断陷湖盆低勘探区源-汇系统与烃源岩预测

Source-to-sink system and hydrocarbon source rock prediction of underexplored areas in rifted lacustrine basins： A case study on northern lows in Zhu Ⅰ Depression， Pearl River Mouth Basin

刘豪 徐长贵 高阳东 林鹤鸣 邱欣卫 剧永涛 汪旭东 李磊 孟俊 阙晓明

Hao LIU Changgui XU Yangdong GAO Heming LIN Xinwei QIU Yongtao JU Xudong WANG Lei LI Jun MENG Xiaoming QUE

烃源岩是沉积盆地含油气系统中决定油气聚集与成藏的关键因素之一。针对盆地或洼陷中勘探程度相对较低、钻井较少且烃源岩指标不丰富等烃源岩预测的难点，以珠江口盆地珠一坳陷北部低勘探区为例，从“找湖（深湖-半深湖）”、“寻泥（深湖-半深湖泥岩）”、“定烃（烃源岩预测与评价）”的角度，开展源-汇系统与烃源岩预测系统性分析。首先，以“找湖”为目的，通过多期构造古地貌恢复，阐明原始盆地面貌与古湖盆发育位置，结合“地震前积确定湖盆边界、坡折体系确定深湖-半深湖分布范围、生化指标确定湖盆古环境特征、构造强度确定湖盆规模”等分析，对低勘探区的深湖-半深湖区进行确认并对潜在发育烃源岩的洼陷进行初步遴选，研究认为文昌期HF33等洼陷和下恩平期HZ5等洼陷具备发育深湖-半深湖泥岩的潜力。其次，通过古物源、古环境和沉积体系的分析，结合构造古地貌发育特征，开展源-汇系统重建及深湖-半深湖相泥岩发育的地质背景分析，通过源-汇系统各配置要素的数值模拟，指出中等物源供给强度、细物源粒度、高湖平面、大可容空间及欠补偿-均衡补偿型盆地有利于富泥型湖泊相沉积。最后，以成熟勘探区已钻遇优质烃源岩的钻井为基础，分析与烃源岩层对应的4类深湖-半深湖地震相及其地质背景，构建成熟区“烃源岩相（烃源岩地震相）”，结合对珠一坳陷主要富烃洼陷富烃要素的系统总结，开展低勘探区优质烃源岩多因素、多维度评价与最终排序。通过研究，指出LF22，HF33，HZ24（上、下文昌组），LF7和HZ10（下文昌组）等洼陷为Ⅰ级潜在富生烃洼陷；HZ5和HZ11洼陷（下恩平组）为Ⅱ级潜在生烃洼陷。部分洼陷烃源岩的预测和评价结果在实际勘探中已得到证实。

Hydrocarbon source rock is one of the key factors controlling oil/gas accumulation in petroliferous system of a sedimentary basin. Focusing on the challenges facing hydrocarbon source rock prediction in basins or lows with relatively low exploration maturity， sparsely distributed drilling wells and insufficient source rock index， we take the underexplored areas in northern Zhu Ⅰ Depression in the Pearl River Mouth Basin （PRMB） as an example to systematically analyze the source-to-sink system and predict source rocks from the perspectives of “searching for lake （deep-to-semi-deep lake）”， “recognizing mudstones （deep-to-semi-deep lacustrine mudstones）”， and “identifying hydrocarbon （hydrocarbon source rock prediction and evaluation）”. First， the original basin features and location of the paleo-lacustrine basin are illustrated by restoring multi-stage tectono-palaeogeomorphology to “find the lake”； and the deep-to-semi-deep lake is identified in the underexplored area together with preliminary selection of potential lows with well-developed hydrocarbon source rocks in combination with analyses including “identifying the lacustrine basin boundary by seismic progradational reflection， determining the scope of the deep-to-semi-deep lake by slope break system， illustrating paleo-environment characters by biochemical index， and defining the lacustrine basin scale by tectonic intensity”. The results indicate that five lows formed during the Wenchang depositional period， and five lows formed during the depositional period of the lower Enping Formation have the potential of developing deep-to-semi-deep lacustrine mudstones. Second， the reconstruction of source-to-sink system and the geological analysis of deep-to-semi-deep lacustrine mudstone development are conducted through analyses of paleo-provenance， paleo-environment and depositional systems， as well as tectono-palaeogeomorphology features； various configuration elements simulation results of the source-to-sink system show that basins characterized by medium sediment supply intensity， fine-grained source materials， high lake level， large accommodation space and under-equal or equal compensation are favorable for the deposition of mud-rich lacustrine facies. Finally， based on data of exploratory wells encountering high-quality hydrocarbon source rocks in mature exploration areas， we analyze four types of deep-to-semi-deep seismic facies and their geologic backgrounds corresponding to hydrocarbon source rock intervals， establish the “hydrocarbon source rock facies （seismic facies of hydrocarbon source rocks）” of the mature exploration areas. Coupled with the systematic summary of hydrocarbon-enrichment factors in main hydrocarbon-rich lows of the Zhu Ⅰ Depression， we assess and rank the high-quality hydrocarbon source rocks in the underexplored areas with multiple factors and from multi-dimensional points of view. The research results also indicate that the first-order potentially hydrocarbon-rich lows include LF22， HF33， and HZ24 （with the lower and upper Wenchang Formation as source rocks）， as well as the LF7 and HF10 （with the lower Wenchang Formation as source rocks）； the second-order potentially hydrocarbon-rich ones are HZ5 and HZ11 （with the lower Enping Formation as source rocks）， with the hydrocarbon source rock prediction and evaluation results of some lows having been testified in practical exploration.

10.11743/ogg20230304