Rate Of Depletion Research Articles

Inter‐Basin Water Transfer Effectively Compensates for Regional Unsustainable Water Use

AbstractGlobally, a persistent decline of freshwater availability has been identified over a number of intensively irrigated agricultural regions. Large‐scale inter‐basin water transfer (IBWT) has been suggested as a key tool for stabilizing regional terrestrial water storage (TWS). However, IBWT projects are prohibitively expensive, and their large‐scale cost effectiveness remains unclear. Here we quantify the IBWT impacts on TWS trends in the North China Plain (NCP), a global hotspot for TWS depletion and IBWT. Based on in‐situ observations, remote sensing, and water balance principles, we provide a framework to disentangle complex climate and anthropogenic impacts on NCP TWS. Results show that the NCP TWS depletion rate was significantly attenuated in 2015–2021, which is primarily attributable to recently enhanced IBWT. Otherwise, the average NCP TWS would currently be 94.9 ± 4.9 mm (or 12.2 ± 0.6 km3) lower. However, the positive effect of IBWT is partly offset by increased crop water consumption (−24.1 ± 5.2 mm or −3.1 ± 0.7 km3). IBWT and agricultural management (i.e., reducing crop density) are both necessary for stabilizing future NCP TWS. Otherwise, a TWS declining trend exceeding 100 mm/year may occur under elevated CO2 conditions. As such, this study verifies the feasibility and effectiveness of IBWT for mitigating regional water shortages, as well as the crucial role of agricultural management in stabilizing regional TWS.

Present and future groundwater depletion rates in Wadi Zabid, Tihama Coastal Plain, Yemen

Present and future groundwater depletion rates in Wadi Zabid, Tihama Coastal Plain, Yemen

Vegetation Health and Forest Canopy Density Monitoring in The Sundarban Region Using Remote Sensing and GIS

The present study explores vegetation health and forest canopy density in the Sundarbans region using Landsat-8 images. This work analyzes changes in vegetation health using two vegetation indices, the Normalized Difference Vegetation Index (NDVI) and Forest Canopy Density (FCD) values of the Sundarbans, from 2014 to 2020. NDVI, comprising two bands, Red and Near-infrared (NIR), shows a declining trend during the period. Two NDVI land cover classification maps for 2014 and 2020 are produced, and the interest area is divided into five classes: Scanty, Low, Medium, and Densely Vegetated Regions and Water Bodies. A single-band linear gradient pseudo-color is used to assess the land cover difference between 2020 and 2014, showing marked changes in densely vegetative areas. The NDVI difference marks the coastal regions with a higher depletion rate of vegetation than the regions away from the seacoasts. FCD has been taken to compare the results of NDVI with it. FCD consists of another four models: AVI (advanced vegetative index), BI (Bare soil index), SSI (scaled shadow index), and TI (thermal index). FCD is also called crown cover or canopy coverage, which refers to the portion of an area in the field covered by the crown of trees. 2014 and 2015 FCD maps are produced with a single band linear gradient pseudocolor with five land cover classifications: bare soil, Bare Soil, Shrubs, Low, Medium, and Highly vegetated regions. Both maps bear a significant resemblance to NDVI land classification maps. Further, the FCD values of the two maps are scaled between 1 and 100, and the area of each class is calculated. To check the veracity of the NDVI and FCD analysis, a Deep Neural Network (DNN) model has been developed to classify each year’s image taken from Google Earth Engine (GEE). It classifies each year’s image with 99% accuracy. The calculation of the area of each class emphasizes the rapid decline of densely wooded vegetation. Almost 80% of the highly forested zone has been diminished and has become part of the medium-forested region. Area inflation in medium-forested regions corroborates the same. The study also analyzes the migration of vegetation density, i.e., where and how many areas are unchanged, growing, or deforested.

