Bentonite Pellets Research Articles

Green Approach in Water-Based Drilling Mud Design to Increase Wellbore Stability

Wellbore instability is one of the most serious problems that can occur during drilling, mainly during drilling oil or gas wells through rocks that contain a higher proportion of clay, such as shales. To prevent wellbore instability, oil companies apply different approaches to strengthen wellbore walls, and use different shale swelling inhibitors. The aim of this research was to apply a green approach and the concept of the circular economy in mud design, and to determine whether mandarin peel powder, which is a waste material, can be used as an inhibitor of shale swelling. For that purpose, pellets consisting of bentonite and quartz in a 50:50 ratio were prepared using a compactor, and bentonite-based drilling mud (BM) with and without mandarin peel powder in concentrations of 0.5, 1, 1.5 and 2% by volume of water. The swelling of quartz–bentonite pellets after 2 and 24 h in each drilling-mud sample was determined at room temperature and 90 °C using a linear swell meter. On the basis of laboratory research, we concluded that increasing the concentration of mandarin peel powder reduces pellet swelling. By adding mandarin peel powder particles between 0.1 and 0.16 mm to the base mud at a concentration of 2% by volume of water, the following was achieved: 44% reduction in API filtration, 61.54% reduction in PPT filtration, 45% reduction in pellet swelling after 24 h at room temperature, and 48.6% reduction of pellet swelling after 24 h at 90 °C.

Water infiltration and swelling pressure development in GMZ bentonite pellet mixtures with consideration of temperature effects

Bentonite pellet mixture (BPM) is considered as a potential buffer/backfill material for geological repository of radioactive waste. Once emplaced in a repository, the initially discrete BPM with heterogeneous porosity would be subjected to groundwater infiltrated from surrounding rock and decay heat released from nuclides, leading to temperature depended processes of water infiltration and swelling pressure development. In this study, Gaomiaozi (GMZ) BPMs were hydrated with distilled water under constant volume condition at temperatures 20, 40, 60 and 80 °C. The water content profiles, dry density profiles and swelling pressure were periodically measured and recorded, respectively. Results indicate that, both water infiltration and swelling pressure development were accelerated by increasing temperature. Due to local swelling formation that brining water ahead and prevailing vapour diffusion through the large interconnected inter-pellet voids, the water infiltration through the BPM was anomalous super-diffusion at non-Boltzmann scale. Accordingly, a non-Boltzmann variable based water infiltration model was developed and verified by the experimental data. The non-Boltzmann variable was inversely related to water content, dry density and montmorillonite content, whereas positively related to temperature. It was proved to be able to qualitatively reflect the mobility of water for different unsaturated soils with different water contents. In addition, a comprehensive explanation of temperature effects on swelling pressure was put forward, stating that the variation of swelling pressure with temperature depended on the competitions among the thermal-induced responses of hydration pressure, water pressure and osmotic pressure. The competitions could be controlled by the clay mineralogy, pore water properties, electrolyte properties and the clay-water-electrolyte interactions at micro scale, and by dry density, thermal mode and drainage condition at macro scale.

Notoginsenoside as an environmentally friendly shale inhibitor in water-based drilling fluid

The demand for non-toxic and biodegradable shale inhibitors is growing in the drilling industry. In this paper, the effect of notoginsenoside (NS) as a new, environmentally friendly inhibitor of shale hydration is systematically studied for the first time. The inhibition performance of NS was evaluated via inhibition evaluation tests, including mud ball immersion tests, linear expansion tests, shale rolling recovery tests, and compressive strength tests. The inhibition mechanism of NS was analyzed using Fourier transform infrared spectroscopy (FTIR), contact angle measurements, particle size distribution determination, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The experimental results demonstrate that NS is able to adhere to the clay surface, forming a hydrophobic film that prevents the entry of water molecules and inhibiting the hydration dispersion of the clay. Because of this, NS can maintain the original state of bentonite pellets in water, which can effectively reduce the swelling rate of bentonite, increase the recovery rate of shale drill cuttings, maintain the strength of the shale, and therefore maintain the stability of the borehole wall during drilling. In addition, NS is non-toxic, degradable, and compatible with water-based drilling fluids. The above advantages make NS a promising candidate for use as an environmentally friendly shale inhibitor.

