Feasibility study on co-mining in the same well of coalbed methane andtight sandstone gas based on gas lift

The coal formed gas enrichment areas in Erdos Basin of China have vertical superimposed distributed coalbed methane and tight sandstone layers. However, most of the coal formed gas wells have low utilization rate and low economic benefit because these gas wells only produce a single type of gas, coalbed methane or tight sandstone gas. This paper focuses on development of a new method to improve efficiency of gas wells. Improved from the closed gas lift pipe, this method mines coalbed methane or tight sandstone gas simultaneously in the same gas well. The principle of the new method is to utilize the energy of upper layer high pressure tight sandstone gas to lift the well fluid of lower layer coalbed methane to the ground through the closed gas lift pipe string. While mining tight sandstone gas, the coalbed methane is depressurized, desorbed, and extracted simultaneously. From the gas lift dynamic curve, this paper analyzes the relationship between gas production and pressure of tight sandstone gas when fluid production and reservoir depths are different. The results provide reference for selecting key parameters on wellhead oil pressure, casing pressure, gas lift depth, annular air volume, and tubing diameter. This paper also provides reference for validation of design and applicable conditions for typical gas wells. The gas lift pipe is suitable for mining upper coalbed methane and lower tight sandstone gas and will provide an efficient and economical method for gas lift co-mining in the same well.