Microscopic occurrence of oil in tight sandstones and its relation with oil sources—a case study from the Upper Triassic Yanchang Formation, Ordos Basin

Niu Xiaobing; Feng Shengbin; Liu Fei; Wang Chengyu; Zheng Qinghua; Yang Xiao; You Yuan

doi:10.11743/ogg20130302

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Microscopic occurrence of oil in tight sandstones and its relation with oil sources—a case study from the Upper Triassic Yanchang Formation, Ordos Basin
Vol. 34, Issue 3, Pages: 288-293(2013)
Online First：28 June 2013，

Published：2013
DOI： 10.11743/ogg20130302
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DOI：

Niu Xiaobing, Feng Shengbin, Liu Fei, et al. Microscopic occurrence of oil in tight sandstones and its relation with oil sources—a case study from the Upper Triassic Yanchang Formation, Ordos Basin[J]. 2013, 34(3): 288-293. DOI： 10.11743/ogg20130302.

摘要

明确低渗透储层孔隙分布及不同尺度孔隙中石油微观赋存状态是认识致密油特征的关键。应用核磁共振测试技术对鄂尔多斯盆地延长组低渗透致密砂岩储层进行研究

发现了鄂尔多斯盆地延长组低渗透致密砂岩储层普遍发育纳米孔隙

具大孔、中孔、小孔、微孔及纳米孔多尺度孔隙发育特征。通过对近源与远源油藏储层多尺度孔隙中石油的微观赋存状态分析

明确了近源油藏储层具从大孔到纳米孔隙连续性赋存石油特征

且微孔至纳米孔隙含油饱满;远源油藏储层石油有选择性地赋存在大至中孔隙中

纳米孔隙不含油。延长组7段(长7)生烃增压产生的异常压力

控制石油在具多尺度孔隙的低渗透致密砂岩储层中差异性赋存

这为认识盆地致密油分布规律提供了理论依据。由此指出长7烃源岩分布区的长8油层组上部、长7油层组和长6油层组下部致密砂岩是今后致密油研究和勘探开发的主要目标。

Abstract

Identifying pore distribution of tight reservoirs and the microscopic occurrence of oil in pores of different scales is critical to understand the characteristics of tight oil.In this study

tight sandstone samples from Yanchang Formation

Ordos Basin

were investigated through Nuclear Magnetic Resonance (NMR) experiment.Nano-scale pores are common in the tight sand of Yanchang Fm and macro-scale

medium-scale

small-scale

micro-scale and nano-scale pores co-exist in the samples.The microscopic occurrence of oil in multiple-scale pores are compared between near-source reservoir and far-source reservoir.In near-source reservoirs

oil exists in all kinds of pores and the micro-pores and nano-pores are saturated with oil.In contrast

in far-source reservoirs

oil selectively occur in macro-scale and medium-scale pores and nano-pores contains no oil.The abnormal pressure caused by hydrocarbon-generation in Chang 7 layer is believed to be the main controlling factor for different occurrences of oil in multi-scale pores in tight reservoir.This provides a theoretical basis for understanding the distribution of tight oil reservoir.It is concluded that the upper Chang 8

the Chang 7 and lower Chang 6 reservoirs within the distribution area of Chang 7 source rock are the main potential targets for tight oil exploration in the future.