煤层气复杂渗流机制下水平井压裂参数优化研究

Study on optimization of fracturing parameters for horizontal wells under complex flow mechanism of coalbed methane

为了优化不同煤层条件下的水平井压裂参数,考虑气体解吸和气水两相流动特征建立了渗流模型,采用PEBI网格和有限体积法进行求解.根据煤层的渗透率和厚度特征,划分了4种煤储层类型,建立了相应的机理模型,进而模拟计算了不同水平井压裂参数下的累计产气量和压力场.研究发现:煤层性质极大影响了多段压裂水平井的产能,通过分析不同煤层性质条件下水平井压裂参数与累计产气量的关系曲线,得到了模拟条件下水平段长度、裂缝半长和裂缝间距的最优值.对于厚度大的煤层建议水平段长度控制在1300m,裂缝间距为75~100m,裂缝半长为60m;对于厚度小、渗透率高的煤层建议水平段长度控制在1500m以上,裂缝间距为75m,裂缝半长则是越大越好;对于性质很差的煤层不建议采用多段压裂水平井开发.

Flow models were established based on gas desorption and gas-water two-phase flow characteristics to optimize fracturing parameters for horizontal wells under different coal seam conditions,and PEBI grid and finite volume method were used to solve the problems.According to the permeability and thickness of coal seams,coal reservoirs were divided into four types,and corresponding mechanism models were established.And then cumulative gas production and pressure field were simulated with different fracturing parameters.The study found that coal seam properties greatly affected the productivity of horizontal wells after fracturing in multiple stages.After analyzing the relationship between fracturing parameters and cumulative gas production under different coal seam properties,optimal horizontal section length,fracture half-length and fracture spacing were obtained under simulated conditions.For thick coal seams,it is recommended that the length of the horizontal section be 1300m,the fracture spacing be 75-100m,and the fracture half-length be 60m.For thin and permeable coal seams,it is recommended that the length of the horizontal section be above 1500m,the fracture spacing be 75m,and the fracture half-length should be longer as possible as it can.For coal seams with poor properties,multi-stage fracturing stimulation is not recommended.