CHARACTERISTICS OF LIGHT HYDROCARBON IN OIL SEEPING ROCKS IN THE HONGHUAYUAN FORMATION OF ORDOVICIAN, HOUBA, ZUNYI

Oil seepage and bitumen have been found in biocalcarenite in the Honghuayuan Formation of Ordovician in Houba,Zunyi.Gas/source rock and bitumen/source rock comparisons have indicated that,light hydrocarbon C₆₊₇ compositions in the Sinian,Cambrian and Ordovician productive formations are almost the same.Star maps of light hydrocarbon in Ordovician oil seeping limestone,Sinian mudstone and Cambrian bitumen sandstone are similar,which means that,oil seepages in the Honghuayuan Formation mainly come from over mature and high mature marine source rocks in the Lower Palaeozoic.Petroleum migrates for a long distance and is reserved in Ordovician.A set of special oil-bearing composition and an exploration field with the O₁h fossil weathered residuum reservoir as the target may exist.To the west of Xingwen-Xuyong,reservoir and cap formation are kept well in the Lower Palaeozoic.Accumulation may be found in proper tectonic traps.Light hydrocarbon C₆₊₇ compositions in Silurian and Permian are quite different from those in Sinian,Cambrian and Ordovician with incomparable star maps,indicating the differences between hydrocarbon generation parent and deposition environment.