四川盆地高石梯地区震旦系灯影组四段硅质岩成因及地质意义

Abstract: Plenty of drilling practices prove that the reservoirs of Sinian Dengying 4 Member, Gaoshiti area of central Sichuan Basin, are related to weathering crust karst. Mainly distributed at 100 m below the topmost Dengying Formation, they are of strong heterogeneity, resulting in hard correlation. Located at 20-50 m below the topmost formation, the upper submember is commonly developed with tight siliceous rocks. And the siliceous-rock effect on reservoir development and distribution has not been made clear. So, the siliceous-rock genesis was investigated by means of core and elemental analysis, and thin-section observation. Results show that (1) these siliceous rocks are mainly composed of laminar algal, dolomitic, and pure siliceous rocks, featured by low-moderate thickness and layered with ribbon and banded structures; (2) with some logging response like high resistivity, low neutron, and low interval transit time, they can be identified easily and correlated in plane. The thickness of Gaoshiti area in the range of 5-25m increases gradually from west to east gradually; and (3) in these siliceous rocks, SiO2 content is mostly higher than 90%. Furthermore, there is more Fe and Mn, and poor Mg, Al, and Ti. The content of trace elements varies a lot, and Ba and Sb are rich. It’s concluded that these rocks are originated from hot-water deposition, and their basement is just the isochronous sedimentary boundary inside the upper submember. By taking this basement as a stratigraphic-corrected standard interface, the karst palaeogeomorphology may be rebuilt, and the isochronous stratigraphic framework can also be established to implement fine correlation and to determine spatial distribution for reservoirs. And a karst model can be defined on the basis of research results on faults and bioherm beach bodies. Keywords: Sichuan Basin; Central Sichuan Basin; Late Sinian; Siliceous rock; Origin; Hot -water deposition; Reservoir distribution
Luo Wenjun1, Xu Wei1, Zhu Zhengping2, Liu Xixiang1, Wang Qiang2, Shen Yan1 and Zhu Xun1 (1. Exploration and Development Research Institute, PetroChina Southwest Oil & Gasfield Company, Chengdu, Sichuan 610041, China; 2. PetroChina Southwest Oil & Gasfield Company, Chengdu, Sichuan 610051, China; 3. Shale Gas Research Institute, PetroChina Southwest Oil &Gasfield Company, Chengdu, Sichuan 610051, China)
关键词 四川盆地 川中地区 晚震旦世 硅质岩 成因 热水沉积 储层分布 DOI: 10.12055/gaskk.issn.1673-3177.2019.03.001
Origin of siliceous rocks in Sinian Dengying 4 Member, Gaoshiti area, Sichuan Basin
第 42 卷 第 3 期
天然气勘探与开发
地质勘探
Hale Waihona Puke 四川盆地高石梯地区震旦系灯影组四段 硅质岩成因及地质意义
罗文军 1 徐 伟 1 朱正平 2 刘曦翔 1 王 强 3 申 艳 1 朱 讯 1
1. 西南油气田分公司勘探开发研究院 2. 西南油气田分公司 3. 西南油气田分公司页岩气研究院
摘 要 大量钻井证实，四川盆地中部高石梯地区震旦系灯影组四段储层与风化壳岩溶相关，主要发育在灯影组顶界之下 100 m 以内，储层非均质性强，对比难度大。上亚段普遍发育硅质岩，位于灯影组顶界之下 20 ～ 50 m，由于硅质岩普遍致密， 对储层发育及分布的影响尚不明确，有必要对其成因开展研究。通过岩心、薄片观察及元素分析，结果表明：①该套硅质岩以藻 纹层硅质岩、含云硅质岩和纯硅质岩为主，薄到中厚层状，普遍具条纹、条带状构造；②具有高电阻、低中子、低声波时差的测 井响应特征，易识别，平面可对比，高石梯地区厚度介于 5 ～ 25 m，自西向东逐渐增厚；③ SiO2 含量多在 90% 以上，其他氧化 物含量低，Fe、Mn 相对富集，Mg、 Al、Ti 相对贫乏，微量元素含量变化大，富含 Ba、Sb 等元素。研究结果认为：该套硅质岩 为热水沉积成因，其底界为灯四上亚段内部等时沉积界面。此认识对后续工作非常重要，可将硅质岩底界作为地层对比标准界面， 据此可恢复岩溶古地貌，可建立等时地层格架进行储层精细对比、明确储层空间展布，可结合断裂及丘滩体研究成果明确岩溶模式。