煤层气静态与流动物质平衡法研究及应用

Study and application of CBM static and flowing material balance methods

煤储层产水气规律不同于常规含水气藏,含气量变化受Langmuir压力及解吸速度的影响,给储层评价带来了难度。通过文献调研发现物质平衡方法在常规油气藏中应用较为广泛,而在非常规储层应用研究较少。在前人的研究基础上根据煤储层流体产出规律,划分煤层气典型生产阶段并建立对应产量预测模型;推导建立静态与流动物质平衡模型,考虑煤储层吸附解吸特征的影响,利用井底流压、累积产量等生产数据确定单井控制储量和储层渗透率。研究结果表明:煤储层孔隙割理自生水量有限,初期高,中后期减弱;煤层物性在生产过程中呈现先下降后上升的特征,受到应力敏感和基质收缩效应的双重影响;静态与流动物质平衡方法均可计算单井动态控制储量,但流动物质平衡方法避免了关井测压对储层产能恢复的伤害,且可得到储层动态渗透率。静态与流动物质平衡方法相比,计算结果较为相近,可为控制储量计算及物性评价提供依据。

Water and gas production law in coal bed reservoir is different from that of conventional containing-water gas reservoir, and gas content change is affected by Langmuir pressure and desorption rate, which bring difficulty to accurate reservoir evaluation. Through the literature research, it was found that the material balance method was widely used in conventional reservoirs, greatly more than that in unconventional ones. On the basis of previous studies, the paper has divided typical production stage, and set up corresponding production model in terms of CBM fluid output law. Meanwhile, static and flowing material balance models were derived and set up to determine single well controlled reserves and permeability by considering the influence of adsorption and desorption characteristics and using bottomhole flowing pressure and cumulative output etc. The research results showed that connate water in coal reservoir pore cleet was finite, high content at initial stage and later weakening; coal bed physical property was featured with falling first and then rising in the process of production, which was affected by stress sensitivity and matrix shrinkage effects. Static and flowing material balance methods can calculate the single well dynamic controlled reserves, but flowing material balance method can avoid the harm of shut-in pressure measurement to the recovery of reservoir productivity, and obtain the dynamic reservoir permeability. Both flowing and static material balance methods have similar calculating results. The research is of great significance to the calculation of controlled reserves and evaluation of physical property.