Evaluation and Recognition of Fracturing Effect in Ultra-Low Permeability Volatile Reservoir

Block F of Z Oilfield is an ultra-low permeability volatile structural oil reservoir, which has the characteristics of deep reservoir burial, poor reservoir physical properties, strong heterogeneity, low difference between formation pressure and saturation pressure, and crude oil volatility. In the early stage, the fracturing test and production test of 3 wells were carried out. The geological characteristics, fracturing methods and fracturing scales of the 3 wells were different, and they showed different fracturing effects. A comparative analysis of related technical indicators such as oil breakthrough time, oil production, gas production, gas-oil ratio and pressure of the test production wells showed that the natural productivity of the production wells in Block F is low, and conventional fracturing has achieved better fracturing effect. However, no better fracturing effect was seen in the initial stage of large-scale fracture network fracturing wells. The flow pressure of the test production wells is lower than the saturation pressure after about one month production, the gas-oil ratio rises, the formation crude oil is gradually degassed, and the production decline trend of oil wells is accelerated. During the development process, advance water injection or simultaneous water injection measures should be taken to supplement the formation energy in time. At the same time, small size choke shall be selected as far as possible to maintain the formation pressure and ensure the development effect.