Matrix Flow Research Articles

Modeling Hydraulically Fractured Shale Wells Using the Fast-Marching Method With Local Grid Refinements and an Embedded Discrete Fracture Model

Summary Recently, fast–marching–method (FMM) –based flow simulation has shown great promise for rapid modeling of unconventional oil and gas reservoirs. Currently, the application of FMM–based simulation has been limited to using tartan grids to model the hydraulic fractures (HFs). The use of tartan grids adversely impacts the computational efficiency, particularly for field–scale applications with hundreds of HFs. Our purpose in this paper is to extend FMM–based simulation to incorporate local grid refinements (LGRs) and an embedded discrete fracture model (EDFM) to simulate HFs with natural fractures, and to validate the accuracy and efficiency of the methodologies. The FMM–based simulation is extended to LGRs and EDFM. This requires novel gridding through the introduction of triangles (2D) and tetrahedrons (2.5D) to link the local and global domain and solution of the Eikonal equation in unstructured grids to compute the diffusive time of flight (DTOF). The FMM–based flow simulation reduces a 3D simulation to an equivalent 1D simulation using the DTOF as a spatial coordinate. The 1D simulation can be carried out using a standard finite–difference method, thus leading to orders of magnitude of savings in computation time compared with full 3D simulation for high–resolution models. First, we validate the accuracy and computational efficiency of the FMM–based simulation with LGRs by comparing them with tartan grids. The results show good agreement and the FMM–based simulation with LGRs shows significant improvement in computational efficiency. Then, we apply the FMM–based simulation with LGRs to the case of a multistage–hydraulic–fractured horizontal well with multiphase flow, to demonstrate the practical feasibility of our proposed approach. After that, we investigate various discretization schemes for the transition between the local and global domain in the FMM–based flow simulation. The results are used to identify optimal gridding schemes to maintain accuracy while improving computational efficiency. Finally, we demonstrate the workflow of the FMM–based simulation with EDFM, including grid generation; comparison with FMM with unstructured grid; and validation of the results. The FMM with EDFM can simulate arbitrary fracture patterns without simplification and shows good accuracy and efficiency. This is the first study to apply the FMM–based flow simulation with LGRs and EDFM. The three main contributions of the proposed methodology are (i) unique mesh–generation schemes to link fracture and matrix flow domains, (ii) DTOF calculations in locally refined grids, and (iii) sensitivity studies to identify optimal discretization schemes for the FMM–based simulation.

Numerical Simulations of Flow and Heat Transfer in a Wall-Bounded Pin Matrix

A detailed computational study was performed for the case of a wall-bounded pin-fin-array in a staggered arrangement, representative of industrial configurations designed to enhance heat transfer. In order to evaluate the level of turbulence modelling necessary to accurately reproduce the flow physics at three (3) different Reynolds numbers (3,000, 10,000 and 30,000), four models were selected: two eddy-viscosity URANS models (k-ω-SST and ϕ-model), an Elliptic Blending Reynolds-stress model (EB-RSM) and Large Eddy Simulation (LES). Global comparisons for the pressure loss coefficients and average Nusselt numbers were performed with available experimental data which are relevant for industrial applications. Further detailed comparisons of the velocity fields, turbulence quantities and local Nusselt numbers revealed that the correct prediction of the characteristics of the flow is closely related to the ability of the turbulence model to reproduce the large-scale unsteadiness in the wake of the pins, which is at the origin of the intense mixing of momentum and heat. Eddy-viscosity-based turbulence models have difficulties to develop such an unsteadiness, in particular around the first few rows of pins, which leads to a severe underestimation of the Nusselt number. In contrast, LES and EB-RSM are able to predict the unsteady motion of the flow and heat transfer in a satisfactory manner.

