Reservoir Depletion Research Articles

Solution of one optimum control problem regarding the depletion of gas reservoir

Using the methods of the optimal control theory, the problem of determining the optimal technological mode of gas deposits’ exploitation under the condition of their depletion by a given point in time is solved. This task is of particular interest for the exploitation of offshore fields, the activity of which is limited by the service life of the field equipment. The considered problem is also of certain mathematical interest as an objective of optimal control of nonlinear systems with distributed parameters. The usefulness and importance of solving such problems are determined by the richness of the class of major tasks that have a practical result. As an optimality criterion, a quadratic functional characterizing the conditions of reservoir depletion is considered. By introducing an auxiliary boundary value problem, and taking into account the stationarity conditions for the Lagrange functions at the optimal point, a formula for the gradient of the minimized functional is obtained. To obtain a solution to this specific optimization problem, which control function is sought in the class of a piecewise continuous and bounded function with discontinuities of the first kind, the Pontryagin’s maximum principle is subjected. The calculation of the gradient of the functional for the original and adjoint problems with partial differential equations is carried out by the method of straight lines. The numerical solution of the problem was carried out by two methods – the method of gradient projection with a special choice of step and the method of successive approximations. Despite the incorrectness of optimal control problems with a quadratic functional, the gradient projection method did not show a tendency to «dispersion» and gave a convergent sequence of controls.

Underground hydrogen storage in a partially depleted gas condensate reservoir: Influence of cushion gas

Hydrogen gas as a clean and renewable kind of energy can be considered to supply electricity demand during peak usage times. Actually, excess electricity cannot be stored in great quantities, but it can be converted to hydrogen, which can be stored and converted to electricity as a peak shaving. However, due to the very low hydrogen energy density in terms of volume, a huge capacity is needed for its storage. Therefore, underground hydrogen storage (UHS) can be evaluated as a solution. This study investigated the effect of cushion gas on underground hydrogen storage in a partially depleted gas condensate reservoir in a real case which is located in the Middle east. To the best of our knowledge, it is the first time the feasibility of underground hydrogen storage in a gas condensate reservoir has been investigated. The effect of some parameters such as cushion gas type, namely; methane, nitrogen, carbon dioxide, condensate existence, the implementation time of storage, hydrogen injection initialization stage, and hydrogen injection/production rate was investigated on hydrogen heating value and recovery during the underground hydrogen storage operation. The results of replacing alternative gases as part of cushion gas showed that the highest amount of hydrogen recovery and purity could be obtained by injecting the nitrogen. While carbon dioxide was the most effective alternative gas to improve condensate production but in terms of hydrogen recovery and purity was not. Also, implementing hydrogen storage in the gas condensate reservoir leads to higher hydrogen recovery than dry gas reservoirs due to the trapping of alternative gases in the condensate phase. However, most of the injected carbon dioxide was produced during hydrogen production, which is unfavorable. This study shows that 60% depletion of the gas condensate reservoir is the best condition to start underground hydrogen storage. Further, applying a hydrogen injection initialization stage indicated that the hydrogen recovery and heating value could be increased. However, it requires a detailed economic evaluation to consider the cost/benefit of initialized hydrogen loss and recovery.

Modeling and Economic Analyses of Graded Particle Injections in Conjunction with Hydraulic Fracturing of Coal Seam Gas Reservoirs

Summary Hydraulic fractures can enhance well productivity from stress-sensitive naturally fractured reservoirs, such as coalbed methane or coal seam gas (CSG) reservoirs. Graded proppant injection (GPI) has been proposed to enhance long-term, far-field interconnectivity between the created hydraulic and short-term, enhanced natural fracture permeability, resulting from fracture fluid leakoff and lowered net effective stress. This novel study shows how applying GPI with hydraulic fracturing treatments resulting in an increased stimulated reservoir volume (SRV) can enhance well productivity and improve CSG well economics. A commercially available reservoir model and history-matched hydraulically fractured coal seam case are used to evaluate well performance differences between a hydraulic fractured reservoir and one including GPI application. A dual-porosity system and the Palmer and Mansoori model are used to simulate initial and long-term permeability accounting for reservoir depletion (i.e., increased net effective stress and matrix shrinkage). A previously validated case study is used to describe the post-embedment benefits of GPI based on the porosity model and history-matched reservoir properties. A net present value (NPV) can then be calculated for each scenario, based on the production differences and typical Australian CSG costs. Our results show that permeability enhancement is achieved beyond the hydraulically fractured region for all post-GPI stimulation cases. An optimal SRV can be found relative to permeability that maximizes the incremental NPV from GPI application. The next most significant parameters after permeability that influence the economic outcomes are fracture porosity and coal compressibility. A larger SRV yields higher cumulative gas production over 30 years with up to 7.2 times increase over gas production without GPI. This study substantially increases our understanding of how to model and understand the benefits of GPI application along with hydraulic fracturing to increase the SRV in CSG wells.

