyl flexible ligands have been prepared and characterized, namely, [Cu(μ-bdb)1.5](PF6)n (1), [Cu(μ-bpb)2](PF6)n (2), and [Cu(μ-bpmb)2](PF6)n (3) (bdb = 1,4-bis(3,5-dimethylpyrazolyl) methyl)benzene; bpb = 1,4-bis(pyrazolyl)butane; bpmb = 1,4-bis(pyrazolyl)methyl)benzene). All compounds were characterized by infrared, powder X-ray diffraction, elemental and thermal analyses, and single-crystal X-ray diffraction. Compound 1, with methyl-substituted pyrazolyl ligand, forms a chain of alternating rings and ribbons in which the copper(I) centers are three coordinated in distorted trigonal planar geometry. In compounds 2 and 3 copper(I) atoms adopt distorted tetrahedral geometries giving two-dimensional sheet structures with 44-sql topology. Interestingly, iodine sorption experiments show that colorless crystals of 2 and 3 remain unchanged in the presence of iodine vapors, while the three-coordinated compound 1 immediately absorbs iodine and turns dark. Anion exchange behavior of compounds 1 and 2 was also investigated both in solution and in the solid state
Effect of Heterogeneity in a Horizontal Well With Multiple Fractures on the Long-Term Forecast in Shale Gas Reservoirs
No full textAbstract
Shale gas reservoirs have become a significant source of gas supply in North America owing to the advancement of drilling and stimulation techniques to enable commercial development. The most popular method for exploiting shale gas reservoirs today is the use of long horizontal wells completed with multiple-fracturing stages (MFHW). The stimulation process may result in bi-wing fractures or a complex hydraulic fracture network. However, there is no way to differentiate between these two scenarios using production data analysis alone, making accurate forecasting difficult.
For simplicity, often hydraulic fractures are considered bi-wing when analyzing production data. A conceptual model that is often used for analyzing MFHWs is that of a homogeneous completion; in which all fractures have the same length. However, fracture lengths that are equal in length are rarely if ever seen (Ambrose et al., 2011).
In this paper, production data from heterogeneous MFHW (i.e., all fracture lengths are not the same) drilled in extremely low permeability reservoirs is studied. First, the simplified forecasting method of Nobakht et al. (2010) developed for homogeneous completions is extended to heterogeneous completions. For one specific case, the Arps decline exponent is correlated to the heterogeneity of the completion. It is found that Arps’ decline exponent to be used after the end of linear flow increases with the heterogeneity of the completion. Finally, it is shown that ignoring the heterogeneity of the completion can have a great effect on the long-term forecast of these wells.</jats:p
Case Studies of a Simple Yet Rigorous Forecasting Procedure for Tight Gas Wells
No full textAbstract
The dominant flow regime observed in many hydraulically-fractured tight/shale gas wells is linear flow. This flow regime may continue for several years, and will ultimately become boundary-dominated flow, at much later times.
Nobakht et al. (2010) introduced a simplified method of production forecasting for tight/shale gas wells which exhibit extended periods of linear flow. The method is simple as it relies principally on a plot of inverse gas rate versus square root time, and it is rigorous in that it is based on the theory of linear flow and combines the linear flow transient period with hyperbolic decline during boundary-dominated flow.
In the present work, this simplified method is reviewed and applied to almost 90 wells producing from the Montney formation in N.E. British Columbia, Canada. The vast majority of these wells exhibit linear flow for extended periods of time.
The advantages of the simplified forecasting method are: (1) It is not biased towards any flow regimes, as no superposition time functions are used; (2) Reliable forecasts can be obtained without invoking pseudo-time and its associated complexities; and (3) The only parameter that needs to be specified externally is the drainage area.
The method can be used for forecasting horizontal wells with multiple hydraulic fractures. By assigning different drainage areas to each fracture, a relationship can be developed between expected ultimate recovery (EUR) and original gas in place (OGIP) assigned to each fracture. This translates into recovery factor versus number of fracture stages. The resulting forecasts can be used directly to examine the economics of multi-stage fracturing.</jats:p
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