Executive Summary

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University of Texas GeoFluids Consortium (UT GeoFluids):
Mudrock Geomechanics & Pore Pressure Prediction
Description & Objectives

1.0     Executive Summary

Overview: UT GeoFluids will study the state and evolution of pressure, stress, deformation and fluid migration through experiments, theoretical analysis, and field study. The Bureau of Economic Geology (BEG) at the Jackson School of Geosciences will partner with the Department of Civil and Environmental Engineering at MIT: BEG will lead the consortium.

Experimental: We will analyze the fabric, acoustic, electrical, and mechanical properties of mudrocks over effective stresses from 0.1-100 MPa. We will study 1) real geologic materials (Gulf of Mexico mudrock, Boston Blue Clay) using resedimentation techniques and 2) core from a range of depths in the subsurface. Analysis of resedimented material allows us to examine material properties of a consistent material at a range of in-situ stresses. Uniaxial consolidation experiments will measure vertical and lateral stress, resistivity, permeability, and velocity (Vp & Vs) during compression. Triaxial experiments will measure strength parameters. We will describe and quantify mudrock fabric at various effective stresses with mercury porosimetry, and x-ray goniometry and image mudrock fabric using electron beam techniques. We will 1) illuminate the origin and evolution anisotropy in mudrocks, 2) document how composition (e.g. clay/silt fraction and clay composition) controls geomechanical properties, and 3) develop a geomechanical model for mudrocks that will better allow us to predict compaction behavior, pore pressure, and borehole stability at geologic stresses.

Poro-Mechanical Modeling: We will develop and apply models that link realistic rheologies, deformation, stress (shear and normal), and pore pressure. Pressure prediction techniques and basin modeling generally assume uniaxial deformation. In areas of central interest to the petroleum industry, deformation is not uniaxial and stress and pressure are coupled in more complex ways. In thrust belts, the lateral stress is greater than the vertical stress and sediment that was originally buried in a basin under uniaxial strain is later deformed in plane strain. In the sub-salt regime, the interaction of isostatically stressed salt with sediment that bears differential stresses results in complex stress and deformation near the salt-sediment interface. To understand and ultimately predict pressures, stresses, and rock properties in these regimes, a new level of understanding, modeling, and analysis must be applied.

Field Study: We will analysize pore pressure in thrust belts and in salt provinces. In the subsalt, we will analyze pressure and stress in and near the Mad Dog field to understand how pore pressure couples with salt advancement and to study the present state of stress and pressure in sub-salt systems. We will study fold thrust systems through ongoing work in the Nankai Trough. We look forward to working with industry data sets in deepwater fold-thrust belts.

Importance: Despite extensive previous work exploring mudrock compressional behavior, there are still major gaps in our understanding of mudrock evolution. We do not yet have an understanding of stress and strength behavior over a large range of effective stresses (0.1-100 MPa) and we do not fully understand the evolution of anisotropy. Our work will lay the groundwork for a new generation of basin modeling algorithms and pressure/stress prediction techniques. This new generation of modeling techniques will go beyond the restrictive assumption that deformation is uniaxial. Instead, we will couple reasonable assumptions about far field stress state with rheological models to predict stress and pressure. The results will allow us to better predict pressure, stress, borehole stability, and hydrocarbon migration in environments critical to exploration: thrust belts and sub-salt.

Reporting: The Consortium will 1) hold Annual Meetings, 2) provide Annual Reports, 3) develop an on-line database of experimental results, 4) provide Company Visits, and 5) provide Notice of Papers Submitted for Publication.

Research Team: The Consortium Team will include Peter Flemings (UT), Ruarri Day-Stirrat (UT), John Germaine (MIT), and Derek Elsworth (Penn State). We envision supporting 10 graduate students and 3 post-doctoral scientists at 3 universities.

How Much?

Start Date:                             June 1, 2009

Duration:                                10 years

Cost:                                       $45,000/year

Project Director:                    Peter B. Flemings, Geoscientist and Professor  


                                                512-750-8411 (w)