Gel Plug Research Articles

Synthesis of Chalcones: An Improved High-Yield and Substituent-Independent Protocol for an Old Structure.

Chalcones are a type of molecule that can be considered as easily synthesizable through aldol condensation or that can be readily purchased from habitual commercial vendors. However, on reviewing the literature, one realizes that there are no standard procedures for such aldol condensations, that there exists a wide range of alternative methods for the aldol condensation (indicating that such a condensation is not always simple), and that, in many cases, low yields are obtained that involve purifications by recrystallization or column chromatography. To develop a robust standard protocol independent of the nature of the substituents present on the acetophenone or the benzaldehyde involved in the aldol condensation leading to the chalcone, we made a comparison between an aldol condensation in KOH/EtOH and a Wittig reaction between the corresponding ylide and benzaldehyde in water. We describe an improved procedure for the Wittig reaction and a protocol for the elimination of the Ph3P=O byproduct (and the excess of ylide used) by filtration of the crude reaction product through a silica gel plug. We thus demonstrate that such an improved procedure can be a general method for the synthesis of chalcones in high yield and excellent purity and is clearly an improvement on the classical aldol condensation.

Abstract P1129: Directing Revascularization In Vivo With Local Controlled Release Of An Optimized Angiogenic Growth Factor Cocktail

Reduced vascular perfusion due to aging, ischemia, or injury impedes healing and tissue function in conditions like skin ulcers and myocardial infarction, motivating development of therapies to restore vasculature locally in target tissues. We hypothesize that specific combinations of signaling molecules stimulate angiogenesis and vascular remodeling in the local tissue environment to increase perfused vessel density. Using a vascular tissue engineering approach with a fractional factorial design of experiments (DOE), we evaluated in vivo angiogenesis of combinations of ten growth factors, cytokines and/or enzymes including VEGF, bFGF, Shh, PDGF, IGF-1, EGF, TGF-β1, Ang-1, MCP-1 and MMP-9 in a subcutaneous gel plug assay in the WT immune competent rat. Our initial assessment with Matrigel identified 5 factors that maximized CD31+ vessel lumen density and aSMA+ encoated vessels at 7 days, warranting further evaluation. We developed a fully defined biomaterial system with covalently bound heparin to alginate mixed with collagen type 1 as an injectable gel. This defined biomaterial prolonged protein release up to 14 days in vitro versus Matrigel and unmodified alginate (2-4 days). The defined biomaterial was used for a second round DOE to deliver high (2 μg) and low (0.5 μg) doses of VEGF, bFGF, Shh, PDGF, and/or IGF-1. The defined biomaterial alone enhanced average lumen diameter 15-fold and endothelial cell infiltration 12-fold versus Matrigel. Perfused lumen density increased 16-fold with high Shh; aSMA-positive lumen wall area increased 4-fold with high VEGF, PDGF, and IGF-1; perfused vessel size increased 3-fold with high VEGF, bFGF, and Shh; and endothelial cell recruitment increased 2-fold with high IGF-1 relative to unloaded controls after 7 days in vivo. Empirical testing of 2- to 5-factor combinations showed that cocktail potency required initiation of angiogenic sprouting by VEGF or bFGF and vascularization responses were strongest in the presence of Shh and IGF-1. In conclusion, we identified sets of highly potent cocktails and leveraged controlled release from a defined biomaterial as a tailored revascularization therapy for local angiogenesis, vascular remodeling, and tissue regeneration.