Geomechanics evolution integrated with hydraulic fractures, heterogeneity and anisotropy during shale gas depletion

Due to reservoir depletion, the reservoir geomechanical parameters, such as stresses, permeability, are changing during shale gas production. A coupled flow-geomechanics model was built to investigate time-lapse geomechanical responses in production before infill well placement of Sichuan Basin shale gas reservoir. In the modelling, hydraulic fractures were simulated from microseismic data and mapped from a geological model to build the flow model. An interface code was improved to build the geomechanical model properties from the geological model, as well as communicates the data between finite difference grids in the reservoir simulator and finite element grids in the geomechanical simulator. In addition, the anisotropy of physical properties and rock mechanical properties was integrated in the flow model and the geomechanical model. Stress-dependent porosity and permeability models were embedded as well. Case studies show that stress evolution and re-orientation are affected by both the trajectory and fractures of producing wells, as well as the heterogeneity of geomechanical properties. Besides, the effect of parallel wells production should be taken into consideration based on the wells-spacing.

Molecular investigation on CO₂-CH₄ displacement and kerogen deformation in enhanced shale gas recovery

CO₂-enhanced gas recovery (EGR) is a promising method that can not only improve the production of adsorbed shale gas but also achieve the geological storage of CO₂. During the injection of CO₂, shale is expected to deform due to both CH₄ desorption-induced shrinkage and CO₂ adsorption-induced swelling. Regardless of the potential effects on gas permeability and transport, the sorption-induced deformation remains poorly understood and is generally overlooked in large-scale simulations of CO₂-EGR. In this paper, Monte Carlo and molecular dynamics simulations are performed to study the CO₂-CH₄ displacement in the type II-D overmature kerogen (i.e., the primary organic matter in shale). Our results indicate that the CO₂-CH₄ displacement efficiency increases with the increase of the CO₂ injection pressure but decreases linearly with the increase of the reservoir depletion pressure. Moreover, the sorption-induced deformation is measured as volumetric strain and analyzed after initial CH₄ saturation, pressure drawdown, and CO₂ injection. It is observed that CO₂ injection can induce a volume expansion of the original CH₄-saturated kerogen up to 5%. In addition, a novel non-linear adsorption-strain model is derived to provide a theoretical basis for kerogen deformation by taking the gas adsorption and deformation coupling into consideration. Different from the conventional linear theory, the increment of volumetric strain induced by gas adsorption becomes much faster when close to adsorption saturation. The derived model can accurately capture the observed non-linearity and predict deformation caused by single-component gas and gas mixtures. Since swelling can further reduce shale permeability, these results imply that CO₂ injectivity and CH₄ production rate may both decline faster than expected in CO₂-EGR.

Multiphysics coupling study of near-wellbore and reservoir models in ultra-deep natural gas reservoirs

Understanding the changes of the near-wellbore pore pressure associated with the reservoir depletion is greatly significant for the development of ultra-deep natural gas reservoirs. However, there is still a great challenge for the fluid flow and geomechanics in the reservoir depletion. In this study, a fully coupled model was developed to simulate the near-wellbore and reservoir physics caused by pore pressure in ultra-deep natural gas reservoirs. The stress-dependent porosity and permeability models as well as geomechanics deformation induced by pore pressure were considered in this model, and the COMSOL Multiphysics was used to implement and solve the problem. The numerical model was validated by the reservoir depletion from Dabei gas field in China, and the effects of reservoir properties and production parameters on gas production, near-wellbore pore pressure and permeability evolution were discussed. The results show that the gas production rate increases nonlinearly with the increase in porosity, permeability and Young’s modulus. The lower reservoir porosity will result in the greater near-wellbore pore pressure and the larger rock deformation. The permeability changes have little effect on geomechanics deformation while it affects greatly the gas production rate in the reservoir depletion. With the increase in the gas production rate, the near-wellbore pore pressure and permeability decrease rapidly and tend to balance with time. The reservoir rocks with higher deformation capacity will cause the greater near-wellbore pore pressure.

