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 good
			elastoplastic fault transformation cap	Elastoplastic compression stage	Bad
			rupture fault transformation cap	Ruputure stage	worst