基于成因机理的地层有机质孔隙度的计算--以冀中束鹿凹陷泥灰岩非常规储层为例

Evaluation of Organic Porosity Based on Its Formation Mechanism:An Example from an Unconventional Marlstone Reservoir in the Shulu Sag,Jizhong Depression

近年来有机质孔隙在泥页岩及泥灰岩致密储层中被发现,成为非常规油气藏中一种重要的储集空间类型。有机质孔隙度的计算是非常规油气评价及勘探中极其重要且急需解决的问题。以冀中坳陷束鹿凹陷泥灰岩为例,从成因角度出发,提供了计算有机质孔隙度的方法。束鹿凹陷泥灰岩为自生自储型非常规油气藏,发育有机质孔隙。有机质孔隙主要为有机质在热演化过程中,由未成熟固体干酪根向低密度烃类流体转化所产生。根据束鹿泥灰岩现今有机地化特征(Ⅰ型及Ⅱ型干酪根、TOC平均1.66%、氢指数(HI)平均451 mg/g、T_(max)平均444℃),推算出其初始氢指数(HIo)平均561 mg/g、初始有机碳TOCo平均1.9%、可转换碳占48%、转化率为31%。最终利用质量平衡方程求得该区有机质在此演化过程中产生的有机质孔隙度为0.68%。

In recent years,organic matter pores have been identified in shale and marlstone tight reservoirs, and act as an important reservoir space type in unconventional reservoirs.Evaluation of organic porosity is an ur-gent problem that needs to be solved in unconventional petroleum evaluation and exploration.This study takes marlstone in the Shulu Sag as an example,providing a method to evaluate organic porosity from the aspect of formation mechanism of organic pores.The marlstone in the Shulu Sag acts as both a source rock and a reservoir for petroleum and organic pores have been identified.Organic porosity is produced as the result of evolution of organic matter from solid immature kerogen to less dense fluid hydrocarbons during thermal maturation.The fac-tors that control organic porosity include kerogen type,thermal maturity,initial total organic carbon,and source rock kinetics.The organic matter in the Shulu marlstone is predominantly Type Ⅰ and Type Ⅱ kerogen,and in a thermally mature zone.Test data show that the average present-day TOC is 1 .66% and the average hydrogen index (HI)is 451 mg/g.The average temperature of maximum yield of pyrolysis (Tmax )values is 444 ℃.Based on the test data,some other parameters were estimated.The average initial hydrogen index (HIo )is 561 mg/g.The initial total organic carbon (TOCo )is 1 .9%.The convertible carbon accounts for 48% of TOCo . The transformation ratio of convertible organic carbon is 31 %.Using a mass-balance relation,the organic poros-ity was estimated,which is approximately 0.68%.