High Pumping Rates Research Articles

Experiments of Sand Distribution among Perforation Clusters in a Horizontal Pipe

ABSTRACT Multistage horizontal fracturing is the key technique in developing shale gas reservoirs. Although the parameters of perforation clusters are almost the same in each stage, production from each perforation cluster is vastly different. One of the factors that influences gas production between perforation clusters is the uneven proppant distribution among perforation clusters. In order to investigate proppant distribution among perforation clusters, the theory on proppant settling along horizontal lateral is presented to calculate the minimal critical velocity. Meanwhile, experiments on 20/40 and 40/70 mesh sand distribution with different concentrations were conducted at different pumping rates utilizing slick water fluids. The experimental parameters of perforation cluster, such as perforation density, length, and distance between clusters are scaled to simulate the actual treatment in shale gas fracturing. Therefore, the experimental results in this study can represent the actual distribution of proppants among perforation clusters. The results are analyzed, and some conclusions are presented. Pumping rate and viscosity are the two important factors that can have a big impact on the sand distribution. At a lower pumping rate, more sand was deposited at the first perforation cluster, whereas at a high pumping rate, more sand was deposited at the third cluster. The viscosity of slick water will also affect sand distribution largely. At a low fluid viscosity, sand distribution was varied much among clusters at the same pumping rate, and sand tended to distribute evenly when the fluid viscosity is increased. Therefore, in order to distribute proppants evenly among perforation clusters, the treatment parameters such as the pumping rate or the viscosity of slick water fluid can be adjusted accordingly.

Research and Application of the Composite Reservoir Stimulation Technology for Ultra-High-Temperature Ultra-Deep Naturally-Fractured Carbonate Reservoirs

The Ordovician buried-hill carbonate reservoir in the northern Jizhong Sag of China is seen with abundance in hydrocarbon resources. Nonetheless, attempts of multiple reservoir stimulation technologies have all failed to make breakthrough, due to its lithological complexity (mixture of dolomite and limestone), ultra-high temperatures (180°C) and high in-situ stress gradients (0.023 MPa/m), Given the aforementioned reservoir geological challenges, reservoir evaluation, technology optimization and plan design starting from the reservoir geological characteristics have been carried out, and the “composite” reservoir stimulation technology for ultra-high-temperature ultra-deep naturally-fractured carbonate reservoirs has been proposed. In terms of the short effective affected distance of acid under high temperatures (180°C), low conductivity sustainability owing to high closure stresses (induced by the burial depth of 5,000 m), extreme difficulties in expanding stimulated reservoir volumes (large lateral in-situ stress differences and long vertical spans), the practice of “multi-stage injection, temporary plugging and diversion, and propped acid fracturing” highlighting high pump rates and combination of low- and high-viscosity fluids (acid and fracturing fluids) has been developed and evolves into the network fracturing technology capable of inter-layer temporary isolation and within-layer diversion. The above technology has been applied in Well AT1x, with high volumes of fluid consumption and the maximum pump rate of 11 m3/min. Safe and efficient operation over six hours featuring challenges such as 3,000 m3 of composite fluids, ultra-high temperatures and ultra-high pressures is achieved. On-site monitoring such as the micro-seismic monitoring and simulation results show that compared with the previous reservoir stimulation, the developed technology presents SRV 3.5 times larger, and results in three-dimensional reservoir reconstruction. The post-fracturing daily gas production amounts to 409,000 m3 and daily oil production, 71 m3. In production testing, the wellhead pressure maintained over 25 MPa, and the daily gas production exceeds 100,000 m3, which indicate stable pressures and production, and a safe wellbore. The application accomplishes the design goal of integrated exploration and exploitation, and geology and engineering, and provides references for reservoir simulation of analogous reservoirs.

