Effects Of Permeability Heterogeneity Research Articles

Simulating the Spatial Extent of Thermally Enhanced Reaction Zones for Low Temperature Thermal Treatment

AbstractLow temperature thermal treatment (LTTT) is a technology that can enhance aqueous‐phase degradation reactions for organic constituents in groundwater. Understanding heat transfer in groundwater is important for the design of LTTT applications. In this study, the effect of permeability heterogeneity on temperature distributions during and after the application of heat was investigated by numerical modeling. An enhanced reaction zone was determined for the hydrolysis of 1,1,1‐trichloroethane (1,1,1‐TCA) using an average half‐life considering the temperature history during and after heating. For hydrolysis reactions, the average half‐life could be reduced substantially by reaching a high temperature for a short period of time because their reaction rates increase exponentially with increased temperatures. Results showed that the enhanced reaction zone was shifted downstream of the heater well zone at high groundwater velocities. This suggests that heaters should be shifted upstream of the target treatment zone to fully utilize the applied heat. In addition, permeability heterogeneity leads to greater macroscopic dispersion at higher velocities. This resulted in higher spreading of heat and faster heat dissipation in the simulations with a heterogeneous permeability condition compared with a homogenous permeability condition. As a result, the enhanced reaction zone was smaller in simulations with higher levels of permeability heterogeneity at a mean velocity of 0.3 m/day.

Impact of gas composition and reservoir heterogeneity on miscible sour gas flooding — A simulation study

Proper handling of the produced sour gas is a big challenge for operating companies due to the serious environmental and technical problems caused by H2S and CO2. The reinjection of the produced sour gas into oil reservoirs is an environmentally friendly as well as an economically attractive method due to the low investment cost and incremental oil recovery. However, the sour gas injection for enhanced oil recovery (EOR) is a relatively new approach with numerous uncovered perspectives, especially in a heterogeneous reservoir. The objective of this study is to investigate the effect of gas composition and reservoir heterogeneity on the miscible displacement of reservoir oil using sour gas.The reservoir oil consisting of 15 mol% H2S and 4 mol% CO2 from an oilfield in the North Caspian region was used. First, the phase behavior alteration of reservoir oil due to the injection of various gases, namely H2S, CO2, CH4, acid, and sour gas was analyzed. Then, the effect of gas type on minimum miscibility pressure (MMP) was investigated based on a semi-analytical tie-line method. Moreover, 2D and 3D numerical simulations were conducted to understand the oil recovery performance of various gas injection options and the effect of permeability heterogeneity on sour gas flooding efficiency. The findings showed that higher H2S content in the injected gas narrows the two-phase envelope and decreases the bubble point pressure. Moreover, it was observed that MMP decreases with increasing H2S concentration, which provides a favorable condition for achieving miscibility. Additionally, an increase in H2S concentration in sour gas improves its oil recovery efficiency by extending gas breakthrough time and elongating the plateau period of oil rate. These results are useful for designing, optimizing, and implementing sour gas injection for EOR in oil reservoirs that have access to sour gas sources.

Effect of permeability heterogeneity on the dissolution process during carbon dioxide sequestration in saline aquifers: two-and three-dimensional structures

The convection–diffusion process of carbon dioxide (CO2) dissolution in a saline reservoir is investigated to shed light on the effects of the permeability heterogeneity. Using sequential Gaussian simulation method, random permeability fields in two and three-dimension (2D and 3D) structures are generated. Quantitative (average amount of the dissolved CO2 and dissolution flux) and qualitative (pattern of the dissolved CO2 and velocity streamlines) measurements are used to investigate the results. A 3D structure shows a slightly higher dissolution flux than a 2D structure in the homogeneous condition. Results in the random permeability fields in 2D indicates an increase in the standard deviation of the permeability nodes enhances the dissolution efficiency, fluctuations in CO2 dissolution flux, separation between the different realizations from the same input parameters, and tendency toward more jagged convective fingers’ shape. Furthermore, the distance between the permeability nodes increases the convective fingers’ dissolution efficiency and jagged structure. The degree of freedom in 3D structures results in a higher chance of escaping from the low permeability zones and reduces the interactions between convective fingers in 3D systems. With the same variance and correlation length between permeability nodes, connectivity between high permeable zones in 3D cases are less than that of 2D cases; therefore, 2D realizations overestimate the dissolution flux of real heterogeneous 3D structures, which should be considered carefully.Article HighlightsCO2 sequestration in two and three dimensional heterogeneous saline aquifers are investigated.3D structures in homogeneous conditions show higher dissolution than 2D structures.2D realizations overestimates the dissolution flux over real heterogeneous 3D reservoirs.

