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Fluid-Loss-Control Additives (FLAs) are used to maintain a consistent fluid volume within a cement slurry to ensure that the slurry performance properties remain within an acceptable range. The variability of each of these parameters (slurry performance properties) is dependent upon the water content of the slurry. If the water content is less than intended, the opposite will normally occur. The magnitude of change is directly related to the amount of fluid lost from the slurry. Because predictability of performance is typically the most important parameter in a cementing operation, considerable attention has been paid to mechanical control of slurry density during the mixing of the slurry to assure reproducibility.
The three-dimensional connectivity of the fluid phases in porous media plays a crucial role in governing the fluid transport, displacement, and recovery. Accurate three-dimensional quantification of the fluid phase connectivity following each fluid injection stage will lead to better understanding of the efficacy and efficiency of the fluid injection strategies. Two metrics for measuring the connectivity in 3D show robust performance; one uses fast marching method to quantify average time required for a monotonically advancing wave to travel between any two pixels and the other uses two-point probability function to approximate the average distance between any two connected pixels belonging to the same fluid phase. The two connectivity metrics are applied on the three-dimensional (3D) CT scans of one water-wet Ketton whole-core sample subjected to five stages of multiphase fluid injection to quantify the evolution of the three-dimensional connectivity of the three fluid phases (oil, water, and gas). The water-wet Ketton carbonate sample (4.9 mm in diameter and 19.5 mm in length) is subjected to five sequential stages of fluid injection: 100%-brine-saturated sample, oil injection, water-flooding #1, gas injection, and water-flooding #2. CT-scan of the core sample was acquired after each injection stage. The metric response for oil phase connectivity drops after each injection process, denoting a reduction in oil connectivity after each fluid injection. The spatiotemporal variations in the connectivity of a fluid phase help understand the fluid displacement across pores of varying sizes depending on the wettability.
ABSTRACT Wave-induced scour plays a key role in the stability analysis of coastal structures, submarine pipelines or cables. There is a rich literature in current-induced scour, but more research is needed to understand the characteristics of wave-induced scour and the mechanisms that are important to the scour process. Sediment transport and flow-induced scour are three-phase (air-water-sediment) flow problems in nature and multiphase flow simulation is a useful tools that can provide information diffcult to obtain from physical tests. Most existing numerical models developed for simulating local scours are based on one-way coupling, which neglects effects of sediment phase on hydrodynamics of the flow. The present study uses a three-phase (air, water and sediment) flow model, which allows for a two-way coupling, to simulate wave-induced local scour problems. The three-phase flow model captures the air-water interface using a modified VOF method, and uses an improved rheology for the sediment phase for better results. The model is validated and verified using one set of existing experiment results for local scour around a submerged horizontal pipe. The detailed flow fields of both the sediment phase and the water phase around the scour are analyzed to understand the scour process. All three-phase flow simulations flow simulations on XSEDE's Stampede2 supercomputers. The applicability of the model to other local scour problems is also discussed. INTRODUCTION Sediment transport involves interaction between water/air and sediment, which is a complicated process frequently happening in nature. Understanding sediment transport is critical for some engineering projects involving pipelines or power cables on seafloor and oil platforms. The interaction between sediment and the flow around the structures may cause local morphological changes: an increased flow rate might lead to local erosion while decreased flow rate may result in deposition. The foundation stability will be affected by these processes. Most existing numerical models treat sediment transport as a passive motion (one-way coupling) following the flow (Roulund et al., 2005) and the transport rate is calculated using published empirical formulas (Lee et al., 2019); this is due to the poor understanding of micro-scale hydrodynamics, turbulence and the computing power available at the time when these models were developed. For instance, Roulund et al. (2005) studied, both numerically and experimentally, the flow and local scour around a vertical pile exposed to a steady current and found that the scour depth was highly affected by the local flow pattern around the pile, such as horseshoe vortex and lee-wake vortex. Wu et al. (2000) developed a three-dimensional (3D) sediment transport model, which treats the bed-load and suspended-load with different empirical or semi-empirical equations, and simulated the sediment transport in an open channel flow; however, the agreement between the numerical and experimental results is less satisfactory close to the bank. Wave-induced sediment transport and scour around a pipeline is a multi-phase phase problem in nature. Even though one-way coupling models are suitable for large-scale practical problem, they do not have a direct consideration on the influence of sediment motion on the flow characteristics. The rapid development of computer hardware has made it possible to develop two-way coupled multi-phase flow models to understand physics involved in the interaction between the sediment and fluid phases and to better simulate the sediment transport and scour processes.
