Feasibility Studies for Using Seismic Methods to Monitor Steamflooding
Danny R. Melton, P. David Carmichael
Studies to evaluate surface and downhole seismic methods for monitoring enhanced oil recovery have been prompted by favorable laboratory results and encouraging field tests reported in the literature. The laboratory tests show that velocity in heavy oil sands decreases by as much as 40% as the temperature increases from 25° to 150°C. A paucity of published results concerning modeling of realistic steam fronts and/or the response of seismic energy propagation to temperature effects creates a need for feasibility studies.
A subsurface geologic model of a steamflood was constructed, using the integrated efforts of a geophysicist and a reservoir engineer. Well-log data from six closely spaced wells in Kern River field were used to develop a three-dimensional subsurface model. Simulated temperature patterns resulting from steam injection were generated by the reservoir engineer for time periods 1 and 2 years after the initiation of steam injection. The temperature contours were converted to seismic P-wave velocity using published velocity-temperature relations for oil-saturated rocks.
Computer modeling was conducted to obtain both surface seismic images and borehole vertical seismic profiles before steam injection and for time periods 1 and 2 years after injection. Successful seismic modeling of details of the advancing steam front requires frequencies of seismic energy higher than those typically realized in routine exploration applications. Our models do show, however, that the gross effects of low-velocity zones can be seen at all frequencies. Fortunately, the shallow depths and close well spacing associated with enhanced oil recovery are amenable to the higher frequencies required for increased resolution of the low-velocity zone itself.
AAPG Search and Discovery Article #91035©1988 AAPG-SEPM-SEG Pacific Sections and SPWLA Annual Convention, Santa Barbara, California, 17-19 April 1988.