Numerical Investigation on Proppant–Water Mixture Transport in Slot under High Reynolds Number Conditions

Water hydraulic fracturing involves pumping low viscosity fluid and proppant mixture into the artificial fracture under a high pumping rate. In that high Reynolds number conditions (HRNCs, Re > 2000), the turbulence effect is one of the key factors affecting proppant transportation and placement. In this paper, a Eulerian multiphase model was used to simulate the proppant particle transport in a parallel slot under HRNCs. Turbulence effects in high pumping rates and frictional stress among the proppant particles were taken into consideration, and the Johnson-Jackson wall boundary conditions were used to describe the particle-wall interaction. The numerical simulation result was validated with laboratory-scale slot experiment results. The simulation results demonstrate that the pattern of the proppant bank is significantly affected by the vortex near the wellbore, and the whole proppant transport process can be divided into four stages under HRNCs. Furthermore, the proppant placement structure and the equilibrium height of proppant dune under HRNCs are comprehensively discussed by a parametrical study, including injection position, velocity, proppant density, concentration, and diameter. As the injection position changes from the lower one to the top one, the unpropped area near the entrance decrease by 7.1 times, and the equilibrium height for the primary dune increase by 5.3%. As the velocity of the slurry jet increases from 2 m/s to 5 m/s (Re = 2000–5000), the vortex becomes stronger, so the non-propped area near the inlet increase by 5.3 times, and the equilibrium height decrease by 5.2%. The change of proppant properties does not significantly change the vortex; however, the equilibrium height is affected by the high-speed flush. Thus, the conventional equilibrium height prediction correlation is not suitable for the HRNCs. Therefore, a modified bi-power law prediction correlation was proposed based on the simulation data, which can be used to accurately predict the equilibrium height of the proppant bank under HRNCs (mean deviation = 3.8%).

Groundwater flow and chloride transport modeling of the alluvial aquifer of lower Soummam Valley, Béjaia, North-East of Algeria

Resulting from lithological conditions and anthropogenic activities as fertilizers use and wastewater discharge, high concentrations of chloride ions were revealed in both surface water and groundwater in Lower Soummam valley, situated in the North-Eastern of Algeria. Using geological, hydrogeological and geochemical data, a conceptual model was designed in order to improve understanding of chloride mass movements within the aquifer. A groundwater flow using PMWIN, coupled with a solute transport numerical model using MT3D code was run. Following a steady state stress period, four transient stress periods were added in order to simulate groundwater level evolution from 2011 to 2030. Groundwater withdrawals, providing from the National Plan of Water, were increased and vertical recharge rate was progressively reduced. Respecting an optimal management of water resources suitable for arid and semi-arid watersheds, successive tests have been conducted in order to mitigate the influence of high pumping rates and low recharge conditions. Recognized as a major term in water budget, water inflows from lateral boundaries representing 54.4%. At the river–aquifer interface, water was exchanged in both upward and downward representing 18% of the total amount of inflow. In coherence with experimental data, simulations indicate an impact of exchange fluxes across the river-aquifer interface. The Cl model simulations show a substantial decrease of Cl loads. According to good hydraulic properties, 90% of simulated wells show a gradual decline in their calculated concentrations, almost located on El Kseur-Oued Ghir pathway. Simulation results could be integrated in the future water resource management plan of Soummam Valley. Such a predictive model, it will be used to lay down water quality restoration strategy.

Groundwater Flow Modelling: A Decision-making Tool for Water Resource Management in Coastal Areas - Case Study of the Oussouye Plateau (South Senegal)

Hydrogeological and hydrochemical investigations were used to develop a conceptual model of the Continental Terminal (CT) aquifer functioning in the Oussouye plateau (South Senegal). Two field campaigns were carried out in June and October 2017 to measure physicochemical parameters and groundwater sampling. The geometry of the CT was established using geophysical technics (electrical methods) and the drilling logs from previous studies carried out in Oussouye region. These investigations led to build the mathematical model under the Visual modflow interface with the Modflow-2000 code developed by USGS. The results show a general trend of groundwater flow towards the Casamance River and its tributaries from piezometric mounds in the central area of the plateau which represent the potential recharge zones. Regarding chemical quality, electrical conductivity varies from 28 to 1314 µs/cm with high variance and standard deviation values reflecting variable sources, geochemical and dilution processes occurring in the plateau. The analysis of water samples shows an excellent groundwater quality. Major ions contents do not exceed WHO standards except Iron (Fe) which are relatively high in some wells. The mathematical model was calibrated in steady state. The average difference between simulated and observed head is 0.009 m and the root mean squared is less than 0.2m. Simulations under transient conditions showed that the groundwater is vulnerable to high pumping rate due to the drawdowns at the catchment wells, which can reach 7 m for 300 m3/d. This significant drawdown should be avoided for this type of piezometric configuration where the maximum hydraulic head is around 5 m. However, the model revealed a sustainable groundwater potential for the needs of local and neighboring populations by 200m3/d.

