川西北下二叠统栖霞组有利成岩作用与孔隙演化

Constructive diagenesis and porosity evolution in the Lower Permian Qixia Formation of Northwest Sichuan

据宏观、微观及地球化学特征等综合分析,川西北下二叠统栖霞组储层段主要的建设性成岩作用有同生-准同生期溶解、埋藏期溶解、构造抬升期溶解、混合水白云石化、埋藏白云石化及重结晶作用。其中埋藏期溶蚀和埋藏白云石化作用对储集层的储集空间贡献最大,其产生的晶间孔、晶间溶孔、洞、缝是现今该层段主要的储集空间;其次是重结晶作用。重结晶作用对储集空间的直接贡献不大,但重结晶作用提高了岩石的有效孔隙度和渗透率从而为后期的溶蚀作用提供了条件;而同生期的溶解作用形成的孔隙由于后期的压实、胶结等作用破坏而几乎消失殆尽。

According to a comprehensive analysis of the macroscopic, microscopic and geochemical characteristics of the Qixia Formation reservoir, the major constructive diagenesis has syndepositional periods of dissolution, buried dissolution, tectonic uplift dissolution, mixed water dolomitization, buried dolomitization and recrystallization, of which the buried dissolution and the buried dolomitization seem to have made the greatest contribution to the reservoir space in that the intercrystaUine pores, intercrystalline dissolution pores, dissolved holes and slits in them constitute the main reservoir space. RecrystaUization possesses the second importance. Recrystallization did not make much contribution to the reservoir space, but it enhanced the effective porosity and permeability of the rocks, thus provided conditions for later dissolution. Nevertheless, the syndepositional dissolution pores have almost completely disappeared due to subsequent pore compaction, cementation and other damages.