NEW APPROACH TO SIMULATION AND EFFICIENCY PREDICTION OF PRECIPITATION AND GEL ENHANCED OIL RECOVERY METHODS

Link for citation: Fedorov K.M., Gilmanov A.Ya., Shevelev A.P. New approach to simulation and efficiency prediction of precipitation and gel enhanced oil recovery methods. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 5, рр.85-93. In Rus. Relevance. The problem of conformance improvement by precipitation and gel technologies application may be associated with mathematical objective with infinitesimal parameter in which size of gel plug placement in the near wellbore zone of injector is significantly less than interwell distance. Existing approaches to modeling this problem do not allow describing all the effects associated with low-volume injections. The objective of the article is to suggest the approach to simulation and efficiency prediction of precipitation and gel injection technologies. Objects: oil reservoirs on which precipitation and gel enhanced oil recovery methods are used. Materials and methods. New approach to modeling such a problem consists of gluing the optimization objective of injection profile conformance and objective of the prediction of surrounding producers’ response. This approach is briefly described in the paper and is validated by the comparison of calculated data with the results of statistical processing of the data of precipitation and gel enhanced oil recovery technologies application on the fields of one of Russian oil companies. Results. Processing of the accumulated field experience in the use of these technologies has shown that the specific values of additional oil production after the operation of conformance improvement grow with the increase in the introduced criterion of processing efficiency – the conformance improvement coefficient and, conversely, decrease with a drop in the well injectivity coefficient after processing. The proposed approach to forecasting and evaluating the effectiveness of the use of technologies to conformance control is the basis of a line of mathematical models for the use of gel, precipitation and suspensions injection technologies.

Performance Evaluation of Polysachharide based Biomaterials for Sand Stabilization

Recent research on soil improvement have showed that the use of biopolymers can significantly enhance the various engineering properties of the soil. Soil improvement using biopolymers has attracted considerable attention in recent years, with the aim to reduce the harmful environmental effects of traditional materials. This report aims to provide a review on the environmental assessment of biopolymers as binders in soil improvement, biopolymer-treated with soil characteristics, as well as the most important factors affecting the behavior of the treated soil. Various geotechnical properties are evaluated and compared, including the unconfined compressive strength, and durability of biopolymer-treated soils. The usage of biopolymers has positive effects on the soil in the form of enhanced strength, However, a thorough understanding of the geotechnical qualities is required in order to completely apply the biopolymer technology to the fields. Biopolymer kinds, soil types, biopolymer contents, curing times, thermal treatment, and mixing techniques all play a significant role in how effective biopolymers are at improving the ground. In this part of study, the pycnometer method, sieve analysis, standard proctor compaction tests, unconfined compression test, durability, gel plug tests, pH test, and FTIR test, were used to understand and analyze the pectin-treated sand. Keywords: Pectin,Geotechnical Engineering,Bio Polymer- Treated soil

Antiangiogenic activity of the penicillin derivative TAP7f in melanoma.

Previously , we demonstrated that the non-antibiotic penicillin derivative TAP7f inhibited melanoma metastasis in vitro and in vivo through the downregulation of β-catenin and integrin αVβ3. As angiogenesis is required for tumor growth and metastasis, we decided to explore the possible antiangiogenic effect of TAP7f. We found that TAP7f inhibited proliferation, migration, tube formation, and actin cytoskeleton organization of human endothelial cells. In a gel plug assay, an in vivo model for angiogenesis, TAP7f also blocked vascular formation induced by fibroblast growth factor 2. Furthermore, when murine B16-F10 melanoma cells pre-treated with TAP7f were injected intradermally in mice, we observed a decrease in the number and thickness of the capillaries surrounding the tumor. Additionally, TAP7f downregulated vascular endothelial growth factor (VEGF) and platelet-derived growth factor-B (PDGF-B) expression in B16-F10 cells and VEGF receptor expression in HMEC-1 endothelial cells. When the antitumor effect of TAP7f was studied in C57BL/6J mice challenged with B16-F10 melanoma cells, a significant reduction of tumor growth was observed. Furthermore, a decreased expression of VEGF, PDGF-B, and the endothelial cell marker CD34 was observed in tumors from TAP7f-treated mice. Together, our results suggest that the antiangiogenic activity of TAP7f contributes to its antitumor and antimetastatic action and positions this penicillin derivative as an alternative or complementary agent for the treatment of melanoma. KEY MESSAGES: • TAP7f inhibits proliferation, migration, tube formation, and actin cytoskeleton organization of endothelial cells. • TAP7f downregulates VEGF receptor expression in endothelial cells. • TAP7f downregulates VEGF and PDGF expression in melanoma cells. • TAP7f inhibits angiogenesis in vivo.

