09122-12

Primary Performer
University of Texas at Arlington

Additional Participants
Iowa State University (ISU)

Abstract
The Barnett Shale is a profitable gas field, but the current gas recovery rate is only 10-15% of the estimated gas in place. Recovery in this extremely tight formation is limited by diffusive gas transport from the matrix storage to the stimulated fracture network. Unfortunately, there are no systematic studies on pore connectivity of the Barnett Shale and its effect on gas diffusion. Chemical diffusion in sparsely-connected pore spaces will not be described by classical Fickian behavior; anomalous behavior is suggested from percolation theory and confirmed in our previous results on different types of rock. The objectives of this project are to evaluate the implications of low pore space connectivity in the fracture-matrix interaction in fractured shale, through the following complementary and innovative experimental and modeling approaches:

• Collect shale samples from the Barnett Formation and characterize the geological, hydrological, and geochemical properties (e.g., porosity, permeability, pore-size distribution, water retention curve, mineralogy, TOC, surface area).
• Using imbibition as a diffusion analog, test rock samples of different height:diameter ratios to probe pore connectivity in shale.
• Examine the edge-accessible porosity and pore connectivity by vacuum-saturating rock samples with a liquid tracer, then using laser ablation coupled with ICP-MS to map tracer distribution.
• Inject Wood’s metal into shale samples and image the distribution of the solidified metal in connected pore geometry using electron microscopy.
• Evaluate natural gas (methane) interactions with crushed shale using column transport experiments under both unsaturated and saturated conditions.
• Investigate methane transport influenced by fracture-matrix interaction in fractured shale and interpret the results based on hydrogeochemical parameters obtained from previous tasks.
• Perform pore network modeling using random walks on 3-D lattices with different pore connectivity, to interpret experimental results involving diffusion, advection, sorption, and fracture-matrix interaction (this task will be performed by the subcontractor at Iowa State University).

The outcomes of this proposal will bridge the knowledge gaps in the pore connectivity effect on diffusive gas transport and gas recovery in fractured shale system, which leads to approached to improved gas recovery and associated economic benefits.

Principal Investigator: Qinhong (Max) Hu