Simple calculations of fluid flow across jointed cataclastic deformation bands

Cataclastic deformation bands in porous sandstones present a potentially significant barrier or baffle to fluid flow because the bands form in complex networks of laterally extensive, tabular zones with permeability up to several orders of magnitude less than that of the sandstone host rock. Previous work suggests that in some geologic settings cataclastic deformation bands become systematically jointed in the subsurface. Calculations presented here demonstrate that under most realistic circumstances, volumetric flow rate across a jointed deformation band can equal or exceed discharge through an equivalent volume of host sandstone. Results indicate that jointed deformation bands are not significant barriers or baffles to fluid movement.     

江苏油田真12断块E2s16储层特征及剩余油分布

真12断块E2s1^6是真武油田主力开发层系，以岩心、测井、生产动态资料为基础，通过流动单元、隔夹层、渗透率韵律类型等，研究与渗透率变化有关的储层非均质性，建立储层物性参数模型，通过油藏数模模拟两类剖面和建立不同含水期集层渗透率模型，研究油藏纵向油水运动规律，研究剩余油分布，为E2s1^6油藏最终提高采收率、改善开发效果提供依据。     

3D Pore-network quantitative analysis in deformed carbonate grainstones

This study consists of a three-dimensional (3D) assessment of the pore network properties (i.e., porosity, pore connectivity, specific surface area) in deformed carbonate grainstones cropping out in Sicily and Abruzzo regions (Italy). Previous studies, including microphotography, mercury injection analysis, and in-situ air permeameter measurements, have reported permeability differences (in the range of two-to-three orders of magnitude) between the carbonate grainstones exposed in Sicily and Abruzzo, that cannot be explained by only considering the differences of porosity. In this study, the pore network properties of suitable rock samples were studied by quantitative analysis of X-ray micro-CT images using both synchrotron and microfocus sources. On the basis of the results, inferences about the control of pore network properties on permeability were made for both host rock and deformation bands. In the host rocks, high values of connectivity seem to be associated with high values of permeability, whereas higher values of the specific surface area seem to correspond to lower permeability. Within the deformation bands (DBs), both porosity and pore connectivity are reduced except for local solution-enlarged stylolites and fractures (slip surfaces) preferentially connected parallel to the DB.     

Linking early diagenesis and sedimentary facies to sequence stratigraphy on a prograding oolitic wedge: The Bathonian of western France (Aquitaine Basin)

To improve the understanding of the distribution of reservoir properties along carbonate platform margins, the connection between facies, sequence stratigraphy, and early diagenesis of discontinuities along the Bathonian prograding oolitic wedge of the northeastern Aquitaine platform was investigated. Eight facies are distributed along a 50 km-outcropping transect in (1) toe-of-slope, (2) infralittoral prograding oolitic wedge, (3) platform margin (shoal), (4) open marine platform interior, (5) foreshore, and (6) terrestrial settings. The transition from shallow platform to toe-of-slope facies is marked in the field by clinoforms hundred of meters long. Carbonate production was confined to the shallow platform but carbonates were exported basinward toward the breakpoint where they cascaded down a 20–25° slope. Ooid to intraclast grainstones to rudstones pass into alternating marl-limestone deposits at an estimated paleodepth of 40–75 m. Three sea-level falls of about 10 m caused the formation of discontinuities corresponding to sequence boundaries. Along these discontinuities, erosional marine hardgrounds formed in a high-hydrodynamic environment at a water depth of less than 10 m, displaying isopachous fibrous cements and meniscus-type cements. The cements pass landward into meniscus and microstalactitic forms along the same discontinuities, which are characteristic of subaerial exposure. During the deposition of transgressive systems tracts, carbonate accumulation remained located mostly on the shallow platform. Energy level increased and carbonates were exported during the deposition of highstand systems tracts forming the infralittoral prograding oolitic wedge. During the deposition of lowstand systems tracts, carbonate production fell to near zero and intraclast strata, derived from the erosion of hardgrounds on the shallow platform, prograded basinward. Early diagenetic cements are related exclusively to discontinuities that are not found within the prograding wedge because of the continuous high sedimentation rate under lower hydrodynamic conditions. This absence of early cementation within the infralittoral prograding oolitic wedge was conducive to porosity conservation, making such features good targets for carbonate reservoir exploration. This study proposes a novel sequence stratigraphy model for oolitic platform wedges, including facies and early diagenesis features.     