Fabrication of a Hydrophobic Hierarchical Surface on Shale Using Modified Nano-SiO2 for Strengthening the Wellbore Wall in Drilling Engineering

Wellbore stability is essential for safe and efficient drilling during oil and gas exploration and development. This paper introduces a hydrophobic nano-silica (HNS) for use in strengthening the wellbore wall when using a water-based drilling fluid (WBF). The wellbore-strengthening performance was studied using the linear swelling test, hot-rolling recovery test, and compressive strength test. The mechanism of strengthening the wellbore wall was studied by means of experiments on the zeta potential, particle size, contact angle, and surface tension, and with the use of a scanning electron microscope (SEM). The surface free energy changes of the shale before and after HNS treatment were also calculated using the contact angle method. The experimental results showed that HNS exhibited a good performance in inhibiting shale swelling and dispersion. Compared with the use of water, the use of HNS resulted in a 20% smaller linear swelling height of the bentonite pellets and an 11.53 times higher recovery of water-sensitive shale—a performance that exceeds those of the commonly used shale inhibitors KCl and polyamines. More importantly, the addition of HNS was effective in preventing a decrease in shale strength. According to the mechanism study, the good wellbore-strengthening performance of HNS can be attributed to three aspects. First, the positively charged HNS balances parts of the negative charges of clay by means of electrostatic adsorption, thus inhibiting osmotic hydration. Second, HNS fabricates a lotus-leaf-like surface with a micro-nano hierarchical structure on shale after adsorption, which significantly increases the water contact angle of the shale surface and considerably reduces the surface free energy, thereby inhibiting surface hydration. Third, the decrease in capillary action and the effective plugging of the shale pores reduce the invasion of water and promote wellbore stability. The approach described herein may provide an avenue for inhibiting both the surface hydration and the osmotic hydration of shale.

Temperature effects on water retention behaviour and structural evolution of GMZ bentonite pellet mixtures

Mixtures of high-density, multi-sized bentonite pellets are considered as a promising buffer/backfill material for deep geological disposal of high-level radioactive waste (HLW). During the operation of a HLW repository, the pellet mixtures will be subjected to ground water infiltrated from surrounding rock and elevated temperatures induced by nuclide decay heat, leading to a complex hydro-mechanical behaviour. In this paper, water retention tests with suction controlled by vapour equilibrium and osmotic techniques, as well as structural observations by mercury intrusion porosimetry (MIP) were performed on three kinds of specimens of Gaomiaozi (GMZ) bentonite at different temperatures (20, 40, 60 and 80 °C), including constant-volume pellet mixtures (PM) and compacted blocks (CB) with an identical dry density (1.45 Mg/m3) and free-swelling single pellets with the same initial dry density (1.95 Mg/m3) as those involved in the PM specimen. For the three kinds of specimens, the water retention capacity decreased with increasing temperature. From a perspective of thermal dynamics theory, it is concluded that in high suction range (> 10 MPa), increasing temperature inhibited the water adsorption and promoted the water desorption process consequently leading to a decreasing water retention capacity. According to the capillary law (Young – Laplace equation), in the low suction range (< 10 MPa), increasing temperature reduces the capillary water content in terms of decreasing the surface tension, contact angle and density of the capillary water, as well as expanding the entrapped pore air. Meanwhile, the MIP test results illustrate that during hydration, most of the large pores (2000–360,000 nm) were gradually converted into medium pores (100–2000 nm) while the change of small pores (6.4–100 nm) and inaccessible pores (< 6.4 nm and > 360,000 nm) were limited. Compared to the effect of suction, the temperature influence on this structural evolution process was relatively slight. Therefore, the temperature-dependent water retention behaviour was mainly caused by temperature-induced changes of water-clay interactions as well as physical properties of adsorbed and capillary water during hydration, rather than the limited changes of pore structure of the specimen.

