Study of the slippage of particle / supercritical CO2 two-phase flow

In this paper, the slippage velocity and displacement between particles and supercritical CO2 (SC-CO2) were studied to reveal the particle-SC-CO2 two-phase flow behavior. Visualization experiments were performed to directly measure the slippage velocity and displacement. Eight groups of experiments involving various pressures (7.89–10.96 MPa), temperatures (38.6–47.5 °C), particle diameters (0.3–0.85 mm), particle densities (2630 and 3120 kg/m3) and SC-CO2 flow rates (0.920–1.284 m/s) were conducted. The measured particle slippage velocities in the flowing direction were approximately 10.3% of the SC-CO2 flow rate. The measured particle slippage displacements were all at the centimeter level, which indicated that SC-CO2 had a superior particle transporting capability that was similar to those of liquids even if it had a low viscosity that was similar to those of gases. A numerical model was built, and analytic slippage calculations were performed for SC-CO2 for additional analyses. The density of SC-CO2 was found to have a greater influence on the slippage than the viscosity. Moreover, a comparison of the slippage between SC-CO2 and water showed that the particle slippage in water was constant, while the particle slippage in SC-CO2 continually accumulated at an extremely slow rate

Swelling and embedment induced by sub- and super-critical-CO2 on the permeability of propped fractures in shale

Swelling and embedment exert significant influence on the evolution of permeability in propped fractures, potentially consuming significant proportions of the original gain in permeability. We measure the evolution of permeability in propped fractures of shale to both adsorbing CO2 and non-adsorbing He – accommodating the impacts of aperture change due to proppant pack compaction and both reversible and irreversible modes of embedment. A linear relation between pressure and log-permeability is obtained for He, representing the impact of effective stresses in proppant pack compaction, alone. Permeability change with pressure is always concave upwards and U-shaped for gaseous subcritical CO2 and W-shaped for supercritical CO2. One exception is for liquid CO2 at high injection pressure where effective stress effects and swelling contribute equally to the change in permeability and result in a linear curve with the lowest permeability. Approximately ~50–70% of the permeability recovers from the recovery of swelling after the desorption of CO2. The magnitude of swelling is recovered from measurements of permeability change and ranges from 0.005 to 0.06 mm, which contributes ~9–56% of the total swelling and induced embedment as evaluated from the adsorbed mass. Swelling also increases embedment by a factor of ~1.84–1.93 before and after the injection of CO2. A new calibration equation representing swelling and induced embedment is generated accommodating Langmuir isothermal sorption and verified against experiments on rocks both admitting and excluding swelling and embedment and for various sorbing and non-sorbing gases. Stability and accuracy of the predictions demonstrate the universality of the approach that may be applied to both enhanced gas recovery and CO2 sequestration

Effect of slickwater-alternate-slurry injection on proppant transport at field scales : a hybrid approach combining experiments and deep learning

Proppant transport in underground fractures plays a key role in mitigating sand screen-out and enhancing the stimulated production for hydraulic fracturing. The effects of field pumping schedules, however, are not fully studied. We investigate the effect of slickwater-alternate-slurry injection on proppant transport at field-practical scales. A new hybrid approach is proposed to directly connect experimental studies with field operations, which consists of observation experiments, calculations, and deep learning (DL) workflow. The experiments reveal that the alternate injection induces the unexpected proppant ridge. The modified calculations (considering the ridge height) are proposed to extract features for training the DL algorithm. The workflow predicts the downhole pressure (mainly governed by proppant injection) for error analyses. Approximately 20.2% of the error is eliminated by considering the proppant ridge, thus demonstrating its effect on proppant injection. The predictions are significantly improved in early and late periods of fracturing operations when the fracture is initially created and highly filled. The sensitivity analysis suggests that the pump rate may dominate the ridge height compared with other hydraulic parameters. The study of proppant ridge complements the mechanisms of proppant transport, which is essential for controlling fracturing pressure and boosting the proppant injection

An evaluation method of supercritical CO2 thickening result for particle transporting

This paper aims to propose an evaluation method for measuring the supercritical CO2 thickening result for particle transporting. By analyzing the particle transporting trajectory in supercritical CO2, the cotangent of particle landing angle (ratio of particle horizontal velocity to vertical velocity) was proposed as a new criterion of thickening result. Previous studies of supercritical CO2 thickening were evaluated and drawn in three dimensions using this new criterion. Moreover, the effects of CO2 density and viscosity on particle vertical and horizontal velocities and the cotangent of particle landing angle were analyzed. The cotangent of particle landing angle is more sensitive to supercritical CO2 density than viscosity. Therefore, supercritical CO2 density should be considered for the evaluation of supercritical CO2 thickening for particle transporting. The particle settling velocity was found to determine the particle transporting distance and also the transporting capability of supercritical CO2. According to this conclusion, the apparatus for experimental evaluation of supercritical CO2 thickening will be miniaturized significantly by the simplification from two-dimensional velocities measurement into one direction, particle settling velocity in vertical direction. Additionally, the supercritical CO2 viscosity was found to have an optimum value, exceeding which the effect of viscosity on particle transporting levels off

