Production of Natural Gas and Fluid Flow in Tight Sand Reservoirs

DE-FG26-04NT42132

Goal:
To study the influence of microscopic flow mechanisms on gas production parameters of tight sand reservoirs.

Background:
The main goal of this research is to identify possible relationships and define dependencies between macroscopic reservoir parameters strongly affected by microscopic flow dynamics and production well performance in tight-gas sand reservoirs. To achieve this goal, the Center for Energy and Technology of the Americas (CETA) will identify microscopic flow mechanisms that affect fluid flow by using pore network simulation and other modeling techniques, that when coupled to homogenization and upscaling tools, can be used to find average macroscopic equations that properly describe the fluid flow behavior at the laboratory scale. The formulation can then be further extended for application at field scales by using dynamic upscaling methods upon determination of reservoir heterogeneity. Subsequently, CETA will evaluate the impact of reservoir features on fluid flow. Such features could be fluid properties, reservoir depth, net sand thickness, reservoir permeability, and data from drilling and stimulation processes.

Performer:
Florida International University, Center for Energy and Technology of the Americas (CETA)

Location:
Miami, Florida 33174

Potential Impact:
The influence of microscopic flow mechanisms on gas production parameters in tight sand reservoirs can help identify possible relation-ships and dependencies between macroscopic reservoir parameters and well performance. Subsequently, these parameters can be used in the development of rigorous, macroscopic equations that more accurately describe the fluid flow behavior in tight-gas reservoirs and allow operators to better assess well completion strategies, predict well performance, and avoid tight-gas well production problems, such as unexpected associated water production.

Results:

• Completed a review of field experiences, lab experiments, flow modeling and reservoir simulators for the description of flow in tight gas sands.
• Submitted an abstract for consideration for the 2005 Society for Petroleum Engineers (SPE) Annual Technical Conference.
• Final report sent in for review.
• Final report accepted for completion of the contract on August 22, 2006.

Current Status and Remaining Tasks:
Ongoing or remaining tasks associated with this study include:

• Conduct a preliminary analysis of the various approaches commonly used for simulation of tight gas sands, such as double-porosity models and dual-mechanistic models.
• Identification of microscopic flow mechanisms that may affect fluid behavior, including the relevance of film flow and other effects associated with clay content and activity, formation water composition (type of ions present) that could produce alteration of the mineral surface charge, and the activation of several electrokinetic phenomena, such as streaming potential.
• Estimate the effect of the average pore size for several rock wetting conditions on the efficiency of relative gas-water flow through tight porous media. This evaluation will be performed using modeling and pore network simulation with samples for three main wetability conditions: wetting ,nonwetting, and intermediate wetting to water.
• Estimate the change of the behavior of fluids when the porous sample contains a certain density of fractures. CETA will also conduct a sensitivity study of the dependence of flow efficiency on fracture morphology and size, fluid-fluid, and rock-fluid properties such as interfacial tension and formation wetability.
• The results indicate that at least one parameter in the reservoir simulation equations currently used by industry may need further testing to verify the changes documented to date in the study.

Project Start: June 30, 2004
Project End: June 30, 2006

DOE Contribution: $111,050
Performer Contribution: $0

Contact Information:
NETL – Tom Mroz (Thomas.Mroz@netl.doe.gov or 304-285-4071) or
FIU ? Dr. Maria Brazo (maria.brazo@ceta.flu.edu or 305-348-1821)

Pertinent Publications:
SPE-97055-PP
Paper Title: A novel modeling approach for two-phase fluid flow in tight sand gas reservoirs
Paper Abstract: A system of macroscopic transport equations that model two-phase (gas-water) flow through tight porous media is presented. The porous medium is modeled using a dual-porosity and dual-permeability approach. Phenomena such as, Knudsen diffusion, electro-kinetic effects, diffusion of dissolved gas in water and water vaporization have been captured in the proposed formulation. The transport equations were discretized in a 2D finite differences scheme and solved numerically. Results are compared with other single and multi-mechanistic approaches commonly used for tight sand reservoirs. We analyze the model predictions for various reservoir properties, initial conditions and exploitation strategies. We observe differences in the predicted gas production from the models considered and the common underestimation when using a single-mechanistic approach. We also present results that possibly explain unexpected water production.