Experimental Study on the Control Mechanism of Non-Equilibrium Retrograde Condensation in Buried Hill Fractured Condensate Gas Reservoirs

During the depletion development of condensate gas reservoirs, when the formation pressure drops below the dew point pressure, the condensate oil and natural gas systems are in the non-equilibrium state of foggy retrograde condensation. The rational use of the non-equilibrium phase characteristics of the foggy retrograde condensation phenomenon during the development process will be beneficial to the recovery of condensate oil and natural gas. In order to clarify the retrograde condensation control mechanism during the non-equilibrium depletion development of condensate gas reservoirs, the phase characteristics of a condensate oil and gas system were studied by constant composition expansion and constant volume depletion experiments. Then, on the basis of a long core depletion experiment and chromatographic analysis experiment, the influence of different pressure drop speeds, fluid properties, and reservoir physical properties on the control effect of non-equilibrium retrograde condensation after the coupling of the fluid retrograde condensation and reservoir core is analyzed. The results show that during the pressure decline process, the condensate oil and gas system will produce a strong foggy retrograde condensation phenomenon, with the saturation of the retrograde condensate increasing and then decreasing. The cumulative recovery of the condensate oil and natural gas, as well as the mass fraction of the heavy components in the condensate oil, increase with the increase in the depletion rate. Different fluid properties and reservoir physical properties have a great influence on the cumulative recovery degree of the condensate oil, and have little influence on the recovery degree of the natural gas. This work has a certain guiding role for the stable production and enhanced recovery of fractured condensate gas reservoirs in subsurface structures of metamorphic rocks.

Surface tension and evaporation behavior of liquid fuel droplets at transcritical conditions: Towards bridging the gap between molecular dynamics and continuum simulations

The phase transition from subcritical to supercritical conditions, referred to as transcritical behavior, significantly impacts the evaporation and fuel–air mixing in high-pressure liquid-fuel propulsion systems. Transcritical behavior is characterized as a transition from classical two-phase evaporation to a single-phase gas-like diffusion regime as surface tension and latent heat of vaporization reduce. However, the interfacial behavior represented by the surface tension coefficient and evaporation rate during this transition which are crucial inputs for Computational Fluid Dynamics (CFD) simulations of practical transcritical fuel spray is still missing. This study aims at developing new evaporation rate and surface tension models for transcritical n-dodecane droplets using molecular dynamics (MD) simulations irrespective of the droplet size. As MD simulations are primarily limited to the nanoscale, the new models can bridge the gap between MD and continuum simulations and enable the direct application of these findings to microscopic droplets. A new characteristic timescale, i.e., “undroplet time,” is defined which marks the transition from classical two-phase evaporation to single-phase gas-like diffusion behavior. The undroplet time indicates the onset of droplet core disintegration and penetration of nitrogen molecules into the droplet, which occurs after the vanishment of the surface tension. By normalizing the time with respect to the undroplet time, the rate of surface tension decay, evaporation rate, and the rate of droplet mass depletion become independent of the droplet size. Calculation of pairwise correlation coefficients for the entire MD results shows that both surface tension coefficient and evaporation rate are strongly correlated with the background temperature, while pressure and droplet size play a less significant role past the critical point. Therefore, new models for surface tension coefficient and evaporation rate spanning from sub- to supercritical conditions are developed as a function of background pressure and temperature, which can be used in continuum simulations. The identified phase change behavior based on the undroplet time shows a good agreement with the phase change regime maps obtained using microscale experiments and nanoscale MD predictions.