Response of Rice (Oryza sativa L.) Cultivars to Variable Rate of Nitrogen under Wet Direct Seeding in Temperate Ecology

Transplanting rice appears to pose many problems, including depletion of freshwater reservoirs and competition for labor. Conversely, direct seeding allows us to overcome shortcomings associated with conventional transplanting. Nitrogen is a crucial nutrient needed for plant growth and yield. Therefore, this study was executed to analyze the influence of nitrogen on the performance of rice genotypes grown by direct seeding in wet soil. The experiment comprised various rice cultivars, i.e., Shalimar Rice-1, Shalimar Rice-3, Shalimar Rice-4, and Jhelum, and nitrogen (N) levels, i.e., 0, 90, 120, and 150 kg/ha. Shalimar Rice-4 produced a maximum grain yield (6.39 t/ha), followed by Shalimar Rice-3 and Jhelum). The application of 150 kg N/ha showed maximum values for growth parameters, yield attributing traits, and grain yield (6.68 t/ha); however, it remained at par with 120 kg N/ha. Crop water productivity was highest in Shalimar Rice-4 (0.49 kg/m3), and the same showed a consistent increase with increasing N levels from 0–150 kg/ha, with a comparable value of 0.49 to 0.51 recorded at 120 and 150 kg N/ha. Moreover, the Shalimar Rice-1 variety required the maximum in growing degree days (GDD) and helio-thermal units (HTU) to attain different phenological stages till physiological maturity (131 days). However, the cultivar Shalimar rice-4 (SR-4) performed better by registering significantly higher heat use efficiency (HUE) (4.44 kg/ha °C/day). Additionally, the highest net return and the benefit-cost ratio were registered by Shalimar Rice-4. B:C ratio of 1.75 was realized from application of 150 kg N/ha, which remained very close to that achieved with 120 kg N/ha. In conclusion, the rice cultivar Shalimar Rice-4 with the application of 120 kg N/ha could boost rice production under DSR in water-scarce regions of temperate northern India.

Determination the initial value and change behaviour of the reservoir permeability via two field measurements

The paper proposes a technique for interpreting the results of hydrodynamic studies of volatile and non-volatile oil wells at two steady-state regimes in order to determine the initial value and coefficient of variation in effective permeability of the reservoir. It is developed based on a binary filtration model, where the hydrocarbon system is represented as consisting of two pseudocomponents and two phases, between which mass transfer of hydrocarbons takes place. The proposed methodology requires well flow rates measured at two different steady-state well conditions for two different reservoir pressures and thermodynamic data of the hydrocarbon system at reservoir conditions. The methodology has been validated using examples of hypothetical volatile and non-volatile oil reservoirs at different rock deformation ratios and for nondeformable reservoirs. It has also been tested under different development stages and measurement conditions. For this purpose, a computer simulation of the oil reservoir depletion process was carried out, the results of which were used as well test data. Satisfactory accuracy and reliability of the outlined approach has been established. As deviations of calculated values of required parameters from their actual values did not exceed 8%.

Aeolian Sand Dune Sedimentary Architecture Is Key in Determining the “Slow-Gas Effect” during Gas Field Production Performance

