延长油田滞后注水区注水开发特征及效果

Characteristics and Effects of Waterflooding Development in the Delayed Waterflooding Areas of Yanchang Oil Field

延长油田地理位置处于黄土高原之中,水资源匮乏,地面条件恶劣,早期开发未实施注水,且井网很不规则。为高效开发石油资源,近年采取补救性注水开发,取得了显著的增油效果,但也暴露了很多问题。本文通过注水区产量、含水、地层压力、注水压力、注采比及采收率分析,研究了延长低渗透油田注水开发特征,评价注水开发效果及注水参数的适应性。不同的油藏性质表现出不同的注水开发特征,反映了对不同注水技术政策的需求。延安组底水油藏和弱底水发育的延长组长2油藏,储层物性相对较好,渗透率在2.0×10-3—80×10-3μm2之间,在温和注水条件下,储层流体以孔隙渗流为主,注水各向受效均衡,油田原有不规则井网基本适应。延长组长6油藏为裂缝性岩性油藏,储层物性差,渗透率在0.3×10-3—2.0×10-3μm2之间,注水开发受储层裂缝及砂体展布方向影响较大,油田原有不规则井网注水适应性差,方向性含水上升快,后期调整困难,沿裂缝强化注水方式很难在老井区实施。指出针对长6油藏不规则井网,常规堵水、调剖措施将是改善注水开发效果的有效途径,并提出增加注水井的"多点少注"的注水开发方式的设想。针对长6油藏纵向多油层复合连片的特点,提出分层注水的必要性。

Yanchang Oil Field is located in the Loess Plateau, where the water resource is deficient and the ground conditions are hostile. In the oil field, waterflood had not been implemented and the well pattern was very irregular in the early development stage. In the recent years, for the efficient development of oil resources, a remedial waterflooding development mode has been implemented. The analysis on oil production, water cut, formation pressure, injection pressure, injection production ratio, and recovery is very important. The waterflood characteristics of Yanchang low permeability reservoirs are analyzed and studied in details and the waterflooding development effect and its influence factors are evaluated based on the waterflood practices of three major reservoirs in Yanchang Oil Field in order to provide the theoretical guidance for the efficient waterflooding development of Yanchang Oil Field. Different reservoir properties show different waterflooding development characteristics and need different waterflood policies. For the bottom water reservoirs of Yan＇an formation, and the Chang 2 reservoirs of Yanchang formation, with weak bottom water development, the physical reservoir properties are relatively good with the permeability range of 2.0×10^-380×10^-3μm^2, under the conditions of mild waterflood, the movement of reservoir fluid is mainly percolation among pores, all directions receive injected water evenly and the original irregular well pattern is basically suitable. Chang 6 reservoir of Yanchang Fm. is a fractured lithologic reservoir with poor physical properties, e.g. the permeability is of 0.3×10^-3-2.0×10^-3μm^2, the waterflooding development is significantly impacted by the fracture directions and sand body distribution directions. The waterflood adaptability for the original irregular well pattern of the oil field is poor due to rapid increase of directional water cut and difficulties in late-stage adjustment. In addition, the strengthened waterflood mode along fractures is difficult to be implemented in the old well areas as well. It is concluded that for the irregular well pattern of Chang 6 reservoir, the measurement involving conventional water plugging and profile control would be an effective way to improve the waterflooding development effect. At the same time, a waterflooding development mode idea for increasing the amount of water injection wells and controlling the injection rate of each injection well is proposed. In addition, based on the features of Chang 6 reservoir, that is, there are many small vertically layers, the necessity for separate-zone water injection is put forward.