松辽盆地长岭断陷沙河子组页岩有机显微组分孔隙演化规律研究

有机质孔隙是页岩储集空间的重要组成部分,具有强烈的非均质性,阻碍对页岩储层质量的正确认识和评价,其本质是受有机显微组分类型及其在生烃过程中孔隙演化的影响。本文采用场发射扫描电镜和荧光显微镜定位观察手段实现特定显微组分孔隙发育特征的表征,结合Image J图像处理技术,对不同演化阶段的显微组分进行定量化统计,总结不同有机显微组分的孔隙演化规律。研究结果表明:固体沥青孔隙度随着成熟度的升高呈现先增加后减小的趋势,在固体沥青反射率SBR_O介于1.6%～2.0%时,固体沥青孔隙最为发育,而以SBR_O=2.0%为界,固体沥青孔隙度开始减小。镜质体和惰质体的孔隙发育规律相似,随着成熟度增加,总体表现出先减小而后微弱增加的趋势。在生油窗阶段,镜质体和惰质体孔隙度最小,无机矿物和固体沥青的充填使胞腔孔隙损失达90%以上,而进入高成熟阶段,固体沥青孔隙的发育使原始胞腔孔隙得到一定程度的恢复,成为镜质体和惰质体残余孔隙的主要贡献者,贡献率达56.73%和100%,可见固体沥青孔隙对页岩储层储集空间的重要性。综合沉积成岩作用和生烃作用,页岩储层在未成熟阶段和高成熟阶段晚期孔隙最为发育,前者有机质以原始胞腔孔隙为主,后者以固体量孔隙为主。明确有机显微组分孔隙演化规律为页岩有利储层预测和页岩气生产开发储层改造提供参考。

Pore evolution of organic maceral in Shahezi Formation shale of Changling fault depression, Songliao Basin

As an important part of shale reservoir space, organic pores possess strong heterogeneity, which hinders the correct understanding and evaluation of shale reservoir quality. The heterogeneity is essentially affected by organic macerals and their pore evolution during hydrocarbon generation process. Through located observation based on the field emission scanning electron microscopy and optical microscopy for pore development of the specific macerals, combined with Image J digital process technique, the pore evolution law of different organic macerals was summarized by quantitative statistics of macerals at different evolutionary stages. The results show that the porosity with solid bitumen is first increased and then decreased with the increase of maturity. The solid bitumen porosity is the highest when SBR_O rangs from 1.6% to 2.0%, while the porosity begins to decrease when SBR_O exceeds 2.0%. The pore development models of vitrinite and inertinite are similar. The both porosity decreases first and then increases slightly as maturity rise. In the oil window stage, the porosity of vitrinite and and inertinite is the lowest, because the filling of inorganic minerals and solid bitumen in the primary cell lumen make the loss of pores more than 90%. In the high mature stage, pore development of solid bitumen makes the original cellular pore getting a certain degree of recovery, becoming the main contribution and accounting for 56.73% and 100% of residual pores of vitrinite and inertinite respectively. It can be seen that solid bitumen pores are of importantance to the shale reservoir. Combined with sedimentary diagenesis and hydrocarbon generation, the pores of shale reservoir are the most developed in the immature stage and the late stage of high maturity. The former is dominated by primitive cell pores, while the latter is dominated by solid bitumen pores. Clarification of the pore evolution pattern of organic macerals can provide a significant reference for favorable shale reservoir prediction and reconstruction of shale gas development.