Modelling Urban Green Spaces Depletion in Akure, Nigeria

The fast progress of urbanization and the accompanying dominance of concrete spaces over natural spaces are fundamental to current debates on urban planning and sustainable development in Nigeria and the world at large. It is worth noting that natural landscapes and greenery are critical to man's quality of life; yet, the majority of the population are going to reside in urban areas, to the detriment of urban green spaces, known as the "lungs of the city." A detailed account urban green spaces in Akure. Using Geographic Information System (GIS) and remote sensing techniques needs to be done. This study examines the status of urban green spaces in Akure, Nigeria to determine the rate of depletion and encroachment green spaces. The spatio-temporal analysis of green spaces in Akure was carried out between 1984 and 2022 using Supervised maximum likelihood classification procedure on Landsat 8 OLI/TIRS, Landsat 7 EMT+ and Landsat 4-5 TM Imageries. It took cognizance of attributes of vegetative cover at varying degrees such as Grasses and Shrubs, Light Vegetation, Secondary Vegetation, and Dense Vegetation. The rate of depletion of green areas, change statistic, socio-economic implication as well as planning implications were addressed. It is believed that assessing and analyzing its social, economic, and environmental impacts on urban inhabitants and their livelihoods would serve as a tool to educate and enlighten urban citizens about the need of including green space scheme into urban designs and planning in Akure.

Performance and Emission Characteristics of CRDI Engine Fuelled with Cotton Seed Oil Blended Biodiesel

The biofuel produced from cottonseed oil can provide a potential solution to the rapid rate of depletion and hazardous emissions of the fossil fuels for the fast-growing world. The present work investigates the suitability of cotton seed oil as a blending agent for production of biodiesel. The biodiesel blend has been tested as an alternate fuel in a common rail direct injection diesel engine from performance and emission point of view. The performance and emission parameters of biodiesel containing 10, 20 and 30 % of cotton seed oil have been compared with those of pure diesel. The experimental results indicated that the biodiesel containing 20% of cottonseed oil exhibited the most optimal performance and emission characteristics. The brake thermal efficiency of the engine decreased by 2.3% while the brake specific fuel consumption increased by 0.047kg/kWh for optimally concentrated biodiesel. Corresponding to same combustion parameters, the hydrocarbon and carbon monoxide emissions reduced by 16.5 and 58 % respectively while the nitrogen oxide emissions increased by approximately 4.8%. Thus, the cotton seed oil can be considered as a potential alternate to pure diesel considering performance and emission characteristics.

Design and numerical analysis of inverted well technique for aquifer recharge estimation

The seasonal polarization due to climate change and population explosion in developing countries is translating into rapid groundwater depletion. In the populous cities relying on groundwater for their water requirements, aquifers are turning into exiguity due to much higher depletion corresponding to recharge rate. Therefore, it is imperative to model the aquifer conditions for extrapolating the future scenario and adopting efficient and safe groundwater recharge techniques based on simulation results to counter the proliferating depletion rate. In this study, an efficient inverted well design with effective multiple filtration compartments is proposed for ground water recharge at natural runoff collection points having high conductivity and effective filtration. The current depletion rate and design recharge capability was assessed by simulating the aquifer conditions along with boundary conditions confined to model town area, groundwater table data of extraction and observation wells in study area from year 2014–2020, precipitation data 2008 to 2020, and other spatial and temporal variations in model town area of Lahore in VISUAL MODFLOW program. The model results exhibited that the depletion rate of Lahore (model town area having a land area of 5.9 km2 approximately) was 0.96 m per year (investigating year 2014–2020), this concurred with the depletion rate recorded by water table observations of extraction and observations wells from year 2014–2020. The depressions in model town park area of Lahore were simulated as recharge points, and 4 inverted wells with their calculated conductivity were simulated in model. The precipitation data with peak runoff generations for 7 years (2014–2020) was intercalated in the model. The results explicated that the simulation of inverted wells recharge technique at natural rainfed depressions of model town park area significantly reduced the depletion rate from 0.93 m per year (2014–2020) to 0.76 m per year (2021–2023) in MODFLOW visual water table contours. Therefore, this inverted well design-based recharge technique can effectively be used for efficient groundwater recharge, and its application at natural depressions in the groundwater dependent cities can effectively hinder and stabilize the depleting ground water resources.