ABSTRACT In this study, an unresolved CFD-DEM was used to investigate a fluid flow and a behavior of sediment particles around a monopile. In order to consider the interaction between particles on the seabed and a current, an improved CFD-DEM solver was implemented within the OpenFOAM framework by proposing a void fraction method based on the kernel function. To validate computational methods, a settling velocity of a single particle, an angle of repose and an incipient motion of particles were simulated and compared with the existing experimental data. Finally, a scour around the monopole was predicted and discussed. INTRODUCTION In relatively shallow water, most offshore wind turbines are based on monopile foundations as bottom-fixed structures. Theses bottom-fixed foundations installed on an erodible seabed are exposed to scour, which may lead to structural failure. Therefore, it is essential to understand how the hydrodynamic environments affects the foundation and the interaction between flow, structure and seabed (Sumer, 2014). In particular, the scour can be defined as the phenomenon that the seabed particles around the foundation structure are transported due to the interaction of the fluid flow and the structure. The scour is a threat to the stability of the structure exposed to currents and waves. In order to alleviate the scour problem, many studies have been conducted experimentally (Dargahi, 1989, Whitehouse, 1998; Sumer and Fredsoe, 2002). In particular, most of the work has been done on scour phenomenon with monopile foundations. It led to various empirical formulas and methods to predict scouring depth and extension (Matutano et al., 2013). On the other hand, the computation can be employed as an alternative tool to study the scour process around structure (Pang et al., 2016). Recently, several computational methods have been developed to estimate the equilibrium scour depth. The scour depth and extent were estimated based on the bed shear stress exerted by the flow field in the Eulerian-based approach (Park et al., 2017). However, the single-phase model usually was not able to consider interparticle interactions in the scour around structures. To deal with this problem, many studies have adopted a two-phase model (Yeganeh-Bakhtiary et al., 2011; Hajivalie et al., 2012). These models can be divided into two types, depending on the method used. One is the so-called Euler-Euler two phase model, which treats the fluid and sediment phases as separate continuous mediums. The other calculate the particle motion individually using a discrete element method (DEM). The advantage of this method is that it can analyze a large amount of particles based on a simple collision model and analyze the exact behavior of the particles. Thus, to consider the interaction between the fluid flow and the seabed soil, a CFD and DEM coupling method is needed. Recently, studies on the sediment transport using the CFD-DEM coupling method have been carried out (Schmeeckle, 2014; Sun and Xiao, 2016), and even the scouring around a submarine pipeline was performed to investigate the flow behavior and particle motions (Yeganeh-Bakhtiary et al., 2013; Zhang et al., 2015). However, there have been only a few studies to realize the scour phenomenon around the monopile using CFD-DEM coupling method.
When an offshore foundation is exposed to waves and currents, local scour could be developed around a pile and even lead to a structural failure. Therefore, understand and prediction for the scour due to sediment transport around foundations are important in the engineering design. In this study, flow and scour around a monopile foundation exposed to a current were investigated by using the computational fluid dynamics (CFD) and discrete element method (DEM) coupling method. The open source computation fluid dynamics library, OpenFOAM, and a sediment transport library were coupled in the OpenFOAM platform. The results of simulations regarding the incipient motion of the particle were presented. The flow fields and sediment transport around the monopile were simulated. The scour depth development was simulated and compared with existing experimental data.
Most of offshore wind turbine farms constructed under 60 m depth are installed as bottom-fixed structures. It is important to install a foundation structure that can stably support the load of the superstructure in a bottom-fixed offshore wind turbine. Bottom-fixed offshore wind turbines consider several design factors depending on the seabed ground and marine environment. Among them, a scour can be defined as the phenomenon that the seabed particles around the foundation structure are transported due to the interaction of the fluid flow and the structure. The scour is a cause of deterioration of the stability of the structure which must withstand the large turnover moment acting on the turbine.
