Abstract: The fracture system of coal bed consists of many different kinds of cracks. The original cracks and new cracks caused by the change of stress can form new network structure. The stimulation mechanism of multi-lateral well for coal-bed methane lies in accomplishing the wide area network effect for linking up the fracture system in a widespread range, enlarging the range of pressure drop in coal bed and decreasing the drag when draining coalbed water. The individual well producing rate and recovery ratio can be significantly enhanced. According to the design theory of fluid series and parallel tubes, the constraint equation about length and diameter of multi-lateral well under turbulent flow and laminar flow conditions were established. The compatibility equation for the structure of multi-lateral well was developed. Furthermore, the theoretical base for structure design of multi-lateral well was presented. According to different coal-bed geological condition, the structure models for multi-lateral well including two kinds of turbulent flow types and three kinds of laminar flow types were designed. Those models can be applied to the optimum design of multi-lateral well for coal-bed methane.

Key words: coalbed methane, multilateral well, fluid tube, laminar flow, turbulent flow, well structure, design model

摘要： 煤层裂缝系统由众多不同类型的裂纹组成,原始裂纹与应力变化产生的新裂纹形成网状结构。煤层气多分支井增产机理在于实现广域面的效应,可以大范围地沟通煤层裂隙系统,扩大煤层降压范围,降低煤层水排出时的摩阻,大幅度提高单井产量和采收率。根据流体管路串联和并联原理,建立了层流和紊流条件下的分支井眼长度与直径的约束方程,推导出多分支井身结构协调方程,建立了多分支井身结构设计的理论基础。根据不同的煤层地质条件,设计出2类紊流型和3类层流型的多分支井身结构模型,可用于煤层气田多分支井优化设计。

关键词: 煤层气, 多分支井, 流体管路, 层流, 紊流, 井身结构, 设计模型