川西侏罗系气藏动态特征及开采对策

Dynamic Character and Production Countermeasure for Jurassic Gas Reservoirs in West Sichuan

新场气田上沙溪庙组和马井气田蓬莱镇组气藏是川西气田的两大主力气藏,其气层平均孔隙度7.90%~10.84%,平均砂岩厚度8.70~30.30m,平均含气饱和度45.80%~55.00%,地层压力系数1.36~2.05,平均有效渗透率分别为0.11m D和0.16m D,累计储量丰度分别为3.23×108m3/km2和1.65×108m3/km2,属于典型的低渗致密砂岩气藏,开发难度较大。气藏开采早期压力、产量递减快,压力月递减2.29MPa;气层连通性差,压力传播范围有限,波及半径一般小于300.00m,单井控制储量低,平均3000.00×104m3;低压低产期长,56.13%~75.62%的可采储量是在井口压力低于3.50MPa阶段采出的。在气藏动态分析的基础上,提出了采用非均匀菱形调整井网及老井挖潜转层提高储量的动用;确定气井投产初期的合理工作制度,提高高压阶段的采出程度;低压、低产阶段是气井产气量采出最多的时期,必须高度重视此阶段的措施维护,以提高气藏采收率为目的。

Gas reservoirs in upper Shaximiao Formation of Xinchang gasfield and those in Penglaizhen Forma- tion of Majing gasfield are the main gas reservoirs in West Sichuan gasfield.They are difficult to produce for they belong to low permeability tight sandstone gas reservoirs.Average porosity is 7.90%-10.84% and average sandstone thickness is 8.70-30.30m in the gas reservoirs.Average gas saturation is 45.80%-55.00% and for- mation pressure coefficient is 1.36-2.05.Average effective permeability is O.11mD and 0.16mD respectively.Cu- mulative reserve abundance is 3.23×10 8m3/km2 and 1.65×10 8m3/km2 respectively.In early period of gas reser- voir production,pressure and output declined quickly with monthly pressure decline of 2.29MPa.Pressure prop- agation range was limited for poor communication of the gas reservoirs with less than 300.00m of swept ra- dius.Reserves controlled by single well is low and the average value is 3000.00×10 4m3.The period of low output at low pressure is long,and 56.13%-75.62% of the recoverable reserves were produced during the stage of wellhead pressure under 3.50MPa.Based on dynamic analysis of the gas reservoirs,heterogeneous rhomb well pattern and tapping the potential in old wells will improve the production of the reserves.Reasonable working system in initial period of gas well production is fixed to increase degree of reserve recovery during the high pressure stage.Most gas production is produced during the period of low output at low pressure,so measure maintenance should be paid more attention to improve recovery efficiency of the gas reservoirs.