沉积学报2025，Vol.43Issue(2)：750-768,19.DOI:10.14027/j.issn.1000-0550.2023.016
天文周期驱动下湖相细粒沉积岩有机质富集模式
Organic Matter Enrichment Model of Lacustrine Fine-grained Sedimentary Rocks Driven by Astronomical Cycles:A case study of the lower Es3 and upper Es4 sub-member in well LY1,Dongying Sag
摘要
Abstract
[Objective]The lacustrine fine-grained sedimentary rocks in Dongying Sag have great prospects for un-conventional oil and gas resources.However,owing to the small grain size,rapid phase transition,and difficult iden-tification of sequence interface,the traditional sequence stratigraphy cannot accurately divide and contrast the strata.At present,the understanding of the organic matter enrichment model is unclear,limiting the progress of unconven-tional oil and gas exploration.Cyclostratigraphy can divide high-frequency sequences and conduct a fine stratigraphic correlation,and can also explore the process of fine-grained rock deposition driven by astronomical cycles,which is an important means to establish the organic matter enrichment model and predict the sweet spot of shale oil.[Methods]Taking well LY1 in Dongying Sag,Bohai Bay Basin,as an example,the cyclostratigraphy of lacustrine fine-grained sedimentary rocks in the lower Es3(Es3l)and upper Es4(Es4u)sub-member were analyzed based on core,geochemical analysis,and natural gamma logging data.[Results](1)The results show that this set of strata records good astronomical period signals,Es3 is mainly controlled by eccentricity and precession period,and Es4 is mainly controlled by eccentricity and obliquity period.During the deposition of Es3l,the thickness of sedimentary cycles con-trolled by 405 kyr long eccentricity,100 kyr short eccentricity,and 20 kyr precession were 46.34 m,14.20-12.23 m,and 2.64-2.09 m,respectively;while during that of Es4u,the thickness of sedimentary cycles controlled by 405 kyr eccentricity,40 kyr obliquity,and 20 kyr precession were 30.54 m,4.00-3.01 m,and 1.83-1.23 m,respec-tively.From Es4u to Es3l,the driving and controlling factors of sedimentary cycle gradually changed from the obliquity to precession cycle.(2)A 39.40-43.47 Ma absolute astronomical time scale was established using stable 405 kyr eccentricity astronomical tuning,with the top age of Es3l at 39.40 Ma as the anchor point.The high-precision astro-nomical time scale restricted the depth of the response to the Miocene Climatic Optimum event of 3 604.2-3 652.1 m,which wasin a warm and humid period,and the lithofacies shows the concentrated development of interbedded lime-stone.(3)Using the temporal properties of cyclostratigraphy,the filter curves of long eccentricity,short eccentrici-ty,and obliquity were used as the reference curves for the fourth,fifth,and sixth order sequence divisions,respec-tively,and ten fourth-order sequences and forty fifth-order sequences were identified.Furthermore,the long eccen-tricity cycle with significant regional contrast characteristics was used as the scale for linking well correlation,and the high precision isochronous stratigraphic framework of the whole area was established.[Conclusions]Astronomi-cal cycles control"source rock preservation conditions"by influencing lake level changes and"organic matter produc-tivity"by influencing terrigenous input.Therefore,the astronomical cycle theory has been introduced to reveal the relationship between mud shale formation and the evolution of climate change,total organic carbon content,and other indicators and establish the sedimentary model under the control of cycles to predict sweet spot intervals,pro-viding a theoretical basis for sweet spot prediction in thick mud shales.By discussing the response of fine-grained sedimentary rocks to eccentricity and precession cycles,we proposed that the organic matter enrichment model under both warm and wet and dry and cold climate conditions,considering that the maximum eccentricity value is beneficial to organic matter enrichment.The climate change caused by eccentricity and precession is the main mechanism of lacustrine high frequency cycle deposition and controls the development of hydrocarbons.This study not only guides shale oil exploration and development in Dongying Sag but also provides theoretical support for unconventional oil and gas exploration in other continental lacustrine basins.关键词
东营凹陷/旋回地层学/细粒沉积岩/天文年代标尺/高频层序/有机质富集Key words
Dongying Sag/cyclostratigraphy/fine-grained sedimentary rocks/astronomical time scale/high-frequency sequence/organic matter enrichment分类
天文与地球科学引用本文复制引用
王浡,石巨业,朱如凯,梁新平..天文周期驱动下湖相细粒沉积岩有机质富集模式[J].沉积学报,2025,43(2):750-768,19.基金项目
国家自然科学基金项目(42102150)[National Natural Science Foundation of China,No.42102150] （42102150）
