Status and Trends in Research on Deep-Water Gravity Flow Deposits

Deep-water gravity flows are one of the most important sediment transport mechanisms on Earth. After 60 years of study, significant achievements have been made in terms of classification schemes, genetic mechanisms, and depositional models of deep-water gravity flows. The research history of deep-water gravity flows can be divided into five stages： incipience of turbidity current theory; formation of turbidity current theory; development of deep-water gravity flow theory; improvement and perfection of deep-water gravity flow theory; and comprehensive development of deep-water gravity flow theory. Currently, three primary classification schemes based on the sediment support mechanism, the rheology and transportation process, and the integration of sediment support mechanisms, rheology, sedimentary characteristics, and flow state are commonly used.Different types of deep-water gravity flow events form different types of gravity flow deposits. Sediment slump retransportation mainly forms muddy debris flows, sandy debris flows, and surge-like turbidity currents. Resuspension of deposits by storms leads to quasi-steady hyperpycnal turbidity currents （hyperpycnal flows）. Sustainable sediment supplies mainly generate muddy debris flows, sandy debris flows, and hyperpycnal flows. Deep-water fans, which are commonly controlled by debris flows and hyperpycnal flows, are triggered by sustainable sediment supply; in contrast, deep-water slope sedimentary deposits consist mainly of debris flows that are triggered by the retransportation of sediment slumps and deep-water fine-grained sedimentary deposits are derived primarily from fine- grained hyperpycnal flows that are triggered by the resuspension of storm deposits. Harmonization of classification schemes, transformation between different types of gravity flow deposit, and monitoring and reproduction of the sedimentary processes of deep-water gravity flows as well as a source-to-sink approach to document the evolution and deposition of deep-water gravity flows are the most important research aspects for future studies of deep-water gravity flows study in the future.

Deep-water gravity flow deposits in a lacustrine rift basin and their oil and gas geological significance in eastern China

The types,evolution processes,formation mechanisms,and depositional models of deep-water gravity flow deposits in a lacustrine rift basin are studied through core observation and systematic analysis.Massive transport of slide and slump,fluid transport of debris flow and turbidity currents are driven by gravity in deep-water lacustrine environment.The transformation between debris flow and turbidity current,and the transformation of turbidity current between supercritical and subcritical conditions are the main dynamic mechanisms of gravity flow deposits in a lake basin.The erosion of supercritical turbidity current controls the formation of gravity-flow channel.Debris flow deposition gives rise to tongue shape lobe rather than channel.Deep-water gravity flow deposits are of two origins,intrabasinal and extrabasinal.Intrabasinal gravity flow deposits occur as single tongue-shape lobe or fan of stacking multiple lobes.Extrabasinal gravity-flow deposits occur as sublacustrine fan with channel or single channel sand body.However,the nearshore subaqueous fan is characterized by fan of stacking multiple tongue shape lobes without channel.The differential diagenesis caused by differentiation in the nearshore subaqueous fan facies belt results in the formation of diagenetic trap.The extrabasinal gravity flow deposits are one of the important reasons for the abundant deep-water sand bodies in a lake basin.Slide mass-transport deposits form a very important type of lithologic trap near the delta front often ignored.The fine-grained sediment caused by flow transformation is the potential"sweet spot"of shale oil and gas.

Sedimentary characteristics of lacustrine deep-water gravity flow in the third member of Paleogene Shahejie Formation in Dongying Sag,Bohai Bay Basin,China

Many types of sedimentary systems occur in the middle of the third member of the Shahejie Formation(E_(2)S_(3)^(2))of the Paleogene in the Dongying Sag east of the Bohai Bay Basin.Due to the topography and material supply,traction and gravity flow depositions are intertwined in this area,and the sand body types are complex and diverse,making it challenging to improve the accuracy of their description and prediction and restricting oil reservoir exploration and development.Therefore,this paper documents our systematic study of the sedimentary characteristics of the southern slope of Dongying Depression,the formation mechanism of different sand body types,and the prediction of sand body distribution.First,according to the coring well’s single-well facies and vertical rock sequence,nine single lithofacies types and five lithofacies association types were identified.Combined with the well logging facies marks of all wells,the depositional models of delta and gravity flow depositional systems were established in the study area.Then,the gravity flow was divided into slip,collapse,debris flow,and turbidity flow according to its development mechanism.Finally,the distribution law of the gravity flow sedimentary facies type was predicted.Gravity flow sliding deposits are primarily distributed near the delta front,slump and clastic flow deposits are distributed near the far slope,and turbidity current deposits are distributed at the far slope.With the gradual shrinkage of the water body in the north-west direction and the continuous advancement of the river delta,the gravity flow sand body gradually disappears in the late E_(2)S_(3)^(2) and transits to delta plain deposition.