Design and Evaluation of Pulsincap System Containing Nanosuspension of Montelukast Sodium for Chronotherapy in Asthma

In the present study, an attempt was made to prepare a pulsincap chronomodulated drug delivery system for the treatment of asthma and associated early morning allergy. Pulsincap capsule was prepared by sealing the drug nanosuspension inside the formaldehyde treated insoluble capsule bodies with a swellable and erodible guar gum plug. The drug, Montelukast sodium (MLS) nanosuspension was prepared by emulsion-solvent evaporation method using HPMC E15 and sodium lauryl sulphate (SLS). Nanosuspension formulations were optimized by using statistical Central composite design (CCD) for the required size and stability. The entire capsules were enteric coated using Cellulose acetate phthalate (CAP). This enteric coat prevents the drug release in the stomach, further the swellable hydrogel plug protect the nanosuspension to maintain the lag phase (5h) and facilitate its burst release in the colon. The length of this lag phase depends upon the concentration and quantity of the hydro gel plug. In order to simulate the GIT environment, the dissolution studies were performed using a sequential pH change method. DSC studies confirmed the absence of drug-excipient interactions. From the design space provided by the CCD, F14 and F15 formulations were considered as optimized. SEM studies were conducted for F14 formulation and this was filled in the Chronomodulated pulsincap systems (CMPs). These CMPs showed the drug release after 5h lag phase. Hence, when CMPs containing MLS nanosuspension is administered during bed time, it starts releasing the drug at the early morning hours to reduce asthma and associated early morning allergies like rhinitis and sneezing. Further, extensive in vivo studies are needed to be conducted to confirm the efficiency of these CMPs.

Developments of polymer gel plug for temporary blocking in SAGD wells

Polymer gels are potential plug agents to solve near wellbore issues. To meet the requirements of harsh reservoir conditions, enhancing the thermal stability and strength of polymer gels is still a challenging problem. In this study, we discuss the properties of phenolic/aldehyde-based polymer gels, aiming to provide suggestions of gel formulations for temporary blocking in SAGD wells. A power law relation, with an exponent of 1.2, was found between the modulus of HPAM gels and the polymer concentrations. It is also found that the strength of gels was increased with the hydrolysis degree and molecular weight of HPAM. Acetic acid and silica nanoparticles were proved to be effective additives to enhance the thermal stability of gels. It is demonstrated that acetic acid catalyzes the decomposing of hexamethylenetetramine (HMT) at low temperatures, while protects the dihydroxybenzene (DBH) from oxidation at higher temperatures. Experiments results showed that the HPAM gels could be stable for more than 7 days at 175 °C, while the co-polymer with heat resistance groups improved the applied temperature to 200 °C. Rupture pressure measurements showed that the polymer gels exhibit great blocking efficiency in sandpacks. However, the rupture pressure in wellbore is relatively lower as a result of squeeze out, rather than the destruction of gel structure. Finally, filed applications in 4 vertical wells and 1 horizontal well were introduced in detail. It is demonstrated that the gel plugs are applicable in a wide range of wellbore temperatures, from 60 °C to 191 °C.

In Situ Pinpoint Photopolymerization of Phos-Tag Polyacrylamide Gel in Poly(dimethylsiloxane)/Glass Microchip for Specific Entrapment, Derivatization, and Separation of Phosphorylated Compounds.

