Seismic pursuit of wormholes

Abstract

Cold production has become increasingly popular in the extraction of heavy oil, due to the development and widespread use of progressing cavity pumps—essentially powerful augers that suck both oil and sand into the well. At the onset of production, these pumps produce about 60% oil and 40% sand. However, production can improve to 95% oil with only 5% sand after a few months. This increase in oil production and reduction in sand production is attributed to the development of high-porosity tubes termed “wormholes.” Roche (2002) describes wormhole development as the creation of a network of “horizontal wells without using a drilling rig.” Operators who plan infill drilling rely on wormhole distribution information to optimize well spacing. It is accepted that aggressive cold production of oil sands will increase oil recovery, and this has been demonstrated in several pools, both in Alberta and Saskatchewan. So, assuming these induced sand channels can boost cold heavy oil production, can we map them? That's a good question because wormholes have small dimensions compared to seismic wavelengths, making their seismic detection extremely difficult. This challenge caused us to perform feasibility tests based on a number of models from the literature. The following describes the results of these tests. We also show some real seismic data with promising indications for wormhole imaging. Much heavy oil recovery in Western Canada involves steam injection. Time-lapse seismology plays a major role in monitoring steam fronts and time-lapse or “4D seismology” is now a standard reservoir characterization tool. However, steam production/injection is costly, and heavy oil production now increasingly uses cold flow techniques. As stated earlier, cold production methods use special pumps, known as progressing cavity pumps (Figure 1). These pumps, similar to an auger or “Archimedes screw” within a flexible sleeve, lift the oil/sand mixtures from the producing formation …