Effect of different exploitation schemes on production performance from the carbonate reservoir: A case study in Xiong'an new area

Operational optimization is the essential factor to maximize the heat production from the thermal reservoir. Well spacing and the arrangement of the production well are the two most pivotal factors for the thermal reservoir which can ensure long-term production at economically acceptable levels. The Xiong'an geothermal area, located in the western margin of the Bohai Bay Basin, is the most developed region of the carbonate stratum and also is one of the areas that have the greatest hydrothermal geothermal resources in China. In this study, based on the temperature data of the carbonate formation and thermosphysical data from the core samples measurement, a three dimensional thermo-hydraulic coupled numerical model was established to assess the geothermal potential of the carbonate reservoir and the effect of different exploitation schemes (mainly involved the injection fluid temperature, injection mass flow rate and lateral well distance) on the thermal reservoir performance was analyzed over a period of 40 years. The effect of permeability heterogeneity on the thermal reservoir performance was also discussed as a case study. The calculation results were then analyzed on the basis of the output temperature decline curves and the cumulative energy production over the entire period from the production well. Among the three important influence factors on the carbonate reservoir performance, the injection temperature has the most significant effect on the energy production rate, followed by the injection mass flow rate and the lateral well spacing.

A Study of the Effect of Fracture Walls on Tracer Transport

Summary Subsurface permeable systems are heterogeneous at multiple scales and are often fractured. Flow and transport in the subsurface formations are impacted by the presence of fractures, both natural and induced. The effects of permeability heterogeneity and fractures on tracer tests are not well-understood. Echo-tracer (i.e., single-well-injection withdrawal) and transmission-tracer (i.e., dipole) tests can provide information on the flow and transport-system heterogeneity in layered formations. The reversal of flow paths in the echo tests tends to cancel out the non-Gaussian, high-permeability flow behavior in the tracer histories, as observed in laboratory experiments. A question arises whether similar Echo-tracer behavior may be observed in tracer responses for an extreme case of heterogeneity, such as a multiporosity fractured permeable system. A fractured rock consists of high-permeability contrast with high fracture permeability and low matrix permeability, often differing by orders of magnitude. The tracer response from an echo test as well as a transmission test in fractured systems, with high level of heterogeneity, is known to be controlled by the extent of molecular diffusion into the matrix. Dispersion may be dominant in the fracture volume, whereas the molecular diffusion is expected to occur across the fracture/wall interface. We discuss the 1D propagator of diffusion, with convection, and its behavior in the presence of a reflecting and absorbing fracture wall. A wave model is presented to understand the tracer transport in a fracture with differential-diffusion properties. The model predicts that diffusion and adsorption of tracer can produce a retardation of the tracer propagation in the fracture in a transmission-tracer test. The retardation leads to a difference in the arrival times of the tracer, which can then be used to calculate the length of a fracture. The model prediction is compared with published transmission-tracer test experimental data in a fractured till rock. Comparison of the model prediction of tracer-front-arrival times shows good agreement. The arrival time depends on the diffusion coefficient, average time of exposure of the solution to the fractured system, the length of the fracture, and the fracture spacing. Prediction of the echo-tracer test shows that for a fractured system, the retardation of the tracer produces a delayed arrival of the diffusing tracer as opposed to the nondiffusing tracer. The study adapts existing techniques for simple-wave description of tracer transport to a fractured system with absorbing walls. The model for prediction of front movement in the fractured system is novel.

Effect of Permeability Heterogeneity on Area of Review

The Area of Review is one of the most important aspects of a geologic CO2 storage site permit application and regulatory requirement. The US Environmental Protection Agency (EPA) has implemented an Area of Review (AoR) requirement for Class VI CO2 injection wells for geologic sequestration. Reservoir permeability is one of the most important parameters controlling AoR evolution but is generally highly heterogeneous and difficult to constrain. We have used a numerical model for Rock Springs Uplift in Wyoming as an example site to characterize how the heterogeneity in reservoir permeability affects AoR. We have performed multiple reservoir simulations using multiple, equally-likely realizations of heterogeneous permeability. We considered multiple CO2 injection scenarios with varying injection rates as well as varying injection and post-site durations. Results of our study demonstrate that uncertainty in permeability heterogeneity can significantly influence AoR for both CO2 saturation and pressure. In our example, the CO2 AoR varied by as much as 2-3 times while the pressure AoR varied over 1.5 – 2 times. Such type of variability can have significant implications in defining AoR for site permit applications.

Effects of permeability heterogeneity on CO2 injectivity and storage efficiency coefficient

AbstractWe study the dependency of CO2 storage efficiency coefficient (E) and injectivity index (Iinj) on the geostatistical parameters of the permeability field. CO2 injection simulations are conducted for multiple realizations of log‐normally distributed permeability fields parameterized by log permeability standard deviation (σ) and dimensionless horizontal correlation length (λ). Results show that the injectivity index increases with increasing λ, the magnitude of the effect depending on σ. Increasing σ leads to poorer injectivity for cases with small λ, but improves injectivity when λ is large. Further analysis indicates that the enhancing effect of σ on injectivity can be attributed to cases with channelized flow, while the decrease effect of σ is seen in more dispersive flow regime. The dependence of injectivity on both λ and σ is captured with a linear correlation between Iinj and a parameter group , where ξ is a dimensionless scaling parameter. The storage efficiency coefficient, on the other hand, decreases with both increasing σ and λ, and a simple linear fit is found between E and the parameter group λσ2, a well‐established heterogeneity parameter group describing e.g. macro‐dispersivity in solute transport studies. These relationships provide potentially useful tools for the preliminary evaluation of a site. Future studies should address the validity of the relationships in alternative injection scenarios and domain geometries. © 2015 Society of Chemical Industry and John Wiley & Sons, Ltd

