典型陆相页岩油层系成岩过程中有机质演化对储集性的影响

doi:10.11743/ogg20190501

摘要/Abstract

摘要： 在简要评述泥页岩层系成岩作用及微纳米孔隙发育特征研究现状基础上，选择渤海湾盆地古近系沙河街组和准噶尔盆地二叠系芦草沟组为实例，围绕陆相富有机质泥页岩层系成岩作用特点及储集空间发育机制进行了分析讨论，重点聚焦于有机质的成岩（生烃）演化过程对储集空间发育的影响。结果表明，早成岩作用阶段，随着成岩压实作用的进行，页岩层系孔隙度显著降低，特别是粗介孔向细介孔转化，致使中-细介孔相对增加；至早成岩作用末期和中成岩作用阶段（东营凹陷3 000~3 700 m深度），在有机质早期生烃等作用的影响下，孔隙度出现新的峰值；此后，成岩压实又占主导地位，孔隙度又急剧下降，但酸性流体溶蚀形成的次生孔隙增多，微米级孔隙增加。酸性流体的溶蚀作用在沙河街组已有所显示，但以芦草沟组最为突出，是储集空间形成的主要原因。对芦草沟组主要储集岩的地球化学分析表明，有机碳含量越高的样品，其碳酸盐矿物的δ¹³C值越偏负，次生溶蚀孔隙也越发育。因此，富有机质页岩层系的成岩作用与一般泥页岩的成岩作用有显著差异，生烃作用形成的有机酸和酸性CO₂等对储层的溶蚀改造和优化具有重要意义，是控制页岩油“甜点”发育的主要因素之一。

关键词: 有机质, 成岩作用, 储集空间, 陆相, 页岩层系, 页岩油

Abstract: Following a review on the research progress of diagenesis and micro-and nano-scale pore development of shale sequences,we take the Paleogene Shahejie Formation in Bohai Bay Basin and the Permian Lucaogou Formation in Junggar Basin as examples to analyze the diagenetic characteristics and reservoir space forming mechanism of organic-rich continental shale sequences.The study focuses on the effect of diagenetic (hydrocarbon-generating) evolution on reservoir space development.The results show that the porosity of the shale decreases significantly along with compaction at the early diagenetic stage; this is especially shown in the transformation from macro-pores to micro-pores,resulting in the relative increase of mesoporosity-microporosity.As of the end of early and the middle diagenetic stages,the porosity may reaches a new peak value at a depth of 3000m to 3700m in Dongying Sag,under the impact of early hydrocarbon generation of organic matters.And then as compaction comes to dominate again,the porosity decreases sharply,even though secondary micro-porosity increases due to acid fluid dissolution.The dissolution of acid fluids occurs in the Shahejie Formation,but it turns to be dominant in the Lucaogou Formation,a major reason for the formation of reservoir space.Geochemical analyses on rock samples from the Lucaogou Formation show that the samples with higher TOC generally have a lower content of δ¹³C in carbonate minerals,and a higher secondary dissolution porosity.Therefore,the diagenesis in organic-rich shale sequences is significantly different from that in ordinary shales.The organic acids and acidic CO₂ accompanying the hydrocarbon generation are of great significance to the modification and improvement of reservoir quality by dissolution,and also major factors controlling the distribution of shale oil sweet spots.

Key words: organic matter, diagenesis, reservoir space, continental facies, shale sequence, shale oil

中图分类号:

TE122.2

胡文瑄,姚素平,陆现彩,等. 典型陆相页岩油层系成岩过程中有机质演化对储集性的影响[J]. 石油与天然气地质, 2019, 40(5): 947-956,1047. doi: 10.11743/ogg20190501 Hu Wenxuan,Yao Suping,Lu Xiancai,et al. Effects of organic matter evolution on oil reservoir property during diagenesis of typical continental shale sequences[J]. Oil & Gas Geology, 2019, 40(5): 947-956,1047. doi: 10.11743/ogg20190501

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