•An improved aggregated HR is proposed and the time-varying HRs are used to adapt to the uneven-distributed runoff.•An aggregation-decomposition model is proposed to guide the joint operation of ...multi-reservoir water-supply system.•Based on the priority analysis, a hierarchical optimization model is established to coordinate multiple purposes.•The aggregated HRs outperforms aggregated SOP and CRs both in water supply quality and hydropower generation.
The derivation of joint operating policy is a challenging task for a multi-purpose multi-reservoir system. This study proposed an aggregation-decomposition model to guide the joint operation of multi-purpose multi-reservoir system, including: (1) an aggregated model based on the improved hedging rule to ensure the long-term water-supply operating benefit; (2) a decomposed model to allocate the limited release to individual reservoirs for the purpose of maximizing the total profit of the facing period; and (3) a double-layer simulation-based optimization model to obtain the optimal time-varying hedging rules using the non-dominated sorting genetic algorithm II, whose objectives were to minimize maximum water deficit and maximize water supply reliability. The water-supply system of Li River in Guangxi Province, China, was selected for the case study. The results show that the operating policy proposed in this study is better than conventional operating rules and aggregated standard operating policy for both water supply and hydropower generation due to the use of hedging mechanism and effective coordination among multiple objectives.
Pore-throat size is a very crucial factor controlling the reservoir quality and oiliness of tight sandstones, which primarily affects rock-properties such as permeability and drainage capillary ...pressure. However, the wide range of size makes it difficult to understand their distribution characteristics as well as the specific controls on reservoir quality and oiliness. In order to better understand about pore-throat size distribution, petrographic, scanning electron microscopy (SEM), pressure-controlled mercury injection (PMI), rate-controlled mercury injection (RMI), quantitative grain fluorescence (QGF) and environmental scanning electron microscopy (ESEM) investigations under laboratory pressure conditions were performed on a suite of tight reservoir from the fourth member of the Lower Cretaceous Quantou Formation (K1q4) in the southern Songliao Basin, China. The sandstones in this study showed different types of pore structures: intergranular pores, dissolution pores, pores within clay aggregates and even some pores related to micro fractures. The pore-throat sizes vary from nano- to micro-scale. The PMI technique views the pore-throat size ranging from 0.001 μm to 63 μm and revealed that the pore-throats with radius larger than 1.0 μm are rare and the pore-throat size distribution curves show evident fluctuations. RMI measurements indicated that the pore size distribution characteristics of the samples with different porosity and permeability values look similar. The throat size and pore throat radius ratio distribution curves had however significant differences. The overall pore-throat size distribution of the K1q4 tight sandstones was obtained with the combination of the PMI and RMI methods. The permeability is mainly contributed by a small part of larger pore-throats (less than 30%) and the ratio of the smaller pore-throats in the samples increases with decreasing permeability. Although smaller pore-throats have negligible contribution on reservoir flow potential, they are very significant for the reservoir storage capacity. The pore-throats with average radius larger than 1.0 μm mainly exist in reservoirs with permeability higher than 0.1mD. When the permeability is lower than 0.1mD, the sandstones are mainly dominated by pore-throats with average radius from 0.1 μm to 1.0 μm. The ratio of different sized pore-throats controls the permeability of the tight sandstone reservoirs in different ways. We suggest that splitting or organizing key parameters defining permeability systematically into different classes or functions can enhance the ability of formulating predictive models about permeability in tight sandstone reservoirs. The PMI combined with QGF analyses indicate that oil emplacement mainly occurred in the pore-throats with radius larger than about 0.25–0.3 μm. This result is supported by the remnant oil micro-occurrence evidence observed by SEM and ESEM.
•PMI and RMI were integrated to construct overall pore-throat size distribution curve.•Specific contributions of different pore-throats on reservoir quality are elucidated.•PMI and QGF studies indicated a pore-throat radius threshold for the oil-charging.
The need for energy is increasing and at the same time production from the conventional reservoirs is declining quickly. This requires an economically and technically feasible source of energy for ...the coming years. Among some alternative future energy solutions the most approachable source is from unconventional reservoirs. As the name “unconventional” implies it requires different and challenging approach to characterize and to develop such a resource. This special issue covers some of the technical challenges for developing unconventional energy sources from shale gas/oil, tight gas sand, and coalbed methane.