The spatiotemporal variations of total column ozone concentration over Ethiopia

We have studied spatiotemporal characteristics of ozone concentration over Ethiopia using data from the Ozone Mapper and Profiling Suite-Nadir Mapper (OMPS-NM). Daily total column ozone data of 108 observation points with spatial resolution 1° × 1° over the study area for the period of 2012–2019 have been analyzed. The spatial variations over the region have been studied by considering longitudinal and latitudinal bands separately through the sample mean difference among different bands using multi-comparison analysis of variance technique in order to identify the clusters in the region. For the temporal variability, we model the total column ozone timeseries observation as a sum of seasonal, trend, and temporally correlated noise components. We have found that the total column ozone concentration has a maximum value of 301DU during summer on August 18, 2013 and a minimum value of 216DU during winter on January 03, 2013 over the study period. The 95% confidence level of the overall mean of the total column ozone concentration during the study period was found to be (261.35 ± 2.38)DU. Our spatial data analysis revealed that the spatial distribution of ozone over Ethiopia can be classified into three clusters: southern cluster (4.5°N–8.5°N and 33.5°E–47.5°E), north-eastern cluster (9.5°N to 14.5°N and 41.5°E–47.5°E), and north-western cluster (9.5°N–14.5°N and 33.5°E–40.5°E). We have checked the coefficient of determination among bands in the same cluster to see if the concentration of ozone in one band can be explained by the concentration in another band for each cluster and confirmed the reliability of the classification. In order to capture temporal characteristics, we have computed the spectral periodogram for each cluster and obtained a power peak at frequency f = 0.002 768 Hz, which indicates that the ozone concentration over the region exhibits an annual cyclic behavior. A truncated Fourier series fit is used to determine the annual seasonal component. The non-parametric Mann–Kendall’s trend test with a 95% confidence level of significant has indicated a decreasing linear trend with a depletion rate of 0.77, 0.73, and 0.43 DU/yr over north-western, north-eastern, and southern clusters, respectively. The analysis of residuals for each cluster indicated that the residuals are normally distributed with no significant outliers, and the model explains 85%, 86%, and 79% of the variance in the north-western, north-eastern, and southern clusters, respectively, demonstrating the reliability of the model considered in this study.

Reservoir capacity loss and sedimentation assessment of Dholbaha dam located in Punjab, India using remote sensing and bathymetric survey techniques

Abstract A study was undertaken to assess the live storage capacity of the Dholbaha reservoir located in Punjab, India using remote sensing and bathymetric survey techniques. The primary objectives included comparing the estimated capacity with findings from a bathymetric survey, refining the elevation-area-capacity curve, and determining the rate of capacity loss due to sediments deposition. This analysis utilized water elevation data spanning from 1987 to 2022 and satellite imageries from Landsat 7, 8 & 9. The satellite data was processed using software tools such as Erdas Imagine and ArcGIS. The water extent of the reservoir was calculated using Modified Normalized Difference Water Index (MNDWI). Over the course of 34 years, the reservoir experienced reductions in its dead, active, and total storage capacities by 81.5%, 19.7%, and 28.9%, respectively. These changes correspond to annual depletion rates of 2.40%, 0.58%, and 0.85%, respectively. The sediment yield from the surrounding catchment area was determined to be approximately 1203.56 m3/km2/year. The findings demonstrate substantial declines in Dholbaha reservoir storage capacities over a 34-year period (1987-2022) attributable to sedimentation. This underscores the critical need for sustainable water management and provides key insights for monitoring and strategic planning. The study advocates immediate, targeted interventions within the catchment area to mitigate sedimentation in the Dholbaha reservoir, highlighting the importance of ongoing sedimentation rate monitoring and collaboration with stakeholders for informed reservoir management and sustainable solutions to maintain water capacity for the region.

Rates of Groundwater Depletion in India Could Triple by Midcentury

Climate change is contributing to crop stress associated with a growing demand for freshwater.

