WELL-LOG ANALYSIS ON KARST MODEL OF ORDOVICIAN CARBONATE IN TAHE OILFIELD

Tectonic movement controls karst sequence and periods. The ka rs ts formed during middle Caledonian and early Hercynian were mainly developed in Ordovician of Tahe oilfield. The karst of middle Caledonian is weak and reserve d in the south sub-Ordovician of Tahe oilfield, characterized by pores. The two karst stages of early Hercynianare strong and reserved in the north sub -Ordovician of Tahe oilfield, characterized by big underground solution cavity and river. Karst system of each stage can be divided into three vertical sectio ns: surface karst layer, vertical infiltration karst layer and horizontal underg round solution underflow karst layer. By means of gamma ray log, caliper log, du al lateral log, compensation density log, compensation neutron log, sonic log an d formation micro resistivity image, Ordovician karst sections in two typical we lls are divided. According to double-peak carbonate, the karst sections in two typical wells are compared and karst spacial distribution and development mo del of Ordovician carbonate in Tahe oilfield is built.