Print this pageGeochemical Sampling Assisting Target Evaluation in Northern South China Sea
CHEN, HAN-ZONG and DI ZHOU
Geochemical sampling has been conducted to assisting target evaluation in northern South China Sea Since 1989. Sub-bottom sediments, near-bottom seawater, and sea-surface air were sampled in 5 cruises; about 50 geochemical indices were determined; anomalies were delineated via robust statistical methods. In the Yinggehai Basin, YA13-1 and LD15-1 gas fields, LT13-1 barren structure and a background area were sampled as training sets for the evaluation of 9 traps. In the Zhujiangkou (Pearl Mouth) Basin, HZ21-1, HZ27-1, and LF22-1 oil fields, HJ32-1 barren structure were sampled as training sets for the evaluation of traps in east Dongsha area and Xiapeng Depression. On board determination of mercury contents in seawater and sea-surface air was realized for the first time by use of a gold-film detector.
Clear geochemical anomalies were found over all of the known oil/gas fields sampled, in a strong contrast against barren structures. Characteristics of anomalies are variable with field type and/or location. In general, the most effective geochemical indices are gaseous hydrocarbon, total scanning fluorescence (TSF), and mercury, assisted by soluble hydrocarbon, phenol, ordinary fluorescence, and carbon isotopic ratios. Composite anomalies closely related to oil/gas fields are characterized by various associations of methane-heavy gaseous hydrocarbon anomaly, X-, Q-, and O-type finger-print of TSF, intensity anomaly of fluorescence, mercury anomaly, and soluble methane and phenol anomaly. Among 27 traps evaluated, 4 have been tested by drilling. Only one turns out different from our suggestion.