Porosity and permeability cutoffs for calculating effective thickness of different types of low-permeability reservoirs and causes of their differences: a case study of the Mesozoic in S region of central Shaanbei slope

Zhang Fengqi; Wu Fuli; Meng Xiaoling; Gao Xingjun; Zhang Hai; Li Chengshan; Wang Baoping

doi:10.11743/ogg20150404

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Porosity and permeability cutoffs for calculating effective thickness of different types of low-permeability reservoirs and causes of their differences: a case study of the Mesozoic in S region of central Shaanbei slope
Vol. 36, Issue 4, Pages: 555-562(2015)
Online First：08 August 2015，

Published：2015
DOI： 10.11743/ogg20150404
稿件说明：

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DOI：

Zhang Fengqi, Wu Fuli, Meng Xiaoling, et al. Porosity and permeability cutoffs for calculating effective thickness of different types of low-permeability reservoirs and causes of their differences: a case study of the Mesozoic in S region of central Shaanbei slope[J]. 2015, 36(4): 555-562. DOI： 10.11743/ogg20150404.

摘要

运用铸体薄片鉴定、扫描电镜、阴极发光与压汞等测试分析，综合多方法相互印证分析了鄂尔多斯盆地S地区中生界主力含油层系有效厚度物性下限，并结合物性变化的定量表征探讨了各主力油层间有效厚度物性下限的差异性成因。结果表明，研究区储层有效厚度物性下限值随埋深增大而变小，延9油层组、长2油层组和长6油层组（长4+5油层组）的孔隙度下限分别为15%，14%和8%，渗透率下限分别为4.0×10

-3

，1.0×10

-3

和0.15×10

-3

μm

。沉积作用形成各储层矿物成分中刚性颗粒含量与粒度大小等差异是其物性差异性形成的基础影响因素，而成岩作用是其差异性形成的最主要原因。各成岩作用类型的具体影响为：各储层初始孔隙度相差较小，长2油层组与延9油层组相比，压实作用和胶结作用共同作用而减少的孔隙度基本相当，差别在于后者的溶蚀改善作用增加的孔隙度稍好于前者；长6油层组（长4+5油层组）与长2油层组相比，压实作用减少的孔隙度和溶蚀作用增加的孔隙度差别均不大，差别在于前者因胶结作用减少的孔隙度大于后者，这是两者物性下限差异的最主要原因。

Abstract

Analytic means including thin section examination

SEM

cathode luminescence

mercury penetration and so on

were applied to determine the cutoffs of porosity and permeability for calculating the effective thickness of the major Mesozoic oil-bearing formations in S region of Ordos Basin.The reasons for the varying cutoffs were also discussed based on quantitative characterization of physical property changes of the formations.The results show that the cutoffs(porosity and permeability)decline with the increase of burial depth.Samples from Yan 9

Chang 2

Chang 4+5 and Chang 6 formations

have porosity cutoffs of 15%

14%

8% respectively

and permeability cutoffs of 4× 10

-3

1× 10

-3

0.15× 10

-3

μm

respectively.The differences in content and grain size of rigid particles in mineral composition of each reservoir caused mainly by sedimentation processes are regarded as the basic factor for the difference of cutoffs

while diagenesis is the major factor.The processes

including compaction

cementation and corrosion

dented the formations in different ways.All the formations had the similar porosity at first.But later on it turned out that Yan 9 had a higher porosity than that of Chang 2 because of their different response to corrosion and Chang 4+5 had lower porosity than that of Chang 2 because of their different behavior under cementation.