A catastrophic flood event which caused massive economic losses occurred in Thailand, in 2011. Several studies have already been conducted to analyze the Thai floods, but none of them have assessed ...the impacts of reservoir operation on flood inundation. This study addresses this gap by combining physically based hydrological models to explicitly simulate the impacts of reservoir operation on flooding in the Chao Phraya River Basin, Thailand. H08, an integrated water resources model with a reservoir operation module, was combined with CaMa‐Flood, a river routing model with representation of flood dynamics. The combined H08‐CaMa model was applied to simulate and assess the historical and alternative reservoir operation rules in the two largest reservoirs in the basin. The combined H08‐CaMa model effectively simulated the 2011 flood: regulated flows at a major gauging station have high daily NSE‐coefficient of 92% as compared with observed discharge; spatiotemporal extent of simulated flood inundation match well with those of satellite observations. Simulation results show that through the operation of reservoirs in 2011, flood volume was reduced by 8.6 billion m3 and both depth and area of flooding were reduced by 40% on the average. Nonetheless, simple modifications in reservoir operation proved to further reduce the flood volume by 2.4 million m3 and the depth and area of flooding by 20% on the average. By modeling reservoir operation with a hydrodynamic model, a more realistic simulation of the 2011 Thai flood was made possible, and the potential of reducing flood inundation through improved reservoir management was quantified.
Key Points
Modeling dam operation with hydrodynamics improved simulation of Thai flood
Impacts of dam operation to flood inundation were explicitly evaluated
Reservoir operation in 2011 reduced flood volumes but it can still be improved
•Multiple solvents and hydraulic fracture designs are numerically tested for EOR.•Fracture Permeability and half-length are the most critical hydraulic fracture parameters for EOR.•Diagnostic contour ...plots for EOR and CO2 storage in tight oil reservoirs are developed.
Improved oil recovery from tight oil reservoirs to fulfill the fossil fuel requirements and the CO2 storage to meet the net carbon zero objectives are the two motivations of this work. CO2 is a major anthropogenic greenhouse gas and its emission to our plants’ atmosphere is hazardous, particularly causing global warming. Therefore, its injection in the sub-surface oil-bearing formations not only improves the oil recovery but also reduces the carbon footprint from the planet. In this study, a mechanistic numerical simulation model is built using typical U.S. tight oil reservoir rock and fluid properties. The reservoir model is equipped with a hydraulically fractured single horizontal well that is subjected to multiple sensitivities using the huff-n-puff technique. Detailed CO2 trapping and diffusivity mechanisms at the nanopore scale are discussed that numerically define the CO2 solubility in formation oil and it’s trapping phenomenon into the nanopore spaces. The results show that CO2 injection works predominantly to achieve significant incremental oil recovery. Also, the reservoir with lighter in-situ fluid composition and higher reservoir pressure further enhances the oil recovery due to improved diffusivity and the solubility of CO2 into the reservoir fluid. It is also found that the increased number of huff-n-puff cycles and the incremental CO2 injection volume in each cycle not only enhance the oil recovery performance but likewise help to trap a larger volume of CO2 into a reservoir. A few diagnostic contour plots are also presented in this study to demonstrate the simultaneous effect of multiple hydraulic fracture parameters and the CO2 injection volume for the directional EOR and CO2 trapping performance. The findings of this study can help for a better understanding of designing EOR operations in tight oil reservoirs to achieve both goals concurrently.
Wonogiri Reservoir, one of the large reservoirs in Indonesia, regulates water for flood control, irrigation, domestic use, and hydropower. It is located at the upper part of Bengawan Solo River ...Basin, Central Java. A closure dike has recently been constructed as a countermeasure against severe sedimentation that separates the reservoir into two parts, i.e., Sediment Storage Reservoir (SSR) and Main Reservoir (MR). A two-gate spillway was constructed in the SSR to facilitate sediment flushing and sluicing. During flood events, it controls reservoir water level jointly with the MR spillway. This brings the need for an update on the reservoir operation rules, especially on the gates opening of the new spillways to maintain the flood control performance. An assessment of reservoir routing simulation results was carried out by considering the overflow from SSR to MR, or vice versa with two options of Control Water Level (CWL), i.e. +135.8 m and +136.3 m. The flood control performance of the new reservoir operation rules was evaluated by considering the reservoir water level recovery, the maximum total outflow discharge, and the dam safety due to the risk of overtopping. These assessments give a foundation for the selection of CWL and the spillway operation to ascertain an optimal flood control of the reservoir.
