Difference of Microfeatures among Diagenetic Facies in Tight Sandstone Reservoirs of the Triassic Yanchang Formation in the Midwestern Region, Ordos Basin

Table 3

Statistics of porosity evolution in diagenesis.

Compaction	Initial porosity, %		Porosity after compaction, %			The ratio of porosity loss due to compaction, %
	Range	Average	Range	Average		Range		Average
	32.96∼39.68	36.87	10.23∼30.14	18.43		30.22∼73.83		50.54
Cementation	Porosity loss due to early cementation, %		Porosity loss due to the midlate cementation, %			Porosity after compaction and cementation, %
	Range	Average	Range	Average		Range		Average
	1.13∼14.72	3.96	2.25∼13.1	6.42		3.39∼10.52		8.19
Corrosion	Increased porosity due to dissolution, %		Final calculation of porosity, %		Porosity measured by gas, %		Error, %
	Range	Average	Range	Average	Range	Average	Range	Average
	0.34∼7.47	2.21	4.82∼13.87	10.33	4.35∼16.77	10.75	0.79∼20.3	6.89