Application of homotopy perturbation method to solve a nonlinear mathematical model of depletion of forest resources

Reduction in forest resources due to increasing global warming and population growth is a critical situation the World faces today. As these reserves decrease, it alarms new challenges that require urgent attention. In this paper, we provide a semi-analytical solution to a nonlinear mathematical model that studies the depletion of forest resources due to population growth and its pressure. With the help of the homotopy perturbation method (HPM), we determine an approximate series solution with few perturbation terms, which is one of the essential power of the HPM method. We compare our semi-analytical results with numerical solutions obtained using the Runge-Kutta 4th-order (RK-4) method. Furthermore, we analyze the model’s behaviour and dynamics by changing the parametric coefficients that represent the depletion rate of forest resources and the growth rate of population pressure and present these findings using various graphs.

Analytical Validation of a Spiral Microfluidic Chip with Hydrofoil-Shaped Pillars for the Enrichment of Circulating Tumor Cells.

The isolation of circulating tumor cells (CTCs) from peripheral blood with high efficiency remains a challenge hindering the utilization of CTC enrichment methods in clinical practice. Here, we propose a microfluidic channel design for the size-based hydrodynamic enrichment of CTCs from blood in an epitope-independent and high-throughput manner. The microfluidic channel comprises a spiral-shaped part followed by a widening part, incorporating successive streamlined pillars, that improves the enrichment efficiency. The design was tested against two benchmark designs, a spiral microfluidic channel and a spiral microfluidic channel followed by a widening channel without the hydrofoils, by processing 5 mL of healthy blood samples spiked with 100 MCF-7 cells. The results proved that the design with hydrofoil-shaped pillars perform significantly better in terms of recovery (recovery rate of 67.9% compared to 23.6% in spiral and 56.7% in spiral with widening section), at a cost of slightly lower white blood cell (WBC) depletion (depletion rate of 94.2% compared to 98.6% in spiral and 94.2% in spiral with widening section), at 1500 µL/min flow rate. For analytical validation, the design was further tested with A549, SKOV-3, and BT-474 cell lines, yielding recovery rates of 62.3 ± 8.4%, 71.0 ± 6.5%, and 82.9 ± 9.9%, respectively. The results are consistent with the size and deformability variation in the respective cell lines, where the increasing size and decreasing deformability affect the recovery rate in a positive manner. The analysis before and after the microfluidic chip process showed that the process does not affect cell viability.

How the energy depletion rate and financial structure can promote environmental sustainability: Empirical evidence from Pakistan using ecological footprints

Financial structure is the primary director of economic activity in a capitalist society, it also has an important societal role in encouraging investments that are beneficial to the natural and human ecosystems. To accomplish this objective, this study addresses the unattended symmetric linkages between financial structure, energy depletion, and environmental degradation using multiple ecological footprints ‘’ (built-up land, carbon land, cropland, fishing grounds, forest products, and grazing land)’’ as an indicator over the period 1985 to 2018 for Pakistan. By using these six indicators as separate regressands, this research quantifies the impact of financial structure and energy depletion by applying the newly developed Augmented Autoregressive Distributed Lag (AARDL) approach. The outcome reveals that financial structure decreases ecological footprints, similarly, energy depletion also decreases ecological footprints. Opposite to it, trade openness increases ecological footprints, while urban population decreases ecological footprints. Given these results, comprehensive environmental and financial structure development policies are directed to achieve environmental sustainable goals.

A simple model for predicting oxygen depletion in lakes under climate change

ABSTRACT The advent of climate change has placed aquatic ecosystems at risk for potential declines in water quality, including an increase in the number of lakes experiencing substantial dissolved oxygen (O2) depletion. Through its influence on the thermal structure of lakes via elevated water temperatures and alterations in stratification phenology, climate change intensifies biogeochemical and ecological processes involved in O2 consumption, giving rise to conditions like hypoxia/anoxia. However, predicting O2 dynamics is difficult, with in situ O2 depletion rates showing considerable lake-dependent variability, underpinned by distinct underlying mechanisms. Our study attempts to overcome these lake-specific features and targets distilling key components of O2 depletion into a simple and transferable conceptual model applicable across a diverse array of lakes and at large scales. Using O2 depletion rates from literature reflecting variability in trophic state, we quantified the typical O2 depletion rate ranges for oligotrophic, mesotrophic, and eutrophic lakes and assessed their temperature sensitivity for a broader climate impact assessment. Our model gave reasonable estimates for O2 depletion and risks of anoxia through 3 explanatory variables: trophic state, stratification duration, and hypolimnion temperature. We validated our model predictions using data from 5 German lakes and assessed the relative importance of the 3 influencing factors. This easy-to-use approach has potential for lake management to attain rapid assessments of possible future problems with O2 dynamics in a given lake, even in the absence of in situ data. Moreover, it allows scaling of O2 dynamics continentally/globally without lake-specific hydrological or morphological details.

