西湖凹陷平北地区煤系烃源岩识别与分布

Identification and distribution characteristics of coal-bearing source rocks in Pingbei area,Xihu Sag

西湖凹陷平北地区平湖组煤系烃源岩发育煤、炭质泥岩、泥岩3种岩性。为明确煤系烃源岩的发育与展布特征,并确定优质烃源岩发育的关键因素,首先通过对平北地区煤系烃源岩地球化学特征的分析与有效烃源岩的评价,建立烃源岩岩性测井识别模型,然后结合岩性分布与泥岩TOC含量预测结果,明确研究区煤系烃源岩的发育特征与分布规律。结果表明:研究区平湖组煤和炭质泥岩为优质烃源岩,TOC质量分数>1.0%的泥岩为有效烃源岩;煤系烃源岩的有机质类型以Ⅱ—Ⅲ型为主,普遍达到低熟—成熟阶段;煤系烃源岩的分布明显受古水深控制,平湖组中段沉积期发生海侵作用,有利于煤系烃源岩发育,煤的沉积中心多分布于隆间洼地,炭质泥岩与煤具有共生关系,有效泥岩随水深增加而变厚;平北地区古地形特征及生长断层的活动速率可影响局部水体变化,为优质煤系烃源岩发育的关键因素。该研究成果对西湖凹陷平北地区的生烃潜力评价、有利区预测具有一定指导意义。

The coal-bearing source rocks of Pinghu Formation in Pingbei area,Xihu Sag,have three kinds of litho-logy:coal,carbonaceous mudstone and mudstone.In order to clarify the development and distribution characteri-stics of various coal-bearing source rocks,and determine the key factors for the development of high-quality source rocks,through the analysis of geochemical characteristics and the evaluation of effective source rocks of coal-bearing source rocks in Pingbei area,the lithologic logging identification model was established.Combined with the prediction results of lithology distribution and TOC content of mudstone,the development characteristics and distribution law of coal-bearing source rocks in study area were clarified.The results show that:the coal and carbonaceous mudstone of Pinghu Formation are high quality source rocks,and the mudstone with w(TOC)>1.0%are effective source rocks.Organic matter types of coal-bearing source rocks are mainly Ⅱ-Ⅲ types,generally reaching low maturity to maturity stage.The distribution of coal-bearing source rocks is obviously controlled by Paleo water depth.Transgression occurred in the middle part of sedimentary period of Pinghu Formation,is conducive to the development of coal-bearing source rocks.The sedimentary centers of coal are mostly distributed in the depression between uplifts;besides,the carbonaceous mudstone and coal have symbiotic relationship.The effective mudstone thickens with the increase of water depth.The Paleotopography and the active rate of growth faults in Pingbei area affect the local water bodies,which are the key factors for the development of high-quality coal-bearing source rocks.The research results have guiding significance for hydrocarbon generation potential evaluation and favorable area prediction in Pingbei area,Xihu Sag.