An improved method for the online preconcentration, derivatization, and separation of phosphorylated compounds was developed based on the affinity of a Phos-tag acrylamide gel formed at the intersection of a polydimethylsiloxane/glass multichannel microfluidic chip toward these compounds. The acrylamide solution comprised Phos-tag acrylamide, acrylamide, and N,N-methylene-bis-acrylamide, while 2,2′-azobis[2-methyl-N-(2-hydroxyethyl)propionamide] was used as a photocatalytic initiator. The Phos-tag acrylamide gel was formed around the channel crossing point via irradiation with a 365 nm LED laser. The phosphorylated peptides were specifically concentrated in the Phos-tag acrylamide gel by applying a voltage across the gel plug. After entrapment of the phosphorylated compounds in the Phos-tag acrylamide gel, 5-(4,6-dichlorotriazinyl)aminofluorescein (DTAF) was introduced to the gel for online derivatization of the concentrated phosphorylated compounds. The online derivatized DTAF-labeled phosphorylated compounds were eluted by delivering a complex of phosphate ions and ethylenediamine tetraacetic acid as the separation buffer. This method enabled sensitive analysis of the phosphorylated peptides.

Hydroxyapatite-hybridized double-network hydrogel surface enhances differentiation of bone marrow-derived mesenchymal stem cells to osteogenic cells.

Recently, we have developed a hydroxyapatite (HAp)-hybridized double-network (DN) hydrogel (HAp/DN gel), which can robustly bond to the bone tissue in the living body. The purpose of this study is to clarify whether the HAp/DN gel surface can differentiate the bone marrow-derived mesenchymal stem cells (MSCs) to osteogenic cells. We used the MSCs which were harvested from the rabbit bone marrow and cultured on the polystyrene (PS) dish using the autogenous serum-supplemented medium. First, we confirmed the properties of MSCs by evaluating colony forming unit capacity, expression of MSC markers using flow cytometry, and multidifferential capacity. Secondly, polymerase chain reaction analysis demonstrated that the HAp/DN gel surface significantly enhanced mRNA expression of the eight osteogenic markers (TGF-β1, BMP-2, Runx2, Col-1, ALP, OPN, BSP, and OCN) in the cultured MSCs at 7 days than the PS surfaces (p < 0.0001), while the DN gel and HAp surfaces provided no or only a slight effect on the expression of these markers except for Runx2. Additionally, the alkaline phosphatase activity was significantly higher in the cells cultured on the HAp/DN gel surface than in the other three material surfaces (p < 0.0001). Thirdly, when the HAp/DN gel plug was implanted into the rabbit bone marrow, MSC marker-positive cells were recruited in the tissue generated around the plug at 3 days, and Runx2 and OCN were highly expressed in these cells. In conclusion, this study demonstrated that the HAp/DN gel surface can differentiate the MSCs into osteogenic cells.

Using 1,2 dimethylimidazole to improve gel thermalstability for wellbore plugging in ultra-high temperature fractured reservoirs

Working fluid loss as well as formation damage is usually encountered as a big challenge during well completion and workover for fossil-fuel production. Polymer gel is widely used for wellbore plugging to isolate the working fluid and the reservoir for controlling fluid loss and protecting the reservoir. However, with the increasing number of ultra-high temperature well (>180 °C) operations, the thermal stability of the gel plug is increasingly required. In this paper, 1,2 dimethylimidazole (C5H8N2) is first used to prepare a gel plug. The effects of C5H8N2 on gel gelation at dynamic heating mode, viscosity, elasticity, thermal stability and temporary plugging performances are evaluated at 190 °C. It is found that the addition of C5H8N2 does not affect the gelation, while a slightly viscosity-reducing effect is exhibited. At 190 °C, the gel without C5H8N2 broke down within 4 hours and lost its temporary plugging performance, while the gel with 20% imidazole remained unbroken after 60 hours. For the fractured core (5 cm in length) plugging experiments, the addition of 15% C5H8N2 significantly increased the breakthrough pressure of gels from 0.2 MPa to 1.9 MPa compared to pure gels (without C5H8N2). The enhancement mechanism of C5H8N2 is investigated. Recommendations for the application of gels with C5H8N2 are given in the paper. This paper provides an avenue for the development of gel plug to deal with wellbore temporary plugging jobs in ultra-high temperature fractured reservoirs.