Short‐term fishery gains mask long‐term resource pains: Spatial fisheries management changes promote hyperstable CPUE in Labrador snow crab Chionoecetes opilio during a period of heavy exploitation

AbstractObjectiveThe snow crab Chionoecetes opilio resource in Assessment Division 2HJ has experienced prolonged high exploitation rates and reduced exploitable biomass over the past two decades. We aimed to explore whether this poor state of the resource is associated with spatial management changes made in 2003 and 2013.MethodsWe tested for differences in fishery performance trends before and after the implementation of spatial management which include standardized CPUE, spatial extent of fishing effort, and size at maturity of male snow crabs.ResultThe results show that spatial regulatory changes were successful in increasing fishery catch rates in the short term but that chronic high exploitation eventually overrode these gains, with contracted fishing patterns leading to increased localized depletion rates on dominant stock components. This ultimately culminated in a downward shift in size at maturity and other concerning biological outcomes.ConclusionThe analysis demonstrates spatial management measures contributed to the present poor state of Assessment Division 2HJ snow crab and that such measures should serve as complements to—not replacements for—stringent quota control.

Depletion of Electroactive Species in Microchannels. Theory and Experimental Validations for Quantitative Abatement of Interfering Species under Stagnant Conditions

The generation of an electroactive-species depleted microenvironment was investigated by taking advantage of confinement in microchannels under stagnant conditions. High depletion rates can be achieved with paired microband electrodes but the time scale of experiment must be carefully delimited based on device geometry, electrochemical cell configuration and species diffusivity. Numerical simulations were thus carried out to reach the situation of interest when the diffusion coupling and lateral diffusion in the microchannel becomes predominant with the operation of the electrodes. The optimal conditions for two minimal cell configurations (i.e., with two or three working electrodes) were delineated by establishing a zone diagram. Experimental validations were successfully performed (i) to illustrate the depletion rate achieved between two side electrodes, and (ii) to demonstrate the selective detection of a target analyte in presence of interfering species by using three electrodes. These situations can easily be extrapolated to the case of regular microelectrode arrays within microchannels.

Exploration of Mangroves Associated Microbes for Bioactive Metabolites

Mangroves are woody plants found growing at transition zones between land and sea in tropic and sub-tropical regions. They arehighly adapted morphologically and physiologically to survive in extreme environments. Mangroves are found worldwide in theirdistribution, with 110 species that belong to 20 different families. In India, mangrove forests are mostly found on the Andaman andNicobar Islands and the West and East Coast. Mangroves have enormous ecological, commercial and biological significance. They arealso regarded as hotspots for microbes because of their rich microbial diversity. Various types of microorganisms like bacteria, fungi,microalgae and macroalgae are abundant in mangrove ecosystems. More recently, fungal endophytes associated with mangroveshave added to their microbial diversity. Many mangrove plants are used as ethno-medicine in traditional health care. Mangroves arealso used as antimicrobial and antiviral agents. Fungal endophytes -colonizing medicinal plants are reported to produce importantbioactive metabolites. These endophytes are believed to produce same and more biologically active metabolites as compared to theirrespective hosts. Many fungal endophytes isolated from mangrove species have produced some important biological active metaboliteslike triterpenes, indole triterpenes, isocoumarin and marinamide. Therefore, the study of fungal endophytes associated with medicinalmangroves may give rise to important endophytic strains that might produce novel and new bioactive metabolites of pharmaceutical,industrial and agricultural importance. Due to the alarming rate of depletion of mangrove genetic resources across the world, it is highlyneeded to explore fungal endophytes associated with mangroves for the inventorisation of new metabolites.