Development of physically based liquid water schemes for Greenland firn-densification models

Abstract. As surface melt is increasing on the Greenland Ice Sheet (GrIS), quantifying the retention capacity of the firn layer is critical to linking meltwater production to meltwater runoff. Firn-densification models have so far relied on empirical approaches to account for the percolation–refreezing process, and more physically based representations of liquid water flow might bring improvements to model performance. Here we implement three types of water percolation schemes into the Community Firn Model: the bucket approach, the Richards equation in a single domain and the Richards equation in a dual domain, which accounts for partitioning between matrix and fast preferential flow. We investigate their impact on firn densification at four locations on the GrIS and compare model results with observations. We find that for all of the flow schemes, significant discrepancies remain with respect to observed firn density, particularly the density variability in depth, and that inter-model differences are large (porosity of the upper 15 m firn varies by up to 47 %). The simple bucket scheme is as efficient in replicating observed density profiles as the single-domain Richards equation, and the most physically detailed dual-domain scheme does not necessarily reach best agreement with observed data. However, we find that the implementation of preferential flow simulates ice-layer formation more reliably and allows for deeper percolation. We also find that the firn model is more sensitive to the choice of densification scheme than to the choice of water percolation scheme. The disagreements with observations and the spread in model results demonstrate that progress towards an accurate description of water flow in firn is necessary. The numerous uncertainties about firn structure (e.g. grain size and shape, presence of ice layers) and about its hydraulic properties, as well as the one-dimensionality of firn models, render the implementation of physically based percolation schemes difficult. Additionally, the performance of firn models is still affected by the various effects affecting the densification process such as microstructural effects, wet snow metamorphism and temperature sensitivity when meltwater is present.

Pressure Transient Behavior of High-Fracture-Density Reservoirs (Dual-Porosity Models)

Naturally fractured reservoirs (NFRs) contain primary (macro), secondary, and tertiary (minor) fractures. These reservoirs are heterogeneous, where fracture properties such as length, conductivity, aperture, and orientation significantly vary spatially. In general, fractures in these reservoirs are very conductive whether they are in a discrete or continuous fracture network. The conventional dual-porosity-type models (Warren and Root in SPE J 3(3):245–255, 1963) are widely used to model NFRs either in conventional or unconventional formations. In shale, the naturally fractured shale is often considered as a dual-porosity model and is coupled with discrete network of hydraulic fractures. Expressing flow by dual-porosity model in the complex pore structure of NFRs is an oversimplification which has demonstrated several deficiencies and inconsistencies with field transient data and field applications. We show that the dual-porosity models are applicable to specific sets of NFRs and under restrictive conditions. In several NFRs, fractures create a network, communicate hydraulically with each other globally, and provide overall conductivity for the reservoir. The matrix provides the overall storage capacity, but it should be conductive enough to pass the fluid towards the fractures. Given the contrast between the conductivity of the fractures and the matrix, several flow regimes may form at microscale. For low contrasts, the conductivities of the matrix and fractures are close enough that the medium behaves as a homogenous medium. For higher contrasts, matrix is not conductive enough to be a part of the overall flow process in the reservoir, so it behaves as a source of fluid to fractures. For very high contrasts, the matrix is almost not conductive, so it cannot pass the fluid to the fracture. In this case, the overall flow will be governed by the flow in the fracture network. Other intermediate cases may also occur. The pressure behavior of continuously fractured reservoirs is investigated for various contrasts in matrix and fracture properties. The homogenized model is obtained by using the two-scale homogenization technique. The homogenization is performed by starting from the microscale flow equations in the matrix and fracture coupled via a set of no-jump boundary conditions on the interface of fracture and matrix. This approach captures the details of the flow both within and between the porous matrix and fracture. A general equivalent macroscopic model is proposed; the macroscopic homogenized model is the average of the microscale equations of flow in fracture and matrix. The equivalent porosity and the equivalent permeability of the averaged medium are derived. The equivalent permeability depends on both the fracture’s permeability and the geometry of each block of nonhomogeneity. The memory effect in the medium is included in the averaged model through an integro-differential term. Memory effect represents the difference between the response time of matrix and fracture to the same pressure drop. Using the homogenization technique, several averaged models for fractured medium can be obtained, depending on the ratio of the fracture to matrix diffusivity, the fracture-to-matrix volume ratio, and the number of scales of nonhomogeneity in the medium. For certain contrasts in matrix and fracture properties, such as the ratio of matrix to fracture permeability and the fracture aperture, the general model reduces to Warren and Root’s model. In general, Warren and Root’s model does not describe every fractured reservoir. The impact of the presence of additional fracture network, such as secondary and tertiary fractures on the equivalent model, and pressure transient behavior is highlighted.

