塔里木盆地顺南—古城地区方解石脉流体来源及其对油气成藏的启示

The fluid origin of calcite veins in Shunnan-Gucheng area of Tarim Basin and its implications for hydrocarbon accumulation

钻井揭示塔里木盆地顺南—古城地区奥陶系碳酸盐岩方解石脉发育,为探讨该区断裂带流体属性及油气成藏事件提供了重要素材。在详细的岩心观察基础上,开展了方解石脉的流体包裹体以及灰岩基质与方解石脉的地球化学特征对比研究。方解石脉具有多类型的烃类包裹体,包括沥青包裹体、三相烃包裹体、油水液相包裹体以及富气包裹体。方解石脉中与烃类包裹体共生的盐水包裹体具有较高的均一温度(130~160℃)。贫18O(δ18O=-13.1‰^-8.7‰)、富87Sr(87Sr/86Sr=0.708879~0.710432)、偏高稀土元素总量和正铕异常表明构造成因方解石脉主要来源于围岩的溶解以及成岩—成烃流体,未发现大气淡水参与的迹象。方解石脉中富含烃类包裹体可能表明研究区北东向走滑断裂带是油气运移与聚集的重要通道。

The high-angle,structural genetic calcite veins of the Ordovician in Shunnan-Gucheng area in Tarim Basin provide a convenient to study the fluid properties and hydrocarbon migration to accumulation events in fault zone of this area.Based on detailed core investigation,studies of fluid inclusions in calcite veins and com⁃parison of geochemical characteristics of limestone matrix and calcite veins were carried out.Multiple types of hydrocarbons inclusion,including dry asphalt inclusion,three-phase hydrocarbon inclusion,oil and water inclu⁃sion,gas-rich inclusion,were found in calcite veins.And the coexisted aqueous inclusions with gas-liquid phase had high homogenization temperature(130-160℃).The distribution characteristics of 18O-depleted(δ18O:−13.1‰to−8.7‰),87Sr-enriched(87Sr/86Sr:0.708879 to 0.710432),relatively high total Rare Earth Ele⁃ments and positive Europium Anomalies indicated that the structural origin of calcite veins were mainly derived from the dissolution of surrounding rocks and diagenetic-hydrocarbon fluids.Participation signs of meteoric wa⁃ter were not proved.The rich hydrocarbon inclusions in the calcite veins indicated that the north-east strike-slip fault zone in Shunnan-Gucheng area is an important channel for hydrocarbon migration and accumulation.