Abstract: 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.

Key words: PDA method, linear well pattern, pseudo-areal well pattern, areal sweep efficiency, vertical drainage efficiency, developed reserves by gas drive, fractured-vuggy reservoir, Tahe oilfield