Hydrodynamic self-lubricating journal bearings analysis using Rabinowitsch fluid lubricant

Abstract In this study, the effects of non-Newtonian pseudo-plastic lubricants behavior, using Rabinowitsch fluid model, on static characteristics of circular self-lubricating porous journal bearings of finite length with sealed ends are highlighted. The nonlinear Reynolds equation based on the Rabinowitsch fluid model has been developed specifically for porous journal bearing cases by considering the fluid flow in the porous matrix described by Darcy's law. The Governing equations are discretized using a centered finite difference scheme and solved numerically using an iterative method. Following to the absence of the porous matrix or the non-Newtonian fluid behavior, the obtained results showed a good agreement with those of the literature review. The static characteristics of hydrodynamic lubrication are calculated numerically for various parameters such as bearing dimensions; the porous bush permeability and the lubricant pseudo-plastic coefficient. It is shown that the dimensionless permeability has significant effects on the static characteristics of the bearings. The pseudo-plastic lubricant coefficient decreases the bearing characteristics (load capacity, pressure) compared to Newtonian lubricant cases. The use of the pseudo-plastic fluids reduces the performance of the bearings and this reduction grows with the porous bearing properties.

An Experimental Study on the Hydromechanical Behaviours of the Evolution of Postearthquake Landslide Deposits

In this study, a series of experiments of the full-scale physical model was employed to investigate the hydromechanical behaviours of the postearthquake landslide evolution, in forms of rill erosion and shallow headward failure on the rill bank slopes under unsaturated conditions. Soil-water characteristic curves (SWCC) were established using the Brooks-Corey (BC) and van Genuchten (VG) models. The stability of the shallow failure was then analyzed via a one-dimensional and unsaturated stability analysis model of the infinite slope. This measurement revealed that the preferential flow and the matrix flow coexisted when infiltration occurred and the VG model performs better in fitting the SWCC than the BC model. Consistent feedback between stability calculations and experimental observations enables the analysis of mechanisms of rill erosion and slope failure of postseismic landslide under the impact of preferential flow. Furthermore, the seepage-induced internal erosion phenomenon was observed in the experiment. This work thus provides a new perspective on the triggering mechanisms of debris flow during the postseismic period.

Time-varying matrix eigenanalyses via Zhang Neural Networks and look-ahead finite difference equations

This paper adapts look-ahead and backward finite difference formulas to compute future eigenvectors and eigenvalues of piecewise smooth time-varying symmetric or hermitean matrix flows A(t). It is based on the Zhang Neural Network (ZNN) model for time-varying problems and uses the associated error function E(t)=A(t)V(t)−V(t)D(t) or ei(t)=A(t)vi(t)−λi(t)vi(t) with the Zhang design stipulation that E˙(t)=−ηE(t) or e˙i(t)=−ηei(t) with η>0 so that E(t) and e(t) decrease exponentially over time. This leads to a discrete-time differential equation of the form P(tk)z˙(tk)=q(tk) for the eigendata vector z(tk) of A(tk). Convergent look-ahead finite difference formulas of varying error orders then allow us to express z(tk+1) in terms of earlier A and z data. Numerical tests, comparisons and open questions complete the paper.

A dot matrix and sloping baffle cathode flow field of proton exchange membrane fuel cell

A novel dot matrix and sloping baffle flow field plate for proton exchange membrane fuel cell (PEMFC) cathode is designed. The plate consists of dispersive and arrayed blocks with sloping angles as shoulders. Features of the plate include a large fluid domain, and air guidance in two directions is achieved by sloping sides of the block. The cell output performance, internal transport process and liquid water removal process of the PEMFC with the matrix flow field are numerically investigated by three-dimensional two-phase full cell model and volume of fluid (VOF) model. The simulation results show that compared with the parallel and serpentine flow field, the matrix flow field can achieve high cell output performance by both improving oxygen supply to gas diffusion layer (GDL) and uniform distribution. Comparing five matrix flow fields with different block sizes and numbers shows that adequate contact area between the plate and GDL for current conductor is critical. For liquid water removal process in the matrix flow field, liquid water is hardly blocked by arrayed blocks and can leave GDL quickly. In summary, the matrix flow field fits high current density demand of PEMFC well, and some new perspectives on flow field design are presented.