Temporal variation of the halide ions (F−, Cl−, Br−, I−) in medium-temperature (46–52 °C) thermal waters from the Sob-1 and Sob-2 wells, the Mura Basin, north-eastern Slovenia

An eleven-year monitoring (1987/88–1999) of chemical composition of Na-HCO3 thermal water from the wells Sob-1 and Sob-2 has shown long- and short-time scale changes occurring as a result of mixed character of abstracted thermal water and overexploitation of the wells. Constantly reoccurring changes of dynamic pressure induced the inflow of variable proportions of water from the most productive aquifer Thermal I and from lower-permeability aquifers in the underlying Lendava Formation which contain abundant CO2. The chloride ions originate from formation waters in the Lendava Formation, and for Thermal I, a local natural background is 80–85 mg/L. The fluoride ions mainly originate from waters in the Lendava Formation but do not correlate entirely with the chloride ions. It is assumed their abundance is largely controlled by interaction of CO2-rich waters with detritial marine carbonates and clay minerals. Temporal variations of concentrations of the bromide and iodide ions in thermal water from the Sob-1 largely correlate with variation of the chloride ions and indicate that the Lendava Formation is their major source. By overexploitation, some low-permeability aquifers in the Lendava Formation have been activated along with leakage from clayey lenses rich in organic matter and coal in the Mura Formation. The sources rich in the bromide and iodide, and iodide and chloride ions have been also recognized in the Sob-2 well at high pumping rate that amounted to 8.7 L/sec.

High Plains Aquifer–State of Affairs of Irrigated Agriculture and Role of Irrigation in the Sustainability Paradigm

Groundwater depletion is a serious issue in the southern and central parts of the High Plains Aquifer (HPA), USA. A considerable imbalance exists between the recharge process and groundwater extractions in these areas, which threatens the long-term sustainability of the aquifer. Irrigated agriculture has a major share in the economy, and it requires high pumping rates in regions vulnerable to large groundwater level declines. A literature review has been conducted to understand the state of affairs of irrigated agriculture in the HPA, along with the dynamics of groundwater decline and recharge using statistical and remote-sensing based datasets. Also, three irrigation management and technology-based approaches have been discussed from the perspective of sustainability. The southern and central parts of the HPA consist mostly of non-renewable groundwater formations, and the natural water storage is prone to exhaustion. Moreover, the aforementioned regions have comparatively higher crop water requirement due to the climate, and irrigating crops in these regions puts stringent pressure on the aquifer. The upper threshold of irrigation application efficiency (IAE) is high in the HPA, and could reach up to 95%; however, considerable room for improvement in irrigation water management exists. In general, the practices of irrigation scheduling used in the HPA are conventional and a small proportion of growers use modern methods to decide about irrigation timing. Among numerous ways to promote sustainable groundwater use in the HPA, deficit irrigation, use of soil moisture sensors, and subsurface drip irrigation can be considered as potential ways to attain higher lifespans in susceptible parts of the aquifer.

Delay-induced instability in phase-locked dual-polarization distributed-feedback fiber lasers

We study experimentally and theoretically a dual-polarization fiber laser submitted to time-delayed frequency-shifted optical feedback. In addition to the usual frequency-locking regime that is expected when the frequency shift is close to the polarization beat frequency, we observe at high pumping rates a dynamical pulsing regime inside the locking range. This regime is experimentally evidenced in a full-fibered experiment based on an erbium-doped distributed-feedback fiber laser in which polarization beat frequency is about 1 GHz. A rate-equation model including the frequency-shifted feedback term reproduces well the experimental bifurcation maps, provided that both the time delay and a phase-amplitude coupling parameter ($\ensuremath{\alpha}$ factor) are taken into account. The impact on microwave-photonics applications is discussed.

