Permeability Correlation Structure Research Articles

Geologic CO2 sequestration and permeability uncertainty in a highly heterogeneous reservoir

To understand the implications of permeability uncertainty in basalt-hosted CCS reservoirs, this study investigates the feasibility of industrial-scale CCS operations within the Columbia River Basalt Group (CRBG). It is generally accepted that plausible constraints on in situ fracture-controlled permeability distributions are unknowable at reservoir scale. In order to quantify the effects of this permeability uncertainty, stochastically generated and spatially correlated permeability distributions are used to create 50 synthetic reservoir domains to simulate constant pressure CO2 injections. Results from this research illustrate that permeability uncertainty at the reservoir-scale significantly impacts both the accumulation and distribution of CO2. After 20 years of injection the total volume of CO2 injected in each simulation ranges from 2.4 MMT to 40.0 MMT. Interestingly, e-type calculations show that the mean CO2 saturation over the ensemble of 50 simulations is concentric around the injection well, however, ensemble variance shows an ellipse of uncertainty that trends parallel to the long axis of CRBG permeability correlation (N40°E). These results indicate that a priori knowledge of permeability correlation structure is an important operational parameter for the design of monitoring, measuring, and verification strategies in highly heterogeneous CCS reservoirs.

Identifying spatial correlation structure of multimodal permeability in hierarchical media with Markov chain approach

Outcrop analogs for aquifers allow measurements of permeability with relatively high-resolution and mapping sedimentary unit types. The spatial bivariate structure of permeability is defined by aquifer architecture. The architecture is often organized into a hierarchy of unit types, and associated permeability modes, across different spatial scales. The composite covariance (or semivariogram) is a linear summation of the auto- and cross-covariances (or semivariograms) of unit types defined at smaller scales, weighted by the related proportions and transition probabilities. It is well-known that an appreciable fraction of the composite variance arises from differences in mean permeability across unit types defined at smaller scales. Previous work has shown that the transition probabilities usually define the spatial bivariate correlation structure. The composite spatial bivariate statistics for permeability (covariance or semivariogram) will not be representative unless data locations allow proper definition of the transition probabilities of the units. Quantification of the stratal architecture can be used to better interpret the transition probabilities and thereby improve a model for the sample covariance and semivariogram. In this paper, we use an inverse modeling algorithm to fit the components of the hierarchical model, written as nested functions, in developing a hierarchical spatial correlation models. Specifically, the least-squares criterion along with prior information and other weighted constraints are used as the objective function for the inverse problem, which is solved by the Gauss–Newton–Levenberg–Marquardt method. The estimated covariance and transition probability models provides accurate representation of the spatial correlation structure of permeability for field-measured data from in Española Basin, New Mexico.

Permeability correlation structure of the Columbia River Plateau and implications for fluid system architecture in continental large igneous provinces

Permeability correlation structure of the Columbia River Plateau and implications for fluid system architecture in continental large igneous provinces

The effect of carbonate cementation on permeability heterogeneity in fluvial aquifers: An outcrop analog study

Spatial variations in permeability have been widely recognized as a dominant control on solute transport and petroleum migration. Outcrop studies are one means of improving our understanding of the nature of permeability heterogeneity and the underlying geologic controls. To date, these studies have either neglected the importance of cementation or investigated only the modern cemented permeability without explicitly considering how cementation has affected permeability. Two outcrops of channel sand deposits in the Plio-Pleistocene Sierra Ladrones Formation, New Mexico are investigated to quantify (1) the effect of cementation on permeability at a given location, and (2) the patterns of cementation and their impact on permeability heterogeneity. We analyzed approximately 400 spatially located samples (∼ 10 cm 3 each) from the two outcrops. Cementation is typically weak to moderate, filling less than 60% of the original pore space. Permeability and cement content are bimodally distributed and negatively correlated. Permeability reduction is investigated by measuring modern permeability, minus-cement permeability, minus-cement porosity, and volumetric cement content. Permeability is reduced locally by up to three orders of magnitude. By combining models of permeability for uncemented sediments and cemented sediments, we derive a model of cemented permeability ( k c) that depends primarily on three factors: uncemented permeability ( k u), original porosity, and cement fraction. Our results suggest that accounting for porosity reduction only may result in an overestimation of k c. Conversely, accounting for porosity reduction, increased specific surface area, and increased tortuosity appears to result in an underestimation of k c. Accounting for porosity reduction and increased specific surface area provide the best estimate of k c. Cementation is highly variable spatially and is poorly correlated with lithofacies. Variogram analysis of cementation and permeability indicates that the spatial distribution of cementation is the dominant control on the permeability correlation structure. The spatially variable cementation also results in an order-of-magnitude increase in the variance of log-permeability. Applying stochastic models of effective flow and transport properties to the results of this study suggest that cementation has a relatively small effect on effective permeability but can potentially increase dispersivity by two orders of magnitude.

