龙门山地区中泥盆统观雾山组岩相古地理恢复
龙门山地区中泥盆统观雾山组岩相古地理恢复 熊连桥 姚根顺 倪超 熊绍云 周刚 王键 郝毅 中国石油勘探开发研究院 中国石油杭州地质研究院 中国石油天然气集团公司碳酸盐岩储层重点实验室 中国石油西南油气田公司勘探开发研究院 振华石油控股有限公司 摘 要： 川西地区近期部分井的油气勘探发现显示, 龙门山地区中泥盆统观雾山组发育展布良好的白云岩储层, 但受龙门山断裂带推覆影响, 观雾山组地层展布特征仍然认识不清、岩相古地理研究仍处于定性分析阶段。为厘清川西龙门山地区中泥盆统观雾山组岩相古地理特征:首先, 基于平衡剖面技术定量恢复了龙门山断裂带北、中、南 3 段的剖面, 建立起野外露头点现今位置与初始位置之间的函数关系, 恢复了露头点的推覆距离, 认为龙门山断裂带总体推覆距离约 40 km, 地层展布恢复后, 观雾山组在彭灌古岛与都江堰之间存在一个沉降中心, 观雾山组整体呈西厚东薄、南厚北薄的分布趋势;其次, 以恢复后的观雾山组地层展布为基础, 通过野外实测、岩心及测井资料综合分析, 重建了龙门山地区观雾山组岩相古地理特征。研究发现, 龙门山地区中泥盆统观雾山组岩石类型以白云岩 (粉晶-细晶白云岩、砾屑-角砾白云岩、生屑白云岩和生物白云岩) 为主, 局部发育灰岩 (泥晶灰岩、生屑灰岩和生物灰岩) 及少量的碎屑岩与碳酸盐岩混合沉积;识别出台地边缘礁滩相、开阔台地相和局限台地相 3 种主要的沉积相类型;台地边缘礁滩相分布于桂溪大木垭地区, 开阔台地发育在 K2 井、擂鼓镇、龙王庙一带, 局限台地位于彭灌古岛宝兴古岛以东至上扬子古陆之间的地区;随着海平面上升, 台地边缘礁滩相呈现出向东迁移的趋势。关键词： 龙门山; 中泥盆统; 观雾山组; 平衡剖面; 地层展布; 岩相古地理; 作者简介：熊连桥, 男, 1986 年 10 月生, 2009 年获中国石油大学 (北京) 地质工程专业学士学位, 现为中国石油勘探开发研究院博士研究生, 主要从事油气地质综合研究。Email:xionglianqiao163.com收稿日期：2017-03-27基金：国家重大科技专项 (2016ZX05004-002) Lithofacies palaeogeography restoration of the Middle Devonian Guanwushan Formation in the Longmenshan areaXiong Lianqiao Yao Genshun Ni Chao Xiong Shaoyun Zhou Gang Wang Jian Hao yi PetroChina Research Institute of Petroleum Exploration and Development; PetroChina Hangzhou Institute of Geology; Exploration and Development Research Institute, PetroChina Southwest Oil China Zhenhua Oil Company Limited; Abstract： Through the recent oil-gas exploration of some wells in the western Sichuan area, it is found that the dolomite reservoirs with favorable distribution are developed in the Middle Devonian Guanwushan Formation of Longmenshan area.But due to the nappe impact from Longmenshan Fault Belt, the distribution characteristics of Guanwushan Formation are still obscure, and the study on lithofacies paleo-geography is still in a stage of qualitative analysis.To clarify the lithofacies paleo-geographic characteristics of the Middle Devonian Guanwushan Formation in Longmenshan area of the western Sichcuan, the following two steps have been conducted: (1) The three profiles, i.e., the north profile, the central profile and the south profile, of Longmenshan Fault Belt are quantitatively restored based on the balanced section technique, so as to create the function relationship between current location and initial location of field outcrop point and restore the nappe distance of outcrop point.It is considered that the total nappe distance of Longmenshan Fault belt is about 40 km, and after the restoration of stratigraphic distribution, there is a