As the operation period of bottom-fixed offshore wind turbines increase, the researches on the scour problem have been done (Whitehouse, 1998; Sumer and Fredsoe, 2002). In particular, experimental and numerical studies on the scour around the monopile, which is the simplest foundation of bottom-fixed structures, have been performed (Dargahi, 1989; Pang et al., 2016). Park et al. (2017) predicted the scour using the bed shear stress by CFD. However, the Eulerian-based CFD approach does not sufficiently take into account the influence of the soil. For the soil transportation simulation, the DEM approach is used. Cundall and Strack (1979) was first presented the basic concept of the discrete element method, which simplified the collision between particles using the spring-dashpot model. In the DEM, small size overlap between the particles is allowed, and the behavior of the particles is analyzed by the repulsive force generated by the particle overlap. The advantage of this method is that it can analyze a large amount of particles based on a simple collision model and analyze the exact behavior of the particles. Thus, to consider the interaction between the fluid flow and the soil, a CFD and DEM coupling method is needed. Recently, studies on the sediment transport using the CFD-DEM coupling method have been carried out (Schmeeckle, 2014; Sun and Xiao, 2016), but there have been only a few studies to realize the scour phenomenon.
Yang, Qingjie (Department of Earth Science, Memorial University of Newfoundland, NL, Canada) | Malcolm, Alison (Research Center for Computational and Exploration Geophysics) | Rusmanugroh, Herurisa (State Key Laboratory of Geodesy and Earth’s Dynamics, Institute of Geodesy and Geophysics, CAS, China) | Mao, Weijian (Department of Earth Science, Memorial University of Newfoundland, NL, Canada)
We derive analytical formulas for the radiation patterns of single parameter perturbations in fluid-saturated porous media. These radiation patterns include two scattered waveforms, fast compressional and shear waves, caused by the perturbation of different model parameters as a function of the scattering and incident angles. The study of radiation patterns in poroelastic media allows us to explore the possibility of reconstructing crucial model properties describing sedimentary rocks, and to examine coupling effects between different parameters during full-waveform inversion (FWI). To verify these analytical expressions, we calculate the corresponding numerical wavefields scattered by perturbations in one parameter, keeping the other parameters fixed to their background values. The poroelastic radiation patterns presented herein provide some understanding of the parameter trade-offs encountered in FWI in porous media.
Presentation Date: Wednesday, October 17, 2018
Start Time: 9:20:00 AM
Location: Poster Station 7
Presentation Type: Poster
To have a good microscopic displacement efficiency enhanced oil recovery (EOR) because of the high original during the miscible gas injection, injection pressure and oil-in-place estimates accompanied by low primary reservoir pressure should be above the minimum recovery potential. BPS is composed of both conventional and unconventional units exhibiting significant variations in lithology, rock texture, clay content, porosity, and total organic carbon. Two wireline-log-derived EOR-efficiency indices are generated for a 200-feet depth interval in the BPS to identify flow units suitable for EOR using light, miscible hydrocarbon injection. The Microscopic Displacement (MD) Index exhibits higher resolution compared to the Ranking (R) Index. MD index relies on a novel method to calculate the miscible free-oil volume from subsurface NMR T2-distribution logs. At a resolution of 1-foot depth interval, several flow units were successfully identified in the Middle Bakken formation that exhibit high miscible-gas-injection recovery potential.