Micro-CT visualization of a promastigote secretory gel (PSG) and parasite plug in the digestive tract of the sand fly Lutzomyia longipalpis infected with Leishmania mexicana.

Leishmaniasis is a debilitating disease of the tropics, subtropics and southern Europe caused by Leishmania parasites that are transmitted during blood feeding by phlebotomine sand flies (Diptera: Psychodidae). Using non-invasive micro-computed tomography, we were able to visualize the impact of the laboratory model infection of Lutzomyia longipalpis with Leishmania mexicana and its response to a second blood meal. For the first time we were able to show in 3D the plug of promastigote secretory gel (PSG) and parasites in the distended midgut of whole infected sand flies and measure its volume in relation to that of the midgut. We were also able to measure the degree of opening of the stomodeal valve and demonstrate the extension of the PSG and parasites into the pharynx. Although our pilot study could only examine a few flies, it supports the hypothesis that a second, non-infected, blood meal enhances parasite transmission as we showed that the thoracic PSG-parasite plug in infected flies after a second blood meal was, on average, more than twice the volume of the plug in infected flies that did not have a second blood meal.

Pressure propagation and flow restart in a pipeline filled with a gas pocket separated rheomalaxis elasto-viscoplastic waxy gel

A clogged waxy crude oil pipeline, entails a high pressure to de-structure the gelled oil and resume its normal operation. Our earlier work, which utilized generalized Newtonian fluid based model, demonstrated that the presence of a gas pocket in-between the gel plugs, delays pressure propagation in the downstream gel plug [L. Tikariha, L. Kumar, Pressure propagation and flow restart in the multi-plug gelled pipeline, Journal of Fluid Mechanics. 911 (2021)]. This delay in pressure propagation is effectively utilized for sequential gel degradation. In the present work, we consider gel as a rheomalaxis elasto-viscoplastic (REVP) fluid, capable in predicting flow stoppage and pressure signal stoppage. The governing equations for mass, momentum balance, and phase equation are solved together with the REVP rheology model. The propagation of pressure in a REVP gel-filled pipeline is directly related to the gel material's elastic response. For a REVP gel, the flow-restart in a gelled pipeline depends on the conditional statement γ>γs (i.e. mean gel deformation overcoming the yield strain). In the case of a single gel plug, no-pressure propagation is predicted at intermediate compressibility, whereas pressure propagation without flow restart is predicted at low compressibility. In these cases, the presence of a small gas pocket instigates the gel breakage process, resulting in a flow restart. The gas pocket delays the pressure propagation in the second gel plug, resulting in a pressure gradient higher than yield stress across the first gel plug. The first gel plug, which deforms under a high-pressure gradient, compresses the gas pocket. This results in a larger mean deformation in the first gel plug, and it overcomes the threshold yield strain limit (γs). At strain values larger than yield strain the gel structure breaks, resulting in a lower elastic strength in the first gel plug. The lower elastic gel strength ascertains a lower pressure gradient in the first gel plug, allowing a largely unattenuated pressure to propagate in the second plug. The propagation of unattenuated pressure in the second gel plug results in a pressure gradient higher than the yield stress. This causes sequential gel breakage, resulting in a successful flow restart in a pipeline longer than a critical length. The present study also demonstrates that the pressure propagation and initial transient flow depend on the gel properties (i.e. gel strength and compressibility) and the number and size of gas pockets in the gel. The insights gained from the present work provide a cost-effective solution to mitigate the flow restart problem.