S2 Measurements Showing Suppression of Higher Order Modes in Confined Rare Earth Doped Large Core Fibers

We present a detailed investigation on higher order mode suppression due to differential gain in large mode area step index fiber amplifiers with confined Yb doping using spatially and spectrally resolved imaging (S2). A novel active fiber with Yb doping confined to the central 30% of the core area is fabricated and its performance is directly compared to a fiber with a conventional homogeneously doped core with almost identical parameters. At high pump rates, S2 and beam pointing stability measurements clearly demonstrate fundamental mode operation of the confined doping few mode fiber, even under imperfect launching conditions and environmental perturbations. In addition, we discuss the mode content as a function of gain in co-pumped fiber amplifiers with and without confined rare earth core doping using a power propagation model for fibers with similar parameters to those used in our experiments. Our simulation results as well as amplification experiments indicate the great potential of the confined doping concept for single mode high power operation.

Implementation of Hydraulic Fracturing Operation for a Reservoir in KRG

This study focuses on procedures to enhance permeability and flow rate for a low permeability formation by creating a conductive path using the hydraulic fracturing model. Well data are collected from the Qamchuqa KRG oil field formation. A Fracpro simulator is used for modelling the hydraulic fracturing process in an effective way. The study focuses on an effective hydraulic fracturing design procedure and the parameters affecting the fracture design. Optimum design of fracturing is achieved by selecting the proper fracturing fluid with a suitable proppant carried in a slurry, determining the formation fracturing pressure, selection of a fracture propagation fluid, and also a good proppant injection schedule, using a high pump rate and good viscosity. Permeability and conductivity are calculated before and after applying the hydraulic fracturing. Fracture height, length, and width are calculated from the Fracpro software, among other parameters, and the production rate changes. From the results, it is observed that by using hydraulic fracturing technology, production will increase and permeability will be much higher. The original formation permeability is 2.55 md, and after treatment, the average fracture conductivity has significantly increased to 1742.3 md-ft. The results showed that average fracture width is 0.187 inch. The proppant used in this treatment has a permeability of 122581 md. The suitable fluid choice is hyper with an apparent viscosity of 227.95 cp, and the proper proppant type is Brady sand with a conductivity of 2173.41 md-ft. Fracture orientation from the Khurmala oil field in Kurdistan is vertical fractures produced at a depth of 1868 m. Fracture half-length, total fracture height, and average fracture width are 220 ft, 42 ft, and 0.47 inch, respectively. After fracturing, the maximum and average area of fracture are 33.748 and 17.248 ft2, respectively. The recommended pump hydraulic horse power is 3200 HHP, and the total required fluid is 1076.3 bbl. In this study, hydraulic fracture is designed, and then, it has been analyzed after that production is optimized.

Experimental study of hydraulic fracture initiation and propagation in unconsolidated sand with the injection of temporary plugging agent

High fluid leak-off rate and low pressurization rate are great challenges for hydraulic fracturing in unconsolidated sands. In this paper, the design of an injection plugging agent as a pad for fracture initiation aid in unconsolidated sands is presented. We have carried out tri-axial hydraulic fracturing tests, focusing on super-high- and high-permeability unconsolidated sands with AE (acoustic emission) monitoring. Powdered oil-soluble materials are used as temporary plugging agents. The laboratory tests demonstrated that three types of fracture geometry, multiple fracture, bi-wing fracture and single-wing fracture, are created. Furthermore, there are continuous AE energy signals with the increase of plugging agent injection, which is a good match with the fluctuated pressure. Moreover, multiple peak fracture points can be observed due to intense grains interaction. In addition, the breakdown pressure has positive relationships with the pump rate and concentration of injection of plugging agents. Multiple fractures only exist for super-high-permeability unconsolidated sands with high pumping rate and low plugging agent concentration, which is primarily due to the plugging agent seal for both hydraulic fracture and the rock matrix. A low injection rate with low plugging agent concentration led to single-wing fracture for high-permeability unconsolidated sands, whereas a high injection rate with high plugging agent concentration led to single-wing fracture for low-permeability unconsolidated sands. Low plugging agent concentration is beneficial for aiding hydraulic fracture propagation along the maximum horizontal stress direction. In addition, the high-pump-rate and low-plugging-agent-concentration scenario and low-pump-rate and high-plugging-agent-concentration scenario have a greater chance of creating bi-wing fracture for super-high-permeability unconsolidated sands, whereas low pump rate and high plugging agent concentration are beneficial for bi-wing fracture for high-permeability unconsolidated sands. Local tortuous fracture path indicate tensile and fracture both exist during unconsolidated sands fracturing. With respect to sand control and large contact area, these treatments should be the better fracturing scenario for unconsolidated sand fracturing design with injection of a plugging agent. The findings of this study can help for better understanding of the fracturing mechanism and optimizing treatment parameters in unconsolidated sands fracturing.

