--> Abstract: New Geochemical Technologies to Reduce The Risk in Gas Exploration ; #90063 (2007)

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New Geochemical Technologies to Reduce The Risk in Gas Exploration

Moldowan, J. Michael1, Zhibin Wei1, Jeremy Dahl1 (1) Stanford University, Stanford, CA

Several new technologies have been developed that can be used to improve gas prospecting, as follows:

(1) Quantitative diamondoid analysis of oils, sediments and piston cores, for recognizing oil to gas cracking, evaporative fractionation and reservoir seal leakage. Petroleum that carries signatures of extensive cracking (abundant diamondoids) together with significant stigmastane concentrations is recognized using quantitative diamondoid-biomarker analysis as mixed from post-mature and normally-matured sources. Liquids showing high cracking profiles provide evidence of gas migration.

(2) Compound specific isotope analysis of diamondoids (CSIAD) provides a fingerprint that may neither be altered by extreme catagenetic conditions in the source rock nor by alterations in the reservoir, such as those that occur during thermochemical sulfate reduction (TSR), thermal cracking and biodegradation. Post-mature, TSR-altered and biodegraded liquids may be correlated with non-altered oils of normal maturity. CSIAD is the most specific way to correlate oil with highly mature condensate, as a proxy for associated gas, and thus provide information about gas provenance in a basin. Mixtures of black oil and cracked condensate often occur, but are seldom recognized (except using diamondoids). The cracked component in such mixtures can be correlated by using CSIAD.

(3) Thiadiamondoids can be used for determining and quantifying the extent of TSR, which can play an important role in oil destruction. Clues to the occurrence of TSR are available from a variety of methods, but thiadiamondoid analysis offers a definitive approach, since the formation of thiadiamondoids requires TSR conditions.

 

Applications from several regions will be used to illustrate.

 

AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California