川东南地区中二叠统茅口组灰泥灰岩储层孔隙特征

Pore characteristics of marl reservoir in Maokou Formation of Middle Permian,southeastern Sichuan Basin

近期川东南多口钻井在茅口组一段灰泥灰岩储层实现了油气勘探突破,其作为一种新类型非常规气藏得到了大量关注。为了进一步弄清该区茅一段灰泥灰岩储层的岩石学特征和储层孔隙特征,基于野外和岩心样品,开展了岩石学和储层孔隙表征工作。研究表明:①茅一段主要发育于外缓坡相,灰泥灰岩的总有机碳含量平均值为0.76%~1.1%,平面上自北西向南东呈增大的趋势,与孔隙度变化趋势相似。②茅一段灰泥灰岩储集空间主要包含有机质孔、无机孔和微裂缝三大类,其中有机质孔可分为独立的有机质孔隙、包裹滑石的有机质孔隙和黄铁矿晶间有机质孔隙,无机孔可分为粒间孔、晶间孔、晶体内部溶孔,微裂缝可分为滑石缝、粒缘缝、应力缝;有机质孔在川东南地区茅一段灰泥灰岩储层中并不占主导地位,微裂缝是灰泥灰岩最重要的储集空间。③通过低温氮气吸附、低温CO_(2)吸附、高压压汞实验以及纳米CT扫描联合表征,灰泥灰岩储层孔隙以细颈广体的墨水瓶形孔为主,微孔、中孔、宏孔均有发育,孔径主要分布在0.4~100 nm,跨度范围较大;灰泥灰岩非均质性明显,连通性较差,裂缝对于连通孔隙有重要影响。茅一段灰泥灰岩为一套新类型非常规储层,鉴于其复杂的矿物组成和特殊的孔隙特征,需加强有针对性的酸化压裂技术攻关,从而促进灰泥灰岩储层的油气勘探开发。

Breakthroughs of oil and gas exploration have recently been achieved via several wells in marl reservoirs of the first member of the middle Permian Maokou Formation in the southeastern Sichuan Basin.As a new type of unconventional gas reservoir,a lot of attention was attracted.In order to understand lithological characte-ristics and pore characteristics of marl reservoirs,lithological,pore types and pore structure characterization,works were carried out based on field and core samples.Results show that:(1)The TOC content of the marl reservoirs,which is mainly in outer gently sloping facies,is 0.76%-1.1%,with an increasing trend from northwest to southeast,similar to porosity changes.(2)Reservoir spaces of the marls mainly include organic pores,inorganic pores and microfractures.The organic pores can be classified into independent organic pores,organic pores with talc and intergranular organic pores of pyrite.The inorganic pores can be classified into intergranular pores,intercrystalline pores,and crystal dissolved pores.The microfractures can be classified into talc fractures,grain boundary fractures,and stress fractures.Organic pores are not dominant in the marl reservoirs,while microfractures are the most important reservoir space.(3)Combined characterization of cryogenic nitrogen adsorption,cryogenic CO_(2) adsorption,high-pressure Hg injection experiments and CT scan show that pores of the marls are mainly ink-bottle shaped with narrow neck and wide body.Micropores,mesopores and macropores are developed,with pore diameters of about 0.4-100 nm.The marls have obvious lithologic heterogeneity and poor connectivity.Fractures have an important influence on the connected pores.The marl in the first member of the Maokou Formation is a new type of unconventional reservoir,which has complex mineral composition and special pore characteristics.Targeted acid fracturing technology should be strengthen to promote the exploration and production of the marl reservoir.