Summary Interpretation of two-phase production logs (PLs) traditionally constructs borehole fluid-flow models decoupled from the physics of reservoir rocks. However, quantifying formation dynamic petrophysical properties from PLs requires simultaneous modeling of both borehole and formation fluid-flow phenomena. This paper develops a novel transient borehole/formation fluid-flow model that allows quantification of the effect of formation petrophysical properties on measurements acquired with production-logging tools (PLTs). We invoke a 1D, isothermal, two-fluid formulation to simulate borehole fluid-phase velocity, pressure, volume fraction, and density in oil/water-flow systems. The developed borehole fluid-flow model implements oil-dominant and water-dominant bubbly flow regimes with the inversion point taking place approximately when the oil volume fraction is equal to 0.5. Droplet diameter is dynamically modified to simulate interfacial drag effects, and to effectively account for variations of slip velocity in the borehole. Subsequently, a new successive iterative method interfaces the borehole and formation fluid-flow models by introducing appropriate source terms into the borehole fluid-phase mass-conservation equations. The novel iterative coupling method integrated with the developed borehole fluid-flow model allows dynamic modification of reservoir boundary conditions to accurately simulate transient behavior of borehole crossflow taking place across differentially depleted rock formations. In the case of rapid variations of near-borehole properties, frequent borehole/formation communication inevitably increases the computational time required for fluid-flow simulation. Despite this limitation, in a two-layer reservoir model penetrated by a vertical borehole, the coupling method accurately quantifies a 14% increase of volume-averaged oil-phase relative permeability of the low-pressure layer caused by through-the-borehole cross-communication of differentially depleted layers. Sensitivity analyses indicate that the alteration of near-borehole petrophysical properties primarily depends on formation average pressure, fluid-phase density contrast, and borehole-deviation angle. A practical application of the new coupled fluid-flow model is numerical simulation of borehole production measurements to estimate formation average pressure from two-phase selective-inflow-performance (SIP) analysis. This study suggests that incorporating static (shut-in) PL passes into the SIP analysis could result in misleading estimation of formation average pressure.
Summary The success of matrix acidizing in carbonates is often dependent on the efficiency of diversion agents, especially for treatments on wells with thick formations or multiple zones, or horizontal wells with long and heterogeneous intervals. Viscoelastic-surfactant (VES) -based self-diversion acid has been used successfully in fields because of its negligible damage to the formation and good diversion ability. Although the diversion ability of VES acid was studied experimentally with small core plugs, the diversion conditions of VES acid under in-situ radial conditions need to be studied. In this paper, we develop a VES radial-acidizing model that simulates VES acid flow, acid/rock reaction, porosity variation, viscosifying, wormholing, and acid diversion in multiple zones. On the basis of the model, extensive numerical simulations are conducted to investigate wormholing behavior of the VES acid, the factors that affect the diversion ability of VES acid, and the diversion conditions of VES acid. The study shows that the VES acid-dissolution patterns depend on the injection rate, and there is an optimum injection rate under which the dominant wormholes are formed. Compared with regular acid, the VES acid provides better acid placement for heterogeneous intervals. The intervals with separation shorter than approximately 150 m can be acidized together with VES acid if the two intervals have a close permeability with no perforation between them. The permeability ratio of the two intervals has remarkable influence on the diversion performance of VES acid. Even though the viscosified fluid acts as a temporary barrier to prevent the fluid from flowing into the higher-permeability formation, the VES acid reduces diversion effectiveness for large permeability contrast. We also investigated the combined effect of permeability contrast and separation of the two intervals on diversion performance. This study provides a basis to select diversion technology and a method to evaluate diversion performance of VES acid for field-acidizing treatments.
With the increasing of extreme weather events, more attention has been drawn to the protection of coastal structures. Wave-induced seabed instability is a major factor that may damage the coastal structures. In this paper, a 2-D quasi-dynamic u-w-p model is developed to examine different seabed behavior under different wave actions. Further, this paper aims to acquire a better understanding of the soil failure process, which will be able to reduce the possible damage of coastal structure caused by extreme weather events. In u-w-p model, acceleration, velocity, and displacement terms are considered separately for both solid and fluid phases. The u-w-p model also can be simplified based on actual condition. The governing equations of u-w-p model are deduced from constitutive law and conservation law under certain assumptions. The numerical solutions are developed by using finite difference method (FDM) and three major factors (pore water pressure, effective vertical stress and shear stress) are outputted from the models as major analysis target. The result shows that both liquefaction and shear failure have low potential to occur in clayey seabed, this may caused by the dense soil structure and low permeability of clay. The pore water pressure vary linearly according to the depth, however, this variation is not significant in clayey seabed (with 6.4% decrease from the surface to bottom). In addition, there is no phase lag in clayey seabed. The excess pore water pressure will not accumulate quickly and reach a massive value inside the clayey seabed.