Research into relative permeability dynamic calculation methods for coalbed methane reservoirs
HUANG Tianhao, WANG Zhiming, ZENG Quanshu, CAI Xianlu, DAI Anna
1 College of Petroleum Engineering, China University of Petroleum-Beijing, Beijing 102249, China 2 State Key Laboratory of Petroleum Resources and Engineering, China University of Petroleum-Beijing, Beijing 102249, China
摘要
为获取煤层气藏气水相对渗透率实际变化特征，进一步深化对煤层气藏气水产出规律的认知，构建了结合煤层气藏实时动用情况的煤层气藏相对渗透率动态计算方法。该方法首先通过多煤层全过程耦合流动模型对目标单煤层或多煤层进行产量历史拟合，获得储层和流体的基本物性参数。而后，基于得到的基本物性参数开展煤层气井全生产周期产能预测，同时，根据储层压降漏斗的实时扩展规律对储层参数进行平均化处理，并结合流体的实际运移情况计算煤层气藏气—水相对渗透率曲线。研究结果表明：本文提出的煤层气藏相对渗透率动态计算方法可在对煤层气藏内部动用情况实时定量分析的基础上，动态计算煤层气藏实际气水相对渗透率。通过本文提出的方法计算得到的气相相对渗透率曲线上存在反转点，其反应储层中的解吸气开始稳定、连续的供应。若不考虑储层压降漏斗实际扩展规律，对储层参数进行全域平均，计算得到的煤层气藏气水相对渗透率将偏低。对于多煤层气藏，窜流效应导致的层间流体质量交换和储层压力下降不可忽略，生产3 y 时气相窜流量与产气量比值可达0.57，水相窜流量与产水量的比值可达0.69。忽略窜流量条件下计算得到的煤层气藏气水相对渗透率偏低，仅为考虑窜流量条件下的42.89% 和24.40%。在煤层气井实际生产过程中，含水饱和度保持在较高值，大于40%，受高含水饱和度的制约，煤层气藏气相相对渗透率值较低，小于0.2。
In order to obtain the actual change characteristics of the gas-water relative permeability in coalbed methane (CBM) reservoirs and to further deepen the understanding of the gas-water production process of CBM reservoirs, a relative permeability dynamic calculation method of CBM reservoirs combined with the real-time production situation of the reservoir was constructed. Firstly, the production history match of the target single coal seam or multiple coal seams is carried out using the multiple coal seam whole process coupling flow model, which is to obtain the basic physical parameters of the reservoir and fluid. Then, based on the obtained basic physical parameters, the full production cycle productivity prediction of the CBM well is carried out. At the same time, the reservoir parameters are averaged according to the real-time expansion behavior of the reservoir pressure drop, and the gas-water permeability curve of the CBM reservoir is calculated based on the averaged reservoir parameters and the actual fluid migration. The results show that the relative permeability dynamic calculation method of CBM reservoirs proposed in this paper can dynamically calculate the actual gas-water relative permeability of the CBM reservoir on the basis of real-time quantitative analysis of the internal production situation of the CBM reservoir. There is a reversal point on the gas relative permeability curve calculated by the method proposed in this paper. The reversal point characterizes the stable and continuous supply of desorption gas in CBM reservoirs. If the actual expansion of the CBM reservoir pressure drop is not considered and the reservoir parameters are averaged in the whole area, the calculated gas-water relative permeability of the CBM reservoir will be low. For multiple coal seam reservoirs, the interlayer mass exchange of fluids and the decrease in the reservoir pressure caused by the crossflow cannot be ignored. The ratio of the crossflow of gas to gas production can reach 0.57, and the ratio of the crossflow of water to water production can reach 0.69 after 3 years of production. The calculated gas-water relative permeability of the CBM reservoir under the condition of ignoring the crossflow is low, which is only 42.9% and 24.4% respectively of the calculated gas-water relative permeability under the condition of considering the crossflow. In the actual production process of CBM wells, the water saturation remains at a high value, more than 40%. Restricted by the high water saturation, the gas relative permeability of CBM reservoirs is low, less than 0.2.
