Seepage model and experiments of drag reduction by nanoparticle adsorption

The hydrophobic nanoparticle （HNP） adsorption is a new technique of drag reduction, which changes the wettability of the porous walls of the core, generates the slip-boundary of the fluid flow and consequently enhances the oil recovery. In the present work, a seepage model with consideration of the slip effect in the micro-channels and the influence of the equivalent pore radius mo- dified by the HNP adsorption is proposed based onthe Darcy＇s law. The permeability of the non-wetting phase in the porous media is calculated according to its dependence on the slip length, while the slip length is determined by a function of the contact angle and the equivalent pore radius. Numerical simulations are performed by use of the COMSOL multiphysics, and an acceptable agreement between experimental and simulation results is achieved （with an error less than 2.5%）. The present model can then be used for the mechanism investigation and the prediction of the oilfield performance.

Monitoring models for base flow effect and daily variation of dam seepage elements considering time lag effect

Affected by external environmental factors and evolution of dam performance, dam seepage behavior shows nonlinear time-varying characteristics. In this study, to predict and evaluate the long-term development trend and short-term fluctuation of the dam seepage behavior, two monitoring models were developed, one for the base flow effect and one for daily variation of dam seepage elements. In the first model, to avoid the influence of the time lag effect on the evaluation of seepage variation with the time effect component of seepage elements, the base values of the seepage element and the reservoir water level were extracted using the wavelet multi-resolution analysis method, and the time effect component was separated by the established base flow effect monitoring model. For the development of the daily variation monitoring model for dam seepage elements, all the previous factors, of which the measured time series prior to the dam seepage element monitoring time may have certain influence on the monitored results, were considered. Those factors that were positively correlated with the analyzed seepage element were initially considered to be the support vector machine(SVM) model input factors, and then the SVM kernel function-based sensitivity analysis was performed to optimize the input factor set and establish the optimized daily variation SVM model. The efficiency and rationality of the two models were verified by case studies of the water level of two piezometric tubes buried under the slope of a concrete gravity dam.Sensitivity analysis of the optimized SVM model shows that the influences of the daily variation of the upstream reservoir water level and rainfall on the daily variation of piezometric tube water level are processes subject to normal distribution.

Low Temperature Wafer Level Hermetic Package with Benzo-cyclo-butene Material

The wafer level hermetic package method was studied experimentally in low temperature for optoelectronic devices with benzo-cyclo-butene(BCB) material. The results show that the bonding temperature is below 250℃, the helium hermetic capability of both silicon-BCB-silicon and silicon-BCB-glass package are better than 6×10~ -4 Pa·cm^3/s. The shear strength is enough for package. The hermeticity is still good after the 15 cycles’ thermal shock test. The relationship between the leakage rate and the distance from the hole to the device border were also discussed with a seepage model.

A systematic approach for estimating water losses in irrigation canals

In order to determine water losses in irrigation canals,a systematic approach was developed,consisting of two main components:a seepage simulation model and a hydraulic simulation model.The SEEP/W module of the Geo-Studio software was used to simulate the seepage rate,and the Hydrologic Engineering Center-River Analysis System(HEC-RAS)hydrodynamic model was used for hydraulic simulation.Different operation scenarios were designed to investigate all possible situations in daily operation of water distribution and delivery systems.The seepage simulation results show that the seepage losses were higher at the bottom and corners of the canal,because the hydraulic gradient was affected by the hydraulic load.The hydraulic simulation results show that due to physical and management infrastructure(using non-automated and operator-based regulation structures),operational losses accounted for a significant volume of losses compared to seepage losses.In most operation scenarios,the maximum seepage loss was 10%,and the remaining 90%was related to operational losses.It is concluded that any factor(decrease or increase of inflow to the canal)that causes an increase or decrease of operational losses is ultimately a determining factor in reducing or increasing total losses.Therefore,management approaches should be adopted to improve performance of the system and reduce losses,especially operational losses,by improving the operation methods of water level regulation and off-take structures.