Summary Aeolian deposits are typically considered to act as homogeneous “tanks” of sand, which do not contain significant heterogeneities that impact the production of hydrocarbons. However, a succession of deeply buried aeolian gas reservoirs from the Permian Rotliegend exhibit a characteristic production decline profile that is typified by high initial flow rates, followed by a rapid decline in bottomhole pressure and decline in flow rate, subsequently followed by stabilization at low flow rates for an extended period (over several decades). This effect has been termed here as the “slow-gas effect,” and this production phenomenon has previously been attributed to structural compartmentalization. This paper presents an alternative, sedimentological hypothesis for the cause of the slow-gas effect based upon facies-controlled permeability differences within aeolian dune trough architectures. To test this, three interwell (km) scale models from well-studied aeolian analogs from Utah and Arizona were modeled with standard geostatistical reservoir techniques and populated with petrophysical properties from producing Rotliegend reservoirs in Germany. These models were subsequently dynamically simulated to analyze production behavior and test whether a similar “slow-gas” production profile could be reproduced. This study finds that the slow-gas effect primarily results from heterogeneities created by the complex interaction of deposition, accumulation, and erosion within aeolian strata, as opposed to the structural compartmentalization of homogeneous tanks of sand as previously thought. Structural compartmentalization and baffling through faulting where present will have an impact on fluid flow; however, it is not considered here to be the primary cause of the slow-gas effect. Results of this work demonstrate the necessity of accurately characterizing and reproducing low permeability heterogeneity in aeolian systems. These heterogeneities can either be modeled explicitly through the use of geostatistical reservoir modeling techniques as done here, or implicitly through the use of characteristic length and transmissibility multipliers. These results have significant implications on our understanding of how tight aeolian systems produce; namely, after depletion of the near-wellbore volume, production from the surrounding reservoir is baffled by a hierarchy of low permeability bounding surfaces and associated transmissibility barriers. Application for enhancing reservoir depletion strategies include optimizing well trajectories to maximize the number of dune penetrations and percentage of net reservoir facies in communication to the well; maximizing the size of the primary reservoir compartment. Neighboring wells should be placed in separate compartments to maximize the amount of fast-flowing gas production during the early production stage. Pressure management can be used to cyclically produce, deplete, and recharge the primary reservoir compartment to manage and optimize recovery during the decline phase and production tail.

Experimental Analysis and Numerical Simulation of the Stability of Geological Storage of CO2: A Case Study of Transforming a Depleted Gas Reservoir into a Carbon Sink Carrier.

Geological storage of CO2 is one of the most economical, feasible, and effective measures to slow down global warming. In this study, a combined long core model was designed to study the seepage characteristics of supercritical CO2 displacement. Moreover, the stability of permanent storage of cushion gas layers formed by supercritical CO2 injection has been systematically studied. The research results showed that in the supercritical temperature and pressure range of CO2, the front edge of CO2 displacement can form a relatively stable seepage zone. Supercritical CO2 displacement can achieve a high gas-storage rate and stable CO2 storage. At the same time, the recovery rate of remaining natural gas has been significantly improved. As the injection pressure increased, supercritical CO2 inhibited the reverse diffusion of natural gas molecules. Therefore, the breakthrough of the supercritical CO2 displacement front under a high pressure lagged behind. However, due to the increase in the density difference of gas molecules, the forward diffusion of supercritical CO2 has been enhanced. Temperature will not significantly affect the displacement and storage effects of supercritical CO2 in gas reservoirs. The increase in injection pressure and reasonable control of the injection rate can delay the breakthrough of supercritical CO2 displacement. These measures are conducive to the stable storage of CO2 and the improvement of remaining natural gas recovery. The implementation of CO2 geological storage is suitable for the later stage of gas reservoir depletion development. The high-density gravitational heterogeneity of supercritical CO2 enables the injected CO2 to form a stable high-density cushion gas layer in the gas reservoir, which can achieve stable CO2 storage for more than 100 years.

COUPLED HYDRO-MECHANICAL MODELING OF GAS FLOW IN SHALE MATRIX CONSIDERING THE FRACTAL CHARACTERISTICS OF NANOPORES

To economically develop shale gas reservoirs, hydraulic fracturing treatments must be applied to artificially introduce pathways for gas to flow out. After hydraulic fracturing, both the induced hydraulic fractures and activated natural fractures provide high permeable channels for gas transport. However, the long-term production performance of shale gas reservoirs is determined by the physical properties of matrix instead of the fractures. In this work, a coupled hydro-mechanical model is developed to investigate gas flow in heterogeneous shale matrix at the microscale. This model considers the mechanical interaction and gas mass transfer between organic matter (OM) and inorganic matter (iOM) during gas depletion. The interesting results show that due to matrix heterogeneity, i.e. co-existence of OM and iOM, the gas flow and mechanical deformation behaviors in shale exhibit regional differences. Specifically, during reservoir depletion, pore pressure, Knudsen number and volumetric strain in iOM are smaller than that in OM while the intrinsic and apparent permeability of OM are smaller than that of iOM. Thus, matrix heterogeneity should be taken into account when characterizing shale gas flow. In addition, sensitivity analysis is conducted to study the influence of fractal parameters on shale apparent permeability evolution. These fractal parameters include nanopore radius fractal dimension, tortuosity fractal dimension and maximum nanopore radius. The analysis indicates that the variation of fractal parameters in iOM results in the change of apparent permeability of both OM and iOM, while the variation of fractal parameters in OM only leads to the change of apparent permeability of OM. The modeling results offer new insights into gas flow behaviors in shale matrix.

