The reservoir space in the fractured-vuggy reservoirs of Tahe Oilfield is diverse in type and size

and spatially discontinuous

typical features for massive oil pools

and different from that of conventional laminar sandstone reservoirs.The gas injection measure for oil recovery enhancement is remarkable in Tahe oilfield.To characterize the massive reservoirs featuring numerous fractures

cavities and other features of heterogeneity in the Tahe oilfield

we proposed an categorization and calculation method of developed reserves through gas drive.Based on PDA production data analysis

the calculation method for total developed reserves of a well group is established by fitting flow reforming pressure and material balance time curves.For weathering crust

underground river

and fault karst

the calculation method of areal sweep efficiency is presented based on the form factor correction coefficient

and calculation method for the vertical drainage efficiency is also proposed based on the 3D distribution of fractured-vuggy reservoirs revealed by seismic cube energy attri-bute.In addition

based on the total developed reserves for a well group

cumulative production before gas flooding

areal sweep efficiency

form factor correction coefficient for irregular well patterns

and vertical drainage efficiency of reserves

the calculation method for gas drive developed reserves of well groups with various well patterns under different karst settings is established.This method has been applied to the Tahe oilfield for in-situ gas injection case studies

which has laid a solid foundation for the optimization of gas drive well group patterns

the calculation of developed reserves in gas drive well groups

and potential EOR analysis of gas injection.