| Seismic time-lapse monitoring of subsurface fluid flow consists of acquiring multiple seismic surveys at a single site, repeated at time intervals in which interesting subsurface fluid movement can take place. Integrated with fluid-flow simulation, geology, rock physics and reflection seismology, time-lapse seismic images can illuminate fluid-flow paths and barriers, and the movement of pressure, temperature, and saturation fronts in the subsurface. Seismic monitoring provides the exciting new possibility of directly imaging where and how fluids are flowing in the Earth.; I develop mathematical relationships that link the theories of fluid flow, rock physics, and reflection seismology. Given an initial description of reservoir geology, I combine fluid-flow simulations, rock physics measurements, and seismic modeling and imaging, to estimate the feasibility of monitoring subsurface fluid flow from surface seismic data. In a case study of the Troll Field offshore Norway, I predict that gas coning from a horizontal oil depletion well should be visible in seismic monitor data for realistic noise levels, survey errors, and acquisition geometry. I process six 3-D seismic field surveys acquired in time-lapse mode over a steam injection site in the Duri Field, Sumatra, Indonesia. Estimated changes in seismic velocity and impedance contrasts between surveys are explained with an integrated interpretation combining fluid flow, core data, and seismic analysis. I find anticipated seismic velocity decreases and impedance changes in the vicinity of the steam injector which correlate with the presence of a hot steam-saturated zone. I find unanticipated seismic velocity increases radiating away from the injector which I interpret to be a transient pressure front. Since the pressure transient propagates much quicker than the thermal and fluid fronts, monitoring its early progress could be a powerful technique to map in situ permeability and predict future flowpaths of fluids and heat. |
