Routine
core analysis, thin section epifluorescence and scanning
electron microscopy (SEM) analyses were performed to delineate the
reservoir qualities, pore systems, and pore network characteristics
of the Devonian Donghetang sandstone samples. Nuclear magnetic resonance
(NMR) measurements were used to gain insight into pore size distributions
of these sandstones. Fractal analysis was performed on the NMR T2 spectrum measured at echo spacings of 0.6 and 1.2 ms. Then
the relationships between NMR parameters and fractal dimension were
investigated. The results show that the pore systems are dominated
by primary intergranular pores with a combination of secondary dissolution
pores, micropores, and microfractures. Samples with the highest reservoir
quality are characterized by a coexistence of primary intergranular
and secondary dissolution pores. The parameter T
2gm (the geometric mean of the T
2 distribution) is a sensitive one for characterizing the pore size
distribution and microscopic pore structure since it shows good correlations
with T
2peak (value of T
2 showing the highest frequency on T
2 spectrum), permeability, and reservoir quality index (RQI).
By using a short echo spacing, more smaller pores can be detected,
resulting in a higher fractal dimension. The calculated fractal dimensions
show strong positive relationships with the NMR T
2peak and T
2gm values. Fractal
dimensions can be used here to represent the complexity degree and
heterogeneity of pore structure, and the coexistence of dissolution
pores and large intergranular pores contributes to a heterogeneous
pore throat distribution and a high value of fractal dimension. The
results are important for petroleum exploitation in the Donghetang
sandstones and can provide insights into pore structure characterization
in sandstones with similar geological settings.
Fractal dimension is a critical parameter to evaluate the heterogeneity of complex pore structure in tight sandstone gas and other low permeability reservoirs. To quantify the fractal dimension of tight sandstone at various pore size classes and evaluate their implications on mineral composition and nano pore structure parameters, we conducted an integrated approach of N2 adsorption/desorption experiment (N2-GA), X-ray diffraction (X-RD), and field emission scanning electron microscopy (FE-SEM) on Sulige tight sandstone reservoirs. By comparing the nine types of fractal dimensions calculated from N2 adsorption data, we put forward the concept of “concentrated” fractal dimensions and “scattered” fractal dimensions (DN2, DN3, DN5, DN7 and DN8) for the first time according to its concentration extent of distribute in different samples. Result shows that mineral composition has a significant influence of a different level on specific surface area (SSA), pore volume (PV), and fractal dimensions (DN), respectively, where the “scattered” fractal dimension is more sensitive to certain specific property of the reservoir, including mineral content and the specific surface area contribution rate (Sr) of type II mesopores (Mesopore-II: 10~50nm). In addition, three type of hysteresis loops were distinguished corresponding to different pore shape combination of N2-GA isotherm curve, which reveals that pore structure heterogeneity is mainly controlled by inkbottle-shaped pores and the volume contribution rate (Vr) of mesopores in this study area. These findings could contribute to a better understanding of the controlling effect of pore heterogeneity on natural gas storage and adsorption.
This paper, using the blade momentum theory combined with dynamic inflow correction and stall delay correction, analyses how periodic surge affect rotor aerodynamics of the NREL 5MW turbine operating at three different regions of its power curve. Results show that surge has the largest effects on rotor aerodynamics in region under rated wind speed while the smallest in region above that. Besides, oscillation amplitudes of rotor aerodynamic loads are in linear correlation with surge frequency and amplitude in most cases, except that rotor power and torque in region above rated wind speed is in linear correlation with the square of surge frequency. Results of this analysis would provide reference data for designs of floating wind turbine systems.
A novel magnetic arsenate imprinted polymer (MIIP) was synthesized through a surface imprinting technique with combined utilization of two different amine containing functional monomers (allylamine and 3-aminopropyl triethoxysilane) and tetraethyl orthosilicate modified magnetic Fe3O4 nanoparticles as a support. The synthesized MIIP was used to investigate the selective adsorption performance for arsenate. The results showed that this MIIP has a high selective As (V) adsorption efficiency and easy for the separation of the adsorbent from aqueous solutions. In the presence of competing ions including Ca2+, Mg2+, Cd2+, Zn2+, Cu2+, Mn2+, Ni2+ and As (III), the synthesized MIIP can selectively and efficiently adsorb As (V) species. Compared with the non-imprinted magnetic polymer (NIP), it was found that this MIIP showed high selectivity coefficients for As (V)/Ca2+, As (V)/Mg2+, As (V)/Cd2+, As (V)/Zn2+, As (V)/Cu2+, As (V)/Mn2+, As (V)/Ni2+, and As (V)/As (III) with 4.46, 5.60, 5.45,8.48,13.5,15.9,38.7, and 102.9, respectively. Langmuir model was applied to fit the adsorption isotherm data, and the maximum adsorption capacity for As (V) was calculated as 7.53mg/g.
There are many heavy oil reservoirs in offshore oilfields in China. Steam and multiple thermal fluid stimulation technologies are of increasing interest and have been applied to an increasing number of projects. During the stimulation or displacement of heavy oil reservoirs during thermal recovery, several factors, such as reservoir heterogeneity, are prone to cause channeling phenomena and affect the thermal recovery effect of steam stimulation. According to the unique requirements for the stimulation of multiple thermal fluids for offshore heavy oil, this study used transmission, blocking and relieving, heat resistance and a comprehensive evaluation of parallel sand tube experiments to conduct a screening evaluation of plugging systems for the stimulation of multiple thermal fluids, screen out a commonly used plugging agent in the current stage and propose corresponding guidance for the selection basis. The results show that foam, gel, foam gel and temperature-sensitive gel systems have a good transmission performance, whereas the oil sludge exhibits a poorer performance. The phenolic resin system exhibits great plugging properties, followed by oily sludge, temperature-sensitive gel, gel, foam gel and foam. Considering about washing resistance properties, phenolic resin system shows the best quality, followed by oily sludge and temperature-sensitive gel. The oily sludge system brings the best performance in plugging a high-permeability channel than phenolic resin gel and temperature-sensitive gel.
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