南海北部大陆边缘盆地地热特征与油气富集

Geothermal characteristics and hydrocarbon accumulation of the northern marginal basins,South China Sea

本文报道了莺歌海盆地、北部湾盆地共148个新测热导率数据,根据收集的钻井温度数据新增计算65个大地热流数据;结合前人研究成果绘制了南海北部大陆边缘沉积盆地的地温梯度图、大地热流分布图;系统归纳了南海北部大陆边缘油气勘探成果.结果表明,南海北部大陆边缘珠江口盆地、琼东南盆地、北部湾盆地、莺歌海盆地的平均热流值分别为68.7±11mW/m2、71.1±13mW/m2、65.7±8.9mW/m2、74.7±10mW/m2,属于典型的"热盆".热流区域分布特征总体上受大地构造背景控制,随地壳厚度从北向南,由陆架到陆坡区逐渐减薄而增高,水热活动与岩浆活动等是引起局部高热流异常的原因.盆地地温场的差异控制和约束了油气分布富集规律,从研究区油气勘探成果中可以发现,该区域的气田多发育于高热流盆地(凹陷),而中-低热流盆地(凹陷)则多孕育油田,油气田具有"北油南气"的分布特征.

A total of 65new heat flow values were calculated in terms of newly determined thermal conductivity and collected temperature logging data.Using these data coupled with those from previous studies,we have constructed a geothermal gradient map as well as a heat flow map for the northern marginal basins of the South China Sea.Furthermore,geothermal characteristics of these basins and their relationship with oil and gas field distribution were analyzed.The results show that the four sub-basins located in the northern South China Sea,namely Pearl River Mouth Basin,Qiongdongnan Basin,Beibuwan Basin and Yinggehai Basin,are typical＂hot basins＂with average heat flow values 68.7±11mW/m2,71.1±13mW/m2,65.7±8.9mW/m2,74.7±10mW/m2,respectively.The overall heat flow distribution pattern in the study area,which gradually increases from the shelf to the slope consistent with crust thinning trend,are generallycontrolled by regional tectonic setting,meanwhile some high local heat flow anomalies are likely to be attributed to faults and magmatic activity.The geothermal field may control and restrict oil and gas accumulation in the study area.Inlight of exploration results from these basins,we find that the gas fields are mostly located in the high heat flow basins（depressions）while the oil fields are more likely to be present in basins with relatively lower heat flow values（depressions）.