Incipient motion behavior of the settled particles in supercritical CO2

The incipient motion process of settled particles in supercritical CO2 was studied through experimental measurements and force analyses. By referring to the theories of sand-wind and sediment restarting, the incipient motion state description and mechanism were optimized to fill the theoretical gaps in particle restarting research in the petroleum industry. Visualization experiments were carried out under various temperature, pressure, and particle conditions. The critical pump rates for the onset of grain motion in supercritical CO2 were measured. A critical pump rate empirical formula was obtained based on the experimental results and a derived Shields number expression. The average critical Shields number in supercritical CO2 was 0.0028. The cohesive force on particles is zero in supercritical CO2 based on its non-interfacial-tension characteristic. The measured spinning rate of the restarting particles in supercritical CO2 was 121 r/s on average. Therefore, the calculated value of the Magnus force was approximately 30% of the force of gravity on particle. Particle incipient motion in supercritical CO2 has a varying driving force (Magnus force) and simple resistant force (lack of cohesive force), which enhances the incipient motion of particles in supercritical CO2

Calculation on the following performance of proppant in supercritical carbon dioxide

As a new type of fracturing fluid, supercritical carbon dioxide (SC-CO2) has now become the research hotspot in domestic and foreign academia. However, the relevant technique is limited by the unclear sand-carrying mechanism. In this study, the concept of following performance is introduced to investigate the sand-carrying performances of fracturing fluid; the following performance of proppant and the sand-carrying performance of fracturing fluid are characterized by the ratio of the proppant horizontal velocity to the fracturing-fluid horizontal flow velocity. Then the following performance of proppant is used as the criteria for evaluating the horizontal sand-carrying performances of SC-CO2. Based on the classic BBO equation, the expression of drag force has been modified; in combination with the auxiliary equations of drag force coefficients, a calculation model has also been established to analyze the following performance of proppant in SC-CO2, which provides the theoretical foundation for evaluating and optimizing the transportation of proppant in SC-CO2. To verify the correctness of the model, an experiment is conducted on the following performance of proppant using the self-developed equipment, and then the factors that affect the following performance of proppant in SC-CO2 are analyzed. The results show that the following perfomance of proppant is slightly affected within the common range of density, which is consistent with the previous experimental results. In addition, a comparative analysis is performed on the following performance of sands in SC-CO2, slickwater and air. The analysis results indicate that the sand-carrying performance of SC-CO2 is more affected by its high-density property but less affected by its low viscosity. Because of high-density and low-viscosity properties, SC-CO2 is far better than air but worse than or approximately equal with slickwater in terms of sand-carrying performances. Especially at a high flow velocity, the horizontal sand-carrying performance of SC-CO2 is comparable to that of slickwater

Review of fundamental studies of CO2 fracturing : fracture propagation, propping and permeating

CO2 fracturing is one potential technique to relieve environmental issues related to the massive hydraulic fracturing of hydrocarbon reservoirs. We summarize fundamental studies on overall procedures of CO2 fracturing and analyze research progress related to fracturing, the propping of the induced fractures and permeating CO2 into, then recovering hydrocarbons from, the formation. The key controlling characteristics in CO2 fracturing at each stage are defined, together with a definition of their relative dominance. Fractures generated by CO2 fracturing are typically viewed as of superior complexity but increased tortuosity. Proppant transport during CO2 stimulation is evaluated through consideration of particle settling, remobilization and flowing behaviours. New views of permeability evolution in propped fractures as a function of CO2 saturation are presented. Correlations among each procedure are revealed to identify common issues and key technical details illuminated through multidisciplinary efforts. The field case studies of CO2 fracturing are collected for the analysis of hydraulic parameters and then compared against water-based fracturing. The mismatch between pumping rate and CO2 viscosity is highlighted, suggesting that the role of wellbore friction is an important topic requiring resolution. Suggestions for the optimization of CO2 thickening, the usage of fine proppants and injected form of CO2 are discussed and illustrated. Other open questions remain with respect to the nature of CO2-rock interactions and their resultant impact on permeability evolution and fracture generation – key issues are identified for future investigations to promote the popularization of CO2 fracturing for the concurrent and complementary recovery of native hydrocarbons and sequestration of carbon emissions

A Simplified Capillary Bundle Model for CO2-Alternating-Water Injection Using an Equivalent Resistance Method

