Horizontal well spacing optimization and gas injection simulation for the ultra-low-permeability Yongjin reservoir

Abstract

Optimal spacing for vertical wells can be effectively predicted with several published methods, but methods suitable for assessing the proper horizontal well spacing are rare. This work proposes a method for calculating the optimal horizontal well spacing for an ultra-low permeability reservoir – the Yongjin reservoir in the Juggar Basin, northwestern China. The result shows that a spacing of 640 m is the most economical for the development of the reservoir. To better develop the reservoir, simulation approaches are used and a new model is built based on the calculated well spacing. Since the reservoir has an ultra-low permeability, gas injection is regarded as the preferred enhanced oil recovery (EOR) method. Injection of different gases including carbon dioxide, methane, nitrogen and mixed gas are modelled. The results show that carbon dioxide injection is the most efficient and economical for the development of the reservoir. However, if the reservoir produces enough methane, reinjecting methane is even better than injecting carbon dioxide.