Abstract
During water injection, increasing pore pressures and decreasing temperatures imply reductions in effective horizontal stresses, particularly in proximity to injection wells. This unloading can lead to activation of the natural faults and fractures by brittle failure in the body of the reservoir, over- or under-burden, or to the creation of hydraulic fractures in the vicinity of injection wells. These geomechanical changes will be associated with anisotropic permeability changes, usually increases, that should be incorporated into reservoir simulation, particularly with the objective of configuring the original, or infill, well pattern to the best commercial advantage.
Highlights
Geomechanical Influences in Water Injection Projects: An Overview — During water injection, increasing pore pressures and decreasing temperatures imply reductions in effective horizontal stresses, in proximity to injection wells. This unloading can lead to activation of the natural faults and fractures by brittle failure in the body of the reservoir, over- or under-burden, or to the creation of hydraulic fractures in the vicinity of injection wells
The evidences of earthquake statistics, earthquakes triggered by other earthquakes, fault and fracture statistics, intepretations of full in situ stress tensors from image logs, and occurrences of microseismicity during perturbation, all point to stress states in the lithosphere being naturally in a self-organized critical state (e.g. Bak, 1997; Grasso and Sornette, 1998; Sanderson and Zhang, 1999; Townend and Zoback, 2000)
It was found that the areas of low modeled magnitudes of minimum principal stress were collocated with areas of high watercuts in the field, again suggesting the involvement of conductive faults in water breakthrough (Fig. 9)
Summary
Aggregations of data from many field cases of secondary and tertiary floods support the above statements. Heffer and Lean (1993) examined the flood breakthrough characteristics (Fig. 2a) of over 80 fields and determined that the anisotropy of breakthrough was strongly correlated with the local azimuth of maximum principal horizontal stress axis (Fig. 2b and Fig. 3). The data was consistent with the activation, in shear, of natural fractures by the flooding as an explanation for this correlation, even though the natural fractures do not provide an obvious contribution to the initial permeability in the reservoir (i.e. the field may not be “naturally fractured” with its conventional meaning). As waterflooding moves the stress state in the formation towards brittle failure, the permeability is likely to increase. This is certainly true for hard rock formations. Zhu and Wong, 1997) Those experiments have all been run with increasing average stresses; it is arguably more probable that decreasing stress states will cause conductive fractures as they fail in brittle shear. The stress perturbations will be most intense close to injector wells, and the Permeability scale
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
