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基于气举的煤层气/致密砂岩气同井合采可行性研究

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

  • 摘要: 在我国鄂尔多斯盆地等地存在多个煤系气富集区,具有煤层气与致密砂岩层垂向上叠置分布的特点,但多数煤系气井单采致密砂岩气或煤层气存在资源利用率低,经济效益差,而两气合层开采可提升开发效益。针对上部高压致密砂岩气层下部低压煤层气的储层叠置关系,提出了一种同井筒气举合采的工艺管柱结构,基于闭式气举管柱的改进,利用上部高压致密砂岩气的能量,将下部煤层气储层的井液举升至地面,实现煤层气储层降压、解吸、产气,达到两气合采的目的。根据气举动态方程,分析煤储层不同产液量、储层深度条件下致密砂岩气的气量、压力等的关系,得出了井口油压、套管压力、气举深度、环空气量、油管直径等气举合采关键参数的选择依据。结合典型井例,给出了设计验证和应用的适应性条件,气举合采管柱适用于上部煤层气与下部致密砂岩气合层开采,为多气合采提供一种有效、经济的排采管柱。

     

    Abstract: 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.

     

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