Characteristics and control factors of feldspar dissolution in gravity flow sandstone of Chang 7 Member,Triassic Yanchang Formation,Ordos Basin,NW China

To clarify the formation and distribution of feldspar dissolution pores and predict the distribution of high-quality reservoir in gravity flow sandstone of the 7^(th) member of Triassic Yanchang Formation(Chang 7 Member)in the Ordos Basin,thin sections,scanning electron microscopy,energy spectrum analysis,X-ray diffraction whole rock analysis,and dissolution experiments are employed in this study to investigate the characteristics and control factors of feldspar dissolution pores.The results show that:(1)Three types of diagenetic processes are observed in the feldspar of Chang 7 sandstone in the study area:secondary overgrowth of feldspar,replacement by clay and calcite,and dissolution of detrital feldspar.(2)The feldspar dissolution of Chang 7 tight sandstone is caused by organic acid,and is further affected by the type of feldspar,the degree of early feldspar alteration,and the buffering effect of mica debris on organic acid.(3)Feldspars have varying degrees of dissolution.Potassium feldspar is more susceptible to dissolution than plagioclase.Among potassium feldspar,orthoclase is more soluble than microcline,and unaltered feldspar is more soluble than early kaolinized or sericitized feldspar.(4)The dissolution experiment demonstrated that the presence of mica can hinder the dissolution of feldspar.Mica of the same mass has a significantly stronger capacity to consume organic acids than feldspar.(5)Dissolution pores in feldspar of Chang 7 Member are more abundant in areas with low mica content,and they improve the reservoir physical properties,while in areas with high mica content,the number of feldspar dissolution pores decreases significantly.

Flow Rate Measurement of Gravity Infusion Set and Functional Evaluation of Drop Counter: A Pilot Study

Developing a novel drop counter by introducing the Internet of Things concept has been vigorously conducted in recent years. Understanding the newly introduced drop counter’s flow rate control accuracy and flow rate count feature is essential for improving safety in infusion management. This study aimed to verify if the new drop counters could secure accurate flow rate and drip count by conducting actual flow rate measurements using gravimetry and functional evaluation. A drop counter was attached to each drip chamber of the infusion set, and an IV drip was conducted at the 100 ml/h flow rate. The weight of discharged physiological saline was measured to plot trumpet curves. Next, three different types of drop counters were evaluated to determine if they maintained drip count accuracy according to the changes in their position angles. The flow rate errors in all conditions indicated trumpet-like curves, exhibiting an overall error range within ±10% in all observation windows. Although every drop counter successfully detected and measured dripping, it was challenging in some counters to detect dripping when the drip chamber was tilted. In comparing adult and pediatric IV sets, the adult IV set was found to be less likely to detect dripping in the angled position. No significant differences in results were confirmed between high and low flow rates, suggesting that the drop count function would not be affected by the flow rate in the ranges of typical infusion practices. Doppler sensors have a wide range of measurements and high sensitivity;the dripping was detected successfully even when the drip chamber was tilted, probably due to the advantages of these sensors. In contrast, miscounts occurred in those equipped with infrared sensors, which could not detect light intensity changes in tilted positions. Understanding the tendencies in flow rate errors in infusion can be valuable information for infusion management.

Seismic geomorphology and main controls of deep-water gravity flow sedimentary process on the slope of the northern South China Sea

