四川盆地七里北区块飞仙关组气藏水层识别及能量分析

Identification and analysis of aquifer and its energy in gas reservoirs of Feixianguan Formation,Qilibei block,Sichuan Basin

四川盆地东北部七里北区块下三叠统飞仙关组气藏为高含硫构造气藏,气藏中部埋深4750 m左右,气藏评价阶段测试资料少,气水界面分布不清。为降低水侵对气藏开发的影响,水层的早期识别和能量判断尤为重要。通过采用纵横波速度比值法、孔隙度—含水饱和度交会图法和P1/2正态分布法进行水层识别并应用MDT测试数据进行了验证,采用与相邻区块物性相近水井类比的方法估算了研究区水层能量。结果表明:①七里北区块飞仙关组气藏气水界面为5832 m;②水层岩性以溶孔鲕状云岩、针孔白云岩和鲕状灰质白云岩为主,高低渗透层段交错分布,物性整体差于气层;③水层体积和弹性能量有限,不足以形成影响气藏生产的有效水驱能量。

Most gas reservoirs of Triassic Feixianguan Formation,Qilibei block,northeastern Sichuan Basin,are high-sulfur structural ones with middle burial depth of 4750 m.There is less test data in the stage of reservoir evaluation.So,it is difficult to determine the distribution of gas-water contact clearly.In order to reduce water-invasion effect on reservoir development,it is quite important to identify the aquifer and judge its energy in the early development stage.In this study,aquifer in reservoirs was identified by means of three methods of P-S wave velocity ratio,porosity-water saturation crossplot,and P^1/2 normal distribution method,and verified by using MDT data.Then,the energy of the aquifer was estimated by taking several water wells with similar physical properties in the adjacent area as the analogs.Results show that,(1)the gas-water contact of Feixianguan gas reservoirs in Qilibei block is at the burial depth of 5832 m;(2)the aquifer is lithologically dominated by dissolved-pore oolitic dolomite,pinhole dolomite,and oolitic limy dolomite.It is featured by high-permeability layer interbedded with low-permeability ones,and worse physical properties than those of gas layer;and(3)for the aquifer,the volume and elastic energy are too limited to provide an effective water-driving force which can influence on reservoir development.