Geomechanics approach to management of naturally fractured reservoirs
- New Mexico Institute of Mining and Technology, ALbuquerque, NM (United States)
- Sandia National Labs., Albuquerque, NM (United States)
Fractures are present in almost all hydrocarbon reservoirs, but it is only when fractures form an interconnected network that their affect on fluid flow becomes important. Fractures not only enhance the overall permeability of many reservoirs, they also create significant permeability anisotropy. Geologists commonly assume that the horizontal permeability anisotropy will be elongate along the dominant trend of subsurface natural fracture systems. Although this can be demonstrated to apply in many simple geologic settings, this predictive concept must commonly be modified for stress changes caused by the post-fracture geologic history of the reservoir. In cases where the local stresses and fractures are superimposed on regional stresses and fractures, the fractures that are parallel to the in-situ maximum horizontal stress may provide the dominant control on reservoir permeability. This can occur even if the stress-parallel fractures are significantly fewer in number than fractures that trend oblique to the maximum horizontal stress, especially where the stress anisotropy is high. The set of fractures that is open and conductive may change with position around a structure as a function of local stress variations. Knowledge of subsurface fracture trends must be used in conjunction with knowledge of the in-situ stress orientations and magnitudes to predict horizontal permeability anisotrophy. Fracture reservoir permeability may also change over the life of a reservoir because perturbations in stress state, caused by drilling, production, and waterflood activities, create changes in the three-dimensional effective stress field, and thus in fracture conductivity. These conclusions are supported by core analyses, in-situ stress measurements, well tests, and production histories of several reservoirs, including naturally fractured reservoirs in North Sea chalk, carbonates in Texas and Alaska, and sandstones in Colorado and Wyoming.
- OSTI ID:
- 54859
- Journal Information:
- AAPG Bulletin, Journal Name: AAPG Bulletin Journal Issue: 11 Vol. 78; ISSN 0149-1423; ISSN AABUD2
- Country of Publication:
- United States
- Language:
- English
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