The Quaternary continental slope of the Baiyun Sag in northern South China Sea is characterized by a complex topography and abundant gravity flow sedimentation.High-resolution 3-D seismic data in this area allow for a detailed study of the seismic geomorphology and deep-water gravity flow depositional process.The Quaternary continental slope in the northern South China Sea is an above-graded slope.An intraslope basin lies within the above-grade continental slope.Slump,erosion,and deposition processes tend to develop a gentle topography and consequently a graded slope.The upper continental slope,which is above the slope equilibrium profile,is dominated by erosion and slumping.Slides,slumps and erosional channels are developed within this continental slope.The intraslope basin is located below the slope equilibrium profile and is potential accommodation space where sediments transported by gravity flows could be deposited,forming lobe aprons.Under the influence of gravity flow supply,gravity flow duration,continental slope topography,equilibrium profile,and accommodation,a slump-erosional channel-lobe depositional system is developed in the Quaternary continental slope in the Baiyun Sag.The deep-water gravity flow depositional process and the distribution of gravity flow sediments are greatly influenced by the continental slope topography,while the continental slope topography at the same time is reshaped by deep-water gravity flow depositional process and its products.The study of the interplay between the continental slope and gravity flow is helpful in predicting the distribution of the deep-water gravity flow sediments and the variation of sediment quality.

Volcanism Pacing Slumping Gravity Flow Deposits during the Late Carboniferous in the Southern Margin of the Junggar Basin,China

Deep-water gravity depositional processes and evolution in arc systems have become topics of intense research focus in recent years.This study discusses the co-evolution of volcanism and deep-water gravity flow deposits at the southern margin of the Junggar Basin,based on petrology,geochronology and geochemical analyses.The results show that a massive collapse of unstable sediments from the slope was triggered by volcanism,resulting in the formation of slumping gravity flows.The occurrence of volcanic beds in the slump deposits confirm that synchronous volcanism likely affected sediment instability,triggering gravity flows.The Th/Yb,Ta/Yb and Th/Ta elemental ratios,U-Pb ages of detrital zircons and paleocurrent directions indicate that the North Tianshan(NTS)island arc represents the provenance of the Qianxia Formation.Moreover,statistical data on the pyroclastic components in the gravity flow deposits reveal an intensity index of volcanism,indicating that volcanism is strongly related to gravity flow deposits,especially in terms of the type and distribution of the deposits.A model for volcanically-triggered deep-water gravity flow deposits is established,in order to provide a more in-depth understanding of the co-evolution of volcanism and gravity flow deposits within the depositional setting of the late Paleozoic NTS oceanic subduction margin in the Junggar Basin.

A method for preventing hydrates from blocking flow during deep-water gas well testing

Based on the research of the formation mechanism and evolution rule of hydrate flow obstacle during deep-water gas well testing,a new method for the prevention of hydrate flow obstacle based on safety testing window is proposed by changing the previous idea of"preventing formation"to the idea of"allowing formation,preventing plugging".The results show that the effective inner diameter of the testing tubing and the wellhead pressure decrease gradually with the formation and precipitation of hydrates during deep-water gas well testing,and it presents three typical processes of slow,fast and sudden changes.There is a safety testing window during deep-water gas well testing.The safety testing window of deep-water gas well testing decreases first and then increases with the increase of gas production rate,and increases with the increase of hydrate inhibitor concentrations.In the case with different testing production rates,a reasonable testing order with alternate low and high gas production rates has been proposed to further reduce the dosage of hydrate inhibitor and even avoid the use of hydrate inhibitors considering the decomposition and fall-off of hydrates.Compared with the traditional methods,the new method based on safety testing window can reduce the dosage of hydrate inhibitor by more than 50%.

Investigation of gravity influence on EOR and CO_(2) geological storage based on pore-scale simulation

Gravity assistance is a critical factor influencing CO_(2)-Oil mixing and miscible flow during EOR and CO_(2)geological storage.Based on the Navier-Stokes equation,component mass conservation equation,and fluid property-composition relationship,a mathematical model for pore-scale CO_(2) injection in oilsaturated porous media was developed in this study.The model can reflect the effects of gravity assistance,component diffusion,fluid density variation,and velocity change on EOR and CO_(2) storage.For nonhomogeneous porous media,the gravity influence and large density difference help to minimize the velocity difference between the main flow path and the surrounding area,thus improving the oil recovery and CO_(2) storage.Large CO_(2) injection angles and oil-CO_(2) density differences can increase the oil recovery by 22.6% and 4.2%,respectively,and increase CO_(2) storage by 37.9% and 4.7%,respectively.Component diffusion facilitates the transportation of the oil components from the low-velocity region to the main flow path,thereby reducing the oil/CO_(2) concentration difference within the porous media.Component diffusion can increase oil recovery and CO_(2) storage by 5.7% and 6.9%,respectively.In addition,combined with the component diffusion,a low CO_(2) injection rate creates a more uniform spatial distribution of the oil/CO_(2) component,resulting in increases of 9.5% oil recovery and 15.7% CO_(2) storage,respectively.This study provides theoretical support for improving the geological CO_(2) storage and EOR processes.

