Design and Demonstration of Creating Underground Gas Storage in a Fractured Oil Depleted Carbonate Reservoir

Abstract

Abstract The supply-demand misbalances of natural gas in China require the creation of underground gas storages (UGS) available during peak winter demand and these UGS will probably play an important role in China natural gas market development. As far as know, among existing UGS in China, fractured oil depleted carbonate reservoir converted into UGS is unprecedented. In this paper, a simulation study using both 3D full-field black oil reservoir model and full-field multi-component reservoir model were undertaken to evaluate and demonstrate feasibility of creating UGS in a buried hill fractured oil depleted carbonate reservoir with bottom water, sufficient closure, a good quality and tight cap rock. History matching of the reservoir and single well pressure, water cut, liquid production rate was performed with the full-field black oil reservoir model. The full-field multi-component reservoir model was used to determine total gas storage capacity, working gas capacity, deliverability and injection capacity of the UGS. The simulation study characterized the UGS working mechanism, analyzed its sensitivity, optimized its design parameters, predicted field performance under various operating conditions and recommended the optimized developing UGS plan. Effects of the other three buried hills on the UGS are also incorporated into the two reservoir models. CNPC is further verifying our research efforts to decide duration of the UGS project. Introduction Underground gas storage (UGS) is a relatively modern technique for mitigation detrimental effect of the supply-demand misbalances that has been developing rapidly and is now an essential part of the gas chain. Total numbers of operational UGS in the world amount 602 and 90 % of which represent the porous storages. Stimulated by the changes taking place on the gas market, underground gas storage will probably continue to be developed in the future years[1]. Storage reservoirs are high-deliverability and often closer to the end user compared to the reservoirs from which the natural gas is originally produced. There are three major types of "reservoirs" common to the underground storage of natural gas[2]:depleted reservoir storage,aquifer storage andsalt cavern storage. Each storage reservoir has very specific producing parameters. Salt caverns have the highest deliverability per storage site, even though the vast majority of working gas resides in depleted oil and gas reservoirs. The first experiment of the gas injection in a reservoir has been made in Canada, Ontario in year 1915. In 1916 was created the first UGS on bases of the depleted field in USA, State of New York. Firstly an aquifer, the salt cavern, abandoned mine and lined rock cavern were used in 1946 (Kentucky, USA), 1961 (Michigan, USA), 1963 (Colorado, USA), and 2002 (Skallen, Sweden) respectively. The transformation of the gas or oil depleted reservoir in a storage facility is simple and cheaper, because they satisfy the required permeability and porosity conditions. However, before developing gas storage in a depleted field, it is vital to check whether it provides the required high throughputs over short periods (from 300 to 5000 Mm3 during the coldest, winter period) and the tightness of the cap rocks. The principle of aquifer storage is to create an artificial gas field by injecting gas into the voids of an aquifer formation. For this reason, existence of an anticline with sufficient closure, a porous and permeable reservoir, and a good quality and tight cap rock are necessary. The principle of USG arrangement in salt cavern consists in dissolving the salt by leaching with water and removing the brine via a single well, which then serves for gas injection and withdrawal. These reservoirs serve to store relatively smaller quantities of gas (ranging from 50 to 500 Mm3). Salt caverns which are also a useful balance to the large porous reservoirs and they offer high deliverability, high degree of availability, short filling period, low percentage of cushion gas and total recovery of cushion gas when decommissioned.