ZJ气田沙溪庙组储层微观孔隙结构及渗流特征研究

STUDY OF PORE STRUCTURE AND SEEPAGE CHARACTERISTICS OF SHAXIMIAO FORMATION RESERVOIR IN ZJ GAS FIELD

针对ZJ气田沙溪庙组气藏36口取芯井478块岩样,基于450样次的孔渗分析以及160样次的薄片观测结果,结合CT扫描(37块)、高压压汞(110块)、恒速压汞(28块)、核磁共振(30块)、应力敏感性分析(8块)以及气水两相渗流(41块)实验,对储层岩石孔隙结构及渗流特征进行了综合研究。根据岩性、物性及孔隙结构建立了储层岩石分类标准,将其划分为3类型。Ⅰ类储层以中细粒岩屑长石砂岩为主,孔隙度>11%、渗透率>0.5×10^(-3)μm^2,最大连通喉道半径>1μm,束缚水饱和度46.53%,有效应力升-降过程中渗透率损失比25.16%。该类储层物性好,孔喉发育,连通性好,束缚水饱和度低、应力敏感性弱,气相渗流能力较强,属优质储层,约占气藏的12%,开发效果好。Ⅱ类储层孔隙度9%~11%、渗透率0.14×10^(-3)μm^2~0.50×10^(-3)μm^2,最大连通喉道半径0.4μm^1μm,平均核磁共振束缚水饱和度55.05%,平均渗透率损失比40.79%,主渗喉道较为狭窄、连通性变差、微观非均质性增强,束缚水饱和度占据孔隙空间更大,气相渗流能力减弱,属中等储层,占气藏的14%左右,开发效果一般。Ⅲ类储层孔隙度7%~9%、渗透率0.04×10^(-3)μm^2~0.14×10^(-3)μm^2,最大连通喉道半径0.02μm^0.4μm,孔喉更加狭小,气相流动受高束缚水饱和度(62.87%)和储层应力敏感性(渗透率损失比49.92%)影响显著,造成流动困难,属差储层,占已评价河道的74%左右,难以建产。

478 Shaximiao Formation rock samples from 36 drilling wells in the ZJ gas field are studied by means of micro-CT scanning analysis, conventional mercury intrusion porosimetry, constant-rate controlled mercury porosimetry, NMR, core percolation testing, pore structure and seepage theory. Based on the lithology, physical properties and pore structure of rock samples, the Shaximiao Formation reservoir rocks are divided into three types. Type I is dominated by mediumfine grained lithic feldspathic sandstones, with porosity over 11%, permeability over 0. 5 × 10^-3 μm^2 and maximum radius of connected throat over 1 μm. Its average irreducible water saturation is 46.53% and the loss of permeability is 25.16%. Therefore,type Ⅰ reservoir is characteristic of lower irreducible water saturation, weak permeability stress sensitivity, higher flow ability and good development result. For type Ⅱ reservoir,its porosity and permeability range from 9 % to 11% and 0.14 ×10^-3 μm^2 to 0. 50 ×10^-3 μm^2 respectively, with maximum radius of connected throat ranging from 0. 4 μm to 1 μm. Its testing irreducible water saturation is 55.05 % and the loss of permeability is 40.79%. So, type Ⅱ reservoir is characterized by narrower throat, poor connectivity and strong heterogeneity. Irreducible water occupies larger amount of pore space and results in lower flowing ability with common development effect. With porosity ranging from 7 to 9% ,permeability from 0.02× 10^-3 μm^2 to 0.14× 10^-3 μm^2 and the maximum radius of connected throat from 0.02 μm to 1 μm, type m reservoir has the narrowest throat, highest irreducible water saturation （62.87M）,with a permeability stress sensitivity of 49.92% ,which seriously affect the gas flow. Therefore,type Ⅲ reservoir is the poorly developed one.