煤层气鱼骨状分支水平井轨道优化设计

An optimal design for herring bone well trajectory drilling through coalbed gas reservoirs

我国的煤层普遍渗透率较低,影响了煤层气开发效果,鱼骨状分支水平井能够有效增大煤层气储层裸露面积、提高煤层气的单井产量,因而近年来被普遍采用。但常规二维轨道设计方法难以满足各分支水平井井眼轨道的设计要求。为此,将各个分支拆分成相对独立的待钻轨道与主井眼轨道,分别加以设计计算——拆分后的井眼轨道可以转化为二维轨道来进行设计;结合鱼骨状分支水平井的特点,建立了分支水平井眼轨道最优化设计模型,并对分支井眼与主井眼的关系进行了分析研究。结果表明:随着井深、造斜率的增加,分支井眼与主井眼的直线夹角增加且分支井眼偏离主井眼的距离是逐渐增大的;在直线夹角一定的情况下,造斜率与井深呈反比关系(造斜率越高所需要的分支井井段越短,造斜率越低则所需要的分支井井段就越长)。

Extremely low permeability of coalbed gas reservoirs will have a negative effect on the coalbed methane development in China.The herring bone wells can effectively maximize the reservoir exposure area to improve the production rate out of each methane gas well so as to be commonly used for coalbed gas development in recent years.However,the conventional 2D trajectory design method is hard to meet the requirements of each horizontal branch for a good herring bone well trajectory design.In view of this,a 2D well trajectory design is first achieved by respective treatment of each branch regarded as an independent unit with the main vertical wellbore.Then according to the features of herring bone wells,a model for the optimization design of herring bone well trajectory is set up and the relationship between each horizontal branch bore and the mother bore is also studied.The results show that with the increase in well depth and the build-up rate,the angle between the branch bore and the mother bore will increase,and the offset of the branch bore away from the mother bore will also gradually increase.For such a constant angle,the build-up rate is in inverse proportion to the well depth,that is,the higher the build-up rate,the shorter the branch;or vice versa.