Facies heterogeneity at interwell-scale in a carbonate ramp,Upper Jurassic,NE Spain

The well-exposed upper Kimmeridgian carbonate ramp near Arroyo Cerezo, Iberian Basin, Eastern Spain, provides an excellent analog to stratigraphically equivalent subsurface reservoirs, such as the carbonate ramps of the Arab-D of the Middle East and the Smackover of the Gulf of Mexico. Critical questions regarding interwell-scale heterogeneity and correlation motifs for low-angle ramp systems can be addressed using continuous exposures that encompass a full range of inner to outer ramp facies. Outcrops in this area provide a complete exposure of the ramp succession in depositional dip direction.At Arroyo Cerezo, a 40-m thick and 1.3-km long, dip-oriented, continuous outcrop has been studied. Lithofacies and bounding surfaces have been mapped on a continuous photomosaic to build a detailed 2D cross-section, complemented by five stratigraphic sections (∼300 m apart) and petrographic analysis. The reconstructed section shows the facies transition from relative proximal- to distal carbonate ramp settings. Carbonate facies associations are grouped according to the dominant carbonate types: buildup-dominated systems and coated-grain dominated systems. Detailed mapping of facies and bounding surfaces documents distinct ramp depositional units with downdip facies changes occurring within the 1.3 km length of the outcrop. The Arroyo Cerezo outcrop indicates that the ramp-facies continuity, when based on a 5–10 km distance well-log correlation, is mostly apparent. Use of detailed spatial and temporal analysis of high-quality outcrop analogs promotes more realistic models for understanding the interwell, meter-scale heterogeneity. And the scale of these depositional heterogeneities, although being below resolution of subsurface tools, governs in fact (along with diagenetic modifications) the fluid flows within a reservoir. The scale of these stratigraphic heterogeneities needs to be considered in order to optimize and enhance hydrocarbon production and last recovery.     

天然气水合物降压开采过程中储层应力规律分析

为了研究天然气水合物降压开采过程的储层应力及其稳定性,运用线性多孔弹性力学和岩石力学知识,考虑水合物储层原始应力、孔隙压力、渗流附加应力及降压开采水合物过程中水合物饱和度的变化,建立了降压开采天然气水合物储层的力学模型,结合墨西哥湾某处水合物藏的基本参数,对降压开采水合物储层应力变化和开采过程的储层稳定性进行研究。结果表明:井底压力是影响水合物储层应力变化的关键因素之一;渗流附加应力在一定程度上减小了储层的应力;水合物分解储层应力发生变化,储层应力在井壁处的波动最大,井壁处是整个储层所受轴向偏应力最大的位置,因此井壁处是优先发生剪切破坏的位置;为了储层的稳定性,降压开采水合物生产压差应小于2.19 MPa。     

Controls on reservoir heterogeneity of tight sand oil reservoirs in Upper Triassic Yanchang Formation in Longdong Area,southwest Ordos Basin,China: Implications for reservoir quality prediction and oil accumulation