Nitrogen stock and leaching rates in a thick vadose zone below areas of long-term nitrogen fertilizer application in the North China Plain: A future groundwater quality threat

Nitrate in groundwater is increasing in many aquifers worldwide due to excessive use of fertilizers. However, the behavior of N-based fertilizer as it leaches through thick vadose zones is still poorly understood, and the long-term effects on groundwater quality in such settings may yet to be fully realized. In this study, deep soil cores were taken below experimental plots where N-fertilizer was applied for nearly 20 years under wheat-maize double cropping in the North China Plain (NCP). N-fertilizer application rates of zero, 400, and 600 kg N ha−1 yr−1 were applied to different plots. Water and N balances were quantified to estimate the leaching rate of NO3−-N below the root zone, and NO3−-N loss via denitrification. Transport pathways of nitrate in the vadose zone were identified using stable isotopes of water (δ18O-H2O & δ2H-H2O) and nitrate (δ18O-NO3− & δ15N-NO3−) from the sampled pore-water and groundwater. The average N transport velocity through the vadose zone ranged from 38 to 41 cm yr−1 and was relatively constant regardless of fertilizer application rate. The transport rates are significantly lower than the long-term rate of groundwater level decline (100 cm yr−1), meaning it is unlikely much of the leachate from chemical N-fertilizers (abundantly applied throughout the region since the 1970s) has entered groundwater via matrix flow. Nitrate isotopes appear to indicate that manure and septic waste (not chemical N-fertilizer) are the major sources of nitrate in groundwater to date. However, stable isotopes show that increased nitrate concentrations in groundwater may also result due to preferential flow in sand layers and/or lateral flow from headwater areas. Denitrification (particularly in the upper 4 m depth of soil) appears to have limited the flux of fertilizer-derived nitrate to some degree. However, the large N stock and generally weak denitrification potential in the deep unsaturated zone, pose a major threat to future groundwater quality. The results have major implications for groundwater quality management in the future.

The depositional history of near-surface Qatar aquifer rocks and its impact on matrix flow and storage properties

Carbonates and evaporites of Paleogene age form the shallow-aquifer rocks mantling most of Qatar, including the Paleocene and Lower Eocene Umm er Radhuma Formation and the Lower to Middle Eocene Rus and Dammam Formations. A core-based study was carried out to improve general understanding of the stratigraphic controls on aquifer matrix properties in Qatar. A cumulative total of 377 m of 10-cm-diameter core was recovered from three boreholes in central and northern Qatar, drilled to depths of greater than 120 m. Sedimentological attributes of these rocks were investigated through core and thin-section description, X-ray diffraction-based mineralogical assessment, as well as whole-rock stable isotopic analysis and integrated with interpretation of gamma-ray logs. Stratigraphic correlation of the penetrated intervals was then undertaken using sequence stratigraphic concepts and isotope stratigraphy (δ13C trends) in the context of recently published regional paleomaps and structural studies. In the area of Qatar, the Umm er Radhuma Formation and the overlying Traina Member of the Rus Formation were deposited in marine settings of two different basins. These basins, which extended to the south and north of Qatar, respectively, are interpreted to have been separated by a topographic high, the location of which was controlled by the presence of high-angle normal faults. The southern basin was more restricted and was the site of extensive evaporite and clay-rich siliciclastic deposition during early stages of Rus Formation. Similar evaporites and fine siliciclastic deposits are not observed in time-equivalent strata of the northern basin. During subsequent deposition of the Al Khor Member of the Rus Formation, as well as the Dammam Formation, the basins appear to have been interconnected, and fine-grained siliciclastic deposits are interbedded with, but subordinate to, carbonate strata across Qatar. Most rocks recovered for this study are dolomitic, and dolomitic rocks free of other mineral phases tend to have significant porosity (20–50%) and permeability (10–1000 mD). Decreased connectivity, flow, and storage capacity are caused by (1) the presence of gypsum beds and nodules (only southern Qatar, upper Umm er Radhuma Formation, and Rus Formation), (2) the presence of pore-occluding clays (typically palygorskite) to varying degrees in all formations, and (3) the occurrence of diagenetic calcites, most commonly in the Dammam Formation. Aquifer quality of the near-surface rocks of Qatar is in large part a function of their depositional history and is to a degree predictable using reconstruction of basin architecture, as well as sequence stratigraphic concepts.