Predicting Fluid Flow Regime, Permeability, and Diffusivity in Mudrocks from Multiscale Pore Characterisation

In geoenergy applications, mudrocks prevent fluids to leak from temporary (H2, CH4) or permanent (CO2, radioactive waste) storage/disposal sites and serve as a source and reservoir for unconventional oil and gas. Understanding transport properties integrated with dominant fluid flow mechanisms in mudrocks is essential to better predict the performance of mudrocks within these applications. In this study, small-angle neutron scattering (SANS) experiments were conducted on 71 samples from 13 different sets of mudrocks across the globe to capture the pore structure of nearly the full pore size spectrum (2 nm–5 μm). We develop fractal models to predict transport properties (permeability and diffusivity) based on the SANS-derived pore size distributions. The results indicate that transport phenomena in mudrocks are intrinsically pore size-dependent. Depending on hydrostatic pore pressures, transition flow develops in micropores, slip flow in meso- and macropores, and continuum flow in larger macropores. Fluid flow regimes progress towards larger pore sizes during reservoir depletion or smaller pore sizes during fluid storage, so when pressure is decreased or increased, respectively. Capturing the heterogeneity of mudrocks by considering fractal dimension and tortuosity fractal dimension for defined pore size ranges, fractal models integrate apparent permeability with slip flow, Darcy permeability with continuum flow, and gas diffusivity with diffusion flow in the matrix. This new model of pore size-dependent transport and integrated transport properties using fractal models yields a systematic approach that can also inform multiscale multi-physics models to better understand fluid flow and transport phenomena in mudrocks on the reservoir and basin scale.

Performance charateristics of a conventional spark ignition petrol engine powered by biogas

This research investigates the use of biogas to run a spark ignition petrol engine and test for the engine performance. Conventional spark ignition petrol engine was modified into a dual fuel engine by changing the engine single fuel carburettor to dual fuel carburettor. The air orifice was closed by 50% to enable cooled start with natural biogas as the low calorific value won't facilitate combustion. The speed, torque, and other engine parameters where measured using a TD200 small engine test set (hydraulic brake dynamometer) interface and emissions of SO2, CO were measured using an emissions analyser. The torque, brake power was higher for petrol by 39% than the biogas due to the lower calorific value of biogas. The exhaust temperature, SO2 and CO was 49% lower for the biogas than the petrol. The comparative analysis of the modified engine showed that petrol can be substituted partly with biogas and the engine used for varying applications because it offers window escape on the hydrocarbon reservoir depletion, green gasses emission from the use of these petrol and landfill emission as well.

A production-based model for a fractured well in unconventional reservoirs

Due to the depletion of conventional reservoirs and the high demand of energy, unconventional reservoirs will be relied on to supply the world's energy for the foreseeable future. Unfortunately, because of their complex storage and flow mechanisms, modelling and analysis of unconventional reservoirs have been very challenging. Although semi-analytical and numerical models have been proposed, these models rely on somewhat simplifying assumptions and require several input parameters. In this paper, a production-based model is proposed to analyze and predict a fractured-well performance in unconventional reservoirs (specifically, tight and shale reservoirs). The model assumes a power law with a stretched exponential cut-off. While the power-law term governs the transient-state period, the stretched exponential term, which is a superposition of exponential decays, governs the boundary-dominated flow period. As a result, the model is capable of matching both the transient state and boundary-dominated flow portions of the data. The model has been validated with a numerical data and applied to several field data. Results of the model have been compared with other existing models. The findings show that the proposed model yields relatively good estimates, and matches both the transient and boundary-dominated flow periods. The proposed model may contribute to the ongoing efforts to improve the analysis and forecasting of fractured-well performance in unconventional reservoirs.

