上扬子地区新地1井五峰组—龙马溪组下段高分辨化学层序地层学与页岩气关系分析

High resolution chemical sequence stratigraphy analysis of Wufeng Formation and Lower Longmaxi Formation in the Well Xindi 1,Upper Yangtze region

【研究目的】本文旨在综合地球化学、高分辨层序地层学理论和方法,探索厚层页岩地层划分对比的化学层序地层新方法,建立上扬子地区新地1井五峰组—龙马溪组下段高精度化学层序地层格架,为研究区页岩气勘探提供科学依据。【研究方法】本研究利用上扬子地区新地1井的岩心、测井及样品分析测试资料,优选出陆源输入强度相关元素组合、自生沉淀强度相关元素组合、有机质吸附及还原强度相关元素组合作为指标体系,进而划分四级化学层序地层。【研究结果】新地1井五峰组划分为LCW层序,龙马溪组下段自下而上细分为MCL1-1、MCL1-2、MCL1-3、MCL1-4四级层序。陆源输入强度相关元素组合总量在层序界面附近相对较高,而最大海泛面附近相对较低;自生沉淀强度及有机质吸附及还原强度相关元素组合总量在层序界面附近相对较低,而在最大海泛面附近相对较高。【结论】不同地化指标体系代表了不同的成因意义,陆源碎屑输入强度和自生沉淀强度越小、有机质吸附及还原强度越大的沉积环境有利于页岩中有机质富集,其旋回性变化对区域海平面变化有相应响应,具有区域一致性,是区域地层对比的重要依据和有力手段。

This paper is the result of geological survey engineering.Objective The purpose of this paper is to synthesize the theories and methods of comprehensive geochemistry and high resolution sequence stratigraphy.The high−precision chemical sequence stratigraphic framework of Wufeng Formation and Lower Longmaxi Formation in Xindi 1 Well,Upper Yangtze region was established to provide scientific basis for shale gas exploration in the study area.Methods We use the core,logging and sample analysis data of Well Xindi 1 in Upper Yangtze region to optimize the indicators system which can divide the chemical sequence stratigraphic.The indicators system contains three elements assemblages:the terrigenous input intensity(TII),the autogenetic precipitation intensity(API),and the organic matter adsorption and deoxidation intensity(ODI).Then the fourth−order chemical sequence stratigraphy is divided by these three elements assemblages.Results Based on the above indicators system,Wufeng Formation of Liutang section is divided into LCW sequence,the lower part of Longmaxi Formation is divided into MCL1−1,MCL1−2,MCL1−3,MCL1−4 fourth−order sequences upwardly.The total amount of elements assemblages related to TII is relatively high near the sequence boundary,but relatively low near the maximum oceanic flooding surface.However,the total amount of element assemblages related to API and ODI are generally lower near the sequence boundary and higher near the maximum flooding surface.Conclusions Representing different genetic significance,the cyclic variation of element assemblages is respond to regional sea level change,and has regional consistency.The sedimentary environment with smaller TII,smaller API and larger ODI is conducive to organic matter enrichment in shale.So it can be used as the basis for regional stratigraphic correlation.