Gravity Flow on Slope and Abyssal Systems in the Qiongdongnan Basin,Northern South China Sea

The study of new seismic data permits the identification of sediment gravity flows in terms of internal architecture and the distribution on shelf and abyssal setting in the Qiongdongnan Basin （QDNB）. Six gravity flow types are recognized： （1） turbidite channels with a truncational basal and concordant overburden relationship along the shelf edge and slope, comprising laterally-shifting and vertically-aggrading channel complexes; （2） slides with a spoon-shaped morphology slip steps on the shelf-break and generated from the deformation of poorly-consolidated and high water content sediments; （3） slumps are limited on the shelf slope, triggered either by an anomalous slope gradient or by fault activity; （4） turbidite sheet complexes （TSC） were ascribed to the basin-floor fan and slope fan origin, occasionally feeding the deep marine deposits by turbidity currents; （5） sediment waves occurring in the lower slope-basin floor, and covering an area of approximately 400 km2, were generated beneath currents flowing across the sea bed; and （6） the central canyon in the deep water area represents an exceptive type of gravity flow composed of an association of debris flow, turbidite channels, and TSC. It presents planar multisegment and vertical multiphase characteristics. Turbidite associated with good petrophysical property in the canyon could be treated as a potential exploration target in the QDNB.

Origin and depositional model of deep-water lacustrine sandstone deposits in the 7th and 6th members of the Yanchang Formation(Late Triassic),Binchang area,Ordos Basin,China

Sandstones attributed to different lacustrine sediment gravity flows are present in the 7th and 6th members of the Yanchang Formation in the Ordos Basin, China. These differences in their origins led to different sandstone distributions which control the scale and connectivity of oil and gas reservoirs. Numerous cores and outcrops were analysed to understand the origins of these sandstones. The main origin of these sandstones was analysed by statistical methods, and well logging data were used to study their vertical and horizontal distributions. Results show that the sandstones in the study area accu- mulated via sandy debris flows, turbidity currents and slumping, and sandy debris flows predominate. The sand- stone associated with a single event is characteristically small in scale and exhibits poor lateral continuity. How- ever, as a result of multiple events that stacked gravity flow-related sandstones atop one another, sandstones are extensive overall, as illustrated in the cross section and isopach maps. Finally, a depositional model was developed in which sandy debris flows predominated and various other types of small-scale gravity flows occurred frequently, resulting in extensive deposition of sand bodies across a large area.

An Upward Shallowing Succession of Gravity Flow Deposits in the Early Cretaceous Lingshandao Formation,Western Yellow Sea

Objective Several well-exposed gravity flow deposits in the Early Cretaceous Lingshandao Formation provide a rare opportunity to study deep-water processes. The main objective of this work is to establish the spatial and temporal relationships between the various gravity flow deposits, and thus to establish their sequence stratigraphic patterns and depositional conditions.

Sedimentary characteristics and model of gravity flow channel-lobe complex in a depression lake basin:A case study of Chang 7 Member of Triassic Yanchang Formation in southwestern Ordos Basin,NW China

To reveal the development characteristics and distribution of gravity flow sedimentary system under micro-paleogeomorphologic units of the Chang 7 Member of Triassic Yanchang Formation in the southwestern Ordos Basin,on the basis of the restoration of the paleogeomorphological form of the Chang 7 depositional period by the impression method,each micro-paleogeomorphologic unit was depicted in-depth,and the characteristics and development models of gravity flow deposits in the study area were studied in combination with outcrop,core,mud logging and log data.The results show that:(1)The paleogeomorphology in the Chang 7 depositional period was an asymmetrical depression,wide and gentle in the northeast and steep and narrow in the southwest.Three sub-paleogeomorphologic units were developed in the basin,including gentle paleo-slope,paleo-slope and paleo-depression,and they can be further subdivided into eight micro-paleogeomorphologic units:bulge,groove,slope break belt,plain of lake bottom,deep depression of lake bottom,paleo-channel,paleo-ridge of lake bottom,and paleo-uplift of lake bottom.(2)There are 9 types of lithofacies and 4 types of lithofacies assemblages of Chang 7 Member.According to lithofacies composition and lithofacies vertical combination,the gravity flow deposit is further divided into 5 types of microfacies:restricted channel,unrestricted channel,natural levee,inter-channel,lobe.(3)Paleogeomorphology plays an important role in controlling sediment source direction,type and spatial distribution of sedimentary microfacies,genetic types and distribution of sand bodies in Chang 7 Member.

