CLASSIFICATION OF SOME NEW-ZEALAND CRUDE OILS AND CONDENSATES BY MEANS OF THEIR TRACE-ELEMENT CONTENTS

Sixteen trace elements (Al, As, Br, Cl, Co, Cr, Eu, Fe, La, Mn, Mo, Ni , Sb, Sc, V and W) were determined in 36 crude oils and condensates fr om New Zealand sedimentary basins, mostly from the Taranaki Basin. Con centrations of Al correlated strongly with ''clay mineral'' elements s uch as Cr, Fe, La, Mn, Mo and Sc. This indicated that most of the trac e elements were bound in entrapped clay fractions. Although a Ni vs. V plot did not allow for effective discrimination of different oils and condensates because the number of Ni values (6) was so small, the abu ndances of both elements were extremely low and in the same range of v alues as Chinese non-marine oils. Principal components analysis of the data showed that two components (involving 15 elements) accounted for 66.9% of the variance of the system. A mutual plot of these two compo nents indicated that the Maui-1 offshore oil and the Waiotapu and Kotu ku seepage oils were separate from the main group of crudes from the T aranaki Basin.