Investigation on healing behavior of unsaturated GMZ bentonite pellet mixture based on compressibility

Investigation on healing behavior of unsaturated GMZ bentonite pellet mixture based on compressibility

Soil–water characteristic curves and hydraulic conductivity of Gaomiaozi bentonite pellet-contained materials

The bentonite pellet-contained material (PCM) is a desired joint sealer for high-level radioactive waste repositories. During the operation of the repository, however, the PCM is unsaturated for most of the period. The water retention capacity and permeability of PCM can thus directly affect the bentonite buffer barrier seepage, nuclide migration, and joint healing. Moreover, the performance of PCM can be strongly influenced by the particle size of bentonite pellets and dry density. In this work, the pressure plate method and vapor equilibrium technique were both utilized to test the soil–water characteristic curves (SWCCs) of the PCMs with varying particle sizes and dry densities. The unsaturated hydraulic conductivity of the PCMs was then predicted by combining the SWCC model and saturated hydraulic conductivity. The results showed that in the low suction range (20–1150 kPa), the dry density and particle size are anti-correlated with the water content. In the high suction range (4200–309,000 kPa), the SWCC is almost insensitive to the variation of dry density and particle size. The Gardner model is suitable for describing the SWCC of PCM. In addition, the hydraulic conductivity of the PCM increases with the rise in particle size, while it decreases as the dry density grows. Finally, the influence mechanism of the SWCC and hydraulic conductivity was further discussed based on the scanning electron microscopy images and pore size distribution curves.

Water retention and compression behavior of MX80 bentonite pellet

Water retention and compression behavior of MX80 bentonite pellet

Thermal properties of GMZ bentonite pellet mixtures subjected to different temperatures for high-level radioactive waste repository

Thermal properties of GMZ bentonite pellet mixtures subjected to different temperatures for high-level radioactive waste repository

Pellets/block bentonite barriers: Laboratory study of their evolution upon hydration

Some deep geological nuclear waste disposal concepts are considering the installation around the waste canisters of bentonite barriers made up of two components: highly compacted blocks to support the canister and a granular buffer material consisting of bentonite pellets to fill the rest of the disposal gallery. The initial characteristics of these two components in terms of dry density, water content and microstructure are very different, but some, yet scarce, experimental evidence showed that saturation with groundwater will tend to homogenise the barrier. Nevertheless, the combined use of pellets and blocks in the same section of the barrier introduces difficulties in the understanding and modelling of the system performance that have to be addressed. With the aim of obtaining qualitative and quantitative information about the hydro-mechanical evolution of initially inhomogeneous bentonite samples (pellets/blocks) upon hydration under isothermal conditions, a series of laboratory tests in decimetre-scale cells was carried out. In most tests hydration took place through the pellets part, but the effect of hydrating through the block was also checked. As well, tests were performed either under low water injection pressure or under low water inflow rate.The results highlighted the role of the large macropores on the initial stages of hydration when this took place through the pellets, and also of the influence of water availability on its redistribution and on pressure build up. Pressure developed for lower degrees of saturation and water spread more homogeneously through the two sample components if hydration was slow. After full saturation differences in dry density across the two components remained, but they were softer if saturation took place at a slow pace, either because of the low water inflow rate or because it occurred through the less permeable block. The microstructure of the bentonite in the two components was very different even after full saturation: although there was an overall trend to pore size homogenisation towards smaller sizes over time, the ratio of microstructural void ratio to macrostructural void ratio kept lower in the pellets than in the block. As well, the number of water layers in the interlayer was higher in pellets samples than in block samples.The research also highlighted the importance of the right assessment of macroporosity (particularly pores larger than 550 μm) from mercury intrusion porosimetry tests and the likely effect of local density on the pressure measured.

