含有机质沉凝灰岩有机质-玻璃质-微孔隙形成演化关系及致密油藏形成意义

Tight oil is the currently domestic and overseas hot field in the exploitation of unconventional oil and gas. The research of its accumulation mechanism is also the international academic frontier of petroleum geology. Tight reservoir of sedimentary tuff containing organic matter is one of the special types of tight oil reservoirs, which is of important scientific significance. But so far we have little knowledge about it. In tuffs containing organic matter, interactions will happen between organic matter and volcanic glass, and further affect the formation and evolution of tight reservoirs. So they are directly related to the prediction of effective reservoirs, accumulation mechanism, and movability evaluation of crude oil in sedimentary tuffs. In this study, tuffs containing organic matter of Permian Tiaohu Formation in Malang Sag, Santanghu Basin, will be researched systematically. First of all, experimental samples will be optimized, and authigenic quartz crystallinity (CI) of them will be tested. In this way, devitrification degrees of tuffs can be determined and reservoir microscopic characteristics can be depicted for the corresponding samples. Secondly, samples with low devitrification degrees will be selected, and sets of simulation experiments will be conducted on them. Experimental conditions are mainly aimed at significantly impact on the role of devitrification such as temperature (maturity), pH (organic acids) and other factors. Then, combined with the actual geological section, we will clarify the devitrification mechanism related to the abundance of organic matter, maturity, organic acids and so on. And we will establish the corresponding geochemical models. On this basis, combined with the tight reservoir characteristics of micro-nanometer pore-throat system (physical properties, micro pore morphology, pores structure and connectivity, etc.), as well as their differences and distribution on the geological section, the influence mechanism of the micro pore-throat system formation and evolution caused by interactions between organic matter and volcanic glass will be clear. Also the corresponding geological models can be established. At last, based on comprehensive analysis of organic matter distribution, evolution of hydrocarbon generation and distribution of crude oil, we can figure out the geological significance of the relationships between organic matter, volcanic glass and micro-pores formation and evolution for formation of tight oil reservoirs of tuff. And this study will provide scientific basis for geological exploration and evaluation of sedimentary tuff tight oil reservoirs.

含有机质沉凝灰岩致密油藏作为致密油藏的一种特殊类型，其有机质-玻璃质相互作用及其对致密储层形成演化的影响，前人研究较少，但科学意义显著。本项目以新疆三塘湖盆地马朗-条湖凹陷二叠系条湖组含有机质沉凝灰岩为例开展研究。首先，优选实验样品，确定脱玻化程度并描述对应的储层微观特征。然后，选取脱玻化程度较低的样品，针对显著影响玻璃质脱玻化过程的温度（成熟度）、pH值（有机酸）等因素，开展系列模拟实验；再结合实际地质剖面，阐明有机质丰度、成熟度、有机酸等影响脱玻化作用的机制，并建立地球化学模型；进而结合致密储层微-纳米孔喉体系特征（物性、微孔隙形貌、孔隙结构与连通性等）及其在地质剖面上的差异性与分布特征，阐明有机质-玻璃质相互作用对沉凝灰岩微观孔喉体系形成演化的影响机制，建立相应的地质模型。最后，综合实验与地质分析、原油分布特征等，揭示有机质-玻璃质-微孔隙形成演化机制对沉凝灰岩致密油藏形成的地质意义

含沉积有机质凝灰岩是三塘湖盆地一种特殊类型的致密储层，对这套致密储层的研究将为我们认识有机质-玻璃质相互作用提供一个很好的机会。本项目通过对二叠系条湖组凝灰岩样品有机地球化学、元素、岩石矿物组成、孔隙类型、石英结晶度和物性等的分析，以及选取脱玻化程度较低的样品，开展系列模拟实验，阐述了有机质-玻璃质相互作用对沉凝灰岩微观孔喉体系形成演化的影响机制，明确了凝灰岩储层微观孔隙形成与演化特征，揭示孔隙演化对凝灰岩致密油藏形成的地质意义。研究表明：条湖组凝灰岩含有沉积有机质，该有机质有一定的生油能力，形成原因主要是火山灰入水后迅速释放营养物质促进藻类勃发造成的，也有陆源有机质的输入。条湖组凝灰岩形成于火山喷发旋回的末期，可以划分为玻屑凝灰岩、晶屑凝灰岩、泥质凝灰岩和硅化凝灰岩，岩石类型受距离火山活动带的远近控制，其厚度分布受火山活动带和沉积古地形共同控制。凝灰岩致密储层的储集空间类型主要是脱玻化作用形成的矿物粒间孔，以微米-纳米级为主，数量巨大。凝灰岩中的原始沉积有机质在演化过程中形成的有机酸有利于脱玻化作用的进行，脱玻化作用是微观孔隙形成的主要原因。火山灰溶解模拟实验表明，火山灰原始组成、溶液PH值和温度是火山灰脱玻化的重要控制因素，其中PH值影响最大。脱玻化形成的单个粒间孔体积小但数量巨大造成了凝灰岩总孔隙度较高，喉道半径小导致渗透率很低。凝灰岩的物性主要受其岩性、脱玻化程度和粘土矿物含量的影响，脱玻化程度可以用石英的结晶度指数来表征。凝灰岩孔隙度的演化有一定的规律，主要受原始物质组成和埋深的影响，条湖组凝灰岩孔隙演化可以划分为正常压实减孔阶段、脱玻化增孔阶段和增孔后演化阶段三个阶段。本项目的研究将对世界其他地区类似凝灰岩储层的孔隙演化和分布预测具有借鉴意义。