Compared to conventional reservoirs, pore structure and diagenetic alterations of unconventional tight sand oil reservoirs are highly heterogeneous. The Upper Triassic Yanchang Formation is a major tight-oil-bearing formation in the Ordos Basin, providing an opportunity to study the factors that control reservoir heterogeneity and the heterogeneity of oil accumulation in tight oil sandstones.The Chang 8 tight oil sandstone in the study area is comprised of fine-to medium-grained, moderately to well-sorted lithic arkose and feldspathic litharenite. The reservoir quality is extremely heterogeneous due to large heterogeneities in the depositional facies, pore structures and diagenetic alterations. Small throat size is believed to be responsible for the ultra-low permeability in tight oil reservoirs. Most reservoirs with good reservoir quality, larger pore-throat size, lower pore-throat radius ratio and well pore connectivity were deposited in high-energy environments, such as distributary channels and mouth bars. For a given depositional facies, reservoir quality varies with the bedding structures. Massive- or parallel-bedded sandstones are more favorable for the development of porosity and permeability sweet zones for oil charging and accumulation than cross-bedded sandstones.Authigenic chlorite rim cementation and dissolution of unstable detrital grains are two major diagenetic processes that preserve porosity and permeability sweet zones in oil-bearing intervals. Nevertheless, chlorite rims cannot effectively preserve porosity-permeability when the chlorite content is greater than a threshold value of 7%, and compaction played a minor role in porosity destruction in the situation. Intensive cementation of pore-lining chlorites significantly reduces reservoir permeability by obstructing the pore-throats and reducing their connectivity. Stratigraphically, sandstones within 1 m from adjacent sandstone-mudstone contacts are usually tightly cemented (carbonate cement > 10%) with low porosity and permeability (lower than 10% and 0.1 mD, respectively). The carbonate cement most likely originates from external sources, probably derived from the surrounding mudstone. Most late carbonate cements filled the previously dissolved intra-feldspar pores and the residual intergranular pores, and finally formed the tight reservoirs.The petrophysical properties significantly control the fluid flow capability and the oil charging/accumulation capability of the Chang 8 tight sandstones. Oil layers usually have oil saturation greater than 40%. A pore-throat radius of less than 0.4 μm is not effective for producible oil to flow, and the cut off of porosity and permeability for the net pay are 7% and 0.1 mD, respectively.     

Fracture patterns and petrophysical properties of carbonates undergoing regional folding: A case study from Kurdistan,N Iraq

The Zagros-Taurus fold and thrust belt hosts a prolific hydrocarbon system. Most hydrocarbon reserves are stored in naturally fractured reservoirs and such fracture systems can therefore have a significant impact on reservoir performance. Fractures are one of the most important paths for fluid flow in carbonate reservoirs, and industrial geoscientists and engineers therefore need to understand and study fracture patterns in order to optimise hydrocarbon production. The observed fracture patterns in outcrops may have implications on fluid flow and reservoir modelling in subsurface reservoirs, and we have therefore undertaken a case study of fracturing associated with regional folding in Iraqi Kurdistan. In this area, some exploration wells currently target Upper Triassic dolostones (Kurra Chine Formation) and/or Lower Jurassic limestones and dolomitised limestones (Sehkaniyan Formation). In both units hydrocarbon production comes mainly from secondary porosity created by dolomitisation, dissolution and fracturing. Both formations have undergone multiple phases of deformation associated with burial, uplift, folding and thrusting. We investigate some fracture pattern characteristics and some petrophysical properties of these units using selected outcrops around the Gara, Ora and Ranya anticlines that form folds directly traceable for 25–70 km. Our outcrop data is compared with subsurface fracture and petrophysical datasets reported from wells in the nearby Shaikhan and Swara Tika Fields. The 1-2-3D fracture attributes collected from outcrops are fracture orientation, type, spacing, intensity, length and cross-cutting and abutting relationships. Fracture orientations show a clear relationship to the local fold axis in both the outcrop and subsurface, although in some cases they appear to relate more to the present day in-situ maximum horizontal stress direction or local strike-slip faulting. Three stages of fracturing are proposed: pre-folding, early-folding and post-folding fractures. In addition, we report petrophysical properties - porosity, permeability and acoustic velocity of both the Kurra Chine and Sehkaniyan formations in relation to their structural position within folds and faults and stratigraphic level. The highest porosities and permeabilities are recorded in the hinges and backlimbs of the Gara Anticline. The best reservoir quality (highest porosity and permeability) is often found in areas associated with replacement dolomite i.e. solution vugs and intercrystalline porosity. The Kurra Chine Formation displays similar trends in velocity-porosity data at both outcrop and the subsurface. However, the Sehkaniyan Formation displays lower acoustic velocity for a given porosity at outcrop compared to the subsurface.     