A study on inventory control strategies of fresh food supply chain considering advertising delay effect

PurposeThe existence of the advertising delay effect and its impact on supply chain operations have been demonstrated in the current study. Therefore, this study develops a timely inventory control strategy for the fresh produce supply chain to address the advertising delay effect in the fresh produce supply chain.Design/methodology/approachThis study proposes a game model based on the Nerlove-Arrow time delay differential equation and Pontryagin's maximum principle. Through comparative analyses of the optimal equilibrium strategies, the authors compare the optimal equilibrium strategies, product goodwill and optimal inventory trajectories for suppliers and retailers under secondary replenishment decisions and decentralized decisions.FindingsThe authors find that (1) Only when the sales cycle meets certain conditions can the overall profit of the supply chain under the secondary replenishment decision be greater than that under the decentralized decision. As the price markup coefficient increases, the total profit of the supply chain first increases and then decreases. (2) With the increase in the delay time, the replenishment quantity during the initial period gradually decreases. After the delay time elapses, the inventory depletion rate under secondary replenishment decisions is faster than that under decentralized decision-making. (3) Although there is a continuously increasing maximum value of product goodwill with the increase in delay time, it becomes difficult to achieve this value for longer delays.Practical implicationsThe authors’ findings provide a theoretical basis for supply chain members of fresh agricultural products to select replenishment and inventory control strategies when adopting different levels of delay in advertising marketing.Originality/valueFirstly, this paper explains the impact of advertising delay effect on fresh produce supply chain from a dynamic perspective, and secondly, it provides guidance on advertising formulation and inventory replenishment for fresh produce retailers under the influence of advertising delay effect.

Mechanism and Main Control Factors of CO2 Huff and Puff to Enhance Oil Recovery in Chang 7 Shale Oil Reservoir of Ordos Basin

The Chang 7 shale oil reservoir has low natural energy and is both tight and highly heterogeneous, resulting in significant remaining oil after depletion development. CO2 huff and puff (huff-n-puff) is an effective way to take over from depletion development. Numerous scholars have studied and analyzed the CO2 huff-n-puff mechanism and parameters based on laboratory core sample huff-n-puff experiments. However, experimental procedures are not comprehensive, leading to more general studies of some mechanisms, and existing CO2 huff-n-puff experiments struggle to reflect the effect of actual reservoir heterogeneity due to the limited length of the experimental core samples. In this paper, CO2 huff-n-puff laboratory experiments were performed on short (about 5 cm) and long (about 100 cm) core samples from the Chang 7 shale oil reservoir, and the microscopic pore fluid utilization in the short samples was investigated using a nuclear magnetic resonance (NMR) technique. We then analyzed and discussed the seven controlling factors of CO2 huff-n-puff and their recovery-enhancing mechanisms. The experimental results show that the cumulative recovery increased with the number of huff-n-puff cycles, but the degree of cycle recovery decreased due to the limitation of the differential pressure of the production. The significant increase in recovery after the CO2 mixed-phase drive was achieved by increasing the minimum depletion pressure as well as the gas injection amount. The soaking time was adjusted appropriately to ensure that the injected energy was thoroughly utilized; too short or too long a soaking time was detrimental. The pressure depletion rate was the main factor in the CO2 huff-n-puff effect in shale. If the pressure depletion rate was very high, the effective permeability loss was larger. In the CO2 huff-n-puff process of the Chang 7 shale oil reservoir, the improvement in oil recovery was mainly contributed to by mesopores and small pores. The huff-n-puff experiments using long cores could better characterize the effect of heterogeneity on the huff-n-puff effect than short cores.