A new method to optimize the fracture geometry of a frac-packed well in unconsolidated sandstone heavy oil reservoirs

Abstract

The worldwide proven recoverable reserves of conventional oil are less than the amount of the heavy oil. Owing to weakly consolidated formation, sand production is an important problem encountered during oil production in heavy oil reservoirs, for which frac-pack technique is one of the most common treatments. Hence, how to obtain the optimal fracture geometry is the key to increasing well production and preventing sand. Due to the faultiness that current optimization of the fracture geometry only depends on well productivity, fracture-flow fraction was used to describe the contribution of the fracture collecting and conducting fluids from the reservoir. The higher the fracture-flow fraction, the more likely bilinear flow pattern occurs, thus leading to smaller flow resistance and better results in oil productivity and sand prevention. A reservoir numerical simulation model was established to simulate the long-term production dynamic of a fractured well in rectangular drainage areas. In order to reach the aim of increasing productivity meanwhile preventing sand, a new method based on Unified Fracture Design was developed to optimize the fracture geometry. For a specific reservoir and a certain amount of proppant injected to the target layer, there exits an optimal dimensionless fracture conductivity which corresponds to the maximum fracture-flow fraction, accordingly we can get the optimal fracture geometry. The formulas of the optimal fracture geometry were presented on square drainage area conditions, which are very convenient to apply. Equivalent Proppant Number was used to eliminate the impact of aspect ratios of rectangular drainage area, then, the same method to optimize the fracture geometry as mentioned for square drainage areas could be adopted too.