Evolution of fluid flow and heat distribution over geological time scales at the margin of unconfined and confined carbonate sequences - A numerical investigation based on the Buda Thermal Karst analogue

Hydrogeological processes acting at the margins of confined and unconfined thick carbonate sequences are particularly interesting due to a complex system evolution including partial uplift of fully confined carbonate systems and subsequent erosion of cover layers. We provide insights into this evolution by simulating coupled density-dependent fluid flow and heat transport based on the Buda Thermal Karst (BTK) system (Hungary) in a 2D vertical plane. Applying an equivalent porous medium (EPM) approach using the Heatflow-Smoker finite element model, scenario modelling of three evolutionary steps was carried out between the fully-confined carbonate stage through to partly and completely unconfined conditions over the western ridge. The numerical simulations were used to derive the main evolutionary characteristics of groundwater flow and heat transport patterns for the unconfined and confined parts of the hydrogeologic system. The initial fully-confined state led to the development of thermal convection cells due to the insulating role of the low-permeability confining layer, which facilitates buoyancy-driven flow by restricting the dissipation of heat. Over geological time, these cells were gradually overprinted by gravity-driven flow and thermal advection due to uplift of the west ridge. The limited thickness of the cover allowed sufficient water infiltration into the system, which led to increased cooling. Further uplifting led to a prevalence of gravity-driven groundwater flow. The results highlight the critical role of confining formations on flow patterns, and their effect on heat distribution and dissipation over geological time scales. The results have important implications for heat accumulation as well as for the development of a deep geothermal energy potential in confined carbonates.     

Integrating hydrodynamic analysis of flow systems and induced-pressure decline at the Otway CO2 storage site to improve reservoir history matching

The CO2CRC Otway Project is the first demonstration scale project for geosequestration of CO₂ in Australia. The storage site is located in the depleted Waarre reservoir of the Naylor gas field contained within a single fault block, in the onshore Otway Basin of Victoria. During 2009, approximately 65,000 tonnes of a mixture of CO₂ and CH₄ (∼80%/20%) was injected into the reservoir, accumulating at the top of the structure.To fully understand the pressure response of a depleted reservoir to CO₂ injection all of the mechanisms that may impact the reservoir pressure, prior to injection, must be identified. In the case of the Otway Project there were five possible mechanisms with potential for impacting the Naylor Field pressure. These are (1) the rate of recovery due to gas production from the Naylor Field; (2) depletion from the nearby Boggy Creek CO₂ production field; (3) depletion from the nearby Buttress CO₂ Field, the source of the CO₂ for injection into the Naylor Field; (4) depletion from the regional Waarre Formation reservoir which has been producing gas (and water) since 1986; and (5) hydraulic potentiometric disequilibrium via connection to other active aquifers.These mechanisms were examined through a regional conceptual hydrodynamic model as part of the pre-injection site characterisation. The reservoir pressure measured at the Naylor-1 well, prior to production, was lower than predicted by the hydrodynamic model. Examination of regional drawdown demonstrated that the reservoir is experiencing pressure decline which could have extended to the Naylor Field at this time.Ongoing monitoring of the Naylor-1 well, prior to injection, showed the depleted reservoir recovering faster than predicted by the reservoir simulation model matched to the production history. Connecting the target fault block to the regional aquifer using a dual aquifer model supported by the hydrodynamic model significantly improved the predicted recovery of the depleted reservoir.     

