Abstract:

According to reservoir characteristics,production performance and percolation mechanism,the fractured-vuggy carbonate reservoirs in Tahe oilfield can be divided into five types.(1) Low saturation fractured-vuggy reservoirs with solution cavities as the main pore type.This type of reservoir is characterized by high initial productivity,long plateau production period,late water breakthrough, and relatively long water-free oil production period.Attention should be paid to changes of formation pressure and timely maintaining pressure through water injection.(2) Low saturation fractured-vuggy reservoirs with fractures and vugs as the main pore type.This kind of reservoirs is characterized by relatively high initial productivity,relatively short plateau production period,early water breakthrough,short water-free oil production,and rapid water-out.Largescale acid fracturing treatment should be avoided during early well completion,and producing pressure drop should be lowered,so as to prolong water-free production period.(3) Low saturation fractured-vuggy reservoirs with fractures and pores as the main pore type.This type of reservoir is characterized by low initial productivity,short plateau production period and rapid water breakthrough. Producing pressure drop should be lowered to slow down bottom water coning.(4) Oversaturation fractured-vuggy reservoirs with gas cap.This kind of reservoir has relatively high initial productivity,late water breakthrough and slow water cut rising speed.Gas production from the gas cap should be minimized so as to maintain driving energy of the gas in the reservoir.(5) Fractured-vuggy heavy oil reservoir.This kind of reservoir has relatively high initial productivity,slowly increasing water cut in impulsion mode.Research should be carried out on formation pressure and recovery schemes.

Key words: fracture and vug, carbonate reservoir, percolation, Tahe oilfield