In-Situ Evaluation of Vapor Properties Using Condensed Vapor Gamma
- Terence P. O'Sullivan (Aera Energy LLC)
- Document ID
- Society of Petrophysicists and Well-Log Analysts
- Publication Date
- August 2015
- Document Type
- Journal Paper
- 334 - 345
- 2015. Society of Petrophysicists & Well Log Analysts
- 0 in the last 30 days
- 75 since 2007
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Gamma-ray (GR) logs from infill wells in heavy-oil development projects frequently exceed 1,000 GAPI, but only through the hot vapor cloud that develops as injected steam displaces heavy oil. GR values in the same sands that are liquid-filled, and immediately below the vapor- filled rock, are typically less than 100 GAPI. Previous work showed that high GR values are caused by drilling-related cooling of vapor-filled rock. Gamma-ray values are thought to increase when water and hydrocarbon molecules approach the dewpoint and condense around a chilled well. As solubilized radon concentrates in these droplets, GR values can increase by ≥100x. After the chilled well begins to reheat and equilibrate with the hot reservoir (36 hours or less) GR values return to normal levels. An experiment demonstrated that the cycle of GR increase and decrease can be repeated indefinitely, simply by chilling the well and then allowing it to warm back.
To put the condensed vapor gamma (CVG) effect into context, logs from thousands of heavy-oil development wells from two large oil fields of the San Joaquin Valley, California, were systematically reviewed.
The observations suggest that it is possible to develop a method for in-situ evaluation of vapor properties. Although the condensation-induced gamma signal has only been documented to occur in wells drilled in heavy-oil steamfloods, the effect could occur in any reservoir containing condensable vapor, provided that the vapor can be cooled to the dewpoint.
Controlled generation of CVG in the laboratory is a logical next step toward improved understanding of this phenomenon. Continuous in-situ observation and monitoring of CVG is also recommended in order to explore the linkage between CVG and development activities.
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