Forecasting the underground waters regime in the pitching aquifers in Huainan mining area

Huainan area is an important coal base of the east of China. In the early part of the 1980s, the study of the underground waters dynamic state in the area was gradually paid close attention to. This paper introduces the observation system of the groundwater dynamic state in the multilayered pitching aquifer, and expounds the hydrogeologic feature and the waterpower relations among aquifers. Furthermore, based on the analysis of the relations of the groundwater dynamic state to surface water, meteoric water and mining shaft outflow rate, this paper establishes main water filled aquifers of mining shaft (C 3-1 ,C 3-2 ,C 3-3 and O 2).In the light of the actual situation of the greatly changing aquifer occurrence and steep dip angle, the “two layer space curved surface seepage model" and the calculating step are all suggested. Since 1991,the groundwater dynamic state of the next year has been predicted (numerical simulation) every year. Contracting with the measured data, we gain a relatively ideal effect.

AN UNSTEADY SEEPAGE FLOW MODEL OF VISCO-ELASTIC POLYMER SOLUTION

With the consideration of the visco―elasticity, the adsorption effect andthe variation of rheological parameters, a seepage flow model of visco-elastic polymer solutions wasestablished. The model was numerically treated with the finite difference method. Then curves ofBottom Hole Pressure (BHP) and formation pressure were drawn. The influences of the relaxation time,the injection rate, the permeability reduction coefficient, the consistency coefficient and thepower-law exponent of the injected fluid on pressure performance were analyzed. This study showsthat it is necessary to consider the visco-elasticity of non-Newtonian fluid in analyzing ofpressure performance in the polymer flooding.

RESEARCH ON SEEPAGE MONITORING MODEL OF EARTH-ROCK DAM

With the characteristics of seepage flow in earth-rock dams, a seepagemonitoring model was established based on the finite element method for 3-D seepage flow togetherwith observed data and was used to analyze and monitor the seepage of dams. In order to find out andmonitor the seepage status of the whole dam, the separation of seepage a-mount for dam body, damfoundation and side banks was made theoretically by using the model. Practical example shows thatthe accuracy of computed results is satisfactory and the separation results are more objective.

Direct shear tests on cemented paste backfill-rock wall and cemented paste backfill-backfill interfaces

Even though a large number of large-scale arch dams with height larger than 200 m have been built in the world, the transient groundwater flow behaviors and the seepage control effects in the dam foundations under difficult geological conditions are rarely reported. This paper presents a case study on the transient groundwater flow behaviors in the rock foundation of Jinping I double-curvature arch dam, the world＇s highest dam of this type to date that has been completed. Taking into account the geological settings at the site, an inverse modeling technique utilizing the time series measurements of both hydraulic head and discharge was adopted to back-calculate the permeability of the foundation rocks,which effectively improves the uniqueness and reliability of the inverse modeling results. The transient seepage flow in the dam foundation during the reservoir impounding was then modeled with a parabolic variational inequality（PVI） method. The distribution of pore water pressure, the amount of leakage, and the performance of the seepage control system in the dam foundation during the entire impounding process were finally illustrated with the numerical results.

Spatio-temporal evolution of pore and fracture structures in coal induced by initial damage and creep behavior:A real-time NMR-based approach OA

Understanding the impact of mining disturbances and creep deformation on the macroscopic deformation and the microscopic pore and fracture structures(MPFS)of coal is paramount for ensuring the secure extraction of coal resources.This study conducts cyclic loading-unloading and creep experiments on coal using a low-field nuclear magnetic resonance(NMR)experimental apparatus which is equipped with mechanical loading units,enabling real-time monitoring the T2spectrum.The experiments indicated that cyclic loading-unloading stress paths initiate internal damage within coal samples.Under identical creep stress conditions,coal samples with more initial damages had more substantial instantaneous deformation and creep deformation during the creep process.After undergoing nearly 35 h of staged creep,the total strains for coal samples CC01,CC02,and CC03 reach 2.160%,2.261%,and 2.282%,respectively.In the creep stage,the peak area ratio of seepage pores and microfractures(SPM)gradually diminishes.A higher degree of initial damage leads to a more pronounced compaction trend in the SPM of coal samples.Considering the porosity evolution of SPM during the creep process,this study proposes a novel fractional derivative model for the porosity evolution of SPM.The efficacy of the proposed model in predicting porosity evolution of SPM is substantiated through experimental validation.Furthermore,an analysis of the impact mechanisms on key parameters in the model was carried out.