The proppant conductivity evaluation is mostly based on the water phase, but the average viscosity of Jimsar shale oil is 123.2 mpa·s, which is far higher than that of water. Therefore, the conductivity test with water phase as the test medium has certain limitations for field guidance. In this paper, the conventional short-term conductivity meter is upgraded, and the influence of proppant with different types and particle size on the conductivity is mainly studied with Jimsar shale oil as the test medium. The experimental results show that 70–140 mesh quartz sand can not be used as the main proppant of Jimsar shale oil, and the combination of multi grain quartz sand can meet fracture-controlled reserves for the demand of shale oil.

The problem of extinguishing oil layer seriously affects the developing effect of fire flooding, it is necessary to reignite in time. In order to make clear the reason of extinguishment, optimize the technical parameters and realize the reignition of extinguishing oil layer, the study firstly analyzed the parameters such as injected volume and pressure, gas composition of producing well in Wellblock Hongqian-1, which clarified the reason of fire extinguishing. Whereafter, the minimum temperature of reignition after short-time extinguishment were investigated by physical simulation experiments. For selecting the kinds of auxiliaries suitable for Hongqian heavy oil, The thermogravimetric behavior of heavy oil with N-hexadecane, paraffin oil and castor oil was studied by means of a synchronous thermal analyzer. The study shows that the main reasons of extinguishment are lack of effective connectivity between injection and production wells, as well as the large fluctuation of injected parameters. Moreover, the extinguishing well in Wellblock Hongqian-1 can be reignited at 250 ℃. Paraffin oil and castor oil are helpful to ignite fire-extinguishing oil layer and promote high temperature oxidation process of Hongqian heavy oil. The study provides certain guiding significance to maintain productive stability and realize the reignition of extinguishing oil layer for Wellblock Hongqian-1.

Recent investigations have indicated that 2-methyltetrahydrofuran (2-MTHF) can be a potential alternative fuel, owing to its renewability and environmentally friendly properties. In this study, the effects of carbon dioxide (CO2), nitrogen (N-2), and helium (He) dilution on the laminar burning velocity (LBV) and cellular instability of 2MTHF-air flames were investigated experimentally and kinetically at a temperature of 423 K, a pressure of 5 bar, equivalence ratios (phi) of 0.7-1.5, and diluent ratios of 0-15%. The results illustrated that CO2 exhibited the strongest ability to reduce the LBVs, followed by N-2 and He. The effective Lewis number (Leeff) of the He diluted 2-MTHF-air flames increased as more He was added to the reactant mixture, thereby indicating that the intensity of diffusive-thermal instability could be diminished by He dilution. In contrast, Leeff was insensitive to CO2 and N-2 dilution. The flame thickness increased and the density ratio decreased as the diluent ratio increased, indicating that all three diluents suppressed the hydrodynamic instability of 2-MTHF-air flames. The relative magnitudes of the stabilizing abilities of these diluents were in the order CO2 > N-2 > He. The stability analysis indicated that the monotonically decreasing critical Peclet number and non-monotonically altered flame thickness caused a non-monotonic variation in the theoretical critical flame radius of 2-MTHF-air flames versus phi. The most chaotic state occurred at approximately phi = 1.3 under all test conditions. Notably, CO2 and He exhibited a similar ability to delay the onset of cellular instability, whereas N-2 demonstrated a weaker ability to do so.

2-butanone has been exploited as a promising next-generation biofuel candidate for its impressive knock resistant properties. However, its combustion characteristics and intrinsic instabilities have not been well explored. In this study, an experimental and theoretical investigation on laminar burning velocity (LBV) and onset of flame instability in spherically expanding flames of 2-butanone-air mixtures was conducted in a constant-volume chamber at temperature of 423 K, pressure of 1-8 bar, and equivalence ratio ( Phi) of 0.7-1.5. The measured LBVs and Markstein lengths of 2-butanone were observed to decrease noticeably as the pressure increased. Four recently established kinetic models were applied to predict the experimental data. Stability analysis was per -formed to investigate the effect of pressure and Phi & nbsp;on the onset of the cellular instability of 2-butanone flames. Results showed that the hydrodynamic instability monotonically increased as pressure increased and non-monotonically varied with increasing Phi. Thermal-diffusive instability increased dramatically as Phi & nbsp;increased while showed less sensitivity to the variation in pressure. The critical conditions at which the flame status turn stable into unstable were also evaluated. The critical Peclet number decreased monotonically as Phi increased, illustrating that fuel-rich flames suffer more severe cellular instability than fuel-lean flames. The critical flame radius decreased as pressure increased in both experimental measurements and theoretical calculations, reflecting that the onset of cellular instabilities of 2-butanone-air mixtures advanced to smaller radius at higher initial pressures.

