鄂尔多斯盆地致密储层微观孔隙结构特征与分类

Study on characteristics and classification of micro-pore structure in tight reservoirs for Ordos Basin

致密储层的微观孔隙结构特征是衡量致密储层油气渗流能力和产量的重要因素,也是目前致密油气藏的研究重点和热点。以鄂尔多斯盆地三叠系延长组长8致密储层为研究对象,通过开展恒速压汞实验和建立微观孔隙结构模型,分析了宏观储层物性参数与微观孔隙结构参数的关系,实现了对致密储层微观孔隙结构的精细划分。研究结果表明:喉道半径越大,总进汞饱和度、喉道进汞饱和度和孔隙进汞饱和度越大,残余的湿相饱和度越小;致密岩心喉道半径及孔隙半径均呈“两端分布少、中间多、左右不对称,粗(正)偏态”的正态分布特征,随着孔隙度和渗透率的增大,正态分布参数α和σ值有增大的趋势;以主流孔喉半径为判别特征参数,将致密岩心孔隙结构类型分为4类:Ⅰ类渗透率大于1×10^(-3)μm^(2),主流孔喉半径大于1μm;Ⅱ类渗透率为(0.5~1)×10^(-3)μm^(2),主流孔喉半径为0.7~1μm;Ⅲ类渗透率为(0.3~0.5)×10^(-3)μm^(2),主流孔喉半径为0.5~0.7μm;Ⅳ类渗透率小于0.3×10^(-3)μm^(2),主流孔喉半径小于0.5μm。致密储层孔隙结构以Ⅲ、Ⅳ类为主,具有孔喉细小,渗透性较差,岩心的孔隙分选性相对较好的特征,形成了一种简单有效的预测致密岩心微观孔隙结构分布规律的经验方法,能够为快速认识致密油藏微观孔隙特征提供支撑。

The microscopic pore structure of tight reservoir is an important factor to measure the oil and gas seepage capacity and production of tight reservoir,and it is also the focus and hotspot of tight reservoir research at present.In this paper,the Chang 8 tight reservoir of Triassic Yanchang Formation in Ordos Basin was taken as the research object,and the relationship between macro reservoir physical property parameters and micro pore structure parameters was analyzed by carrying out constant rate mercury injection experiment and establishing micro pore structure model,so as to realize the fine division of micro pore structure of tight reservoir.The results show that the larger the throat radius,the larger the total mercury saturation,and the larger the throat mercury saturation and the pore mercury saturation,the smaller the residual wet phase saturation.The throat radius and pore radius of the tight core show the normal distribution characteristics of “less distribution at both ends,more in the middle,asymmetric left and right,and coarse(positive)skewness”.With the increase of porosity and permeability,the normal distribution parameters α andσtend to increase.Taking the radius of main pore throat as the discriminant characteristic parameter,the pore structure of tight core can be divided into four types:type Ⅰ,permeability is greater than 1×10^(-3)μm^(2),and main pore throat radius is greater than 1μm;type Ⅱ,permeability is(0.5-1)×10^(-3)μm^(2),and main pore throat radius is 0.7-1μm;type Ⅲ,permeability is(0.3-0.5)×10^(-3)μm^(2),and the main pore throat radius is 0.5-0.7μm;type Ⅳ,permeability is less than 0.3×10^(-3)μm^(2),and the main pore throat radius is less than 0.5μm.The pore structure of tight reservoir is mainly types Ⅲ and Ⅳ,which is characterized by small pore throat,poor permeability and relatively good core pore sorting.In this paper,a simple and effective empirical method is developed to predict the distribution of microscopic pore structure in tight cores,which can provide support for rapid understanding of microscopic pore characteristics in tight reservoirs.