鄂尔多斯盆地东南部延长组7段页岩有机孔发育特征及其影响因素

Characteristics and controlling factors of organic pores in the 7th member of Yanchang Formation shale in the Southeastern Ordos Basin

近年来的研究发现,鄂尔多斯盆地东南部延长组7段(长7段)中-低成熟度页岩中发育有机孔,但是对于影响陆相页岩储层中有机孔发育的影响因素有待进一步深入研究。借助氩离子剖光和场发射扫描电镜分析等技术,研究了鄂尔多斯盆地东南部长7段页岩中不同类型固体有机质中有机孔发育特征,并统计分析了不同成熟度页岩样品中干酪根和运移固体有机质的有机孔径和有机孔面积占有机质面积的百分比(S R),以此为基础讨论了影响有机孔发育的主要因素。结果表明,长7段中不同成熟度页岩(R o:0.50%~1.25%)中有机质均发育有机孔,但是干酪根和运移固体有机质中的有机孔发育程度具有明显差异。沉积有机质(干酪根)主要以顺层富集、孤立分散及与粘土矿物共生3种形式赋存在页岩中,有机孔发育程度相对较低,有机孔面积占有机质面积的百分比介于0~44.13%,一般小于10%,平均6.03%;有机孔孔径主要在10~40 nm。运移固体有机质主要赋存在刚性颗粒粒间孔/粒间溶蚀孔、刚性颗粒与粘土矿物间粒间孔/粒间溶蚀孔和黄铁矿晶间孔等无机矿物孔中,有机孔发育程度较高,有机孔面积占有机质面积的百分比介于0~46.51%,一般小于30%,平均23.05%;孔径较大,主要在50~100 nm。长7段页岩中有机孔的发育程度主要受控于固体有机质类型、运移有机质丰度和有机质成熟度,运移固体有机质丰度越大,有机质成熟度越高,有机孔越发育。

Recent studies have shown that organic pores are developed in the medium-to-low-maturity shale of the 7th member of Yanchang Formation in the Southeastern Ordos Basin,but the influencing factors on the development of organic pores in the continental shale reservoir need to be further understood.With the aid of argon ion polishing and FE-SEM observation,we observed the characteristics of organic pores in Chang 7 shale in the Southeastern Ordos Basin.Statistical analysis was made on the organic pore sizes in kerogen of different maturity and different types of migrated solid organic matters,and also on the ratio of organic pore area to the total organic matter area(S R)of these organic matters.Thereaf-ter,main factors affecting the development of organic pores were discussed.The results indicate that organic pores were widely developed in shales of diverse maturity(R o:0.5%-1.25%)in the Chang 7 member,but there were significant differences in the development of organic pores in kerogens and migrated solid organic matters.Sedimentary organic matter(kerogen)occurs mainly in the form of enrichment along beddings,isolated dispersion and combination with clay minerals in shale and has relatively lower degree of organic pore development.The ratio of the organic pore area to the total organic matter area ranges from 0%to 44.13%,averaging at 6.03%,but generally less than 10%.The majority of organic pores ranges from 10 nm to 40 nm in size.The migrated solid organic matters mainly occurs in inorganic mineral pores,including inter-particle pores/inter-particle dissolution pores in rigid particles,inter-particle pores/inter-particle dissolution pores between rigid particles and clay minerals,intercrystalline pores in pyrite of shale.These organic matters have relatively higher degree of organic pore development.The ratio of the organic pore area to the organic matter area varies from 0%to 46.51%,averaging at 23.05%and generally less than 30%.In addition,the pore size is larger,mainly ranging from 50 nm to 100 nm.The development of organic pores in the Chang 7 member shale is mainly controlled by the organic matter type,the abundance of migrated solid organic matters and the maturity of organic matter:positively correlated with higher content of migrated solid organic matters and more maturity of the organic matters.