Heterogeneity and influencing factors of marine gravity flow tight sandstone under abnormally high pressure:A case study from the Miocene Huangliu Formation reservoirs in LD10 area,Yinggehai Basin,South China Sea

The characteristics of reservoir heterogeneity of the marine gravity flow tight sandstone from the Miocene Huangliu Formation under abnormally high pressure setting at LD10 area in Yinggehai Basin are studied,and the influencing factors on reservoir heterogeneity are discussed,based on modular formation dynamics test,thin sections,XRD analysis of clay minerals,scanning electron microscopy,measurement of pore throat image,porosity and permeability,and high pressure Hg injection,as well as the stimulation of burial thermal history.The aim is to elucidate characteristics of the heterogeneity and the evolution process of heterogeneity of the reservoir,and predict the favorable reservoirs distribution.(1)The heterogeneity of the reservoir is mainly controlled by the cement heterogeneity,pore throat heterogeneity,quality of the reservoir heterogeneity,and the diagenesis under an abnormally high pressure setting.(2)The differences in pore-throat structure caused by diagenetic evolution affected the intergranular material heterogeneity and the pore throat heterogeneity,and finally controlled the heterogeneity of reservoir quality.(3)Compared with the reservoir under normal pressure,abnormally high pressure restrains strength of the compaction and cementation and enhances the dissolution of the reservoir to some extent,and abnormally high pressure thus weakening the heterogeneity of the reservoir to a certain degree.The favorable reservoirs are mainly distributed in the gravity flow sand body under the strong overpressure zone in the middle and lower part of Huangliu Formation.

Characteristics and formation of high quality reservoirs in sediment gravity flows of Gangzhong area,Huanghua depression

Reservoirs can be developed in the sediment gravity flows.However,high quality reservoirs are found widespread in sediment gravity flows of Gangzhong area,Huanghua depression,Bohai Bay Basin,East China.Characteristics and formation of these reservoirs are key problems to be solved.Through comprehensive analysis of thin section petrography,scanning electron microscopy and X-ray diffraction,two distinct rules were obtained.1) These high quality reservoirs have apparent characteristics:lithology consists mainly of medium-fine grained sands; moderately-well sorted and rounded; intergranular pores dominating >70% of the entire pores,surface per unit pore volume reaches 15%; average porosity is 21% and average permeability is 55×10-3 μm2.2) Types of sedimentary microfacies and dissolution strongly control on the formation of high quality reservoirs.Main channels and sandy braided bars have the best reservoir properties.Because that sediments are mainly medium-fine grained sands in high-energy environments.The favorable primary porosity and permeability may promote calcite cementation and help to produce more secondary pores.Besides,at the depth of 2500-3200 m,basically matching threshold of oil generation,organic acid expelled when organic matter became mature,and H+ released during clay mineral transformation.These both result in the dissolution of calcite cements and create large volume pores,then physical properties improve correspondingly.Moreover,deep hydrothermal fluid intrusion may also have impacts on the development of secondary pores.

FINITE ELEMENT ANALYSES OF THE EXTRUSION FLOWS OF BOGER FLUIDS WITH END-DRAWING AND GRAVITY-DRAWING

The spinning flow of Boger fluids and the gravity-drawing extrusion flow of a Newtonianas well as a Boger fluid have been simulated by using the stream-line finite element method and thetechnique of matching the finite element solutions with those of one-dimensional spinning equations.The recoverable shear strain is proved not to be a basic parameter in characterising thespinning flow of Boger fluids.For Newtonian fluids this technique predicts the experimental jetshape accurately.For Boger fluids,the numerical simulation agrees with the experimental data of spin-ning flow reported by Sridhar et al.,but seems to give an insufficient swelling and over contractionof the jets when drawn by its own weight,compared with the experimental results of Trang andYeow.It implies that the Oldroyd-B model fitting the viscometric-flow data fails to describeaccurately the elasticity and extensional viscosity in the extrusion flow of Boger fluids with gravi-ty-drawing.