Numerical Modeling of Fracture Propagation During Temporary-Plugging Fracturing

Summary Temporary-plugging fracturing (TPF) is becoming a promising technique for maximizing the stimulated-reservoir volume in tight reservoirs by injecting diverting agents to plug the preferred perforations and/or hydraulic fractures (HFs). Previous work has developed diverting agents and evaluated their blocking efficiency. However, the mechanism and dominant influence factors of HF growth during TPF remain poorly understood to date, which restricts the application of this technique. To understand the problem and help improve the TPF design, this study simulated the HF-propagation process during TPF in a naturally fractured formation using a previously developed 3D discrete-element-method (DEM) -based complex fracture model. Plugged fracture elements with negligible permeability were incorporated into the model to characterize the blocking intervals of diverting agents within HFs. Parameters, including horizontal differential stress (Δσh), natural-fracture (NF) properties, the number of pluggings, plugging positions, and pumping rate, were investigated to determine their effects on the HF/NF-interaction behavior and the resulting HF geometry. The change in injection pressure before and after plugging under different conditions was also recorded in detail. Modeling results show that the HF/NF-interaction behavior might surprisingly change before and after plugging the preferred HF, ranging from HF crossing of NFs to HF opening of NFs. Notably, Δσh is still the most influential geological parameter that governs the HF-growth behavior during TPF. For a moderate Δσh (=8 MPa), the growth of a single planar HF before plugging can be changed easily into a complex HF network (HFN) through opening of NFs after plugging in the target stimulated region (TSR). In this case, the complexity and covering area of the resulting HFN is closely related to the NF density (positive correlation) and plugging positions. However, for a high Δσh (=12 MPa), opening (usually partially) the NFs after plugging is difficult even in formations with a high density of NFs. In such a case, a large volume of fluid, a high pumping rate, and several repeat pluggings during TPF are necessary. The results of this study help to understand the HF-growth mechanism during TPF and help to optimize the treatment design of TPF and to adjust it in a timely manner.

Proof‐of‐Concept Modeling of a New Groundwater Sampling Approach

AbstractThis note provides a proof‐of‐concept modeling study to examine the theoretical feasibility of a new groundwater sampling approach, the high‐stress low‐flow approach, for improving the representativeness of groundwater samples and shortening the sampling duration. The approach consists of two‐phase pumping: an initial high pumping rate followed by low‐flow purging and sampling. We conceptualize the sampling process by pumping in a fully penetrating, large‐diameter well in a confined aquifer and mixing within the well screened zone, which are characterized by the aquifer‐responding time scale for aquifer water dominating the inflow ratio and the well‐mixing time scale, respectively. We derive an analytical solution to evaluate the sample concentration and representativeness. Results show that higher pumping rates in phase 1 create larger drawdowns and overstressed flow fields when switching to lower pumping rates in phase 2, thereby slowing down the drawdown within the well and preventing downward movement of the well casing water. As a result, the ratio of aquifer water into the well screened zone and in water pumped can rise sharply at the pumping‐switch moment, and the aquifer‐responding time scale and groundwater sampling duration can be significantly shortened. The proposed high‐stress low‐flow approach is particularly effective in systems limited by long aquifer‐responding time scales, which are typically encountered in low‐permeability aquifers. Based on the analytical solution, we also provide preliminary guidelines and graphic tools to select the pumping rate ratio and the switching time. Our proof‐of‐concept modeling study demonstrates great potential of the new groundwater sampling approach in field applications.

