Abstract:

The diversity of pore types is the main cause for strong heterogeneity of the carbonate reservoirs in the Yijianfang formation in Tuofutai area of Tarim basin, making it challenging to evaluate the reservoir effectiveness. On the basis of core and thin section observations, and according to the imaging logging data, the vugs in the carbonate rock are divided into dissolved vug and cavity, and the fractures are divided into structural fracture, dissolution fracture and pressolution fracture. According to the pattern of vug-fracture association, the pore spaces of the Yijianfang formation carbonate reservoirs in the study area are classified as fracture, fracture-vug and vug. The quantitative classification criteria for the reservoirs were established by combining electrical conductivity, fracture porosity and deep lateral resistivity variation. To be specific, the reservoir with the electrical conductivity less than 0.008 and the fracture porosity less than 0.13% is considered as vuggy reservoir; the reservoir with the electrical conductivity ranging from 0.008 to 0.024 and the fracture porosity of 0.13%-0.60% is considered as fractured-vuggy reservoir; and the reservoir with the electrical conductivity greater than 0.024 and the fracture porosity higher than 0.60% is regarded as fractured reservoir. According to the cumulative effective pore thickness, average effective porosity and productivity, the classification and discrimination charts for fractured-vuggy type reservoirs and vug type reservoirs were established. The vuggy and fractured-vuggy reservoirs in the Yijianfang formation in Tuofutai area are mainly Category Ⅱ reservoirs, with the daily liquid production of more than 50 t and 55 t, respectively.

Key words: Tarim basin, Tuofutai area, Yijianfang formation, carbonate reservoir, well logging, classified evaluation, productivity, fracture-vug