Integrated analysis of reservoir quality, pore structure, depositional and petrologic characteristics, and types and degree of diagenetic alterations was done in this study by employing petrophysical ...evaluation, thin section observation, stable isotope analysis, scanning electron microscopy combined with EDS, X-ray computed tomography, and high-pressure mercury intrusion. The purpose was to investigate the macroscopic and microscopic heterogeneities, and the effects of depositional factors and diagenetic alterations responsible for them. The results indicate that the Chang 8 tight oil sandstone of the Longdong area in the Ordos Basin can be divided into three categories, namely the Type I reservoir, with porosity greater than 10% and permeability greater than 1.0 mD, having sparse lenticular distributions in the mouth bar of the braided delta front, the Type II reservoir, with porosity of 6–10% and permeability of 0.1–1.0 mD, mainly distributing in the distributary channel, and the Type III reservoir, with porosity less than 6% and permeability less than 0.1 mD, having a reticular distribution in the distributary bay. The Type I reservoir has an intergranular pore (Inter-P) dominant pore system with a greater pore-throat radius (1–10 μm), a larger pore volume and better connectivity. The Type II reservoir has a mixed system consisting of intragranular pores (Intra-P) and Inter-P with a pore-throat radius of 0.1–1 μm, smaller pore volume, and worse connectivity. The Type III reservoir is characterized by an Intra-P dominated system with a radius between 10 and 500 nm, smallest pore volume and worst connectivity. The wide range of porosity, permeability, and pore structure parameters can be attributed to the frequent variations in depositional facies and diagenetic alterations. Larger grain size, higher content of quartz and feldspar, and moderate grain-coating chlorite content (less than 8%) are favorable for the preservation of intergranular pores and dominate the formation of the Type I reservoir. The mesogenetic calcite and ferrocalcite cementation and pore-filling kaolinite precipitation obstruct the intergranular space and are the predominant factors tightening the reservoirs in the distributary channel and distributary bay, leading to multi-scale heterogeneities. Secondary porosity from dissolution plays a much more important role in contributing to the porosity and permeability of the Type II and III reservoirs than of the Type I reservoir. The study provide a comprehensive understanding for the multi-scale heterogeneities and can be used to predict the potential high-quality zones in tight oil sandstone reservoirs.
•Three different types of reservoirs are identified in tight oil sandstone reservoir.•Thin section, SEM, HPMI and X-ray CT are integrated to characterize pore structure.•Reservoir quality and pore structure are closely correlated in different reservoirs.•Calcite and kaolinite cementation are dominant in tightening the sandstone reservoir.•Variations of depositional and diagenetic factors decide multi-scale heterogeneities.
The estimation of reservoirs impact on flood peak reduction at the catchment scale is of fundamental importance for risk assessment and planning purposes. It is generally addressed using detailed ...hydrologic‐hydrodynamic simulations or simple, empirically based indices. The former provide detailed results, at the cost of a large amount of information and high computational efforts; the latter are cost‐effective and simple, yet they generally provide approximate results. A promising compromise between the two is the physically based attenuation index R $\mathcal{R}$, based on the concept of equivalent reservoir; R $\mathcal{R}$ was recently proposed in the literature to estimate the impact of multiple reservoirs located in series along the main channel, based on the assumption of rectangular catchment. In this work, we extend the equivalent reservoir approach to a generic catchment, with any shape and without restrictions on the location of the reservoirs. For an effective assessment of the method, we also introduce the novel concept of Reservoir‐influenced Instantaneous Unit Hydrograph (RIUH); the RIUH can be derived using a Monte Carlo procedure to include the effects of reservoirs on the Instantaneous Unit Hydrograph. Simulations of numerous fictitious reservoir configurations in a real basin demonstrate the potential of the methods in reproducing the attenuation effect. Remarkably, an average error of 3%–5% exists between R $\mathcal{R}$ and the peak reduction of a less simplified reality (RIUH). Finally, we provide a global, catchment‐scale application of the attenuation index, which constitutes an effective tool for the evaluation of each reservoir in managed catchment system and the design or planning of new hydraulic infrastructures.
Key Points
A simplified reservoir attenuation index R $\mathcal{R}$, applicable to a generic catchment and any reservoir location, is proposed
We introduce the novel concept of Reservoir‐influenced Instantaneous Unit Hydrograph to easily include reservoirs effects in Instantaneous Unit Hydrograph
We provide a global, catchment‐scale application of R $\mathcal{R}$ that constitutes an effective tool for risk assessment and reservoir design
Abstract Reservoirs are designed and operated to mitigate hydroclimatic variability and extremes to fulfill various beneficial purposes. Existing reservoir infrastructure capacity and operation ...policies derived from historical records are challenged by hydrologic regime change and storage reduction from sedimentation. Furthermore, climate change could amplify the water footprint of reservoir operation (i.e. non-beneficial evaporative loss), further influencing the complex interactions among hydrologic variability, reservoir characteristics, and operation decisions. Disentangling and quantifying these impacts is essential to assess the effectiveness of reservoir operation under future climate and identify the opportunities for adaptive reservoir management (e.g. storage reallocation). Using reservoirs in Texas as a testing case, this study develops data-driven models to represent the current reservoir operation policies and assesses the challenges and opportunities in flood control and water supply under dynamically downscaled climate projections from the Coupled Model Intercomparison Project Phase 6. We find that current policies are robust in reducing future flood risks by eliminating small floods, reducing peak magnitude, and extending the duration for large floods. Current operation strategies can effectively reduce the risk of storage shortage for many reservoirs investigated, but reservoir evaporation and sedimentation pose urgent needs for revisions in the current guidelines to enhance system resilience. We also identify the opportunities for reservoir storage reallocation through seasonal-varying conservation pool levels to improve water supply reliability with negligible flood risk increase. This study provides a framework for stakeholders to evaluate the effectiveness of the current reservoir operation policy under future climate through the interactions among hydroclimatology, reservoir infrastructure, and operation policy.
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