滇东煤层气井动态渗透率变化特征及其工程优化

Dynamic Permeability Variation Characteristics and Engineering Optimization of CBM Wells in Eastern Yunnan

滇东地区煤层气资源量丰富,但是一直未能实现大规模商业性开发。为实现滇东地区煤层气井的产能突破,首次引入压力降落试井分析方法,对滇东地区煤层气井饱和水单相流阶段的煤储层动态渗透率进行了反演,并提出了改造初始渗透率和见气前渗透率的概念。研究发现,煤储层的改造效果与累计压裂液的总量、累计支撑剂的总量无关,而与储层改造规模(单位米厚压裂液和单位米厚支撑剂)密切相关。改造规模越大,煤储层改造效果越好。为确保滇东煤层气井能获得商业性开发气流,单位米厚压裂液和单位米厚支撑剂分别大于200m^(3)/m、12m^(3)/m。同时,煤层气井在排采初期降压幅度应小于0.017MPa/d,减少煤储层渗透率损害。

Coalbed methane(CBM)resources are abundant in eastern Yunnan,but large-scale commercial development has not been realized.To realize the productivity breakthrough of CBM wells in eastern Yunnan,this paper introduces the pressure drawdown well test analysis method for the first time,inverts the dynamic permeability of coal reservoirs in the single-phase flow stage of saturated water in CBM wells in eastern Yunnan,and puts forward the concept of initial permeability after reservoir stimulation and permeability before gas production.The study found that the stimulation effect of coal reservoirs is not related to the total amount of cumulative fracturing fluid and the total amount of cumulative fracturing sand,but is closely related to the scale of reservoir stimulation(fracturing fluid per meter thickness and fracturing sand per meter thickness).The larger the stimulation scale,the better the effect of coal reservoir stimulation.To ensure that the CBM wells in eastern Yunnan can obtain commercial gas flow,the fracturing fluid per meter thickness and the fracturing sand per meter thickness are greater than 200m^(3)/m and 12m^(3)/m respectively.At the same time,the depressurization amplitude of CBM wells should be less than 0.017MPa/d at the initial stage of drainage to reduce the permeability damage of coal reservoirs.