Zuleima T. Karpyn

Deterministic Modeling of Fluid Flow through a CT-scanned Fracture Using Computational Fluid Dynamics

Abstract Modeling flow through fractures is a major challenge in the design of recovery mechanisms from naturally fractured reservoirs, since proper structural characterization of fracture networks and fracture transport properties are rarely available. We investigate single-phase flow dynamics in a rough fracture model constructed from high-resolution X-ray computed tomography images, using computational fluid dynamics. Flow simulations gave a detailed description of pressure and velocity fields and showed that this approach can be used for the deterministic analysis of single-phase flow through fractures. Our results demonstrate the formation of preferential flow channels and their correlation with local structural characteristic of the fracture.

Investigating Matrix/Fracture Transfer via a Level Set Method for Drainage and Imbibition

Multiphase flow and transport phenomena within fractures are important because fractures often represent primary flow conduits in otherwise low permeability rock. Flows within the fracture, between the fracture and the adjacent matrix, and through the pore space within the matrix typically happen on different length and time scales. Capturing these scales experimentally is difficult. It is therefore useful to have a computational tool that establishes the exact position and shape of fluid/fluid interfaces in realistic fracture geometries. The level set method is such a tool. Our progressive quasistatic (PQS) algorithm based on the level set method finds detailed, pore-level fluid configurations satisfying the Young-Laplace equation at a series of prescribed capillary pressures. The fluid volumes, contact areas and interface curvatures are readily extracted from the configurations. The method automatically handles topological changes of the fluid volumes as capillary pressure varies. It also accommodates arbitrarily complicated shapes of solid confining surfaces. Here we apply the PQS method to analytically defined fracture faces and aperture distributions, to geometries of fractures obtained from high-resolution images of real rocks, and to idealized fractures connected to a porous matrix. We also explicitly model a fracture filled with proppant, using a cooperative rearrangement algorithm to construct the proppant bed and the surrounding matrix. We focus on interface movement between matrix and fracture, and snap-off of non-wetting phase into the fracture during imbibition in particular. The configuration of fluids is strongly affected by asperities in unpropped fractures and by the locally open regions at the proppant/matrix interface. The area of phase in contact with the matrix is nonlinear with phase saturation and strongly hysteretic, and thus transfer functions based on saturations should be used with caution. The effect of coupling fracture capillarity and matrix capillarity on multiphase flow properties depends on the relative sizes of typical pore throats in the matrix and typical aperture in the fracture. The simulations agree with direct obsevations of fluid configurations in fractures.

Development of a coal shrinkage?swelling model accounting for water content in the micropores

Changes in cleat permeability of coal seams are influenced by internal stress, and release or adsorption of gas in the coal matrix during production/injection processes. Coal shrinkage?swelling models have been proposed to quantify such changes; however none of the existing models incorporates the effect of the presence of water in the micropores on the gas sorption of coalbeds. This paper proposes a model of coal shrinkage and swelling, incorporating the effect of water in the micropores. The proposed model was validated using field permeability data from San Juan basin coalbeds and compared with coal shrinkage and swelling models existing in the literature.

A Study of Hydraulic Fracture Conductivity and Its Dependence on Proppant Wettability

Abstract Engineering design of hydraulic fracturing proppants typically focuses on maximizing permeability retention under stress, resistance to high temperatures, and controlling properties such as specific gravity and particle size; less attention is paid to the proppants wetting characteristics and their potential impact on the deliverability of a hydraulic fracture. The purpose of this work is to investigate the effect of proppant wettability on the conductivity of hydraulic fractures through laboratory measurements. Results demonstrate a competing effect between permeability and wettability, the latter having a diminished impact on displacement efficiency at high permeability values.

Estimation of Fracture–Matrix Transport Properties from Saturation Profiles Using a Multivariate Automatic History Matching Method

Abstract This study focuses on the development and implementation of a numerical model of multiphase flow in a fractured core sample by describing the capillary pressure–relative permeability characteristics. An automated history matching approach is proposed to determine relative permeability and capillary pressure curves simultaneously for both matrix and fracture consistent with a core flood reservoir model performance, which relies on a commercial reservoir simulator coupled with an optimization protocol. The results indicate that the proposed approach successfully predicts relative permeability and capillary pressure curves of a fractured core sample and provides a foundation for field-scale history matching with simultaneous estimation of transport properties.

MULTIVARIATE PRODUCTION OPTIMIZATION OF A NATURAL GAS FIELD

Abstract This paper presents two numerical models: a gas well model and a modified gas well model, which respectively analyse the effect of selected parameters on the final production performance of a natural gas field, and predict the combination of these design parameters for profit maximization. A sensitivity analysis is accomplished with the gas well model, thus displaying the individual and combined impact of the chosen design parameters on the system performance in terms of production rate. This is done by testing the model with several production scenarios. An economic survey is added to the previous analysis and the modified gas well model helps to determine the combination of parameters that will best allow the attainment of a given field production target, in terms of maximization of the net present value of the project.

On the Calculation of Static Bottom-Hole Pressures in Gas Wells

Abstract In “Static Bottom-Hole Pressure in Wells” (Petroleum Science and Technology, 2006, 24:113–116), Hashim and Makola present a method for the calculation of static pressure gradients in vertical wells. In the present discussion, the methodology proposed by Hashim and Makola is examined and alternate guidelines for the calculation of static pressure gradients are provided. In particular, this work examines their proposed mathematical simplifications and practices that could compromise the accuracy of the calculations. References to recommended practices and procedures for calculating static bottom-hole pressure in gas wells are also presented.

Modified Invasion Percolation Models for Multiphase Processes

This project extends current understanding and modeling capabilities of pore-scale multiphase flow physics in porous media. High-resolution X-ray computed tomography imaging experiments are used to investigate structural and surface properties of the medium that influence immiscible displacement. Using experimental and computational tools, we investigate the impact of wetting characteristics, as well as radial and axial loading conditions, on the development of percolation pathways, residual phase trapping and fluid-fluid interfacial areas.

Single-phase and multi-phase fluid flow through an artificially induced, CT-scanned fracture

Single- and multi-phase flow through rock fractures occurs in various situations, such as transport of dissolved contaminants through geological strata, migration of dense non-aqueous phase liquids through fractured rocks, sequestration of carbon dioxide in brine-saturated strata, and oil recovery. The presence of fractures in a reservoir plays a major role in the fluid flow patterns and the fluids transport. In this study the Brazilian test technique was employed to induce an extensional fracture with dimensions of about 9.2 (cm)× 2.7 (cm)×0.77 (cm) in a layered Berea (calcite-cemented) sandstone sample. High-resolution X-ray micro-tomography (CT) imaging was used to determine the geometry of the fracture. A post-processing code was developed and used to computationally model the fracture geometry; Gambit was then used to generate an unstructured grid of about 1,000,000 cells. Single-phase and two-phase flow through the fracture were studied using FLUENT. The Volume of Fluid (VOF) model was employed for the case of two-phase flow. Flow patterns through the induced fracture were analyzed. In geological flow simulations, flow through fractures is often assumed to occur between parallel plates. The combination of CT imaging of real fractures and computational fluid dynamic simulations may contribute to a more realistic and accurate description of flow through fractured rocks.