越南白虎油田缝洞型基岩油藏特征与开发对策

Characteristics and Development Strategy of Fracture-cavern Basement Oil Reservoir in White Tiger Field,Vietnam

白虎油田位于越南东南兰龙盆地早新生界中央隆起带基岩断块,以花岗岩和花岗闪长岩为主。白虎油田基岩油藏原始地层压力为41.7MPa,油藏温度为140℃,属于常温常压油气藏。原始相对密度为0.654,泡点压力为22.4MPa。原始气油比为190m^3/t,原始黏度为1.5mPa·s,地下原油相对密度为0.4。该油藏储量规模接近10×10~8t,单井日产油低的上百吨,高的可达几千吨,是少见的高储量丰度、高产能的基岩油气藏。微裂缝以及伴生洞对油气储集的贡献在70%～80%;采取底部注水形成人工底水的驱动方式,直井和侧钻井的注采井网,保持地层压力在泡点压力1～2MPa之上;油井自喷为主兼顾气举的开发技术对策,以及井网调整、吸水剖面与产液剖面调整、注采液量调整等对策的应用,保证了油井外利用效率,使该油藏保持了长达15a的稳产高产,最高年产油达1300×10~4t,采收率可达39.3%。

White Tiger oilfield,located on a faulted basement block along the Lower Cenozoic central uplift belt in Cuu Long basin,Vietnam,is mainly composed of granite and granodiorite.Its basement reservoir is 41.TMPa in original pressure,140℃ in temperature,0.654 in original oil relative density and 22.dMPa in bubble point pressure,with original gas-oil ratio 190m^3/t,original viscosity 1.5mPa·s and subsurface crude relative density 0.4.With the oil reserves close to 10×10^8t and the daily single-well production from a hundred to a few thousands tons of oil,it is a rare basement reservoir of high abundance and productivity.The contribution of microfractures and their associated caverns to hydrocarbon accumulation may accounts for 70% -80%,and the formation pressure has been maintained at 1-2MPa over the bubble point pressure by an artificial bottom-water drive of basal injection and an injection-production pattern of vertical and lateral wells. A development technique strategy used in the field is dominance of flowing oil production with a consideration of gas lift,and a series of modification measures at various levels were adopted,such as well pattern ,injection profile,liquid production profile and injection and recovery liquid volumes.Therefore,the efficiency of oil wells were ensured,resulting in 15 years of stabilized and high production in this reservoir,with the maximum annual oil output 1300×10^4t and the recovery factor 39.3%.