Sedimentary mineralogical and petrological methods in combination with oxygen-carbon isotope and electron probe were used to analyze the distribution

forming environment and material sources of the carbonate cements in the Zhuhai Formation in Wenchang A sag

Pear River Mouth Basin.The result indicates that the carbonate cements significantly affect reservoir quality.When the content of carbonate cements is greater than 5%

the reservoir quality significantly deteriorates.Furthermore

the distribution of carbonate cements show obvious regularity both vertically and horizontally.The content of carbonate cements in the 1

st

and 2

nd

members of Zhuhai Formation are higher than that of the 3

rd

member

and it is higher in the southern fault zone than the center of the sag.The carbonate cements are dominated by middle ferric calcite and late ferric dolomite

followed by siderite and dolomite as well as local early crystal stock calcite.The forming of carbonate cements is resulted from decarboxylation of organic acid and influenced obviously by freshwater.In addition to dissolution of calcareous foraminifer

feldspar dissolution and clay mineral transformation provide abundant calcium for the carbonate cements development.