板876地下储气库水砂体评价与扩容利用

由常规枯竭型气藏改建的地下储气库仍然以气藏砂体(气砂体)为研究目标,与气藏砂体相邻的含水层(水砂体)亦能作为地下储气库的扩容空间,但这部分砂体很少被关注。板876地下储气库在储层精细描述基础上,结合气藏和气库的注采动、静态分析结果,评价了水砂体的分布范围和发育规模,利用精细地质模型计算了水砂体的总孔隙体积、未动用的及可动用的孔隙体积,应用板876地下储气库数值模拟技术对水砂体的扩容空间进行了验证,结果表明水砂体储集空间对地下储气库的扩容和运行效率具有现实意义。     

Modeling sediment transport in the swash zone: A review

A critical review of conceptual and mathematical models developed in recent decades on sediment transport in the swash zone is presented. Numerous studies of the hydrodynamics and sediment transport in the swash zone in recent years have pointed out the importance of swash processes in terms of science advancement and practical applications. Evidently, the hydrodynamics of the swash zone are complex and not fully understood. Key hydrodynamic processes include both high-frequency bores and low-frequency infragravity motions, and are affected by wave breaking and turbulence, shear stresses and bottom friction. The prediction of sediment transport that results from these complex and interacting processes is a challenging task. Besides, sediment transport in this oscillatory environment is affected by high-order processes such as the beach groundwater flow. Most relationships between sediment transport and flow characteristics are empirical, based on laboratory experiments and/or field measurements. Analytical solutions incorporating key factors such as sediment characteristics and concentration, waves and coastal aquifer interactions are unavailable. Therefore, numerical models for wave and sediment transport are widely used by coastal engineers. This review covers mechanisms of sediment transport, important forcing factors, governing equations of wave-induced flow, groundwater interactions, empirical and numerical relations of cross-shore and longshore sediment transport in the swash zone. Major advantages and shortcomings of various numerical models and approaches are highlighted and reviewed. These will provide coastal modelers an impetus for further detailed investigations of fluid and sediment transport in the swash zone.     

Fracturing and cementation of shallow buried Miocene proximal alluvial fan deposits

Fluid flow in fractures and host rocks has been investigated in shallow buried Miocene alluvial fan deposits. A structural, petrographical (optical, CL, SE microscopes and XRD) and geochemical (microprobe and δ¹⁸O-δ¹³C stable isotopes) study has been performed in normal faults affecting Serravalian-Tortonian siliciclastic rocks of the Vallès-Penedès basin. These faults formed during the development of the Vallès-Penedès fault-related syncline, which caused the rotation of the earliest fractures. Faulting occurred continuously before, during and after host rock cementation. Rocks affected by faulting are represented by clay-rich gouges, which formed thanks to the high phyllite clast content within the otherwise clean and mature sandstones and conglomerates. Despite the low permeability of these rocks, cross-fault and fault-parallel fluid flows occurred in most of the faults.Host rocks and veins were cemented by two generations of calcite, i.e. Cc1 and Cc2. Cc1 precipitated from meteoric waters at shallow burial conditions whereas Cc2 precipitated from meteoric waters in a confined aquifer.Palygorskite has been identified in shear zones within the gouges indicating their later formation by interaction of Mg-rich fluids with previous smectites. These fluids probably derived from Miocene seawater expelled from the underlying Transitional–Marine Complex “TMC” by compaction.Sedimentation, fracturing and cementation occurred in a very short lapse time of about 6–7 Ma, between the Serravalian-Tortonian age of the sediments and the end of the extensional tectonics in the Vallès-Penedès fault (Pliocene).     

Reservoir characterization and multiscale heterogeneity modeling of inclined heterolithic strata for bitumen-production forecasting,McMurray Formation,Corner, Alberta,Canada