subsidence center between Pengguan Paleo-island and Dujiangyan of the Guanwushan Formation.On the whole, Guanwushan Formation tends to be thicker in the west while thinner in the east and thicker in the south while thinner in the north. (2) Based on the stratigraphic distribution of Guanwushan Formation after restoration, the lithofacies paleo-geographic characteristics of Guanwushan Formation in Longmenshan area are reconstructed by field measurement and comprehensive analysis on core and well-logging data.Meanwhile, the study shows that the rock types of the Middle Devonian Guanwushan Formation in Longmenshan area are dominated by dolomite (silty crystal-fine grain dolomite, gravel-brecciated dolomite, bioclastic dolomite and biogenic dolomite) ;in local area are developed limestone (micrite, bioclastic limestone and biogenic limestone) and a small a-mount of mixed sediments consisting of clastic rocks and carbonate rocks.Three main sedimentary facies types are identified, including platform-margin reef flat facies, open platform facies and restricted platform facies.The platform-margin reef flat facies is distributed in Guixi-Damuya area, the open platform is developed in Well K2-Leigu Town-Longwangmiao, while the restricted platform is located in the areas between the east of Pengguan Paloe-island-Baoxing Paleo-island and the Upper-Yangtze Paleo-land.As the sea level rising, the platform-margin reef flat facies shows the tendency of eastward migration.Keyword： Longmenshan; Middle Devonian; Guanwushan Formation; balanced profile; stratigraphic distribution; lithofacies paleo-geography; Received： 2017-03-27四川盆地大部分地区缺失泥盆系, 在川西龙门山地区, 泥盆系南北长、东西窄, 沿龙门山断裂带呈条带状展布1。在四川盆地的油气勘探实践中, 泥盆系长期被作为油气勘探的潜在层系2-3, 针对泥盆系的油气勘探局面一直未打开。随着川西北部下二叠统油气勘探的开展, 部分井对二叠系下伏地层的跟踪研究表明川西北部地区泥盆系观雾山组白云岩存在良好的油气勘探前景3。尤其在2016 年, ST3 井对中泥盆统观雾山组测试获得日产超过 1×10m 天然气, 油气勘探的突破燃起了众多学者对龙门山地区观雾山组白云岩储层研究的兴趣。早期钻探的 K2 井观雾山组主要为灰岩, 出现气测异常;TJ1 井观雾山组主要为细晶白云岩, 出现气侵, 说明川西地区观雾山组具备储集流体的条件。通过ST3 井对观雾山组取心, 学者们认识到观雾山组存在台地边缘礁滩沉积, 意味着川西地区观雾山组可能存在规模更大的优质储层。天井山泥盆系古油藏早已进入学者们的视野, 并且具备寒武系、志留系优质烃源岩供烃4, 筇竹寺组泥岩在北川至青川一带厚度达 600 m 以上5, 川西北矿山梁地区低成熟沥青具有较强的产气潜力, 是一种重要的生气有机母质6;中泥盆世末期, 全球规模的海平面上升7-8为区域盖层的发育创造了条件, 总体看来, 川西龙门山地区观雾山组具备良好的天然气成藏条件。然而, 川西龙门山地区观雾山组埋深超过 7 000m, 野外露头多沿龙门山断裂带分布, 盆地内仅有数口井钻遇泥盆系, 地震资料局限在川西北部盆地内, 对川西地区观雾山组地层分布特征认识不清, 整体对观雾山组的研究程度还很低。关于川西龙门山地区观雾山组的沉积相, 刘文均等9认为, 龙门山地区泥盆系处于裂陷盆地沉积环境;马永生10认为, 观雾山组沉积期, 龙门山地区属于陆缘盆地, 但是研究对象尺度过大, 仅对川西地区观雾山组沉积相类型及分布进行了简要概括, 并未对观雾山组沉积相进行详细描述;还有学者将观雾山组划分为碳酸盐缓坡沉积1,11-12, 并将观雾山组自下而上划分为生
