Mineral composition

micro-pore characteristics and well-logs from five wells were used to study the sealing capacity of the Ordovician carbonate rocks in Tazhong area

Tarim Basin.The Ordovician Lianglitage and Yingshan formations are at substage A-B of the middle diagenetic stage and substage A of the late diagenetic stage.For the Lianglitage Formation grainstone

the breakthrough pressure (BP) is 1.81-29.76 MPa

and the threshold radius (TR) is 13.89-77.35 nm

.For the marlstones

the BP is 14.33MPa and TR is 25.9-44.51 nm.For the micritic limestone with band of argillite

the BP is 0.98-10.35 MPa and the TR is 13.52-142.60 nm.The BP and the TR of the Yingshan Formation limy dolomites are 0.98-10.35 MPa and 13.52-142.60 nm.Thus

the marlstone and partial grainstone of the Lianglitage Formation and the Yingshan Formation dolomite limestone have certain sealing capacity

with thickness over 5 m

BP over 5 MPa

TR between 10-20 nm

pore throat radium less than 0.1 μm.In addition

the tight interval consisted of dolomite limestone with high resistivity of 4-10 m thick in the Yingshan Formation is thought to be local caprocks in Tazhong area.Its existence is one of the main factors resulting in the oil/gas distribution pattern in the Ordovician Yingshan Formation in Zhong-1 well

i.e.oil in its upper part and gas in its lower part.