低煤阶煤层气藏物质平衡方程建立及应用

Establishment and Application of Material Balance Equations for Low-rank Coalbed Methane Reservoirs

针对低煤阶煤储层孔隙结构特征和储集机理,考虑煤基质较大孔隙中游离气、水的影响,建立了一个新的欠饱和低煤阶煤层气藏物质平衡方程。结合低煤阶煤层气藏的地质和生产动态资料,利用该物质平衡方程即可确定其地质储量。通过实例应用验证了新方程的准确性和适用性。与不考虑煤基质较大孔隙中游离气、水影响的陈元千方法相比,新方程计算的低煤阶煤层气藏地质储量值与实际值之间的误差更小,因此煤基质较大孔隙中存在的大量游离气和水在实际应用中不可忽略。新方程为低煤阶煤层气藏的动态储量评价分析提供了一种更加有效的方法。

According to the pore structure and storage mechanism,considering the effects of free water and gas in the macropores of coal matrix,a new material balance equation was established for the undersaturated low rank coalbed methane reservoirs.The original gas in place（OGIP）for low rank coalbed methane reservoirs can be effectively determined by the new equation in combination with the geological and dynamic production data.Moreover,the case study verified the validity and applicability of these equations.Compared with the Chen Yuanqian′s method,the relative error between the actual and predicted OGIP by the new material balance equation is smaller,and therefore substantial free water and gas in the macropores of coal matrix should not be neglected in practical applications.The new material balance equation provides a more effective reserve estimation method for low rank coalbed methane reservoirs.