Stress-sensitivity analysis of rock mechanical and petrophysical properties of fractured tight sandstone under true-triaxial stresses in the laboratory

In the process of oilfield production, effective stresses usually increase continuously and act as unequal triaxial stresses on the reservoir. However, most studies on rock stress sensitivity are conducted under conventional triaxial or uniaxial stress conditions, which cannot truly represent the in situ stress environment. In this work, two groups of fractured tight sandstones sampled from northwestern China were tested under true-triaxial stress environments to study the stress sensitivity of mechanical and petrophysical properties. The sandstones are elastically deformed under experimental stress conditions, showing an apparent correlation with fracture angles. The acoustic wave velocity increases linearly with the stresses, and the shear wave velocity is strongly affected by fracture angle and anisotropic effective stresses. The permeabilities decrease exponentially and show significant anisotropy with increasing effective stress, which is less stress sensitive when the fracture strike is parallel to the maximum horizontal principal stress than when it is perpendicular. This work successfully reveals the stress sensitivity of anisotropic permeability, stress-strain behavior, and acoustic wave velocity of fractured tight sandstone during reservoir depletion. The testing results provide an innovative method to accurately measure the anisotropic rock properties, offer new ideas about fractures identification, and have profound significance for exploration and development of tight reservoirs.

Influence of the depth of gas-lift gas injection into tubing and its consumptions on the flow rate of a water-cut gas well

The features of the development of gas deposits in the water drive and watering of wells are characterized. The sequence of application of various methods of operation of water-cut gas wells is considered, depending on the degree of depletion of the gas reservoir and the water factor. The expediency and conditions for the use of the gas-lift method for the operation of water-cut gas wells have been substantiated. Using the calculation method proposed by the authors, studies of the effect on the flow rate of gas that flows from the reservoir and the bottomhole pressure of the gas-lift gas flow rate and the depth of its injection into the tubing were carried out for the conditions of a model water-cut gas well. It was found that with an increase in the gas-lift gas flow rate, the bottomhole pressure first decreases and reaches a minimum and then increases, while the gas flow rate, on the contrary, first increases, reaching a maximum, and then decreases. With an increase in the depth of gas-lift gas injection into the tubing, the bottomhole pressure decreases, the gas flow rate increases, and the difference between the maximum and minimum values of the gas-lift gas flow rate increases, within which a water-cut gas well can be operated by the gas-lift method. According to the results of statistical processing of the calculated data, it was found that the greatest change in gas flow rate and bottomhole pressure occurs up to the values of the ratio of the depth of gas-lift gas injection into the tubing and the length of the tubing, equal to 0.50-0.55.

Multiscale Pressure/Volume/Temperature Simulation of Decreasing Condensate/Gas Ratio at Greater than Dewpoint Pressure in Shale Gas-Condensate Reservoirs

Summary In shale gas-condensate reservoirs, when the initial reservoir pressure is greater than the dewpoint pressure, the condensate/gas ratio (CGR) has been observed to decrease continuously as the pressure drops to less than the initial reservoir pressure. This abnormal behavior cannot be explained with conventional pressure/volume/temperature (PVT) models that ignore the presence of nanopores in shale rock. Herein, for the first time, we present a study that provides a physical explanation for the observed CGR trends by including the effect of nanopores on the fluid phase behavior and depletion of shale gas-condensate reservoirs. Our model uses multiscale PVT simulation by means of a pore-size-dependent equation of state (EOS). Two lean gas-condensate cases (shallow and deep reservoirs) are investigated. The simulation results show that hydrocarbons distribute heterogeneously with respect to pore size on the nanoscale. There are more intermediate to heavy hydrocarbons (C3–11+) but fewer light ends (C1–2) distributed in the nanopores than in the bulk region. At the end of depletion, because of confinement effects, large amounts of intermediate hydrocarbons are trapped in the nanopores, causing condensate recovery loss. Multiscale depletion simulations suggest that a decreasing CGR can occur at the beginning of production when the reservoir pressure is higher than the dewpoint pressure. Such behavior is caused by the nanopore depletion in the shale matrix, which is a process of selectively releasing light hydrocarbon components. We also present a novel approach to model the nonequilibrium fluid distribution between the fracture and nanopores using a simple local-equilibrium concept. Our results indicate that the nonequilibrium fluid distribution increases the CGR drop because of the compositional selectivity of the nanopore in favor of intermediate and heavy hydrocarbons. NOTE: This paper is published as part of the 2021 SPE Reservoir Simulation Conference Special Issue.

