鄂尔多斯盆地东部盒8段、太原组致密砂岩储层特征及低产因素

Characteristics and low yield factors of H8and Taiyuan Formation tight sandstone reservoir in the east of Ordos Basin,China

鄂尔多斯盆地致密气资源丰富,主要赋存于上古生界致密砂岩储层中。以岩心观察、分析试验等资料为基础,对鄂尔多斯盆地东部二叠系太原组、盒8段致密砂岩储层岩石学特征、孔隙特征、物性特征和成岩特征等进行研究,探讨其低产因素,为气藏开发提供依据。结果表明：盒8、太原组致密砂岩均以岩屑砂岩和岩屑石英砂岩为主,但其储层特征及低产原因有较大差别。盒8砂岩杂基含量少,原生粒间孔发育,但均被后期成岩矿物完全充填,以高岭石晶间孔为主;太原组砂岩杂基含量高,原生粒间孔不发育,储集空间以溶孔为主,形成于早成岩晚期-晚成岩早期阶段。太原组喷发岩岩屑、长石、火山灰的溶解为储层提供了较为丰富的储集空间;但晚成岩高温阶段形成的丝状、网状伊利石矿物充填孔隙,堵塞喉道,影响储层的渗流能力,是造成储集性能较差的主要原因之一。片状喉道为主、有效上覆压力大、软组分含量高、应力敏感性强,加之较低的原始含水饱和度、气藏压力低（压力系数为0.6~0.8）,致使储层在钻井、压裂、酸化等过程中容易吸水,造成的水锁效应,是研究区低产的又一主要原因。

The tight sandstone gas resource in Ordos Basin is rich and large gas fields are mostly hosted in the tight sandstone reservoir of the Upper Paleozoic. The petrologic characteristics,pore characteristics,physical properties and diagenetic features of H8 Formation and Taiyuan Formation of Permian in the east of Ordos Basin are researched by means of core observation and analytic techniquesin this paper.Then,the paper studies the low yield factors so as to provide the evidence for the effective development of the gas reservoirs.The result shows that the reservoirs of H8 Formation and Taiyuan Formation in the east of Ordos Basin are mainly comprised of lithic sandstone and lithic quartz sandstone.But the difference between the two reservoirs in reservoir characteristics and low yield factor is notable.H8 Formation sandstone is characterized by minor amount of matrix and developing primary intergranular pores which are fully packed by the late diagenetic minerals and its reservoir space is mainly the intercrystal pore.The Taiyuan Formation sandstone has major amount of matrix,poor primary intergranular pores and developing dissolution pores which formed in the late stage of early diagenetic period and the beginning of late diagenetic period.The dissolution of high mica and eruptive rock,feldspar and volcanic ash of Taiyuan sandstone produces abundant reservoir spaces.But silk-net-like illite forming at the high temperature stage during the late diagenetic period packed in pores,plugged up pore throats and affected the percolation ability.This is one of the main reasons to cause the poor reservoir property.The dominant sheet or curl throat,the high effective overburden pressure,the high mica content,the strong stress sensitivity,the low original water saturation and the low reservoir pressure（pressure coefficient：0.6~0.8）easily lead to the reservoir＇s water lock effect in the processes of drilling,fracturing and acidification.This is another main reason of low yield in research area.