In Situ Nutrient Removal from Rural Runoff by A New Type Aerobic/Anaerobic/Aerobic Water Spinach Wetlands

Rural runoff with abundant nutrients has become a great threat to aquatic environment. Hence, more and more attention has been focused on nutrients removal. In this study, an improved aerobic/anaerobic/aerobic three-stage water spinach constructed wetland (O-A-O-CW) was used to improve the removal of nitrogen and phosphorus of rural runoff. The removal rate of the target pollutants in O-A-O-CW was compared with the common matrix flow wetland as well as the no-plant wetland. The results showed that the O-A-O-CW significantly increased the chemical oxygen demand, total phosphorus, ammonium-nitrogen, nitrate, and total nitrogen removal rate, and the corresponding removal rate was 55.85%, 81.70%, 76.64%, 89.78%, and 67.68%, respectively. Moreover, the best hydraulic condition of the wetland, including hydraulic retention time and hydraulic loading, was determined, which were 2 days and 0.45 m3·m−2·day−1, respectively. Furthermore, the removal mechanism of the constructed wetland was thoroughly studied, which included the adsorption of nitrogen and phosphorus by the matrix and water spinach, and the nitrification and denitrification by the bacteria. The results demonstrated that the mechanisms of nitrogen removal in the new type wetland were principally by the nitrification and denitrification process. Additionally, adsorption and precipitation by the matrix are mainly responsible for phosphorus removal. These results suggested that the new O-A-O-CW can efficiently removal nutrients and enhance the water quality of the rural runoff.

Geometric multigrid methods for Darcy–Forchheimer flow in fractured porous media

In this paper, we present a monolithic multigrid method for the efficient solution of flow problems in fractured porous media. Specifically, we consider a mixed-dimensional model which couples Darcy flow in the porous matrix with Forchheimer flow within the fractures. A suitable finite volume discretization permits to reduce the coupled problem to a system of nonlinear equations with a saddle point structure. In order to solve this system, we propose a full approximation scheme (FAS) multigrid solver that appropriately deals with the mixed-dimensional nature of the problem by using mixed-dimensional smoothing and inter-grid transfer operators. Numerical experiments show that the proposed multigrid method is robust with respect to the fracture permeability, the Forchheimer coefficient and the mesh size. The case of several possibly intersecting fractures in a heterogeneous porous medium is also discussed.

Measurement Method Has a Larger Impact Than Spatial Scale For Plot‐Scale Field‐Saturated Hydraulic Conductivity (Kfs) After Wildfire and Prescribed Fire in Forests

AbstractWildfires raise risks of floods, debris flows, major geomorphologic and sedimentologic change, and water quality and quantity shifts. A principal control on the magnitude of these changes is field‐saturated hydraulic conductivity (Kfs), which dictates surface runoff generation and is a key input into numerical models. This work synthesizes 73 Kfs datasets from the literature in the first year following fire at the plot scale (≤ 10 m2). A meta‐analysis using a random effects analysis showed significant differences between burned and unburned Kfs. The reductions in Kfs after fire, expressed by the ratio of Kfs Burned/Kfs Unburned, were 0.46 (95% confidence interval of 0.31‐0.70) combining wildfire and prescribed fire and 0.3 (95% confidence interval of 0.13‐0.71) for wildfire. No significant differences for Kfs were observed between wildfire and prescribed fire or moderate and high fire severity. Both Kfs magnitude and variability depended more on measurement method than measurement support area at the plot scale, with methods applying head ≥0.5 cm producing larger estimates of Kfs. It is recommended that post‐fire efforts to characterize Kfs for modeling or process‐based interpretations use methods that reflect the dominant infiltration processes: tension infiltrometers and simulated rainfall methods when soil matrix flow dominates and ponded head methods when macropore flow is critical. Published 2019. This article is a U.S. Government work and is in the public domain in the USA.

