Accomplishments

Experimental
UT GeoFluids has pioneered the application of resedimentation to the systematic study of mudrock material behavior at high stress levels (up to 100 MPa (14 KSI)). We have shown that the lateral stress ratio, friction coefficient, strength, and compression behavior are stress dependent and that this behavior varies systematically with liquid limit (an easily measured parameter). We have developed models to describe smectite‐rich (Gulf of Mexico) and illite‐rich mudrocks and we have developed generalized models based on liquid limit. We have embarked on a systematic program to measure velocity (Vp & Vs) at a range of stresses and we are integrating these measurements with observations of mechanical properties. Based on our experimental results, we have developed simple spreadsheets that provide material properties as a function of depth (e.g., permeability, lateral stress ratio, friction angle, velocities – Fig. 1). These spreadsheets are freely available to UT GeoFluids members.

Fig. 1: Our experimental results are available to UT GeoFluids Members as simple spreadsheets that summarize the behavior of mudrocks and provide material properties as a function of depth. They can be used to predict fracture gradient and strength.
Fig. 1: Our experimental results are available to UT GeoFluids Members as simple spreadsheets that summarize the behavior of mudrocks and provide material properties as a function of depth. They can be used to predict fracture gradient and strength.

Geomechanical Modeling
UT GeoFluids is a leader in the development of forward evolutionary geomechanical models that couple porous fluid flow with deposition and complex geologic loading. We have advanced our fundamental understanding on how salt advance perturbs pressure and stress in nearby sediments, and, in return, how overpressure affects the evolution of a salt system (Fig. 2). We have studied how pressure and stress evolve in fold and thrust belt systems, both in the wedge and footwall sediments. We have demonstrated that both mean and shear stress contribute to porosity and pressure changes. We have identified zones within these systems where drilling risk is high.

We have invented a method to couple seismic velocity with geomechanical modeling to predict pressure and the full stress tensor in complex geologic settings. Our approach incorporates the impact of mean and shear stress on pore pressure and stress. We and several of our industry partners are now applying this approach. We have built software to illustrate the impact of mean and shear stress on pore pressure predictions.

Fig. 2: Coupled evoluationary geomechanical models represent the frontier of basin models. They solve for the full stress tensor, incorporate complex material behavior, and simulate fluid flow and associated overpressure. They are a fundamental advance over uniaxial models (e.g. Temis or Petromod).
Fig. 2: Coupled evoluationary geomechanical models represent the frontier of basin models. They solve for the full stress tensor, incorporate complex material behavior, and simulate fluid flow and associated overpressure. They are a fundamental advance over uniaxial models (e.g. Temis or Petromod).

Field Studies
Our advances are rooted in systematic field studies. We have analyzed pressure and stress in the Mad Dog Field and demonstrated the importance of incorporating mean and shear stress into pressure prediction. We have studied pore pressure at Macondo and showed how lateral flow along the sandstone resulted in the pressure regression at the well location. We have coupled measured velocities with geomechanical modeling at Mad Dog to improve pressure and stress prediction across the field (Fig. 3). We have explored pressure, stress, and porosity evolution in fold and thrust belts.

Figure 3: We enhance pressure and stress prediction by coupling velocities with geomechanical modeling. Prediction using the full stress tensor (FES; (a) in figure) yields a narrower drilling window than the vertical effective stress method (VES; (b) in figure).
Figure 3: We enhance pressure and stress prediction by coupling velocities with geomechanical modeling. Prediction using the full stress tensor (FES; (a) in figure) yields a narrower drilling window than the vertical effective stress method (VES; (b) in figure).

UT GeoFluids

Peter B. Flemings, Jack Germaine, Co-Directors
J.J. Pickle Research Campus
10100 Burnet Rd, Austin, TX 78758
+1 512-475-8738

 

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