An appraisal of the hydro-mechanical behaviour of polysaccharides, xanthan gum, guar gum and β-glucan amended soil

The study aims to investigate the hydro-mechanical behaviour of the polysaccharide amended sand-clay mixture and analyse the soil – biopolymer interaction. Parameters like permeability, strength and heavy metal attenuation capacity of the amended soil were characterized and studied particularly for its use in landfill applications. The permeability of the soil was investigated for a period of one year. The results of the investigation show that all the selected polysaccharides significantly reduce the permeability and improve the heavy metal adsorption capacity of the sand-clay mixtures. The biopolymer also contributes to the increase in the strength of the soil. The improved mechanical properties of the amended soil can be ascribed to the bio-clogging through gel plug formation and bonding action of the biopolymers. Xanthan gum amended soil showed the least permeability, highest strength and adsorbed the selected heavy metals almost entirely, showing the best performance as a liner material.

Guar gum-stabilized soil: a clean, sustainable and economic alternative liner material for landfills

Biopolymers have attracted much attention in the field of geo-environmental engineering as they provide a carbon–neutral alternative for soil stabilization and heavy metal removal. This study explores the possibility of using guar gum-stabilized soil (GGSS) as a landfill liner by improving the hydromechanical behaviour and heavy metal attenuation capacity of the poorly graded sand–clay mixture. The results demonstrate that the unconfined compressive strength improved by 1.75 folds, and hydraulic conductivity after 120 days of curing decreased by 2.72 × 105 folds at 2% guar gum addition. Additionally, it withstands adverse environmental conditions and increases the heavy metal attenuation capacity of the soil. Leachate studies show that GGSS has a good capacity to adsorb heavy metals like lead, copper, cadmium and zinc. Micrographs from the scanning electron microscope demonstrate gel plug formation and bioclogging in the soil matrix with the addition of guar gum leading to favorable modifications in the geotechnical properties of the stabilized soil. The durability of the stabilized soil strongly depends on the biopolymer concentration. The soil stabilized with a higher dosage shows better resistance against alternate cycles of wetting and drying than lower dosages due to weak inter-particle connection. Guar-stabilized soil is also more economic than conventional bentonite liners. The study demonstrates that guar gum can be considered as an ideal liner material for landfills with specific advantages like replacing a nonrenewable material, bentonite with clean and renewable material, guar gum.

Pressure propagation and flow restart in the multi-plug gelled pipeline

An understanding of pressure propagation mechanisms is crucial in finding suitable conditions for the temporary storage, transmission and attenuation of a large pressure signal in a multi-plug gelled pipeline. The current work investigates the transient flow start in a multi-plug gelled pipeline, filled with a weakly compressible, thixotropic waxy gelled crude oil. A multi-plug gel can form either naturally or artificially. We solve time-dependent mass and momentum conservation equations for the gas phase and conservation equations together with a shear-history-dependent constitutive model for the gel phase to capture the transient phenomena. An advection equation traces the motion of the gel–gas interface using the volume of fluid method. The results of this work show that pressure propagation in the first gel plug compresses it. The compressed first gel plug further compresses the gas pocket, which delays pressure propagation in the downstream gel. The delay in the pressure propagation through the second gel plug creates a high-pressure gradient in the first gel plug. A high-pressure gradient in the first gel results in faster degradation of the first gel. Degraded gel offers a substantially lower resistance to flow, allowing a high-pressure gradient in the second gel. A steeper pressure gradient assists the breakage of the next gel plug and results in a sequential gel breakage. This sequential gel breakage allows flow restart in a long pipeline. The results also indicate that the compressibility of the gas pocket dominates the overall compressibility of the system, controlling both pressure propagation and flow-restart time.

Activation of toll-like receptor signaling in endothelial progenitor cells dictates angiogenic potential: from hypothesis to actual state.