Bitumen reservoirs dominated by inclined heterolithic stratification (IHS) formed in large point bars of the Aptian (Lower Cretaceous) McMurray Formation in the northwestern part of the Corner oil sand lease (Alberta, Canada) were investigated to establish their value. Hybrid production technologies were applied to thin pay, typified by homogeneous reservoir sand units thicker than 5 m at the base overlain by IHS (so-called ‘thin pay’), as well as IHS-dominated reservoirs in which the IHS extends down to the base of the reservoir. High-resolution seismic data and well data (core, dipmeter, HMI) were used to map four facies associations, comprising a total of 16 sedimentary facies, as well as various fluid contacts to assist in reservoir characterization and risk assessment. The conceptual depositional model was based on the analysis of the migration and re-orientation history of the IHS-dominated point bars reflecting lateral accretion, downstream migration, rotation and relocation of the bars. Multiple reactivation events, which control the heterolithic nature and reservoir quality of the deposits, create developable “pools”.Seven electrofacies (with generally increasing mud content) were defined and used as input to construct vertical proportion curves that relate the electrofacies distribution to geomodel statistics in the main reservoir zone. At the electrofacies scale, numerical effective porosity-permeability models were created using micromodeling and minimodeling concepts. The geometrical shape of the electrofacies in the geomodel was investigated using non-stationary Truncated Gaussian (TG) facies simulation to enforce the stacking patterns. Each geomodel area was characterized using one variogram to efficiently compute the horizontal and vertical variogram ranges and average azimuths. Sequential Gaussian simulation (SGS) was used to map the distribution of key petrophysical parameters such as effective porosity, effective water saturation and V_shale. Empirically derived saturation versus elevation profiles for each electrofacies were included in the modeling. The distributions from the micro- and mini-modeling were introduced using probability field (P-field) simulation. To investigate the amount of connected resources (the degree of connectivity of good sand as well as IHS) were extractable flow simulation studies were performed at the pad scale. In preparation for reservoir simulation, connectivity calculations within the local pool geomodel realizations were tailored for the reservoir heterogeneities (i.e., IHS) that are expected to have a major impact on the specific thermal and gravity drainage extraction processes. The geomodel realizations were ranked by expected pseudo-dynamic behaviour with connected exploitable pay as a critical parameter.     

Flow and bed shear stresses in scour protections around a pile in a current

Transport of bed sediment inside and beneath the scour protection may cause deformation and sinking of the scour protection for pile foundations. This may reduce the stability of the mono pile and change the natural frequency of the dynamic response of an offshore wind turbine installed on it in an unfavourable manner. Using physical models and 3D computational fluid dynamic (CFD) numerical simulations, the velocity and bed shear stresses are investigated in complex scour protections around mono piles in steady current. In the physical model the scour protections consisted of an upper cover layer with uniformly distributed coarse stones and a lower filter layer with finer stones. For the numerical simulations, the Flow-3D software was used. The scour protection layers were simulated with different numerical approaches, namely regularly arranged spheres, porous media, or their combinations (hybrid models). Numerical simulations with one or four layers of cover stones without filter layer were first computed. Three additional simulations were then made for a scour protection with a cover layer and a single filter layer. Finally, a simulation of a full scale foundation and scour protection was made with porous media approach.Based on the physical and numerical results, a method to determine the critical stones size to prevent motion of the base sediment is established and compared to a full scale case with sinking of scour protection (Horns Rev I Offshore Wind Farm, Denmark). It is also found that the CFD simulations are capable of calculating the flow velocities when the scour protection is represented by regular arranged spheres, while the turbulence in general is underestimated. The velocity can also be calculated using porous media flow approach, but the accuracy is not as good as for spheres. The deviation is more severe for more complex scour protections. In general, computational models provide valuable information for the prediction and design of scour protections for offshore wind farms.     

New insights into the carbonate karstic fault system and reservoir formation in the Southern Tahe area of the Tarim Basin