Development of swelling pressure for pellet mixture and compacted block of GMZ bentonite

Bentonite pellet mixture is considered as a candidate buffer/backfill material for construction of artificial barrier in high-level radioactive waste (HLW) repository. Compared to that of a compacted bentonite block, one of the most obvious features of this material is its initially discrete pellets and significant structural heterogeneity, leading to a distinctive swelling behaviour. In this paper, a comparative study concerning development of swelling pressure on hydration was conducted on pellet mixture and compacted block of Gaomiaozi (GMZ) bentonite specimens with an identical dimensions (50 mm in diameter and 35 mm in height) and dry density (1.45 Mg/m3). Results show that, within the initial 72 h, the swelling pressure of pellet mixture increases at a lower rate and achieves a lower peak value than those of the compacted bentonite block. Then, the swelling pressure of the pellet mixture varies slightly while that of the compacted bentonite block decreases significantly before increasing again. Eventually, the swelling pressure for the two specimens approaches to an almost similar final stable value, 0.939 MPa and 0.947 MPa, respectively. Based on an insight into the mechanism of swelling pressure development, a new theory on competition between the accumulated and dissipated wedging pressures (AWP and DWP) within the specimen was proposed for interpreting the different developments of swelling pressure between the two specimens. As water infiltrates, the AWP continuously increases, while the DWP firstly increases and then decreases. At a given infiltration time, the AWP of pellet mixture is smaller than that of compacted bentonite block due to accommodation of the pellets swelling deformation by inter-pellet voids. While within the initial hundreds hours of infiltration, the DWP within pellet mixture could be larger than that in compacted bentonite block due to the deformation (swelling or compression), damage (cracking or collapse) and displacement (rotation or dislocation) of the pellets. For both specimens, the macro and micro void ratios decrease while the meso void ratio increases with infiltration, leading to a gradually homogenized pore structure. Taking the pore size distribution curve of the middle layer of compacted bentonite block specimen after 720 h hydration as a reference, a porosity homogenization index (PHI) was defined to reflect the degree of pore structure homogenization. Generally, the PHIs of the upper, middle and lower part of the two specimens decrease with infiltration time. At a given time, the PHIs of pellet mixture are higher than those of compacted bentonite block but the difference between them decreases, leading to corresponding decrease of the swelling pressure difference. Considering the low swelling pressure (<1.0 MPa) of the current pellet mixture, it is necessary to improve its swelling capacity either by denser compaction or property modification for the safety of long-term operation of a HLW repository.

Insights into the water retention behaviour of GMZ bentonite pellet mixture

Insights into the water retention behaviour of GMZ bentonite pellet mixture

A new thermal analysis model with three heat conduction layers in the nuclear waste repository

A mathematical model for three layer media with different thermal conductivities is presented for analyzing the three-dimensional heat conduction of the repository. The solutions to the temperature distribution in the bentonite block layer, bentonite pellet layer and surrounding rock were derived through applying the Fourier and Laplace transforms upon the heat conduction equations. These analytical solutions can be used to obtain the evolution of temperature fields at the repository site. Finally, a parametric study is carried out to assess the effects of geometry dimension and thermal conductivity on the thermal performance. The results show that the three layer model was demonstrated more accurately to simulate the temperature field in the repository through comparative analysis with the existing double layer model and line heat source model. The thickness of the bentonite pellet layer will lead to a significant increase in the peak buffer layer temperature because of its low thermal conductivity.

Influence of tailor-made TiO2/API bentonite nanocomposite on drilling mud performance: Towards enhanced drilling operations

A novel tailor-made TiO2 nanoparticles-bentonite (TNBT) nanocomposite-enhanced drilling mud was tested. The drilling mud showed excellent performance; (i) lubricity was enhanced, (ii) thin and well-intact mud cakes were created, (iii) coating was provided on shale and bentonite plugs, and (iv) clay and shale swelling were mitigated, hence these features ensured a platform for sustainable oil and gas well drilling. The synthesised TNBT nanocomposite followed the one-third bridging rule, i.e., these nanoparticles can bridge nanopore throats in shale pellets and American Petroleum Institute (API) standard bentonite pellets. The tailor-made TNBT nanoparticles were characterized by X-ray diffraction, and scanning electron microscopy. The coefficient of friction and filtrate loss of TNBT-enhanced muds were determined with a lubricity tester, and an API filter press, respectively. Additionally, shale and clay swellings were determined with a linear swell meter. The coefficient of friction was reduced after 0.8 g of TNBT was added to 350 ml drilling mud, resulting in a 35% enhancement in mud lubricity. The new mud also drastically mitigated the swelling in shale and clay when compared to conventional mud. The swelling inhibition was attributed to an increase in the mud viscosity and improved nanopore plugging characteristics, which resulted in less water infiltration. Thus, drilling mud supplemented with the tailor-made TiO2 nanoparticles-bentonite nanocomposite showed superior characteristics and a good potential for field operations.

