超压对川东南地区五峰组-龙马溪组页岩储层影响分析

四川盆地东南部保存条件较好的五峰组-龙马溪组页岩普遍存在超压,且在其他地质条件相同的情况下,超压页岩储层相对于常压、低压储层具有更高的孔隙度.研究表明,富有机质页岩在适中的热演化过程中,由于烃类的大量生成,形成较多有机质孔隙,增加了页岩储层储集空间;另一方面,烃类大量生成造成的超压对页岩储层储集空间保存具有至关重要的作用.川东南五峰组-龙马溪组优质页岩储层孔隙以有机质孔、黏土矿物孔等塑性孔为主,且缺少刚性矿物颗粒支撑,易被上覆地层有效应力压实.但超压的存在对于页岩储层具有保护作用,抵消了上覆地层有效应力对页岩储层的机械压实,从而使已形成的页岩孔隙保存下来,使页岩储集空间得以保留.研究超压对页岩储层孔隙度影响机制以及超压页岩储层发育模式对于四川盆地五峰组-龙马溪组页岩气勘探、开发具有重要意义.

Analyses of Influences on Shale Reservoirs of Wufeng-Longmaxi Formation by Overpressure in the South-eastern Part of Sichuan Basin

There commonly exists overpressure in Wufeng-Longmaxi shales in the area with favorable preservation conditions in the south-eastern part of Sichuan Basin and the porosity of reservoirs with overpressure is higher than that of reservoirs with common or lower pressure. The studies show that during the course of evaluation, a great deal of hydrocarbons generated in organic-rich shales led to the development of overpressure system: on one side a great deal of hydrodarbons are generated and a great deal of organic pores are formed to increase the reservoir space; on the other side the overpressure system due to a great deal of hydrodarbons generated is favorable to preserve the reservoir space. The pores of shale reservoirs of Wufeng-Longmaxi Formation are dominated by plastic pores such as organic pores, clay mineral pores etc., which are easy to be compacted by overlying strata. It is considered that the existence of overpressure system can partially resist the mechanical compaction from the overlying strata to protect shale reservoirs and preserve the storage space. It is important to study the mechanism and mode of pores in shale reservoirs in Wufeng-Longmaxi Formation in Sichuan Basin for shale gas exploration and development.