塔中北坡走滑断裂对碳酸盐岩油气差异富集的控制机理

Nearly one billion tons of oil equivalent have been proven in Ordovician carbonates on the northern slope in the Tazhong Low Rise. Controlled and complicated by strike-slip faults, oil and gas are distributed in a large area, and featured by heterogeneity of quasi-layered reservoir beds, while the proportion of high performance wells is less than 30%. The key issue in this project is the control mechanism of strike-slip fault on differential hydrocarbon enrichment in carbonates, which can be sub-divided into two aspects: one is the origin of segmental small-scale NE-trending strike-slip faults, the other is constraint on prioritized migration direction of hydrocarbon by strike-slip faults. The research includes identification of segmental strike-slip fault and its origin, confirmation of oil and gas infill points under the control of strike-slip faults, and constraint on selective hydrocarbon migration by strike-slip faults. Key technologies used are attribute analysis of 3-D seismic data and strike-slip faults recognition through high-density interpretation, fracture identification through imaging logging, pathway system modeling through both combination of geology and geochemistry and combination of static data and dynamic production testing data, and physical modeling experiments of oil-bearing structures. The unique feature of this project is applied basic research for extension to international frontier, with multi-disciplinary synergy, and close connection with exploration and development practice. The research results will have great significance in enriching the theory of hydrocarbon play in marine origin carbonates, clarifying the mechanism of differential hydrocarbon enrichment, optimizing and implementing high performance well blocks, and achieving high success rate and effectiveness of hydrocarbon exploration and development.

塔中北斜坡奥陶系碳酸盐岩中发现油气储量近10亿吨油当量，油气大面积、多层叠置、准层状分布，为走滑断裂控制和复杂化，高效井比例不足30%。本项目关注的关键科学问题是走滑断裂对碳酸盐岩油气差异富集的控制机理，进一步分解为北东向小尺度走滑断裂分段的成因机制和走滑断裂对油气优势运移方向的制约作用两个方面。研究内容包括走滑断裂分段性识别及成因机制、走滑断裂控制下的油气注入点确认、走滑断裂对油气选择性运移的制约作用三个方面。关键技术包括三维地震数据体属性分析及高密度解释走滑断裂识别技术、成像测井裂缝识别技术、地质与地球化学结合和静态资料与动态试采资料结合的输导体系建模技术、构造物理模拟实验技术。本项目的特色是拓展国际前沿、多学科联合、紧密结合勘探开发部署的应用基础研究。研究成果对于丰富海相碳酸盐岩油气成藏理论、明确油气差异富集机理、优选和落实高效井区、提高油气勘探成功率和开发成效具有十分重要的意义。

塔中隆起寒武-奥陶系海相碳酸盐岩厚度大、分布面积广，勘探结果显示油气水分布规律十分复杂。多个油气层之间有水层、同一个含油气区块内油气井之间有出水井，这些现象宏观上无法用传统的石油地质理论解释清楚，严重影响了后续的勘探开发进程。基于新的三维地震资料，发现了走滑断裂，且其起到了改造储层、输导油气、分割区块的作用。本项目针对核心科学问题，设置主要研究内容为：走滑断裂分段性识别及成因机制研究（包括主干走滑断裂延伸性及其与次级断裂的组合关系；主干走滑断裂分段点识别与分段划分；走滑断裂分段的成因机制）、走滑断裂控制下的油气注入点确认（井间油气性质及地球化学参数变化规律研究，从运移方向追寻油气来源；井间试采动态数据变化规律研究，从输导网络追踪油气来源；相关地球化学参数耦合与油气注入点确认）、走滑断裂对油气选择性运移的制约（包括走滑断裂破碎带或伴生裂缝带发育特征，垂向运移通道；走滑断裂倾向变化与地层倾向的组合方式，侧向运移通道及效应；走滑断裂控制下的油气分块差异富集模式）。通过4年的研究，明确了走滑断裂是塔中北斜坡油气分块富集的边界，断裂分段的转折点是油气注入口。在每一个块体内油气水正常分异，在块体中的高部位富集油气，分块是关键。本项研究成果不仅促进了塔中北斜坡一系列油气田的高效探明、加快了该区勘探开发一体化进程，同时，对于塔北隆起哈拉哈塘、热瓦普、英买力等地区油气富集规律的认识也起到了很好的借鉴作用。其科学意义就在于，通过走滑断裂的精细刻画及其成藏效应的深入分析，圆满地解释了看似纷繁复杂的油气水分布关系，明确了走滑断裂的存在及其分段点在油气成藏、富集中的关键控制作用。