Geomechanic models using finite element methods show how Cooper Basin structure and sand body geometry impacts stress variation and hydraulic fracturing results
Nicole Ditty A and Dennis Cooke AAustralian School of Petroleum, The University of Adelaide.
The APPEA Journal 55(2) 439-439 https://doi.org/10.1071/AJ14074
Published: 2015
Abstract
Unconventional reservoirs such as tight sands and shales require hydraulic fracture stimulation to improve productivity. The success of reservoir stimulation is controlled by the local stress field but decisions are often made knowing only the average stress field.
This study uses geomechanical modelling to help explain lateral stress variability using structural geology, lithology contrast and boundary conditions. Changes in vertical and horizontal stresses are related to depth, lithology and structural position, yet these effects are not always accounted for. This is evident in the Cooper Basin, Australia, where, for example, unexpected changes in minifrac pressure are commonly observed in adjacent wells in a field. This study presents results from conceptual geomechanical models to help explain such variations in stress.
Model scenarios are constructed using finite element package to investigate the impact of structural position, rock mechanical properties and stress regime on the patterns of horizontal and vertical stress magnitudes in a layered antiform sequence. Key findings suggest that:
stress magnitude is affected by structural positioning;
different patterns of stress exist across different lithologies; and,
stress regime impacts on patterns of stress, especially in combination with curvature of structures.
These challenge traditional methods of one-dimensional mechanical earth models and show that, rather than employing methods developed for simple layer-cake geology in extensional basins, geomechanical models should be constructed in two- or even three-dimensions. Results of this study highlight part of the solution to the unconventional resource potential of the Cooper Basin. Improved prediction of field-scale stress variations should enable further optimisation of hydraulic fracture stimulation treatments.
Nicole Ditty graduated from the University of Adelaide with qualifications in civil engineering (honours) and science. She joined an Adelaide-based consultancy as a geoscientist, where she got her first experience with geomechanics. She chose to return to study, starting a masters in petroleum engineering and undertaking research as part of the Australian School of Petroleum’s GeoFrac consortium. Nicole has held positions on SPE, YPP and APOGCE committees. She is working as a fracture stimulation engineer at Santos Ltd in Adelaide while continuing her post-graduate research part-time. |
Dennis Cooke divides his time between two endeavours: GeoFrac, an industry-sponsored research consortium, at the University of Adelaide’s Australian School of Petroleum and his own geophysical technology business. Dennis’ past positions include chief geophysicist at Santos and interpreter and QI technical support at Arco International. Dennis has been the vice president of the SEG and president of the ASEG. His professional society focus is on providing technical education to early career geoscientists. He received a PhD in geophysics from the Colorado School of Mines and an undergraduate degree in geology from the University of Colorado. |
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