Human endothelial progenitor cells (EPCs) were isolated from cord blood samples and enriched by magnetic activated cell sorting method based on the CD133 marker. Cells were incubated with different doses of bacterial lipopolysaccharide, ranging from 2, 5, 10, 50, 100, 200, 250, 500, to 1000µg/ml, for 48h. The cell survival rate was determined by using MTT assay. To confirm activation of the toll-like receptor signaling pathway, PCR array analysis was performed. Protein levels of ERK1/2, p-ERK1/2, NF-ƙB and TRIF proteins were measured using western blotting. The content of TNF-α and lipoprotein lipase activity were analyzed by immunofluorescence imaging. Flow cytometric analysis of CD31 was performed to assess the maturation rate. Cell migration was studied by the Transwell migration assay. The expression of genes related to exosome biogenesis was measured using real-time PCR analysis. In vivo gel plug angiogenesis assay was done in nude mice. Lipopolysaccharide changed endothelial progenitor cells' survival in a dose-dependent manner with maximum viable cells in groups treated with 2µg/ml. PCR array analysis showed the activation of toll-like signaling pathways after exposure to LPS (p<0.05). Western blotting analysis indicated an induction of p-ERK1/2 and Erk1/2, NF-kB and TRIF in LPS-treated EPCs compared with the control (p<0.05). Immunofluorescence staining showed an elevation of TNF-α and lipoprotein lipase activity after lipopolysaccharide treatment (p<0.05). Lipopolysaccharide increased EPC migration and expression of exosome biogenesis-related genes (p<0.05). In vivo gel plug analysis revealed enhanced angiogenesis in cells exposed to bacterial lipopolysaccharide. Data highlighted the close relationship between the toll-like receptor signaling pathway and functional activity in EPCs.

Impact of hydration and gelling properties of guar gum on the mechanism of soil modification

Soil improvement and treatment is a necessity off-late in response to the growing demand for construction spaces. Also, for the emphasis of development in the right direction, it is necessary to select a sustainable and economic technique to treat the soil. Biopolymers present such an eco-friendly alternative material for soil treatment. This study investigates the viability of using guar gum, a polysaccharide for improving the geotechnical properties of clay soil. Guar gum is solvable, non-ionic and hydro-colloidal in nature. The viscosity of guar solutions increases significantly with the gum content but the change in pH with viscosity is very marginal. Its nature to form bio-film and gel plug leads to a substantial decrease in the permeability of the treated matrix. Its tendency to form viscous gels, hydrate and form hydrogen bonds helps in improving the stiffness of the soil matrix and thereby enhances its strength. The treated soil behaves like clay in stiff consistency, failing at higher loads and lower strains with higher stiffness modulus. The formation of hydrogen bonds is a function of time, and hence, the strength of the treated soil–guar mixtures also increases with age. Though biopolymers are susceptible to decay and degradation, the rate of degradation is retarded and strength gain is observed throughout the period of investigation (i.e. 90 days).

Study of Gel Plug for Temporary Blocking and Well-Killing Technology in Low-Pressure, Leakage-Prone Gas Well

Summary A gel-plug system for temporary blocking technology is proposed in this paper to address the prevalent leakage of killing fluid in low-pressure wells; the low technical strength of existing gel plugs for temporary blocking in well killing; difficult-to-control crosslinking time; and gel embrittlement and the difficulty of breaking certain gel plugs. A mixture of etherified galactomannan plant gum, isooctanol polyoxyethylene ether surfactant, and oil phase was used as a thickener. An inorganic salt complex containing long-chain polyhydroxy alcohol was used as a crosslinker and the concentration of long-chain polyhydroxy alcohol far exceeds the theoretical amount required to complex the metal ion. A mixture of polyhydroxy alcohol with a small amount of weak acid was used as a crosslinking regulator. Finally, a mixture of sodium thiosulfate and long-chain quaternary ammonium salt surfactant was used as a stabilizer. Laboratory evaluations showed that this gel-plug system can be directly pumped into the wellbore after being mixed homogeneously, and the viscosity of the system on the surface can be controlled by the amount of crosslinking regulator. The viscosity of the gel-plug system after gelling was high (viscoelastic solid colloid); the initial viscosity reached 30 000 mPa·s at 120°C and retained a semisolid gel shape after aging for 72 hours. Right-angle thickening occurred when the gel warmed to target-zone temperature. The acidic liquid breaker acted quickly, and the viscosity of the broken fluid was lower than 5 mPa·s after 1 to 4 hours. This gel plug for temporary blocking and well-killing technology was successfully applied in a low-pressure, leakage-prone gas well. No gas, pressure, or liquid remained in the open well after killing, the wellhead was successfully replaced, and the tubing was successfully removed. The gel plug also exhibited self-healing: The hole formed by the tubing could be filled and sealed automatically by the gel plug in the annulus. The static friction (outer wall) of 73-mm tubing in the gel plug was 39.6 t/km; the dynamic friction (outer wall) after tubing removal was 7.2 t/km. This gel plug thus shows promise as a temporary blocking technology in workover operations of low-pressure, leakage-prone gas wells.