Behavior comparison of films of Mexican bitumen and its asphaltene and maltenes fractions at interfaces

The oil industry has been focused on bitumens and heavy oils due to the depletion of petroleum reservoirs. For this reason, we studied the interfacial behavior comparison of films of bitumen and their asphaltene and maltene fractions by means of the Langmuir balance and Brewster angle microscopy at the air–water interface. The films were transferred by Langmuir-Blodgett technique onto mica and grids to be further analyzed by AFM and SEM at different surface pressures. We found that the isotherm behavior of the bitumen depends on the amount of its asphaltene and maltene fractions, although the isotherm behavior of asphaltene and maltene fractions are quite different. BAM images of the bitumen and asphaltene samples show the formation of two- and three-dimensional domains, being the asphaltene domains the most rigid and compact structures. Maltenes seems to form large areas of mono- or bi-molecular films, and their structures are like those reported for lipid monolayers. The AFM images for the bitumen morphology exhibited polydisperse mesostructures with spherical and disk-like shapes, while asphaltene images revealed disk-like microstructures and some of these microstructures coalesce, resulting in the formation of worm-like and other small structures. AFM images of the maltene film revealed that they form a fine plaster that might agglutinates the asphaltenes. SEM images of bitumen film show a smooth and slightly porous surface with some layer detachments, holes and bright spots embedded, while asphaltene images presented porous surfaces with spherical- or drumstick-like structures. Maltene SEM images showed a surface with irregular pores. The results support a better understanding of the bitumen, asphaltene, and maltene fractions and suggest that the interfacial behavior of bitumen presents a synergy between its asphaltene and maltene fractions.

Star Formation and Quenching of Central Galaxies from Stacked Hi Measurements

Abstract We quantitatively investigate the dependence of central galaxy Hi mass (M Hi ) on the stellar mass (M *), halo mass (M h ), star formation rate (SFR), and central stellar surface density within 1 kpc (Σ1), taking advantage of the Hi spectra stacking technique using both the Arecibo Fast Legacy ALFA Survey and the Sloan Digital Sky Survey. We find that the shapes of M Hi –M h and M Hi –M * relations are remarkably similar for both star-forming and quenched galaxies, with massive quenched galaxies having constantly lower Hi masses of around 0.6 dex. This similarity strongly suggests that neither halo mass nor stellar mass is the direct cause of quenching, but rather the depletion of the Hi reservoir. While the Hi reservoir for low-mass galaxies of M * < 1010.5 M ☉ strongly increases with M h , more massive galaxies show no significant dependence of M Hi with M h , indicating that the main effect of halo is to determine the smooth cold gas accretion. We find that the star formation and quenching of central galaxies are directly regulated by the available Hi reservoir, with an average relation of SFR ∝ M H I 2.75 / M * 0.40 , implying a quasi-steady state of star formation. We further confirm that galaxies are depleted of their Hi reservoir once they drop off the star formation main sequence and there is a very tight and consistent correlation between M Hi and Σ1 in this phase, with M H I ∝ Σ 1 − 2 . This result is consistent with the compaction-triggered quenching scenario, with galaxies going through three evolutionary phases of cold gas accretion, compaction and post-compaction, and quenching.

The application of biochar alleviated the adverse effects of drought on the growth, physiology, yield and quality of rapeseed through regulation of soil status and nutrients availability

The depletion of soil fertility and freshwater reservoirs in dry and arid conditions of the world are alarming for food and crop productivity. Although many research studies have explored the effect of biochar on plant growth and soil fertility, however, information on the role of biochar on rapeseed under drought stress is limited. The current study was conducted to investigate the effect of biochar on photosynthesis, antioxidants activities, osmolytes contents, growth and yield of rapeseed under drought stress. Rapeseed plants at the flowering stage were subjected to two moisture conditions, no stress (NS) and drought stress (DS) along with four biochar treatments (B0:0, B15:15, B30:30 and B60:60 t ha−1). Drought stress negatively affected rapeseed growth due to the over-production of hydrogen peroxide (H2O2) by increasing 45 %, malondialdehyde (MDA) 21 % and electrolyte leakage (EL%) 40 % in (BO + DS) treatment as compared to control (BO + NS). However, the addition of biochar at 30 t ha−1 alleviated the hostile effects of drought stress in rapeseed to reduce the contents of MDA, H2O2, EL by increasing the activities of superoxide dismutase (SOD) by 63 %, peroxidase (POD) 48 %, and catalase (CAT) 62 % compared to stress-controlled treatment (BO + DS). The results revealed that biochar could alleviate the harmful effects of drought stress by enhancing the activities of antioxidants, osmoprotectants, soil fertility, and the physiological processes of rapeseed which indicate that the biochar application might be a sustainable strategy to enhance rapeseed growth under drought stress.