Ⅲ类水合物藏水平井降压开采产气动态及影响因素分析

Analysis of gas production dynamic and influencing factors in depressurization production of horizontal wells in ClassⅢhydrate reservoir

水平井是实现Ⅲ类天然气水合物藏高效降压开采的重要手段之一。为明确Ⅲ类水合物藏水平井降压开采的生产动态及变化规律,建立了以Ⅲ类水合物藏为研究对象的、基于Tough+Hydrate水合物降压开采模型,从气体分解速度、累计产气量、产气峰值和产水等角度分析了水平井产气动态,研究了水合物饱和度、束缚气饱和度、生产压力和水平段长度对产气过程的影响。研究结果表明,产气曲线存在显著的峰值,可分为波动上升、快速下降和缓慢下降3个阶段,且在开采初期的产水量较大;产气速度峰值随着水合物饱和度和束缚气饱和度的增加而降低且出现时间延后;随着生产压力的降低和水平段长度的增加,产气速度峰值上升且整个生产进程加快。根据上述分析,在生产初期应合理配置产出水处理装置,保障安全生产。对于水合物饱和度和束缚气饱和度较高的储层,可采用压裂等辅助手段释放产能。除常规水平井外,还可采用多分支水平井来增加接触面积,进一步提升产能。

Horizontal well is one of the important means to realize efficient depressurization production of ClassⅢgas hydrate reservoir.In order to obtain the production dynamic and change rules of depressurization production of horizontal wells in ClassⅢhydrate reservoir,a depressurization production model with ClassⅢhydrate reservoir as the research object is established based on Tough+Hydrate to analyze the horizontal well gas production dynamic from the viewpoints of gas decomposition rate,cumulative gas production,gas peak rate and water production rate,and to study the impact of influencing factors on gas production process,including hydrate saturation,included gas saturation,production pressure and horizontal section length.The results show that,with a obvious peak value,the gas production curve can be divided into three stages,including fluctuating rise,rapid decline and slow decline,and the water production rate is relatively high at the early stage;With the increase of hydrate saturation and included gas saturation,the peak gas rate decreases and delays;The peak gas rate rises and the whole production process is accelerated with the decrease of production pressure and increase of horizontal section length.According to the above analysis,the treatment plant of produced water should be reasonably deployed at the initial production phase to ensure safe production.For reservoirs with high hydrate saturation and included gas saturation,measures such as fracturing can be applied to release productivity,and in addition to conventional horizontal wells,multi-lateral horizontal wells can also be used to increase contact area and further improve the productivity.