珠江口盆地文昌X-2油田新近系珠江组低阻油层成因机理

珠江口盆地文昌X-2油田珠江组发育一套低阻油层,该套油层电阻率与水层电阻率非常接近,给储层流体识别和含水饱和度计算带来较大困难,目前其低电阻率成因机理尚不够明确。基于铸体薄片、CT扫描、X衍射等实验分析资料,结合地质、测井资料和导电数值模拟技术,从宏观与微观角度对低阻油层的成因机理进行了详细分析。研究结果表明:若条带状分布的泥质含量高于20%,泥质在岩石中连续性较好,可提供较好的导电网络,因此油层电阻率仍然低于1.6Ω·m,与水层差距不明显。低幅度构造和浅海沉积环境是低阻油层形成的主要宏观成因,复杂孔隙结构、细岩石粒度、高束缚水饱和度、高含量且条带状分布泥质是低阻油层形成的主要微观成因。

Genetic Mechanism of Low-Resistivity Neogene Zhujiang Formation in Wenchang X-2 Oilfield of Pearl River Estuary Basin

A set of low-resistivity oil reservoirs is developed in the Zhujiang Formation of Wenchang X-2 Oilfield in the Pearl River Estuary Basin.Resistivity of the oil reservoirs is very close to that of the water layers,which creates challenges in identifying reservoir fluids and calculating water saturation.At present,the genetic mechanism of these low resistivity oil reservoirs is yet to be clear.Based on mercury injection,nuclear magnetic resonance,casting thin section,CT scan,X-ray diffraction and other experimental analyses,and integrated with geological and well-log data and electrical conductivity numerical simulation technology,the genetic mechanism is analyzed from both macro-and micro-scale perspectives.The results show that if the banded shale content is above 20%,the rocks(with the shale)have a good continuity and can provide good conductive network.The resistivity of the oil reservoirs is below 1.6Ω·m,and the resistivity differences between oil reservoirs and water layers are not distinct.Low-amplitude structures and shallow-sea sedimentary environment are the major macroscopic causes of the low-resistivity oil reservoirs.Complex pore structure,fine rock granularity,high irreducible water saturation,high banded-shale content are the major microscopic causes of low-resistivity oil reservoirs.