An integrated workflow for fracture propagation and reservoir simulation in tight oil

Various fracture-propagation models have been used to capture complex hydraulic fracture (HF) geometry. However, they cannot obtain the production performance. Besides, many researchers developed reservoir simulators to obtain production performance with given fracture geometry. However, these geometries are easy to deviate from the reality of a certain reservoir. To fill this gap, there is an urgent demand to integrate the simulation of fracturing and production processes. In this work, we present an integrated workflow for fracture-propagation and reservoir simulation for tight oil. First, we employ cohesive zone model (CZM) to simulate fracture propagation. In comparison with previous studies, our CZM can simulate complex fractures. Then, we apply the complex fracture geometry to embedded discrete fracture model (EDFM). In this reservoir simulator, nonlinear flow in the tight matrix, complex HF geometry, and pressure-dependent fracture permeability (stress sensitivity effect) are considered simultaneously. Finally, we obtain production performance of this fractured well. To verify the reliability of our models, we compare the results of laboratory experiment and commercial simulator with CZM and EDFM, respectively. Using this workflow, we studied the effect of geological factor (i.e. natural fracture distribution) and fracturing schedule (i.e. injection rate) on production performance. Results reveal that the cumulative oil production in the case with regular natural fracture (NF) is 1.67% higher than that with staggered NF, and 14.6% higher than that without NF. There is an optimal injection rate to maximum production performance. In this case, medium injection rate increases cumulative oil production by 2.42% than higher injection rate, and 1.1% than lower injection. Most importantly, the continuous simulation of fracturing and production processes is implemented in our proposed simulation workflow. In this way, this workflow can be used to optimize both fracturing and production schedule to maximize production performance and/or economic benefit for tight oil in our future work. Furthermore, our method can be further extended to the simulation of multi-stage fractured horizontal well (MFHW) in tight oil or other unconventional oil and gas resources.

A simulator for production prediction of multistage fractured horizontal well in shale gas reservoir considering complex fracture geometry

Shale gas is becoming an increasingly supplementary energy source because of its clean-burning and abundance. Economic gas production in shale requires the techniques of horizontal drilling and multistage hydraulic fracturing to create complex fracture network (CFN). How to accurately describe the characteristics of geometry and flow mechanisms of the CFN and select the most efficient approach for modeling are challenging. In this paper, a production forecasting model for multistage fractured horizontal well (MFHW) with CFN in shale is proposed based on the multiple interacting continua (MINC) theory (organic/inorganic matrix, natural fractures system) and lower-dimensional discrete fracture network (DFN) model (hydraulic fractures system). The model is designed to describe the unconventional flow mechanisms in shale system, such as fractal porous media and non-Darcy multiscale flow in ultra-tight matrix, ad-desorption on organic materials’ surface, rock un-consolidation within natural fractures, high-velocity turbulent flow near well range, and multiphase behaviors. We also propose a novel hybrid control volume finite element (CVFE) and finite-difference (FD) simulation method to obtain the numerical results of the model based on the unstructured 3D tri-prisms. The accuracy of the simulator is successfully validated and sensitivity analysis of some key factors (e.g.: fractal model permeability, Langmuir volume, heterogeneities of reservoir and fractures, well platform) are conducted to evaluate the impacts on production performance. Combing with the micro-seismic monitoring (MSM) data and engineering analyses, the DFN model is applied in Longmaxi shale formation to obtain the history matching with the field data and predict the production.

Fractographic evaluation of welded joints of PPS/glass fiber thermoplastic composites

Joints obtained by resistance welding of polyphenylene sulphide (PPS) laminates reinforced with bidirectional glass fiber (GF) fabrics were investigated by fractographic analyses. The welded joints were tested under lap shear loading at room temperature. The fracture surfaces were analyzed by scanning electron microscopy (SEM) technique. Electric resistance welding technique uses the matrix flow property, when the thermoplastic is heated above the softening temperature (for amorphous polymers) or above the melting temperature (for semicrystalline polymers), to promote the welding between the laminates. Fractographic aspects of the studied fracture surfaces show that the interfacial adhesion of matrix/heating element was efficient, with the presence of intralaminar and interfacial failures. The intralaminar failure was predominant in laminates with higher values of shear strength (9.6 MPa). On the other hand, interfacial failure was predominant in laminates with lower values of shear strength (1.9 MPa). The mechanical performance measured for the welded joints was attributed to the polymer chains interdiffusion mechanism in the welding region as well as to the good polymer anchoring in the mesh of heating element. The fractographic analyses performed proved to be an adequate tool because provide information to evaluate the quality of welding process of thermoplastic composites.