Implementation of horizontal well CBM/ECBM technology and the assessment of effective CO2 storage capacity in a Scottish coalfield

In this study the theoretical and effective methane recovery and CO2 storage potential of four coal seams within a well characterised section of a CBM license in Scotland are estimated, considering different horizontal well patterns, the effect of permeability heterogeneity and the composition of the injected fluid. The study concerns the Airth area of the Clackmannan coalfield in the Scottish Midland Valley. The effort on building the static earth model and the history match results of the pre-existing vertical and newly drilled horizontal wells is briefly described. Initial simulations of the horizontal well primary methane production and CO2/flue gas enhanced recovery enabled the length, configuration and alignment of the horizontal wells to be optimised for the long-term simulations. This configuration was then used to estimate the Effective Capacity of a selected area within the Airth field for CBM, ECBM and CO2 storage. To evaluate the impact of permeability heterogeneity and uncertainty on reservoir performance and Effective Capacity for methane recovery and CO2 storage, multiple realisations of possible permeability distributions across the selected area were geostatistically generated. Initially, primary production runs were performed using 100 permeability distributions with a median value of around 1 mD. A number of realisations with different median permeabilities were then selected and used for flue gas (13 % CO2/87 % N2) and mixed gas (50 % CO2/50 % N2) enhanced CBM recovery and CO2 storage runs.

The effects of combined horizontal and vertical heterogeneity on the onset of convection in a porous medium: Moderate heterogeneity

The effects of hydrodynamic and thermal heterogeneity, for the case of variation in both the horizontal and vertical directions, on the onset of convection in a horizontal layer of a saturated porous medium uniformly heated from below, are now studied analytically for the case of moderate heterogeneity (rather than the weak heterogeneity previously studied), for the case of a square box where the properties vary in a piecewise constant or linear fashion, with conducting impermeable top and bottom boundaries and insulating impermeable sidewalls. In order to allow for the moderate heterogeneity the order of the Galerkin expansion employed has been increased, and the expansion of a determinant of high order has been avoided by the use of a least squares methodology to find the critical value of the Rayleigh number Ra. It is found that the effects of permeability heterogeneity and conductivity heterogeneity each cause a reduction in the critical value of Ra in all cases, and the effects of horizontal and vertical heterogeneity are still approximately additive.

The effects of combined horizontal and vertical heterogeneity on the onset of convection in a porous medium

The effects of hydrodynamic and thermal heterogeneity, for the case of variation in both the horizontal and vertical directions, on the onset of convection in a horizontal layer of a saturated porous medium uniformly heated from below, are studied analytically for the case of weak heterogeneity. It is found that the effect of such heterogeneity on the critical value of the Rayleigh number Ra based on mean properties is of second order if the properties vary in a piecewise constant or linear fashion. The effects of horizontal heterogeneity and vertical heterogeneity are then comparable once the aspect ratio is taken into account, and to a first approximation are independent. For the case of conducting impermeable top and bottom boundaries and a square box, the effects of permeability heterogeneity and conductivity heterogeneity each cause a reduction in the critical value of Ra, while for the case of a tall box there can be either a reduction or an increase.

The effects of permeability heterogeneity on miscible viscous fingering: A three-dimensional magnetic resonance imaging analysis

The three-dimensional evolution of the viscous fingering instability has been visualized directly with magnetic resonance imaging (MRI). Miscible displacement of thin solute bands by aqueous solvent was investigated in packed beds of 30 μm chromatographic particles. Fingering behavior into samples of glycerol and a protein, bovine serum albumin (BSA), with viscosity ratios ranging from 1 to approximately 4, were compared. The three-dimensional morphology and dynamics of fingers were monitored to approximately millimeter spatial resolution using MRI. Linear and nonlinear fingering behavior were observed. Permeability heterogeneities with length scales on the order of the finger wavelength induced complex three-dimensional fingering patterns. Sample and column boundary effects on fingering dynamics were also noted. The differences in fingering behavior observed between albumin and glycerol samples are consistent with the wavelength predictions of linear stability analysis and the large differences in molecular diffusivity.

Effect of Viscous Crossflow on Miscibility Development in a Two-Layer Flow System: Part I - Ternary Vaporizing Gas Drives

SUMMARY This paper examines the effect of permeability heterogeneity and viscous crossflow on ternary vaporizing gas drive displacements. Material balance equations that describe multicomponent, multiphase flow in a two-layer system are solved by finite differences for the case of maximum (vertical equilibrium) viscous crossflow between layers. The effects of interlayer permeability ratio and operating pressure on composition paths, composition and saturation profiles, and oil recovery are reported. Fluid mixing due to viscous crossflow is shown to cause significant amounts of two-phase flow in displacements that would be multicontact miscible in the absence of crossflow. Although the induced two-phase flow reduces local displacement efficiency, viscous crossflow improves overall recovery because a decrease in mobility contrast between layers reduces channeling, and because some oil is moved from the low permeability layer to that with faster flow.