Investigating the hydromechanical behaviour of bentonite pellets by swelling pressure tests and discrete element modelling

Bentonite pellet mixtures are candidate material for the sealing of galleries in radioactive waste disposals. The hydromechanical behaviour of assemblies of bentonite pellets is investigated upon partial hydration through (1) suction-controlled swelling pressure tests in the laboratory and (2) discrete element method simulations. The combination of these experimental and numerical approaches highlights that, before the mixture homogenization, the swelling pressure develops in two phases. The first phase is characterized by an increase in contact forces between pellets. The second phase is characterized by plasticity at contacts between pellets and is controlled by the progressive decrease in pellet strength and stiffness upon hydration. In addition, numerical results highlight that the swelling pressure measured in the laboratory can be influenced by the sample preparation, the cell size, and the diameter of the pressure sensor.

Removal of methyl orange by heterogeneous fenton process using iron dispersed on alumina pillared bentonite pellet

Introduction: Heterogeneous Fenton is one of the Advanced Oxidation Processes (AOPs) and has been proven to be effective on azo dye degradation. However, a low-cost catalyst and factors affecting the processes of this system were further investigated.&#x0D; Methods: In this study, pellets of iron alumina pillared bentonite (PFeAPB) were prepared by dispersing iron ions on alumina pillared bentonite pellet. Catalyst activity and lifetime were investigated via efficiencies of Methyl Orange (MO) decolorization and Chemical Oxygen Demand (COD) removal, a typical dye type of textile wastewater. Characteristics of the PFeAPB catalyst were examined by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area, and X-ray fluorescence (XRF).&#x0D; Results: Results of batch experiments showed that specific surface area of the PFeAPB catalyst was 111.22 m2/g higher than its precursor by 2 times (57.79 m2/g). Goethite, Hematite and Maghemite phases with approximately 11.5% of iron elements containing in the catalyst were detected via XRD and XRF. Experimental conditions of pH, initial MO solution, Hydrogen Peroxide concentration, reaction time and catalyst loading were 2.0 ± 0.1, 12.7 mmol/L, 150 min and 20 g/L, respectively, to achieve 88.68 ± 5.69% of MO decolorization and 50.27 ± 6.05% of COD removal while dissolved iron in this heterogeneous Fenton process was below standard limit (2 ppm). Catalyst activity decreased by 5.22% in decolorization efficiency after the two first reusages.&#x0D; Conclusion: These primary results showed the potential of applying PFeAPB catalyst in heterogeneous Fenton process with low iron leaching into water.&#x0D;

From double to triple porosity modelling of bentonite pellet mixtures

The present work analyses the hydro-mechanical behaviour of bentonite pellet mixtures using a macroscopic overlapping continua approach based on a triple porosity model. Two macrostructural functional levels are considered (inter-pellet pore space and void space between the clay aggregates inside the pellets) as well as a microstructural level (corresponding to the space inside the aggregates). This triple porosity approach reveals that, when assuming a double porosity model, the intrinsic permeability, the tortuosity and the degree of saturation of the single macrostructural level under consideration are the average values of the state functions of the adopted triple porosity model, but are not state functions themselves.The analysis also illustrates that, when assuming the same liquid pressure for the two macrostructural levels of the triple porosity model, it is relatively easy to expand upon the calculation procedures initially developed for a double porosity model to include a triple porosity model.When evaluating the applicability of the model, quality results were obtained, comparable to those of a triple porosity model, for both open and closed bentonite pellet mixtures. The results are better than those obtained with a double porosity model, since the state functions have a stronger physic base when using a triple porosity approach. Encouraging results are also obtained when analysing the overall swelling of a bentonite block and a mixture of bentonite pellets, using the same parameters for both materials. Therefore, given its capacity for relatively simple incorporation in a double porosity models, the model offers an interesting tool for researchers working on improving the characterisation of bentonite pellet mixtures.

