琼海凸起不同电阻率油藏原油特征及成藏过程

Differences of Crude Oil in Low and High Resistivity Reservoirs and Processes of Reservoir Forming in Qionghai Swell in Western Pearl River Mouth Basin

对比琼海凸起低电阻率与高电阻率油藏原油特征发现,相对于高电阻率油藏,低电阻率油藏原油的密度和含硫量较低,成熟度稍高,生烃母质含有较多陆源有机质且氧化程度更高,为富含黏土矿物。琼海凸起低电阻率与高电阻率油藏有着不同的成藏过程:早期生成的以文昌B凹陷文昌组原油为主的混合原油,优先充注到琼海凸起下部充注压力较小的高渗透储集层,形成了高电阻率油藏;随着高电阻率油藏逐渐趋于饱和,晚期大量生成的以文昌A凹陷恩平组原油为主的混合原油,充注到琼海凸起上部充注压力较大的低渗透储集层,形成了低电阻率油藏。琼海凸起广泛发育的低电阻率油藏指示其周缘生烃凹陷具有较大的生烃强度,是今后勘探的重点。

The widespread Low-resistivity oil reservoirs in Qionghai swell in western Pearl River Mouth basin of South China Sea are often associated with the underlying high-resistivity reservoirs.This paper makes comparisons of the crude oils from such two types of reservoirs,and suggests that the low-resistivity reservoirs are normally lower in oil density and sulfur content,with slightly higher maturity,more terrigenous organic matters in kerogen and enriched clay mineral deposited in an oxidizing environment,and such two types of crude oils have different reservoir-forming processes： the early formed mixed oil dominated by the Wenchang oil is preferential to charge into underlying high-permeability reservoir with low charging pressure,thus forming high-resistivity oil reservoirs;with more and more oil saturation of high-resistivity reservoir,the great amount of late formed mixed oil dominated by Enping oil of Wenchang-A sag is then charged into the upper low-permeability reservoirs with higher charging pressure,thus forming low-resistivity oil reservoirs.It is concluded that the wide distribution of the low-resistivity oil reservoirs in Qionghai swell indicates its surrounding or marginal hydrocarbon-generating sags should have higher hydrocarbon-generating intensity and be regarded as targets for further petroleum exploration.