埋藏压实作用对前陆盆地深部储层的作用过程与改造机制

An effect of burial compaction on deep reservoirs of foreland basins and its reworking mechanism

针对中西部前陆盆地储层经历了早期长期浅埋、后期快速深埋的特有埋藏方式,开展地质过程约束下的成岩模拟实验,分析埋藏压实作用对库车前陆盆地深部储层的作用过程与改造效果。通过砂岩面孔率、视压实率、减孔率及孔径、喉径等储层物性参数的定量评价,表明埋藏压实作用直接影响储层视压实率、减孔率,同时也控制了不同粒级砂岩储层的孔径与喉径变化。在早期缓慢的浅埋藏阶段,压实作用使粗砂岩、中砂岩等粗碎屑颗粒存在较少的碎裂纹及颗粒位移和重排,细砂岩、粉砂岩等细颗粒呈较杂乱排列。在后期快速埋藏压实阶段,随着埋深增大,压实作用使骨架颗粒趋于定向排列;近源沉积的粗砂岩、中砂岩等碎屑颗粒大量发育裂纹和成岩缝,前渊沉积的粉砂岩不发育颗粒裂纹但存在成岩缝。快速深埋作用下形成的碎屑颗粒裂纹与成岩缝是深部储层发生溶蚀和提高渗透性的主要原因。

The burial history for reservoirs of foreland basins in the central and western China is characterized by long term shallow burial at the early stage and rapid deep burial at the late stage. Under a geological process constraint, we conducted a series of simu lation experiments on diagenesis and analyzed the burial compaction process of deep reservoirs in the Kuqa foreland basin and its re working effect. By quantitative evaluations of reservoir physical property parameters, such as plane porosity, apparent compaction percentage, porosity reduction rate, pore and neck diameters, a direct effect of burial compaction on the apparent compaction per centage and porosity reduction rate was verified, meanwhile, burial compaction of reservoirs was found to control variations in pore and neck diameters of sandstones with different grain size. At the early slow and shallow burial stage, compaction might result in not only less grain crackles as well as grain displacement and rearrangement in clastic rocks, such as coarse and mesograined sandstones, but also a random grain arrangement of aphanides, such as packsands and siltstones. At the late rapid burial compaction stage, along with increasing burial depth, compaction might lead to an oriented arrangement tendency for skeleton grains, and crackles and diage- netic fractures widely developed in clasitc grains representative of near-source deposition, such as coarse and mesograined sand stones, while sihstones deposited in foredeep belts showed less-developed grain crackles but some diagenetic fractures. Therefore, crackles and diagenetic fractures of clastic grains formed under rapid deep burial are attributed to a major cause for dissolution occur fence and permeability enhancement of deep reservoirs.