As worldwide hydrocarbon exploration has extended from shallowly to deeply buried strata, reservoir quality has attracted substantial and persistent interest in petroleum geology. In particular, deeply buried strata (>5500 m) in the Tarim Basin have attracted considerable attention because carbonate reservoirs that have experienced fracture or dissolution have also been shown to demonstrate considerable hydrocarbon potential. Therefore, it is necessary to determine how these reservoirs are developed and distributed in detail from both scientific and practical standpoints.In this paper, we address this issue using a case study in the southern Tahe area, which is contained within the largest Palaeozoic marine oilfield in China. In the northern Tahe area, mega-paleokarst systems developed in the Ordovician strata; however, the reservoir quality in the southern part of the Tahe area is relatively poor because it is covered by insoluble formations during karstification. Observations of cores and analyses of images of well logging demonstrate that these reservoirs are dominated by caves, vugs and fractures that have developed near faults. We speculate that the faults penetrating insoluble formations represent the main dissolution passages that originally developed these karstic fault systems. Additionally, we analyse a series of outcrops, seismic data, and structures to characterize the spatial geometry of these major faults and their surrounding fractures in detail. Most of these are strike-slip faults, and their subsequent reservoirs can be divided into three categories based on their development, including dendritic, sandwich and slab reservoirs. Recent studies demonstrate that karstic fault reservoirs are most common traps in the study area. Although various types of carbonate karstic fault reservoirs are represented in this region, the dendritic karstic fault reservoir is the most hydrocarbon-rich.Guided by these initial results, 108 wells were drilled from 2013 to 2014, producing 485 thousand tons of oil and yielding success ratios greater than 89%. The average production of dendritic reservoirs is 37.4 tons per day (t/d), while those of sandwich and slab types are 20.2 t/d and 14.0 t/d, respectively. These results represent significant references for future hydrocarbon exploration and the development of similar deeply buried karstic fault reservoirs in the Tarim Basin and elsewhere.     

The numerical study of wave-induced pore water pressure response in highly permeable seabed

The coupling numerical model of wave interaction with porous medium is used to study waveinduced pore water pressure in high permeability seabed.In the model,the wave field solver is based on the two dimensional Reynolds-averaged Navier-Stokes(RANS) equations with a k-ε closure,and Forchheimer equations are adopted for flow within the porous media.By introducing a Velocity-Pressure Correction equation for the wave flow and porous flow,a highly efficient coupling between the two flows is implemented.The numerical tests are conducted to study the effects of seabed thickness,porosity,particle size and intrinsic permeability coefficient on regular wave and solitary wave-induced pore water pressure response.The results indicate that,as compared with regular wave-induced,solitary wave-induced pore water pressure has larger values and stronger action on seabed with different parameters.The results also clearly show the flow characteristics of pore water flow within seabed and water wave flow on seabed.The maximum pore water flow velocities within seabed under solitary wave action are higher than those under regular wave action.     

A coupled numerical model for simulation of wave breaking and hydraulic performances of a composite seawall

A numerical model is developed by combining a porous flow model and a two-phase flow model to simulate wave transformation in porous structure and hydraulic performances of a composite type low-crest seawall. The structure consists of a wide submerged reef, a porous terrace at the top and an impermeable rear wall. The porous flow model is based on the extended Navier-Stokes equations for wave motion in porous media and k−ε turbulence equations. The two-phase flow model combines the water domain with the air zone of finite thickness above water surface. A unique solution domain is established by satisfying kinematic boundary condition at the interface of air and water. The free surface advection of water wave is modeled by the volume of fluid method with newly developed fluid advection algorithm. Comparison of computed and measured wave properties shows reasonably good agreement. The influence of terrace width and structure porosity is investigated based on numerical results. It is concluded that there exist optimum value of terrace width and porosity that can maximize hydraulic performances. The velocity distributions inside and in front of the structure are also investigated.     

基于桁架模型和多孔介质模型的柔性网衣和周围流场单向耦合方法研究

柔性网衣作为渔业养殖的重要组成部分,其水动力的计算分析对网箱的安全使用至关重要。基于桁架模型和多孔介质模型对柔性网衣和流场单向耦合计算的数值模拟方法进行了研究。通过code_aster软件基于桁架模型计算出网衣变形后节点坐标和网衣受力,然后将节点坐标导入OpenFOAM识别出网衣变形后的多孔介质区域,并基于多孔介质模型模拟水流作用下网衣周围的流场和计算网衣的受力。为了验证模型的正确性,将不同工况对圆形网衣的数值模拟结果与物理试验数据进行比较,包括code_aster中计算的网衣变形形状、OpenFOAM模拟的网衣周围流场以及在code_aster和OpenFOAM中计算的网衣受力。计算结果表明,圆形网衣在单纯来流下变形明显,与试验结果保持一致,证明了网衣变形和水动力单向耦合方法的准确性。