Heavy Oil / Oil Sands
What are Heavy Oil and Oil Sands?
Heavy oil is oil that is not recoverable in its natural state through a well by ordinary production methods and requires heat or dilution. Heavy oil makes up about 15% of the world’s remaining oil reserves. It usually contains impurities such as sulphur, heavy metals, waxes and carbon residue that must be removed before it is refined.
Oil sands are mixtures of sand, water, clay and crude bitumen. Each oil sand grain has three layers: an ‘envelope’ of water surrounding a grain of sand, and a film of bitumen surrounding the water.
Thermal In-Situ Recovery
For both oil sands and heavy oil, steam is often used to facilitate production by softening the bitumen, diluting and separating it from sand grains, and enlarging or creating channels and cracks through which the diluted oil can flow. These techniques recover between 25 and 60% of the bitumen in the reservoir, more than most conventional light crude oil wells.
SeisMovie continuous recording system provides real-time monitoring of SAGD production
The two most successful methods are:
- Steam-assisted gravity drainage (SAGD) which involves drilling two horizontal wells one above the other. Steam is continuously injected through the upper wellbore, softening the bitumen, which then drains into the lower wellbore and is pumped to the surface.
- Cyclic steam stimulation which is a three-stage process involving several weeks of steam injection, followed by several weeks of “soaking” and then the oil is produced by the same wells in which the steam was injected. As production declines, the injection phase is restarted.
Bitumen has also been recovered using cold methods where deposits are considered too thin to make steam injection economical.
CGG recently processed these multicomponent data from a heavy oil survey in Alberta, Canada. The primary objective was to obtain an improved understanding of the reservoir via joint interpretation of the PP and PS images. Note how the reservoir interval is almost transparent on the PP data (left) yet shows clear internal structure on the PS image (right).
CGG has developed many techniques for using seismic data to:
- Increase Productivity:
- Using seismic attributes from petrophysical inversion the shale proportions can be reliably predicted, so that shale plugs can be avoided, as these can cause barriers to the SAGD process.
- Reservoir thickness and depth, including highs and lows on the basal unconformity, can be identified on multicomponent seismic, using PSDM and from stochastic and petophysical inversion.
- 4D seismic, especially permanent reservoir monitoring using SeisMovie, can be used to track the steam front in order to identify the optimum time for re-injection or for positioning new wells, and allowing real-time production decisions to be made.
- Reduce Risk:
- Multicomponent data can be used to map the formation and for reservoir modelling in order to identify the best drilling locations for the wells.
- High water saturation prior to production can be identified from petrophysical inversion.
- Stress and fracture analysis can be used to avoid steam breakthrough