微构造对低渗透油气成藏的控制作用——以鄂尔多斯盆地丰富川油田西区为例

低渗透岩性油藏成藏作用主要受控沉积相和成岩作用。但是,勘探实践表明,在砂体背景之上分布的微构造对低渗透油气成藏具有明显的控制作用。位于鄂尔多斯盆地中东部的丰富川油田西区为多层系低渗透复合含油区,油气成藏类型复杂多样。笔者以该区为例,在对该区主要含油层系微构造及其演化特征研究基础上,探讨鼻状隆起构造对油气富集成藏的控制作用。研究表明,丰富川油田西区在东高、西低的西倾单斜背景上发育多个自东向西倾没的鼻状隆起构造;本区侏罗纪古河道下切深度小,残余的长1厚层泥岩限制了油气向上运移,延安组石油富集程度明显弱于延长组。低幅度鼻状隆起微构造对长2和长4+5油气成藏具有明显的控制作用,长2油层组顶面构造高点清楚,微隆起构造对油气富集控制作用非常明显,长2油藏具上油下水特征,发育低水和边水,油水界面清楚,具有岩性-构造油藏的基本特征。而长4+5和长6油藏除了岩性油藏外,也发育构造-岩性复合油藏。研究表明,微构造研究对低渗透油层油气富集规律研究和老油区扩边勘探具有重要指导意义。

Controls to Oil Accumulation in Sandstone Beds with Low Permeability by Micro-Structure:Example from Western Area of Fengfuchuan Oilfield in Northern Shaanxi

Western exploration area of Fengfuchuan Oilfield, located in the middle-eastern part of Ordos Basin, is the multi-layer composite petroliferous region of low permeability, with complicated type of reservoir accumulation. And the development of micro structure controls reservoir enrichment of some layers. This becomes an important direction for expansion and continuous exploration in oil region. This paper is based on the analysis of micro structural characteristic, formation and evolution in the Yan 9, Yan 8 of Yan' an Formation and Chang 2, Chang 4+5, Chang 6 of Yanchang Formation which are the main oil-bearing sequences, and is based on the study of accumulation time and migration law, combined with the differences of multiple factors superposition of reservoir enrichment. And this paper shows the relationship between micro structure and reservoir enrichment. The micro structure is the nose-shaped uplift developed on the background of slope in different horizons, in which the nose uplift area developed in Yan 9, Yan 8, Chang 2 and parts of Chang 4+5 reservoir and the main sandbody superimposition part become a favorable area for migration and accumulation of oil and gas. Synthetic analysis uses the relationship between micro structure in this region and reservoir enrichment, and selects 5 favorable exploration target areas in the study area. Of the 5 favorable exploration target areas, in Ding 20 well area, Yao 304 well area, Ding 85 well area and Yao 243 well area, the tectonic uplift of both sides of the zonal range is the key zone of oil and gas exploration in the Yanchang Formation. The ancient branch valley and slope on both sides developed in the Renjiagou and Guozhuang become a favorable exploration area for ancient landform reservoir of Yanan Formation. This study can provide a reliable guarantee for oil exploration in the future.