垂直压裂井开发下致密砂岩气藏压力分布研究

Study of Pressure Distribution in Tight Sandstone Gas Reservoirs Developed by Vertically Fractured Wells

川西气区属于典型的致密砂岩气藏,直井或水平井压裂后才能获得工业天然气产量,措施后产量压力递减快,采收率低,加密调整井对邻井干扰严重。为厘清致密砂岩气藏开发后地层压力分布,采取针对性措施,提高气藏采收率,提出了Voronoi网格数值模拟法,建立了压裂井数值模型,研究了致密砂岩气藏压裂井地层压力在横向及纵向上的分布,分析了气井的配产、生产时间、地层渗透性等因素对地层压力剖面的影响。结果表明,在平面上,地层压力在压裂裂缝方向和垂直于裂缝方向上渗流不对等,形成椭圆渗流区域;纵向上,压降梯度与气井配产、生产时间成正相关,与地层渗透率成负相关。新场气田沙溪庙组气藏沙二1气层在压裂裂缝方向上,在距井筒60~100m气层中,压力降占生产压差的80%左右。基于地层压力分布特点,采取了部署菱形井网的加密井、优化气井配产及低产水井间开管理等措施,实施后剩余储量区得到有效动用,提高了采收率,延长了气井稳产时间。

The western Sichuan gas province belongs to the typical tight sandstone gas reservoir.Industrial production of natural gas is obtained only in the fracturing of vertical wells or horizontal wells.The production and pressure of the fractured gas well declined rapidly in the production process.The recovery efficiency of the gas reservoir is low. Infilling adjustment wells seriously affect adjacent wells.In order to know the forma- tion pressure distribution of the tight sandstone gas reservoir after development,specific measures is taken to improve the recovery efficiency of the gas reservoir.The method of Voronoi grid is adopted for numerical simulation.The numerical model of fractured well is established.Lateral and vertical formation pressure distribu- tions are studied in the fracturing wells of tight sandstone gas reservoir.The influence of gas well production allocation,production time,formation permeability and other factors on the formation pressure profile is ana- lyzed.The results show that the formation pressure is non-uniform distributed along the direction of fracture and being perpendicular to the direction of fracture,which results in elliptic pressure swept area.In the verti- cal,pressure drop gradient has positive correlation with gas production allocation and production time and negative correlation with permeability.In the fracture direction ,about 80% of the production pressure difference is pressure drop in 60-100m away from the wellbore in No.1 gas layer of Sha2 in Shaximiao Formation of Xinchang gas reservoir.Based on the characteristics of formation pressure distribution,measures such as deploy- ing the lozenge well spacing in the increased fracture direction,optimizing gas well proration and intermittent management for the low-production water well have been taken.After implemented,remaining reserves area has been produced effectively with oil recovery enhanced and period of stable production longer.