Yan Xinlu, Tang Shuheng, Fu Xiaokang, Dong Xianshu, Li Zhongcheng, Deng Zhiyu, Meng Yanjun
College of Mining Engineering, Taiyuan University of Technology, Taiyuan 030024, China.
China United Coalbed Methane (Shanxi) LTD., Taiyuan 030032, China.
ACS Omega. 2024 Jul 12;9(29):32210-32225. doi: 10.1021/acsomega.4c04970. eCollection 2024 Jul 23.
Advanced description of pressure drop funnel is crucial in coalbed methane (CBM) production because of dewatering and depressurization methods. Improving the precision of the pressure drop funnel description facilitates obtaining the actual production status and productivity potential, both pivotal for responsible development plans. The study presents a semianalytical model that integrates pressure profiles and material balance equations, incorporating inner and outer boundary conditions, and dynamic reservoir characteristics. The pressure propagation characteristics in undersaturated coal reservoirs are described during the production life of CBM wells, and the model is validated using two wells with different production characteristics. The results indicate that the effect of water saturation on the expansion of the drainage radius surpasses that of the desorption radius, demonstrating a more precise prediction of the production boundary when dynamic water saturation is considered. Additionally, a rapid drop rate of bottomhole flowing pressure triggers simultaneous propagation of the drainage and desorption radii, resulting in a smaller production boundary and fewer well-controlled resources. Conversely, an appropriate production strategy results in a larger drainage radius and lower boundary pressure before massive gas desorption, thereby facilitating efficient propagation of the pressure drop funnel. Moreover, the pressure drop funnel characterized by the model can compute the dynamic CBM resources and recovery efficiency of a single well, providing a valuable basis for assessing productivity potential. In summary, this model offers a time-saving and practical tool for describing the dynamic pressure drop funnel in various CBM production stages and promoting efficient development for undersaturated CBM reservoirs.
由于煤层气（CBM）生产中的排水和降压方法，压降漏斗的高级描述至关重要。提高压降漏斗描述的精度有助于获取实际生产状态和产能潜力，这两者对于合理的开发计划都至关重要。该研究提出了一个半解析模型，该模型整合了压力剖面和物质平衡方程，纳入了内边界条件和外边界条件以及动态储层特征。描述了煤层气井生产寿命期间欠饱和煤储层中的压力传播特征，并使用两口具有不同生产特征的井对该模型进行了验证。结果表明，水饱和度对排水半径扩展的影响超过了解吸半径的影响，这表明在考虑动态水饱和度时对生产边界的预测更为精确。此外，井底流动压力的快速下降速率会触发排水半径和解吸半径的同时扩展，导致生产边界变小且控制的资源减少。相反，适当的生产策略会在大量气体解吸之前导致更大的排水半径和更低的边界压力，从而促进压降漏斗的有效扩展。此外，该模型表征的压降漏斗可以计算单井的动态煤层气资源和采收率，为评估产能潜力提供有价值的依据。总之，该模型为描述煤层气不同生产阶段的动态压降漏斗和促进欠饱和煤层气藏的高效开发提供了一种省时实用的工具。