Investigation of the hydro-mechanical behaviour of GMZ bentonite pellet mixtures

Bentonite pellet mixtures are considered as one of the candidate sealing materials for deep geological disposals of radioactive waste. One of the particularities of this material is the initial heterogeneous distribution of pellets and porosity within the mixture, leading to complex hydro-mechanical behaviour. In this paper, the hydro-mechanical properties of GMZ bentonite pellet mixtures were investigated in the laboratory by carrying out water retention tests on pellet mixtures under constant-volume condition and single pellets under free swelling condition, as well as a infiltration test on a column specimen of pellet mixture. In the infiltration test, the relative humidity and radial swelling pressure were monitored at five heights, the axial swelling pressure was also recorded. The instantaneous profile method was applied to determine the unsaturated hydraulic conductivities. Results show that, in high suction range (> 10 MPa) the water retention curve of pellet mixture under constant-volume condition was comparable to that of a single pellet under free swelling condition, while in low suction range (< 10 MPa) the latter exhibits a much higher water retention capacity. Due to clogging of large pores, the unsaturated hydraulic conductivity decreases as suction decreases to around 25 MPa. However, with further suction decrease, the hydraulic conductivity increases continuously until the value at saturated state, as in the case of most unsaturated soils. The radial swelling pressure at different heights develops with local sudden increase and decrease, which was attributed to local rearrangement of pellets upon wetting. By contrast, as the axial swelling pressure was measured on the global surface of the specimen, it develops in a more regular fashion.

Water-retention properties and microstructure changes of a bentonite pellet upon wetting/drying; application to radioactive waste disposal

Like bricks of compacted bentonite/sand mixtures, mixtures made up of pellets and powder of bentonite are considered as a possible material to make the sealing plugs used to fill up galleries and ensure long-term watertightness in deep radioactive waste disposal. Pellets/bentonite mixtures have a low permeability, high swelling capacity, good radionuclide retention capability and operational advantages in terms of placement in the galleries. Following a previous in-depth characterisation of bentonite pellets/powder mixture conducted by the same group, an investigation of the water-retention properties and microstructure changes of a bentonite pellet subjected to wetting/drying cycles under free swelling conditions was carried out by means of mercury intrusion porosimetry (MIP) and X-ray microtomography. A complete description of the changes in water content, void ratio and degree of saturation of the pellet was provided. Data showed that the free swelling of the pellet is due to the combined effect of both crack propagation at the macro scale, and the swelling of bentonite grains, governed by hydration mechanisms along the smectite faces at the nano scale. Significant development of a crack network is observed between 38 and 9 MPa. For suctions below 9 MPa, there is a significant decrease of the platelet thickness and an increase in the disorder of the platelet assembly, resulting in the average MIP entrance pore radius increasing to 0·4 μm within the expanded bentonite grains.

Investigation on vibration induced segregation behaviour of crushed GMZ bentonite pellet mixtures

Mixture of high-density bentonite pellets are considered as a potential buffer/backfill material for high-level radioactive wastes (HLW) repository. One of the outstanding problems of this material is the particle segregation induced by vibration during transportation and emplacement. In this work, the vibration-induced segregation behavior of crushed GMZ (Gaomiaozi) bentonite pellet mixtures with different size distributions was experimentally investigated using a cylindrical container under vertical vibrations. The degree of segregation was evaluated by a weighted coefficient of variation (WCV) reflecting the changes in particle size distribution before and after vibration. Results show that generally the WCV increases with decreases of particle size ratio, the mass fraction of the fine size class and the number of size classes of the mixture. The influences of particle size ratio and distribution were interpreted by two dominant mechanisms including percolation and convection, and could be incorporated into a particle characteristic index (PCI). Further analysis shows that the WCV monotonously increases with the increase of PCI and the relationship between them can be well described using a sigmoid function. Finally, based on the analyses of the experimental results, strategies for reducing segregation were proposed.