基于粒间孔贡献量的致密砂岩储层分类——以徐家围子断陷为例

粒间孔是颗粒支撑碎屑岩储层最重要的一类孔隙,其相对含量及连通关系共同决定储层品质,尤其对于孔喉结构多样的致密砂岩。粒间孔具有"大孔被细喉沟通"的连通关系,明显不同于"类树形孔隙网络"的粒内孔,利用恒速压汞孔隙体进汞可有效区分粒间孔主导空间分布范围,在此基础上,通过核磁共振定量评价粒间孔对孔隙度的贡献,联合渗流理论及恒速压汞的喉道分布定量评价其对渗透率的贡献。致密砂岩粒间孔主导空间对孔隙度贡献范围为9%~64%,其对渗透率的贡献变化范围为0~87%,两者呈明显正相关;粒间孔对渗透率的贡献量越大,其内流体可动性越好;粒间孔对孔渗的贡献量明显受机械压实和以黏土为主的胶结作用共同影响。选取粒间孔主导空间对渗透率的贡献量(K_(in))为关键参数,将致密砂岩储层划分为粒间孔主导型(K_(in)≥50%)、混合型(10%K_(in)50%)和粒内孔主导型(K_(in)≤10%)3类,该分类综合考虑了对成岩作用敏感的粒间孔主导空间在整个岩石储集和渗流能力及流体可动性等方面的贡献,有效弥补了单纯使用喉道或孔隙大小参数划分具有多样孔喉结构致密储层的不足。

Classification of tight sandstone reservoirs based on the contribution of intergranular pores:a case study of Xujiaweizi fault depression

As the most important type of pores in the grain-supported clastic reservoirs, intergranular pores can control the reservoir quality by their relative contents and mutual connectivity, especially for tight sandstones with various pore-throat structures. The intergranular pores exhibit the connective pattern of "large pores connected by narrow throats", which is significantly different from the intragranular pores with "tree-like pore network". The rate-controlled porosimetry can be used to effectively distinguish the distribution range of intergranular-dominant pores. On this basis, the contribution of intergranular pores to porosity is quantitatively assessed by nuclear magnetic resonance, while that to permeability is calculated by the joint percolation theory and throat distribution from rate-controlled porosimetry. The contribution of intergranular pores to porosity in tight sandstones varies from 9 % to 64 %, showing a significantly positive correlation with that to permeability varying from 0 to 87 % . The higher the contribution of intergranular pores to permeability is, the greater the fluid mobility in intergranular pores will be. The contribution of intergranular pores to porosity and permeability is obviously affected by the combination of the mechanical compaction and clay-dominated cementation. Based on the contribution of intergranular-pore dominant space to permeability (K_in)as a key parameter, tight sandstone reservoirs are classified into the intergranular pore-dominant type (K_in>50 % ), mixed type (10 % < K_in < 50 % )and intragranular pore-dominant type (K_in<10 % ). This classification takes into account the contribution of the space dominated by intergranular pores with high sensitivity to the process of diagenesis to the overall rock reserving and porous flow capability, fluid mobility and other aspects, effectively compensating the limitations in the single use of pore-throat or pore size parameters for classifying tight reservoirs with various pore-throat structures.