Factory-Model Approach Improves Performance of Coiled-Tubing Drillout

This article, written by JPT Technology Editor Judy Feder, contains highlights of paper SPE 191689, “Factory-Model Approach for Successful Coil-Tubing-Unit Drillout Operations in Unconventional Wells,” by Jesus Barraza, SPE, and Chris Champeaux, SPE, Chevron; Heath Myatt, SPE, and Kyle Lamon, C&J Energy Services; Ryan Bowland, Spartan Energy Services; Troy Bishop, SPE, and Jerry Noles, SPE, Coil Chem; and Rocky Garlow, RGC Consulting, prepared for presentation at the 2019 SPE Hydraulic Fracturing Technology Conference and Exhibition, The Woodlands, Texas, USA, 5–7 February. The paper has not been peer reviewed. As drilling and fracturing operations improve, there is a need to adapt current coiled-tubing (CT) drillout processes to a more fit-for-purpose approach applicable in any area, regardless of lateral length, number of plugs, and reservoir target. This paper presents a factory-model approach to improving CT drillout performance that has been used successfully for more than 3 years and has become standard practice. The paper includes detailed discussion of the methodology used to create a successful, repeatable, and operationally safe process; field case studies and results; and engineering, design, and implementation of new technologies to improve the process. Introduction CT practices have become increasingly effective in plug drillout operations by reducing the operational cost, environmental exposure, and time to production. Techniques for no-wiper or short trips and plug milling, added benefits from extended-reach bottomhole assemblies (BHAs), and improved fluid-system monitoring methods have helped enhance overall performance. However, there are still components within each of these techniques that can be evaluated. Background and Methodology Results of a thorough evaluation of the CT drillout process revealed that the factors with the greatest influence on improving performance included the following: Wellbore trajectory Plug type CT size BHA selection Fluid-rheology quality assurance/quality control (QA/QC) Real-time modeling Communication Wellbore trajectory is an important factor because it has a major effect on the ability of a CT unit to reach plug-back total depth. High tortuosity in the lateral section can cause plug parts and sand to settle on the low side of the wellbore, making adequate cleaning of the hole by increasing overall friction difficult. Proper plug type and design serve two purposes: to provide a barrier between stages during hydraulic-fracturing operations and to be easily removed from the wellbore during drillout. Ideally, a fully composite plug should be selected because the lower specific gravity of the material aids in removal. The proper CT size can lead to a more-successful drillout because it allows for higher pump rates, leading to better hole cleaning. Additionally, larger outer-diameter CT (23/8 in. or greater) ensures sufficient weight on bit (WOB) in the toe of longer laterals to reduce friction pressure and protect against helical buckling.

A study on the impact of anthropogenic and geogenic factors on groundwater salinization and seawater intrusion in Gaza coastal aquifer, Palestine: An integrated multi-techniques approach

Groundwater salinization and seawater intrusion (SWI) is a widespread issue affecting many arid and semi-arid coastal regions such as the Gaza Strip, Palestine. The aims of this study were to acquire a comprehensive understanding of the role of anthropogenic and geogenic factors on controlling groundwater salinization and to assess the SWI extent and the hydrogeochemical processes involved. To achieve these objectives, an integrated approach of hydrogeological, hydro-geochemical, and statistical techniques combined with geostatistical semi-variogram modeling was applied on a comprehensive dataset using software (Stata/SE 12, ArcGIS 10.4 and Surfer 16 Golden software Inc.). The results indicate that the intensive groundwater exploitation creates a huge cone of depression covering 75% of the study area and reduces the water table to as much as 19 m below mean sea level (BMSL) at 4.3 km from the shoreline, causing SWI. The extension of SWI depends strongly on the lithological characters of the area. It reached to 48.6% with inland encroachment around 3 km in the northern area. Moreover, the spatial distribution and high pumping rates have significantly influenced the spatial pattern of SWI. Hierarchical cluster analysis (HCA) yielded nine distinct hydrogeochemical signature clusters. Factor analysis (FA) approves that the high groundwater salinization was the result of three main factors loadings that account for 83.86% of the total variance These factors are F1 as salinization (mainly SWI), F2 as mixing of sewage invasion and water hardness and F3 as carbonate dissolution. Factors scores clarify the areas which are more impacted by the different hydro-geochemical processes. Ionic deltas and ionic ratios reveal the dominance of reverse ion exchange process. Moreover, the distinct surplus of sulfate along the sea shoreline may indicate the existence of old seawater transgression. This integrated approach should be useful for efficient groundwater management of the Gaza coastal aquifer system as well as for other similar aquifers.

Coherent and incoherent switching of cavity solitons in an optically injected VCSEL

Intensity and population dynamics are studied for two different switching techniques used for creation and deletion of cavity solitons (CSs) in vertical cavity surface emitting lasers with external injection. For coherent switching, we use transient Gaussian pulse in and out of phase with the external injection respectively for switching on and off. Studies of the regimes of 10% and 20% above laser threshold revealed that Hopf instability is the cause of more switching energy required for creation of CSs in higher pumping rates. We also propose a novel method for incoherent switching using local injection of carriers in doughnut form for creation of CSs and in Gaussian shape for their deletion.