Effect of Microstructural Flexibility on Methane Flow in Kerogen Matrix by Molecular Dynamics Simulations

We investigate the flow of methane in a kerogen matrix with microstructural flexibilities at various pressures. The matrix is constructed by compressing a collection of 60 type II kerogen macromole...

Use of History Matching and Pressure Analysis for Improving Conformance Assurance Using the in Salah Co2 Storage Case Study

Time-lapse seismic imaging of the CO2 plume in the high-porosity Utsira Formation at Sleipner has proven very valuable in building confidence that the injected CO2 is safely contained within the storage unit in this world-first industrial scale offshore storage project. The In Salah CO2 storage project, with the more challenging low-porosity reservoir properties on the other hand, has provided the CCS community with a contrasting case to consider how conformance assurance can be achieved through a robust multi-disciplinary understanding of the injection/storage processes. This paper highlights the role of history matching and pressure analysis for improving conformance assurance, using the In Salah CO2 storage project case study. We show how the injection well performance can be characterised by periods of matrix and fracture flow, and how the characteristics of tensile and shear fracture modes can be identified using a holistic analysis of reservoir history-matching parameters and monitoring datasets.

Numerical and conceptual evaluation of preferential flow in Zarqa River Basin, Jordan

Farmers along the main reach of the Zarqa River Basin (ZRB) commonly utilize treated wastewater for irrigation. Deep percolation is expected to occur as a result of irrigation, and it is expected that preferential flow pathways may facilitate the downward movement of irrigation water. Therefore, the aim of this research was to investigate the susceptibility of soils near Zarqa River to preferential flow, and the HYDRUS and Soil and Water Assessment Tool (SWAT) models were used. The methodology consisted of taking tension infiltrometer measurements along the Zarqa River to determine the main physical properties relevant to preferential flow, such as infiltration rate and macroscopic capillary length, followed by investigating the downward water movement using HYDRUS and SWAT. The HYDRUS simulations were conducted using single porosity (SP) and dual porosity (DP) constitutive functions pertaining to matrix and preferential flow, respectively. The in situ tension infiltrometer measurements were used to parameterize the surface layer of the HYDRUS DP model. HYDRUS simulations showed that preferential flow occurring in the surface layer of the soil profile controlled the vertical movement of soil water in excess of field capacity. The comparison between SWAT, SP and DP showed that both SWAT and DP were capable of simulating preferential flow in arid watersheds. However, SWAT simulations of lateral discharge and deep percolation resemble that of the DP only when the evaporation soil compensation factor (ESCO) was set to a value of 0.8 and the length of the soil slope was set to its maximum value. This research recommends using HYDRUS model to verify SWAT model predictions of soil water redistribution in the soil profile and to improve the parameterization of the SWAT model. The research also suggests an approach for the combined use of both models.

Karst flow processes explored through analysis of long-term unsaturated-zone discharge hydrochemistry: a 10-year study in Rustrel, France

The unsaturated zone of karst aquifers influences the dynamics and the chemistry of water. Because of a lack of direct access, other than via caves, flows in the aquifer matrix and the smallest conduits remain poorly characterized. The few artificial underground structures in the unsaturated karst provide a rare opportunity to study the variety of flow processes. At the low noise underground research laboratory (Laboratoire Souterrain a Bas Bruit, LSBB) in Rustrel (France), 12 variables (temperature, pH, electrical conductivity, alkalinity, major anions and cations, total organic carbon) have been monitored on 12 perennial or temporary flows and leakages over a 10-year period covering contrasting climatic periods. This unique dataset of 1,135 samples has been used to discriminate, identify, and rank the processes associated with the hydrochemical variability of these different types of flows. A principal component analysis and a hierarchical cluster analysis, using mean values and standard deviation of the flow along the principal components, were performed. The results indicate that seasonal variability, mean water residence time, and the depth of acquisition of the chemical characteristics are the main factors of the variability of chemistry at the monitored flow points. Distinguished clusters highlight the great diversity of flows and processes occurring in the fine pathways that may be neighboring the large and structured fractures and conduits. Long-term monitoring with various climatic conditions appears to be a useful tool for assessing this diversity.