Improved understanding nanocomposite gel working mechanisms: From laboratory investigation to wellbore plugging application

Fluid loss is serious in low-pressure fractured reservoir. In this paper, the technique of wellbore isolation for temporary plugging is proposed to reduce the loss of workover fluid. Based on radical polymerization, the high-strength nanocomposite gel plugging agent was prepared by introducing nano-silica. Firstly, the strength properties of gel plug were studied through stress and strain evaluation, viscosity modulus test and wellbore sealing pressure evaluation, respectively. The working mechanism was revealed by infrared spectroscopy (FTIR), environmental scanning electron microscopy (ESEM) and differential scanning calorimetry (DSC) analysis. The study shows that under 50% compression strain, the compression capacity of the nanocomposite gel with 5% nano-silica is nearly three times higher than that of without adding nano-silica, and the thermal stability is improved by 38%, which has the potential to buffer the pressure of the liquid column in the bottom hole and perform good thermostability. Secondly, the actual wellbore simulation system confirmed its ability to seal the perforation zone. Result shows that the pressure-bearing gradient is 20 MPa/100m in the oil tube, and gel plug length can be designed according to the positive pressure demand. The addition of nano-silica makes the network of nanocomposite gel becoming denser, in favor to store more energy. The hydrogen bond generated in the nanocomposite gel increases its mechanical strength. Finally, the successful application of the nanocomposite gel for wellbore temporary plugging in a low-pressure carbonate gas well was summarized. This study provides an avenue to develop various nanocomposite gels for downhole jobs.

Thermal degradation behavior of seawater based temporary plugging gel crosslinked by polyethyleneimine for fluid loss control in gas well: Kinetics study and degradation prediction

Polymer gel served as a temporary plugging agent for fluid loss control during well completion and workover has received great attention in recent years. Gel breaking as well as flowback is the most concern after the downhole operations such as perforation, replace tubing. Using oxidative breaker as chemical method or jetting nozzle as mechanical strategy were mainly employed to remove gel. The former often fails to fully contact with the gel, and the gel breaking efficiency is not ideal. The latter, although effective, greatly increases the cost of operation. Thermal degradation of gel plug at reservoir temperature after the operation is more welcome. In this paper, we combined aging experiments, Fourier Transform Infrared Spectroscopy (FTIR) analysis, Scanning Electronic Microscopic (SEM) and Differential Scanning Calorimetry (DSC) experiment to reveal the degradation mechanism of seawater based temporary plugging gel crosslinked by polyethyleneimine (Abbreviated as “gel plug”). In addition, the fluid loss control ability and formation damage characteristic of the gel plug were evaluated through core flooding experiment. The dynamic process of gel degradation was studied by DSC technology, and the thermodynamic parameters were respectively calculated by Kissinger, Flynn-Wall-Ozawa, Horowitz-Metzger and Coats-Redfern model. According to the desired activation energy, Semenov equation and relevant data were used to derive the model for predicting gel degradation time. The developed model conforms to the aging experimental results with correlation coefficient of 0.988. This study provides knowledge for the optimization of temporary plugging gel technology in high-temperature gas wells.