Lasing threshold of thresholdless and non-thresholdless metal-semiconductor nanolasers.

The recently developed plasmonic and photonic metal-semiconductor nanolasers feature unique properties, such as ultra-small mode volume and footprint, high Purcell factor, and ultra-fast modulation. However, it is often difficult to recognize when the transition to lasing occurs, while the most important feature of laser radiation, i.e., coherence, is available only above the lasing threshold. Here we systematically study the second-order coherence properties of metal-semiconductor nanolasers at both low- and high-pump rates. We find the lasing threshold using a clear coherence definition and derive a simple expression for the threshold pump current (optical pump power), which can be applied to most thresholdless and non-thresholdless metal-semiconductor nanolasers.

Numerical simulation of casing deformation during volume fracturing of horizontal shale gas wells

Casing deformation problems occur frequently during volume fracturing of shale gas wells. It is crucial to assess the casing deformation near heel (the beginning of the horizontal wellbore trajectory) where natural faults exist among 84.6% of the deformation positions in some shale plays. Based on the source mechanism, the fault slip distance was derived from microseismic inversion. Then, three-dimensional physical and finite element models were established using a stage finite element model procedure to investigate the influences of fault slippage on casing stress and displacement. Other factors such as pump rate, fracturing pressure, formation anisotropy, formation elastic modulus, cement sheath elastic modulus, casing size, and cement sheath thickness were taken into consideration. The results show that (1) fault slippage is an important mechanism of casing deformation near heel. The casing has a higher risk of deformation under the conditions of fault slippage combined with high external stress and internal pressure. (2) Under different slip distances, the casing Mises stress dramatically increases with an increase in the cement sheath and formation elastic moduli and the ratio of the casing diameter to the thickness Dout/t. (3) The high pump rate, high inner casing pressure, large formation anisotropy, and small cement sheath thickness can aggrandize casing stress. The calculated casing displacements using this model obtained good agreement when compared to the deformations of the actual wells. Countermeasures such as avoiding natural fault areas, using cement with an elastic modulus smaller than 10 GPa, using a higher grade and smaller diameter casing with a value of Dout/t smaller than 12.7 can be effective to prevent casing deformation during multi-fracturing operation.

Prediction of Field Drag Reduction by a Modified Practical Pipe Diameter Model

AbstractSlick water fracturing is a successful stimulation technology for gas shales. Due to the high pumping rates associated with slick water fracturing, drag reduction (DR) is critical to the success of field operations. In this study, three drag‐reducing agents were tested in a laboratory setup and the results were compared with data from numerous slick water fracturing treatments in the field in China. The results show that, as long as the slopes of effective pipe radius versus velocity from the laboratory‐scale tubes and from the field pipes are close, field drag reduction can be predicted by a modified correlation between DR and velocity established in the laboratory. The modified practical pipe diameter model should be useful in the design of slick water fracturing treatments and the selection of drag‐reducing agents in the laboratory.

Magnetically Actuated Beating Cilia for Pre-Concentration of Bacteria

Detecting low concentrations of bacteria in food samples is a challenge. The pre-concentration and separation of the target bacteria from the food matrix can be enhanced using improved fluid handling. We have demonstrated a method for pre-concentration of bacteria from a liquid sample making use of arrays of artificial cilia. The cilia are defined using thin film processes on a glass substrate and are actuated magnetically with an external magnetic field. We demonstrate particle capture with cilia, by functionalizing the surface of the cilia with streptavidin protein and capturing biotin labelled particles on its surface. The functionalized cilia are incorporated inside a microchannel and biotin labelled particles are introduced into array of the cilia. The oscillating cilia are also capable of creating a net fluid flow which can be used for fluid pumping and mixing. We study the kinematics of the elastic cilia, with their asymmetric stroke, and demonstrate that it depends on two dimensionless numbers. To demonstrate pumping effects with arrays of cilia, we incorporate them on the inner walls of microchannel loop and measure the pumping rate while varying many of the parameters of the system. We report high pumping rates and characterize the fluid handling capability of such systems in terms of two dimensionless parameters.