Mancos Shale In-situ Stress Estimation and Fracture Simulation Across the Uinta Basin

Trevor Stoddard, Lauren Birgenheier, John McLennan, and Justin Wriedt
University of Utah

Accurate hydraulic fracturing simulations require an adequate knowledge of the in-situ stress state. The stress levels regulate vertical growth, spatial complexity, and treating pressures during hydraulic fracturing. With a few exceptions, stress information in the Mancos Shale in the Uinta Basin is sparse. Stress data were acquired from the literature, from diagnostic injection methodologies and from treatment records. These were contoured to a 4-dimensional volume to be utilized in optimizing Mancos Shale hydraulic fracturing operations across the Uinta Basin. Gradients estimated from treatment reports from instantaneous shut-in pressure (ISIP) values were compiled into a set of matrices along with breakdown pressure and average pressure for 103 wells across the Uinta Basin. Formation Micro-Imaging (FMI) log-based borehole breakout data from above and below the Mancos indicate a consistent NNE-SSW minimum in-situ principal stress direction. Limited diagnostic fracture injection test (DFIT) data provided representations of the minimum in-situ principal stress and aided in calibration of calculated values. A 4-dimensional volume presenting these values across the basin was generated using MATLAB© software. A logging-based approximation to estimate rock mechanics properties such as Young's modulus and Poisson's ratio (and the corresponding stresses) lithologically has also been incorporated to aid in property estimation for hydraulic fracture simulations in commercially available software. Using the MATLAB© created volume and contour slices the fracture gradients across the basin were used in hydraulic fracture simulations using commercially available software. The purpose is to infer relevant characteristics of stimulation treatments and how to best stimulate the Mancos Shale to optimize production. Natural discrete fracture networks (DFN) have been created in the Mancos using FMI logs and bootstrap statistics. The addition of the DFN to the production simulations within the hydraulic fracturing simulation software adds to the accuracy of the production predictions. A further correlation between the most prospective stratigraphic intervals and lithofacies will add consistency to these overall predictions, with the final goal being the ability to efficiently stimulate the Mancos Shale to maximize production.

AAPG Search and Discovery Article #90169©2013 AAPG Rocky Mountain Section 62^nd Annual Meeting, Salt Lake City, Utah, September 22-24, 2013