小断块单元油藏单井多周期CO_2吞吐强化采油研究

Study on single well multicycle CO_2 huff-and-puff forced production in small fault block unit reservoir

低渗小断块油藏控制单元井间连通性差、边界封闭、地层能量有限、开采中地层能量下降很快,难以采用早期注水等方式大规模开采。用CO2吞吐强化采油对此类油藏可能是一种有效的方法,为此进行了相关研究:首先对油井目前流体进行相态研究,然后对油藏流体进行CO2膨胀实验,再将注气前、后的地层流体的物性进行对比,确定CO2增产机理;在此基础上建立单井CO2吞吐的数值模拟模型并对注气前生产历史进行拟合,用拟合好的模型对CO2吞吐强化采油过程中周期注入量、注气速度、焖井时间和生产速度等因素进行敏感性分析,从而得出适合于小断块单元油藏单井CO2吞吐强化采油的优选方案,并对第一周期生产指标进行了预测,在此基础上,对第二周期的周期注入量进行了分析,得出相关油井已不适合进行第二周期吞吐的结论,为油井CO2吞吐强化采油可行性的工艺方案设计提供了技术依据。

Low permeability small fault block reservoir control unit has features including poor inter-well connection, sealed borderline, limited formation energy and fast formation energy drop during production. Therefore, it is hard to adopt early stage water injection method to do large scale production. CO_2 huff and puff forced production can be a possible effective way for this kind of reservoir. For this purpose study has been carried out. First, phase state study is conducted on current fluids in oil well. Second, CO_2 expansion experiment is conducted to reservoir fluids. Third, physical properties of formation fluids before and after gas injection are correlated to determine the mechanism of CO_2 production stimulation. Based on this, numerical simulation model of single well CO_2 huff-and-puff is established and production history before gas injection is matched. With the matched model, sensitivity analysis is performed on cyclic injection volume, gas injection rate, shut-in time and production rate during CO_2 huff-and-puff forced production. Consequently, optimized solution of single well CO_2 huff-and-puff forced production fitting small fault block unit reservoir is obtained, and production indexes of the first cycle are predicted. Based on this, cyclic injection volume of the second cycle is analyzed, reaching a conclusion that the well is not applicable for the second cycle of huff-and-puff. Technical reference is provided to the technical solution design of oil well CO_2 huff-and-puff forced production feasibility.