Oil recovery factors for many of the world's oil fields have improved over the years, but implementing new technologies, expanding existing technologies to other reservoirs, and understanding the processes better can improve recovery further. That can be gleaned from many of the papers presented at the Society of Petroleum Engineers and US Department of Energy 13th Symposium on Improved Oil Recovery last month in Tulsa.
Water, steam, and carbon dioxide gas injection remain the more common ways for improving recoveries, but various research and pilot projects aim to adapt these methods to a greater variety of reservoirs and refine the processes so that they are more predictable.
Air injection in lighter oil reservoirs, horizontal injectors that rejuvenate mature miscible floods, alkaline-surfactant-polymers, and water-alternating-gas in the North Sea were among the topics discussed at the symposium.
Presentations
R.G. Moore, of the University of Calgary, discussed work at the university that indicated air injection has considerable potential in fields that produce lighter-gravity crude oil, especially in areas without an existing infrastructure for delivering CO2 for injection. He said the process will work as long as operators inject sufficient quantities of air and determine beforehand if the oil will spontaneously ignite.
In another Canadian paper, by K. A. Edwards et al., Conoco Canada Ltd.-formerly Gulf Canada Resources Ltd.-discussed the benefits gained from reinitiating hydrocarbon miscible flooding with horizontal injectors and reduced well spacing in the South Swan Hills Unit in northwestern Alberta. South Swan Hills produces from a carbonate reef with an OOIP of 850 million bbl.
They said four patterns have been developed to date; the first two have completed solvent injection and are now on chase-water injection. Recovery has been 800,000-900,000 bbl/pattern of incremental oil, or more than 10% of pattern OOIP from areas that were part of the original miscible flood.
In the pattern, the horizontal well is low in the pay section to allow sweeping of that part of the reservoir that was missed because of gravity override during injection into vertical wells.
A paper by Clara Hernández, et al., of Petroleos de Venezuela SA described how single-well chemical tracer tests measured residual oil saturation in a zone before and after it had been swept by alkaline-surfactant-polymer (ASP) fluid. ASP injection reduced residual oil saturation at the well to 13-19% from 28-34% at Lagomar VLA-6/9/21 Area, C4 Member, Lake Maracaibo, Venezuela.
Simultaneous water-alternating-gas improved oil recovery in Siri field off Denmark, the subject of a paper by Lars Inge Berge et al., of Statoil AS. The authors indicated that the main contribution of the process comes from improved sweep, oil swelling, and reduced residual oil saturation, although maintaining injectivity is a main concern with the method.
In the process, the associated produced gas is mixed with injection water at the wellhead and injected as a two-phase mixture. Statoil has used the process from the start of production in Siri field in 1999.