The Gravity Flow on a Shelf-Edge-Slope-Basin-Floor Complex in Qiongdongnan Basin,Northern South China Sea

The Qiongdongnan Basin lies in the west part of the northern South China Sea.To the west the basin is bound by the Red River Fault and the Yinggehai Basin,to the east by the Pearl River Mouth Basin,and to the south by the Xisha Rise.In this study,the sequence stratigraphic framework was set up and 11 third-order sequences were distinguished.Based

Temporal and Spatial Seasonal Variations in Quality of Gravity Flow Water in Kyanamira Sub-County, Kabale District, Uganda

The study was designed to investigate temporal and spatial seasonal variations in quality properties of gravity flow water samples collected from Kigata, Kacuro, Kihanga, Kitibya and Kanjobe located in Kyanamira Sub-County, Kabale District, Uganda. Physical, chemical and biological parameters such as pH, temperature, dissolved oxygen, total dissolved solids, electrical conductivity, turbidity, colour and total suspended solids, total hardness, total alkalinity, chloride, fluoride, nitrates-N, nitrites-N, ammonium-N, sulphates, total phosphate, sodium, calcium, magnesium and some heavy metals were analyzed. Total iron, lead, chromium, copper, zinc, manganese and cadmium were analyzed by atomic absorption spectrometry. Two of the basic biological parameters for drinking water such as faecal coliforms and salmonella were analyzed by incubation followed by counting colony forming units (CFUs). Statistical presentations of data including cluster analysis, dendrograms and principal component analysis were used with the assistance of PAST software. Temperature, pH, TDS dissolved oxygen, cations, anions (chemical parameters) and salmonella, faecal coliforms were the major contributing parameters to gravity flow water’s quality variations during both seasons. Values of pH ranged between 3.78 and 4.84 from March to August in all study sites and they were consistently below the WHO permissible pH range of 6.5 - 8.5. Total suspended solids ranged between 0.66 and 2.17 mg·L-1 and were above the recommended WHO limit of zero value in all study sites. Salmonella and faecal coliforms colonies were present in scaring numbers in the wet season. In March, salmonella counts at Kacuro (14 CFU) and Kanjobe (128 CFU) while faecal coliforms counts at Kacuro (515 CFU) and Kanjobe (228 CFU). The findings of this study call for special attention when using gravity flow water.

Effect of tapered angles in an artery on distribution of blood flow pressure with gravity considered

The tapered angles of an artery significantly influence the local hemodynamics. However, as gravity is considered, little is known about the effect of tapered angles on the hemodynamics. In this study, we explored whether the effect of tapered angles on the distribution of blood flow pressure (DBFP) differed with gravity considered or not. Numerical simulations of the DBFP in a single vessel were performed based on such tapered angles as 0°, 0.5° and 1°. In the model used for simulation, gravity was introduced as a body force. We obtained the following simulations: i) The larger the tapered angles were, the better distributed the blood flow pressure;ii) The tapered effect was an important factor leading to nonlinearity in blood flow pressure;iii) Gravity affected DBFP coupling with the tapered angles, yet independently influenced the dimension of the DBFP. At the same time, the effective intensity of gravity decreased with the increase of tapered angles.

A nonlinear Schrodinger equation for gravity waves slowly modulated by linear shear flow

Assume that a fluid is inviscid, incompressible, and irrotational. A nonlinear Schr?dinger equation(NLSE) describing the evolution of gravity waves in finite water depth is derived using the multiple-scale analysis method. The gravity waves are influenced by a linear shear flow, which is composed of a uniform flow and a shear flow with constant vorticity. The modulational instability(MI) of the NLSE is analyzed, and the region of the MI for gravity waves(the necessary condition for existence of freak waves) is identified. In this work, the uniform background flows along or against wave propagation are referred to as down-flow and up-flow, respectively. Uniform up-flow enhances the MI, whereas uniform down-flow reduces it. Positive vorticity enhances the MI, while negative vorticity reduces it. Hence, the influence of positive(negative)vorticity on MI can be balanced out by that of uniform down(up) flow. Furthermore, the Peregrine breather solution of the NLSE is applied to freak waves. Uniform up-flow increases the steepness of the free surface elevation, while uniform down-flow decreases it. Positive vorticity increases the steepness of the free surface elevation, whereas negative vorticity decreases it.