南堡凹陷厚层泥岩的封盖作用及期与油气的关系

CAPPING OF THICK MUDSTONES AND ITS RELATIONSHIP WITH OIL AND GAS IN THE NANPU DEPRESSION

南堡凹陷下第三系内共发育了 5套厚层泥岩 ,属中 -深湖相沉积 ,具有分布广、厚度大、含砂率低等特点 ,对热、流体形成有效封盖作用 ,导致其内部及下伏地层高古地温梯度、高矿化度以及深蚀作用等异常带发育 ,同时也是研究区异常高压发育的主要原因之一。厚层泥岩内能形成岩性油气藏 ;它们的封盖作用增强了异常带内的热演化 ,促进了有机质的热成熟和生烃作用发生 ;深蚀作用使异常带内砂岩次生孔隙发育 ,改善了储层物性 ;厚层泥岩封盖作用评价对分析深部 ( 4 0 0 0m以下 )含油性提供了理论依据 ;根据北堡和老爷庙地区异常热流体活动特征合理推测了超压分布 ,对油气勘探具有重要的指导意义。

There are five sets of thick mudstones with wide distribution and low sediment change in the Lower Tertiary of the Nanpu Depression, which were deposited in medium-deep lake environment. The mudstones show efficient capping on thermal flux and hydrocarbon fluid, which results in development of high paleogeothermal gradient, high salinity and deep corrosion in the interior of mudstones and underlying formation. It is the main cause for formation of overpressure. Some lithologic hydrocarbon pools can be formed in the thick mudstones. As a result of its capping, thermal evolution of organic matter in abnormal belts was enhanced and hydrocarbon was generated. Deep corrosion accelerated forming of secondary pores in sandstones in the abnormal belt, so physical properties of reserviors was improved. A reasonable prediction of overpressure based on abnormal hydrothermal fluid activity in Beipu-Laoyemia area provided important guide for hydrocarbon exploration in the area.