Multistage hydraulic fracturing is used in horizontal wells to increase the production of tight oil. Fracturing fluids are used in hydraulic fracturing to ensure proppants are suspended, but fluid residuals can cause formation damage and reduce rock permeability; meanwhile, fracture conductivity can be further reduced due to the flowback of proppants during the early stage of production. In this study, steel plates and hydraulically fractured reservoir rocks are tested in a modified API cell to understand the impacts of flowback rate, fracturing fluid, and closure stress on proppant flowback and fracture conductivity. When the closure stress increased from 21 to 30 MPa, retained permeability decreased by slickwater from 35.71 to 29.84% in steel plates; during the flowback, more than 47% of proppants flowed back, and the fracture conductivity increased by 10 times under 21 MPa, which shows the limitation of the API method on the study of proppant flowback. When shale plates are used, the critical flow rate that prevents the proppant flowback was found to be 5.5 X 10(-4)-1.6 X 10(-3) m/s for the 30/50 mesh sands (around 55-340 m(3)/d for a typical horizontal well), and the retained permeability decreased from 23.33 to 22.86% due to an increase of closure stress from 21 to 30 MPa. Results of this study can guide the optimizing of the flowback scheme in the field that minimizes the proppant flowback in different fracturing fluids.

A spherical propagating flame experiment was performed to study the laminar burning velocities (LBVs), Markstein lengths, and onset of instability of flame fronts for dimethyl carbonate (DMC) at 373 K and initial pressures up to 8 atm, over the equivalence ratios of 0.7-1.5. An investigation of replacing synthetic air (21% O-2/79% N-2) with a mixture of 85.7% helium and 14.3% O-2 was carried out to present an in-depth analysis of instability for DMC spherical flames. The LBVs of both DMC/O-2/N-2 and DMC/O-2/He mixtures are observed to exhibit a downward trend with increasing pressures and reach their peak values in a slightly fuel-rich region near an equivalence ratio of 1.1. Measurements were subsequently compared to the simulations using three kinetic models available in the literature, revealing that the Alexandrino model yields better consistency with experimental LBVs. Sensitivity analysis was adopted to study the effect of pressure on DMC oxidation, in which sensitivity variation coefficients and normalized sensitivity variation coefficients were calculated to recognize the impressionable reactions to varying pressures. The results reveal that the increase in the initial pressure greatly facilitates some chain termination reactions, consequently causing competition to the dominated chain-branching reaction O-2 + H = O + OH, hence leading to the reduction in LBVs. Flame instability analysis indicates that the elevated initial pressures expand the instability of flame fronts and promote the formation of cellular structures. With the increase of the equivalence ratio, the flames would suffer stronger instability. While oxidizers with a diluent gas of helium can effectively suppress the cellular instability, it can be attributed to the higher diffusivity and lower specific heat of helium.

This study experimentally and numerically determined the laminar burning velocities (LBVs) of methane-air and dimethyl ether-air flames with the addition of CH2CFCF3 (HFO-1234yf) to assess its suppression capability. Experiments were conducted using an optically tracked, constant-volume combustion vessel at 0.1 MPa and 298 K. The experimental data on the laminar burning velocities were compared with the numerical predictions obtained using a recently developed kinetic model for describing CH2CFCF3 combustion. Good agreement between the modeling results and predictions was observed for the stoichiometric and rich flames (phi = 1.3), whereas for the lean conditions (phi = 0.6), the modeling results had relatively large over predictions (by up to 44%) on the suppression effectiveness of CH2CFCF3 for high agent volume fractions. The measurement results indicated that the LBV reductions caused by the addition of CH2CFCF3 to CH4-air and DME-air flames were nearly equivalent to those of CF3Br under rich conditions. For the lean mixtures, CH2CFCF3 caused a significant increase (by up to 180%) in burning velocity for all test concentrations. The modeling of flame propagation using a detailed model was performed to interpret the switch in the relative performance of CH2CFCF3 with the mixture's stoichiometry.

The laminar burning velocities (LBVs) and cellular instability of 2-methyltetrahydrofuran (2-MTHF) were investigated at the unburned temperature of 423 K and pressures from 1 to 10 atm in a cylindrical constant-volume vessel. The LBVs of 2-MTHF/air flame exhibit a notably dropping with increasing pressure. The cellular instability analysis indicates that the critical flame radius of 2-MTHF/air mixture monotonically increases with increasing pressure and the flame surface suffers more badly cellularity under higher pressures. The critical flame radius exhibits non-monotonic variation versus phi and the most unstable flames appear at phi approximate to 1.3. It is observed that the measured Markstein length of 2-MTHF/air mixture decreases with increasing phi and P-u, leading to an earlier formation of wrinkling and cracks with respect to preferential-diffusional instability. Further investigation found that by using a mixture of 14.2% oxygen with 85.8% helium in place of air as bath gas at 10 atm can effectively suppress the cellular instability. Two recently developed models were used to simulate the experimental results and explore the chemical kinetic effects on LBV. Reaction path analysis reveals that the most consumption of 2-MTHF/air at stoichiometric conditions is through the abstraction of H-atom to form radical C5H9O-5. While the competitiveness of decomposition by C-C scission yielding CH3 and tetrahydrofuran radical is relatively weak. Sensitivity analysis illustrates that smallspecies reactions show a controlling effect on LBV. The increasing pressure leads to an evident increase in the sensitivity coefficient of the recombination reaction H+O-2 (+M) = HO2 (+M). The reduction of H atom concentration will cause competition to the initiation reaction H + O-2 = O + OH. This could lower the overall oxidation rate and reduce the burning velocity. (C) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.