多期岩浆侵入事件对长昌凹陷烃源岩热演化的影响

最新研究表明长昌凹陷发育多期岩浆侵入事件。针对多期岩浆侵入事件对长昌凹陷烃源岩热演化的影响尚不明确的问题，文章依据最新地震、地化、钻井等资料，利用地震相技术在凹陷内识别出9个四期岩浆侵入体；在此基础上，运用三维盆地模拟技术对岩浆侵入事件进行热模拟，定量评价多期岩浆侵入事件对凹陷内烃源岩热演化影响。模拟结果表明，岩浆侵入体对烃源岩热演化有促进，但影响范围有限，岩浆体规模与其影响范围有如下规律：岩浆体直径小于2 km，对烃源岩热演化影响范围的半径小于2 km；岩浆体直径大于2 km而小于5 km，影响范围半径小于5 km；岩浆体直径大于10 km而小于20 km，影响范围半径小于16 km。因此长昌凹陷烃源岩主体热演化基本不受岩浆侵入事件的影响，且其可能带来非烃充注风险。结合岩浆侵入体对研究区两口钻井影响的分析，厘定长昌凹陷生烃门限为海底以下2300~2500 m。这些研究为凹陷下一步油气勘探奠定了基础。

The Influence of Multi-stage Magmatic Intrusion Events on ThermalEvolution of Source Rocks in Changchang Sag

The latest studies show that multi-stage magmatic intrusion events occur in the Changchang Sag of the Qiongdongnan Basin, northern South China Sea; however, the influences of these magmatic intrusions on the thermal evolution of source rocks in the Changchang Sag are still unclear. With the latest seismic, geochemical and drilling data, and the seismic facies technology, we identified nine magmatic intrusions of four stages in the sag. We then conducted 3D basin modeling to quantitatively assess the impacts of these magmatic intrusions on the thermal evolution of source rocks in the Changchang Sag. The results indicate that magmatic intrusions can accelerate the thermal maturity of source rocks, but the influence scope is limited. The size of intrusive body and its influence scope have the following rules: when the diameter of the magmatic body is less than 2 km, and the radius of its influence scope is also less than 2 km; the diameter of magmatic body is larger than 2 km but less than 5 km, and the radius of its influence scope is less than 5 km; while the diameter of magmatic body is larger than 10 km but less than 20 km, and the radius of its influence scope is less than 16km. Therefore, magmatic intrusion events do not affect the thermal evolution of source rocks in the Changchang Sag, but they may bring non-hydrocarbon charging risks. Based on the analysis of the influence of magmatic intrusions on two drilling wells in the Changchang Sag, the hydrocarbon generation threshold of the Changchang Sag is determined to be 2300-2500 m below the seafloor. These findings have laid a foundation for next oil and gas exploration in this sag.