Richard G. Hughes

Pore Scale Modeling of Rate Effects in Imbibition

We use pore scale network modeling to study the effects of flow rate and contact angle on imbibition relative permeabilities. The model accounts for flow in wetting layers that occupy roughness or crevices in the pore space. Viscous forces are accounted for by solving for the wetting phase pressure and assuming a fixed conductance in wetting layers. Three-dimensional simulations model granular media, whereas two-dimensional runs represent fracture flow.We identify five generic types of displacement pattern as we vary capillary number, contact angle, and initial wetting phase saturation: flat frontal advance, dendritic frontal advance, bond percolation, compact cluster growth, and ramified cluster growth. Using phase diagrams we quantify the range of physical properties under which each regime is observed. The work explains apparently inconsistent experimental measurements of relative permeability in granular media and fractures.

Network modeling of multiphase flow in fractures

We develop a pore-scale model of wetting in a single fracture. A variable fracture aperture distribution is represented as a square lattice of conceptual pores connected by throats. We borrow concepts from network modeling of flow in porous media to generate a fracture model that includes the effects of flow in wetting layers, snap-off, and cooperative piston-like advance. Cooperative filling accounts for both the curvature of the wetting front in the fracture plane and the effect of the fracture aperture itself. Viscous forces are accounted for using a perturbative method and simulations are performed for horizontal flow, as well as gravity stable and gravity unstable displacements. The wetting phase relative permeability and the trapped non-wetting phase saturation are computed for a fracture whose aperture distribution has been measured using CT scanning.

Feasibility Investigation and Modeling Analysis of CO2 Sequestration in Arbuckle Formation Utilizing Salt Water Disposal Wells

The rate of CO2 production in many states, primarily from coal-fired power plants, is such that it only takes a few years to fill up any depleted oil and gas reservoirs. In order to reduce the level of CO2 in the atmosphere and to minimize the cost of sequestration, the injection of CO2 into aquifers utilizing disposal wells has been targeted. In this paper, an analysis of one particular case, namely, the Arbuckle formation in Oklahoma, was carried out to demonstrate its feasibility for CO2 sequestration. First, a general review for CO2 sequestration into aquifers utilizing existing disposal wells is presented. The limiting criteria for CO2 sequestration in terms of the geology of the aquifer, lithology of the host rock, cost of operation, impact on reservoir properties, depth of the completed interval to maintain supercritical conditions for CO2, injection pressure and rate to minimize gravity segregation, mobility ratio to prevent viscous fingering, and chemical interaction of aqueous and solid phases are discussed. Then, the existence of residual oil in the aquifer and its effect on reaction chemistry concerning the potential CO2 sequestration applications in the Arbuckle formation are evaluated. This investigation was conducted by means of simulation of the prevailing processes. The cutoff points from dissolution to precipitation for each constituent in terms of different CO2 injection rates were obtained by utilizing the simulation models GEM-GHG and PHREEQC and were supported by a database of 150 disposal wells from which 25 wells were completed in the Arbuckle formation. We critically evaluate the current state of knowledge, identify areas needing research, and offer practical approaches for the evaluation of potential CO2 sequestration sites using commercial disposal wells.

Phenomenological Modeling of Hydrate Formation and Dissociation

The proposed hydrate formation and dissociation models describe fairly well the behavior of the experimental data for different experimental conditions and apparatus, while providing important insights into the mechanism of the hydrate formation and dissociation processes.

DEVELOPMENT OF RESERVOIR CHARACTERIZATION TECHNIQUES AND PRODUCTION MODELS FOR EXPLOITING NATURALLY FRACTURED RESERVOIRS

For many years, geoscientists and engineers have undertaken research to characterize naturally fractured reservoirs. Geoscientists have focused on understanding the process of fracturing and the subsequent measurement and description of fracture characteristics. Engineers have concentrated on the fluid flow behavior in the fracture-porous media system and the development of models to predict the hydrocarbon production from these complex systems. This research attempts to integrate these two complementary views to develop a quantitative reservoir characterization methodology and flow performance model for naturally fractured reservoirs. The research has focused on estimating naturally fractured reservoir properties from seismic data, predicting fracture characteristics from well logs, and developing a naturally fractured reservoir simulator. It is important to develop techniques that can be applied to estimate the important parameters in predicting the performance of naturally fractured reservoirs. This project proposes a method to relate seismic properties to the elastic compliance and permeability of the reservoir based upon a sugar cube model. In addition, methods are presented to use conventional well logs to estimate localized fracture information for reservoir characterization purposes. The ability to estimate fracture information from conventional well logs is very important in older wells where data are often limited. Finally, a desktop naturally fractured reservoir simulator has been developed for the purpose of predicting the performance of these complex reservoirs. The simulator incorporates vertical and horizontal wellbore models, methods to handle matrix to fracture fluid transfer, and fracture permeability tensors. This research project has developed methods to characterize and study the performance of naturally fractured reservoirs that integrate geoscience and engineering data. This is an important step in developing exploitation strategies for optimizing the recovery from naturally fractured reservoir systems. The next logical extension of this work is to apply the proposed methods to an actual field case study to provide information for verification and modification of the techniques and simulator. This report provides the details of the proposed techniques and summarizes the activities undertaken during the course of this project. Technology transfer activities were highlighted by a two-day technical conference held in Oklahoma City in June 2002. This conference attracted over 90 participants and included the presentation of seventeen technical papers from researchers throughout the United States.

Development of Reservoir Characterization Techniques and Production Models for Exploiting Naturally Fractured Reservoirs

This research was directed toward developing a systematic reservoir characterization methodology which can be used by the petroleum industry to implement infill drilling programs and/or enhanced oil recovery projects in naturally fractured reservoir systems in an environmentally safe and cost effective manner. It was anticipated that the results of this research program will provide geoscientists and engineers with a systematic procedure for properly characterizing a fractured reservoir system and a reservoir/horizontal wellbore simulator model which can be used to select well locations and an effective EOR process to optimize the recovery of the oil and gas reserves from such complex reservoir systems.