CO2-alternating-water injection is an effective way of enhancing recovery for low-permeability oil reservoirs. The injection process is one of the essential issues that are facing severe challenges because of the low permeability and poor pore space connectivity. Previous researchers mentioned that water injection ability could be decreased by around 20% after the CO2-flooding; hence, it is necessary to quantify the water injectivity variation during an alternated injection process. In this paper, a CO2 convection-diffusion model is established based on the seepage law of CO2 and dissipation effect. The relationship between the width of miscible flooding and injection time is defined. Besides, an equivalent resistance method is introduced for developing a capillary bundle model for featuring an unequal diameter for CO2 water vapor alternate flooding. CO2-oil and CO2-water interactions are analyzed using the new model. The effects of oil viscosity, pore throat ratio, CO2 slug size, and equivalent permeability of the capillary bundle on water injection are analyzed. The result indicates that water injection ability increases with the rise of CO2 slug size and equivalent permeability of the capillary bundle and decreases with the increase of viscosity and pore throat ratio

A novel transcription factor Rwdd1 and its SUMOylation inhibit the expression of sqr, a key gene of mitochondrial sulfide metabolism in Urechis unicinctus

Sulfide-quinone oxidoreductase (SQR) is a key enzyme of sulfide metabolism in metazoans, and responsible for oxidizing sulfide into thiosulfate and transmitting the generated electrons to the ubiquinone. It has been revealed that the sqr mRNA level increases significantly in echiuran worm Urechis unicinctus exposed to sulfide, and HSF1, NF1 and Sp1 have been verified to participate in its transcriptional regulation. In this study, we obtained 23 potential transcription factors interacting possibly with the proximal region (-391 to +50) of sqr promoter, and focused on the RWD domain-containing 1 (Rwdd1), a protein with the maximum number of clones in yeast one hybrid (Y1H) screening, to investigate its transcriptional regulation to U. unincitus sqr. The ChIP and EMSA assays identified that the Rwdd1 can bind directly to the promoter (+18/ +36) of U. unicinctus sqr. The point mutation and transient transfection experiments discovered that TACG was the key sequence of the DNA element bound by the Rwdd1. Furthermore, the U. unicinctus Rwdd1 (UuRwdd1) was identified to be a transcription repressor inhibiting the sqr promoter activity, and the SUMOylation of UuRwdd1 at the lysine of 90th enhanced its inhibitory effect on sqr transcription further. Western blotting found Rwdd1 responded to sulfide in hindguts from U. unincitus, and the protein content showed a remarkable drop in hindgut nuclei in the early sulfide exposure, and then increased significantly both in the total protein and the nuclear protein extract. We suggested that the Rwdd1 is a novel transcription factor, and these data improve our understanding of the sqr transcriptional regulation and the mitochondrial sulfide metabolism

Celastrus orbiculatus extracts induce apoptosis in mTOR-overexpressed human hepatocellular carcinoma HepG2 cells

Abstract Background Celastrus orbiculatus (Celastraceae) are used as traditional Chinese medicine to treat inflammation and cancer. This study aims to evaluate the effect of Celastrus orbiculatus extract (COE) on the apoptosis in human hepatic carcinoma HepG2 cells with mTOR overexpression. Methods The stable expression of mTOR in HepG2 cells (HepG2/mTOR+) were established by lipofectin transfection of GV238-mTOR recombinant plasmids and further antibiotic selection. Human hepatic carcinoma HepG2/mTOR+ cells were treated with different concentrations (20, 40, 80, 160, and 320 μg/mL) of COE for 24 h. The cell proliferation upon COE treatment was detected by MTT. Apoptosis was measured by Flow Cytometry. The activity of mTOR signaling pathway was detected by Western Blotting. Results COE significantly inhibited the proliferation of HepG2/mTOR+ cells. The expression levels of Bax and Caspase-3 protein were increased in the HepG2/mTOR+ cells in a dose-dependent manner. The proteins expression of Bcl2, Bcl-2 L12, mTOR, phospho-mTOR, 4EBP1, phospho-4EBP1, P70S6k, and phospho-P70S6k in HepG2/mTOR+ cells were reduced in dose-dependent manners. Furthermore, COE and mTOR inhibitor rapamycin (RAPA) synergistically induced apoptosis in HepG2/mTOR+ cells by regulating apoptosis-related proteins and inhibiting mTOR signaling pathways. Conclusion COE could inhibit the proliferation of HepG2/mTOR+ cells, and induce the cell apoptosis. The mechanisms may be related to the regulation of the expression of Bcl-2, Bcl-2 L12, and mTOR signaling pathways. These data suggest that COE may be a potential treatment for human hepatocellular carcinoma