影响碳酸盐岩盖层有效性的岩石力学性质研究

The effectiveness of cap rocks is one of the key factors in hydrocarbon accumulation. The current exploration and deployment, however, mainly relies on reservoir prediction results, not enough attention paid on cap rocks is the main reason that results in failure of many wells. Exploration has proved that carbonate rock can be not only reservoirs, but also caps. Study on the mechanism of carbonate cap rock is extremely important for the evaluation of marine petroleum resource as well as the determination of exploration direction. The mechanical properties of carbonate rock will experience brittle ductile transition with the change of the buried depth at the process of structural evolution. This project applies physical property test, X ray diffraction, triaxial rock mechanics experiment and rock CT scan methods to focus on the underground conditions of brittle to ductile transition of carbonate rocks under certain confining pressure and temperature, to understand the characteristic and micro structures of fractures in brittle and ductile state respectively and analysis the sealing capacity affected by such difference, sealing capacity of carbonate cap rocks in different structural evolution stages was deeply analyzed combined with stratigraphic burial history. The main controlling factor of effective carbonate cap rock will be determinated in North Slope of Tazhong uplift in Tarim Basin. The research results not only have an important theoretical significance to further understand the sealing mechanism of carbonate cap rocks, but also have practical significance on enriching evaluation methods of marine hydrocarbon resources and improving the reliability of exploration.

盖层有效性是制约油气成藏的关键要素之一，但目前勘探部署主要借助于储层预测结果，对盖层没有足够的重视是造成部分井失利的直接原因。勘探实践证明，碳酸盐岩不仅可作储集体，还可以作油气盖层，对碳酸盐岩盖层有效性的研究在海相层系油气资源评价和勘探方向的确立方面非常重要。在构造演化过程中随着埋深的变化碳酸盐岩力学性质会发生脆延性转换，本项目从岩石力学角度采用物性测试、全岩X射线衍射、三轴岩石力学实验和全岩CT扫描等方法，重点研究碳酸盐岩在一定围压和温度下发生脆延性转换的地质条件，了解在脆性和延性状态下碳酸盐岩所发育的裂缝性质和微观结构差异及其对封盖有效性的影响，结合地层埋藏史，深入分析不同构造演化阶段碳酸盐岩盖层封闭能力，确定塔中北坡碳酸盐岩有效盖层的主控因素。本项目研究结果不仅对深入了解碳酸盐岩盖层封闭机理具有重要的理论意义，同时对丰富海相油气资源评价方法和提高勘探可靠性也将具有一定的现实意义。

盖层的发育演化是油气藏得以保存的最为重要的因素，目前针对盖层和保存方面开展了不少研究，但大多数研究成果都来自于对泥页岩和蒸发岩等传统优质盖层，缺少对碳酸盐岩盖层有效性的研究。为了揭示碳酸盐岩盖层在油气成藏中的作用，本文针对塔中北坡中、下奥陶统碳酸盐岩盖层有效性开展研究。运用平衡剖面和构造物理模拟实验方法对塔中北坡构造演化及断裂成因机制进行了解剖；通过地震、测井、岩心和薄片四个尺度对碳酸盐岩特征进行了分析；利用三轴压缩岩石力学实验方法确定了碳酸盐岩脆-延性转换条件，并揭示了影响其力学性质发生变化的主控因素；运用地球物理方法对有效盖层进行了分布预测；在此基础上对储盖组合进行了优选。通过对塔中北坡运动学过程的剖析，结合物理模拟实验方法揭示了基底剪切滑动与塔中隆起沿I号断裂带的差异推挤是塔中北坡NE向走滑断层发育的关键，NE向走滑断层是破坏盖层完整性与整体性的重要因素。识别出塔中北坡主要发育一间房组上段高GR段、鹰山组上段高GR段和鹰山组上段高阻段等三套碳酸盐岩盖层。运用不同围压和温度状态下的三轴压缩岩石力学实验方法，确定了塔中北坡奥陶系不同层位的碳酸盐岩盖层的脆-延性转换深度；奥陶系一间房组泥晶灰岩在地下4900m时处在脆-延性转换状态；鹰山组灰岩脆-延性转换的地下深度确定为6700米，并确定了白云石含量以及石英含量的增加使泥晶灰岩盖层脆-延性转换深度增加，且石英含量比白云石含量对碳酸盐岩脆-延性转换的影响更大。项目资助下发表论文5篇，提交一项发明专利，参加国际会议2次，培养硕士研究生2名，其中1名已经取得硕士学位，1名在读。项目预算经费20万元，支出17.7446万元，结余2.2554万元，结余经费将在后续研究中执行完毕。

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