珠江口盆地惠州凹陷主力烃源岩测井预测及评价

Prediction and evaluation with logging of main source rocks in Huizhou Sag,Pearl River Mouth Basin

利用惠州凹陷文昌组与恩平组声波时差、自然伽马、电阻率、密度和中子孔隙度等测井参数对烃源岩有机碳含量(TOC)的响应特征,建立了单井及惠州凹陷综合的五元回归定量预测模型。应用该模型对12口钻井进行了泥质烃源岩TOC测井预测,获得了这些井文昌组、恩平组烃源岩连续的TOC曲线,并按陆相泥质烃源岩评价标准计算了好与很好、中等与差烃源岩的厚度。结果表明,TOC预测结果相对误差大多在20%内,且单井模型略优于综合模型。层位上,恩平组中等烃源岩厚度比例在50%以上,其次为差烃源岩,好烃源岩厚度占比一般低于20%;文昌组好与很好烃源岩厚度比例大多高于75%,因此文昌组烃源岩整体优于恩平组。横向上,惠西半地堑最优,惠东半地堑次之,惠南半地堑与惠北半地堑烃源岩相对不够发育。烃源岩测井预测纵向分辨率高,但受钻井分布所限难于揭示烃源岩空间展布。测井约束下综合地球物理烃源岩评价应具有更广阔的应用前景。

The prediction models of 5 variate regression equation for individual well and the Huizhou Sag were built according to the response relationship of TOC to the well logging values of sonic transit time, natural gam-ma, resistivity, density and neutron porosity from the Wenchang and Enping Formations. By using these predic-tion models, the organic carbon content of mudstone source rocks of the Wenchang and Enping Formations of 12 wells was calculated, and the thickness of source rocks of different ranks, including good and very good, middle and poor, was obtained according to the evaluation criterion of mudstone source rocks in Chinese lacustrine ba-sins. Most relative errors of TOC predicted by well logging are less than 20%, and the prediction results from in-dividual well model are better than those from collective model. In the Enping Formation, the source rocks of middle rank take higher percentage than 50% in thickness for most wells, poor source rocks take subdominant, and good and very good source rocks just take lower percentage than 20% in thickness. In the Wenchang Forma-tion, good and very good source rocks take higher percentage than 75% in thickness for most wells, and middle and poor source rocks just account for very small proportion in thickness. So, as main source beds in the Huizhou Sag, the Wenchang Formation is more favorable than the Enping Formation. Among 4 half-grabens of Paleogene developed in the Huizhou Sag, the western Huizhou half-graben is most favorable for source rock generation, the eastern Huizhou half-graben less, and the northern and southern Huizhou half-grabens poorest. Limited by well distribution, it is difficult to characterize the spatial distribution of source rocks even though the vertical resolu-tion of logging is high. The predication and evaluation of source rocks with the method of well-constrained com-prehensive geophysics should illustrate a wider prospect of application.