Abstract:

Ordovician carbonate reservoirs in Tahe Oilfield could be divided into three types.Type I is fracture pore and fracture solution cavity resavoirs with low laterolog resistivity of both shallow and deep formations,high gamm ray value,increased acoustic time and neutron log valuse;type Ⅱ is fracture reservoirs with mid higher laterolog resistivity of both shallow and deep formations,gamma ray value similar to that of limestone;type Ⅲ is poor in fractures and pores, but the highest resistivity,low gamma ray value,and overlapped shallow and deep laterolog resistivities.Then reservoir parameters could be calculated through well log normalixation and core reposition.Accordineg to the calculated parametres and log data,the lower limits of rock mass porosity and fracture porosity are 2% and 0.05% respectively.The fracture porosity of the reservoirs are determined to be≥0.05%,≥0.05% and <0.05%,and their pore porosity≥2%,<2% and <2% respectively.It has been proved that well log interpreltation results fit in with the actural porosity and fractural distribution of the reservoirs studied.

Key words: carbonate rock, log response, parameter calculation, porosity, error analysis, low limit of porosity