Relationship between fluvial bounding surfaces and the permeability correlation structure

Results of three meter‐scale outcrop studies suggest a quantifiable relationship between fluvial bounding surfaces and the permeability correlation structure. Mapping of bounding surfaces and in situ measurements of permeability were obtained in three types of deposits: a low‐energy channel deposit, a paleosol, and a high‐energy channel deposit. For the low‐energy channel deposit only second‐order surfaces separating lithofacies were mapped. The variogram exhibits anisotropic exponential behavior, and an analysis of variance (ANOVA) suggests that the within‐facies variation dominates over between‐facies variation. The paleosol contained no internal bounding surfaces and exhibited a “bellshaped” variogram consistent with a smoothly varying style of heterogeneity. Both firstand second‐order bounding surfaces were mapped in the high‐energy channel deposit. Results of the ANOVA suggest that the between‐facies variation dominates over the within‐facies variation. A model of spatial correlation using superposition of independent processes acting over different scales provides a good fit to the data. These three studies suggest that fluvial bounding surfaces provide a geological basis for conceptualizing and modeling heterogeneity in alluvial deposits.

Relationship between Oriented Calcite Concretions and Permeability Correlation Structure in an Alluvial Aquifer, Sierra Ladrones Formation, New Mexico

ABSTRACT Fluvial deposits of the Sierra Ladrones Formation (Pliocene-Pleistocene) contain abundant elongate calcite concretions that are interpreted to have precipitated in the saturated zone parallel to the direction of groundwater flow. The orientation of these concretions is coincident with the orientation of the permeability correlation structure, as determined from architectural element mapping and permeameter measurements. In cases where the paleo-groundwater flow closely corresponds with the direction of fluvial deposition, measurement of concretion orientations in alluvial rocks and sediments may provide a means of rapidly estimating the major axis of the permeability correlation structure over large areas.

Seepage beneath water retaining structures founded on spatially random soil

The effect of stochastic soil permeability on confined seepage beneath water retaining structures has been studied. Random field concepts for the generation of soil permeability properties with a fixed mean, standard deviation and spatial correlation structure have been combined with finite element methods to perform Monte Carlo simulations of the seepage problem. Analyses have been performed for a dam with two cut-off walls. The results of parametric studies to gauge the effect of the standard deviation and correlation structure of the permeability on the output statistics relating to seepage quantities, exit gradients and uplift pressures are presented. In all cases, comparison is made with results that would be achieved on a deterministic basis. Flow rates and other quantities are shown to be affected significantly by the standard deviation and the correlation structure of soil permeability. L'article étudie l'influence de la perméabilité d'un sol stochastique sur l'infiltration confinée existant sous une structure de retenue d'eau. Des analyses aléatoires, permettant de générer les propriétés de perméabilité du sol pour une moyenne, un écart-type et un facteur de corrélation donnés, ont été combinées à des méthodes par éléments finis afin de réaliser des simulations de Monte-Carlo pour l'infiltration. Des analyses ont été réalisées pour un barrage comportant deux parois étanches. L'on présente les résultats de l'étude paramétrique réalisée afin de quantifier l'influence de l'écart-type et du facteur de corrélation de la perméabilité sur les statistiques relatives aux quantités infiltrées, au gradient de sortie et aux pressions ascendantes. Dans chacun des cas, des comparaisons ont été établies avec les résultats que l'on aurait obtenus à partir d'une base déterministe. Les débits et autres quantités semblent être significativement affectés par l'écart-type et le facteur de corrélation de la perméabilité du sol.

Architecture of the Sierra Ladrones Formation, central New Mexico: Depositional controls on the permeability correlation structure

Statistical models of hydrogeological heterogeneity are often used in aquifer and reservoir characterization. The number of data required to estimate objectively the spatial correlation structure of permeability, however, is often prohibitive. The objective of this study was to develop a better understanding of how information about depositional processes can be used to characterize hydrogeological heterogeneity. An outcrop of the fluvial/interfluvial Sierra Ladrones Formation of New Mexico was studied for this purpose. On the basis of previous studies of paleogeography and our own field observations, deposits of the Sierra Ladrones Formation are interpreted as marginal ancestral Rio Grande flood-plain and tributary deposits. Architectural elements were mapped over a 0.16-km[sup 2] peninsular outcrop of Pliocene-Pleistocene deposits of the central Albuquerque Basin. Geostatistical analysis of the architectural-element map data indicates non-orthogonal anisotropy in the horizontal direction. The orientations of the strongest (N30[degree]W) and weakest (N90[degree]E) correlation correspond to the orientation of the tributary system and the ancestral Rio Grande flood plain, respectively. In the vertical direction, the correlation structure exhibits exponential behavior corresponding to the average-element thicknesses. The results demonstrate that information about depositional environment can be used to help to quantify statistically subsurface heterogeneity. 28 refs., 9 figs., 1 tab.