致密砂岩气储层微观孔隙结构与分形特征——以松辽盆地长岭气田登娄库组为例

Microscopic pore structure and fractal characteristics of tight sandstone gas reservoir:A case study of Denglouku Formation in Changling Gas Field,Songliao Basin

致密砂岩储层的孔隙结构是决定其储层物性及油气产能的重要因素,也是当前致密储层研究的热点。以松辽盆地长岭气田登娄库组致密砂岩为研究对象,通过核磁共振、恒速压汞、铸体薄片及扫描电镜等实验资料,用定性和定量相结合的方法对致密气储层孔隙结构特征进行表征;基于饱和和离心状态下测量的T_(2)谱进行分形分析,探讨孔隙结构参数与可动流体之间的关系,开展储层孔隙结构分类评价研究。结果表明:登娄库组致密气储层孔隙类型多样,主要发育残余粒间孔、长石溶蚀孔和黏土矿物晶间孔,孔喉关系以大孔细喉和小孔粗喉为主,核磁共振T_(2)谱呈双峰或单峰分布。研究孔隙结构特征与可动流体关系发现,最大连通喉道半径才是控制可动流体大小的主要因素。致密气储层孔隙结构具有分形特征,离心状态T_(2)谱计算的分形维数D_(2)(2.3551~2.8035)要高于饱和状态的D_(1)(2.2399~2.7557),表明微小孔隙域决定了微观复杂性,中大孔隙域控制了宏观储层品质。综合储层的储集能力和流体的赋存特征将长岭气田登娄库组致密气储层划分为3种类型,Ⅰ类孔隙结构多为小孔粗喉类型,最大连通喉道半径下限为0.8μm,分形维数小,为优质储层。研究成果定量表征了孔隙结构的复杂性,为致密气储层评价与分类提供了新思路,可以指导致密气储层的勘探开发。

The pore structure of tight sandstone reservoir is an important factor to determine its reservoir physical properties and oil and gas production capacity,and it is also a hot spot in the research of tight reservoir.The pore structure characteristics of tight sandstone of Denglouku Formation in Changling Gas Field,Songliao Basin were characterized by qualitative and quantitative methods based on the experimental data of nuclear magnetic resonance,constant velocity mercury injection,cast thin section and scanning electron microscopy.Based on the T_(2) spectra measured in saturated and centrifuged states,the heterogeneity and complexity of pore structure were quantitatively characterized,and the relationship between petrophysical parameters,NMR parameters and fractal dimension was discussed.The results show that:The pore types of tight sandstone reservoirs in Denglouku Formation are diverse,including residual intergranular pores,feldspar dissolution pores and intergranular pores of clay minerals.The pore-throat relationship is mainly characterized by large pores and thin throats and small pores and coarse throats.The NMR T_(2) spectrum shows bimodal or unimodal distribution.The relationship between pore structure characteristics and movable fluid shows that the maximum connected throat radius is the main factor controlling the size of movable fluid.The fractal dimension D(2.3551-2.8035)calculated by T_(2) spectrum in centrifugal state is higher than that in saturation state(2.2399-2.7557),which indicates that the micro pore domain determines the micro complexity of tight sandstone,and the large pore domain controls the macro reservoir quality of tight sandstone.The tight sandstone reservoirs of Denglouku Formation in Changling Gas Field can be divided into three types based on the reservoir capacity and the occurrence characteristics of fluids.The typeⅠpore structure is mostly of small pore and coarse throat type,the lower limit of the maximum connected throat radius is 0.8μm,and the fractal dimension is small,so it is a high-quality reservoir.The results are helpful to reveal the heterogeneous combination of the pore system and quantitatively characterize the complexity of the pore structure,so as to guide the exploration and development of tight gas reservoirs.