Table 2: Types of argillite cap and its characteristics of Paleogene-Neogene strata in the Zhanhua Sag.

Features and sealing capacity of each category Features and sealing capacity of subcategories
   Types Features Sealing capacity Sub-categories Features Sealing capacity
Porosity cap argillaceous sedimentary, mainly through compaction, and without fractures or faults destruction   Overall good High porosity Porosity more than 23% Good Mostly good with some bad
Medium porosity Porosity from 20%-23% Better
Low to Ultra-Low porosity Porosity less than 20% Best
Fracture transformation cap destruction by fractures Partial destruction Fracture transformation cap Worse in fractures Good and bad
Fault transformation cap destruction by faults Large-scale destruction plastic Fault transformation cap Plastic compaction stage Good Mostly bad with some
elastoplastic fault transformation cap Elastoplastic compression stage Bad
rupture fault transformation cap Ruputure stage worst