Evaluation of the Timing of Different Stages of Collaborative Construction of Underground Gas Storage and Natural Gas Flooding

ABSTRACT: An underground gas storage (UGS) rebuilt from oil reservoir is constructed in collaboration with natural gas flooding, which is a new type of UGS developed in recent years and is called collaborative type UGS. The collaborative type UGS aims to improve the recovery of the original reservoir as much as possible while building the UGS. At present, the construction process of cooperative type UGS has been divided into three stages: oil displacement, collaboration and UGS. However, the transition time node of different stages is still fuzzy, which is very important for the construction of collaborative type UGS. Therefore, in order to clarify the starting time nodes of each state of collaborative type UGS construction, a method is proposed to dividing stages of collaborative type UGS construction based on the full research of cases which the UGS were converted form the oil reservoirs. On the basis of this classification method, a new analytical model of injected gas volume in different construction stages is build based on a new type of gas flooding characteristic curve and material balance method. Finally, we confirmed that our model is well suited for collaborative type UGS. The predicted production of our model is very close compared to the actual production data, and thus the methodology should be attractive to the industry. This study extends existing analytical model methodology for collaborative type UGS and is relatively easy for reservoir engineers to understand. 1. INTRODUCTION Underground gas storage (UGS) is a kind of artificial gas field or gas reservoir formed by injecting commercial natural gas transported by long distance pipeline into underground space. It has important functions such as regulating gas supply in different seasons, strategic energy reserve and obtaining economic benefits. According to statistics from the latest World Natural Gas Congress (GIOUSE, 2018), a total of 689 underground gas storage facilities have been built around the world, with the total working gas volume accounting for 11.8% of the total annual consumption of natural gas. There are 4 types of reservoirs commonly used for underground gas storage 1) oil reservoir 2) gas reservoir 3) aquifer and 4) salt cavern, each of the storage reservoirs has very specific producing parameters (Ding, 2011; Jiang, 2021;). Figure 1 shows the proportion of working gas in different types of underground gas storage.