Summary
Production decreases the pore-fluid pressure and increases the effective
stress acting on the load-bearing-grain framework that makes up the reservoir.
As a result, the reservoir deforms and compacts, and because it is connected to
the rocks around it, there will be deformations and displacements in these
rocks also. Well known geomechanical effects of production include surface
subsidence, wells damaged by shear, and time shifts in 4D seismic. Less well
known is how the changes in the stress field itself should be taken into
account in operations - e.g., to design infill wells and to plan production
stimulation by hydraulic fracturing or waterflooding of the reservoir.
We present a geomechanical model for the initial stress field and
production-induced stress changes in and around a steeply dipping hydrocarbon
reservoir penetrated by two large salt domes. The model integrates 3D seismic
and geological understanding, geomechanical data from wells and analogues, and
depletion patterns from fluid-flow (dynamic) simulation. Our model results
confirm published models of principal-stress orientation in rocks pierced by
salt domes. The depleted-model results show stress changes up to several MPa in
magnitude compared with the preproduction stress state, but only limited
changes in the stress orientations. The model highlights the influence of
structural dip and time-dependent salt/sediment interaction on stress
changes.
We then describe the application of the model in wellbore stress analysis
for infill wells and in a water-injection scheme that has, we believe, been
severely impacted by injection-induced fractures propagating in the reservoir
from the injector wells toward the producer wells. We explain how the latter
application uses a 3D flow-simulation model coupled to a dynamic
fracture-propagation model. The geomechanical model provides key input: stress
magnitude and stress orientation. Results are validated against a more
conventional analysis of real-time pressure data.
In both applications, the integration of geomechanics in 3D static and
dynamic models improved insight into the rock response to drilling and
waterflooding, thus helping to optimize production.
© 2011. Society of Petroleum Engineers
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History
- Original manuscript received:
10 August 2010
- Meeting paper published:
15 June 2010
- Revised manuscript received:
16 December 2010
- Manuscript approved:
25 January 2011
- Published online:
25 October 2011
- Version of record:
13 March 2012
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