Reserve Calculation Of Carbonate Fracture-vuggy Reservoirs Based On Volume Evaluation

Carbonate fracture-vuggy reservoir is the main type of marine carbonate reservoirs in China,and some huge oilfields had been found in north and central uplift in Tarim basin.However,because of the strong heterogeneity in its geometry and physical properties,it is difficult to evaluate the reserves of these kinds of oil and gas reservoirs effectively.In this paper,a case study on the block of well ZhongGu 15,Central Uplift in Tarim Basin.Integrated with detailed observations of cores and thin sections,the petrological characteristics of fracture-vuggy carbonate reservoir in Ordovician Yijianfang and Lianglitage formations were identified;Using FMI and conventional logging data,the types of the fracture-vuggy reservoirs were divided;Based on threedimensional seismic dataset,the spatial distributions of each reservoir type were delineated,and combined with the production data of oil and gas,the reserves of the upper Ordovician in the area are evaluated.The results showed that: the main lithology type in upper Ordovician is bright crystal grain limestone,the main reservoir space are dissolved vugs and cracks.Based on the arrangement relationship of caves,vugs and fractures,four types of fracture-vuggy reservoirs were divided: cavernous reservoirs,vuggy reservoirs,fracture reservoirs and fracture-vuggy reservoirs.According to the fault,fracture and fluid properties,four fracture-cave units are recognized and their reserves were as calculated respectively.This evaluation approach can assess the reserves of fracturevuggy reservoirs effectively,and can be applied to other similar oilfields.