海上低渗油藏注水水质关键参数界限研究——以涠洲11-4N油田流沙港组为例

Key parameter limits of water injection quality in offshore low permeability reservoir:A case study of Liushagang Formation in Weizhou 11-4N Oilfield

针对海上低渗储层微观孔隙结构认识不清,影响注水水质关键参数界限确定的问题,以涠洲11-4N油田流沙港组为例,从室内实验角度出发,通过恒速压汞实验刻画各区块储层微观孔隙结构特征,在此基础上开展注水水质实验,评价水质关键参数对储层渗流能力的影响。研究结果表明:喉道大小及分布是决定储层渗流能力的主要影响因素,渗透率与主流喉道半径有较好的幂函数关系,流一段、流三段主流喉道半径主要分布在4μm、1μm左右,前者流动能力较强;注入水中悬浮物颗粒粒径、颗粒质量浓度、细菌含量增加会大幅度增加注水压力,降低岩心渗透率。以储层吸水指数伤害程度20%为下限,建立了不同渗透率级别的注水水质关键参数界限,流一段储层推荐注入海水中悬浮物颗粒质量浓度小于等于2.0 mg/L、悬浮物颗粒直径中值小于等于3.0μm、细菌小于等于100个/mL。据此指导注水并配合海水软化处理技术,实现了涠洲11-4N油田主力层位的有效开发。

The unclear understanding of the micro pore structure in the offshore low permeability reservoir affects the determination of the key parameter limits of water injection quality.Therefore,water injection quality evaluation experiment is carried out based on the characterization of reservoir micro pore structure in Liushagang Formation of WZ11-4N Oilfield studied by indoor constant velocity mercury injection experiment,then to evaluate the influence of the key parameters of water quality on the seepage capability.The results show that the throat size and distribution are the main factors that determine the seepage capability of reservoir.There is a good power function relation between permeability and mainstream throat radius.The throat radius of the first section in the Liushagang Formation is about 4μm,while 1μm for the third section,and the former has strong flow capacity.The increase of the particle size,particle concentration and bacterial content of the suspended solids in the injected water will greatly increase the injection pressure but decrease the core permeability.Taking the damage degree of water absorption index to reservoir,20%,as the lower limit,the key parameter limits of injected water quality of reservoirs with different permeability levels are established.For the first section of the Liushagang Formation,the water quality of the recommended injected seawater are of the concentration that the suspended solids particles is less than or equal to 2.0 mg/L,the median diameter of suspended solid particles is less than or equal to 3.0μm,and the number of bacteria per milliliter is less than or equal to 100.According to the guidance of these above data,the effective development of the main formation in Weizhou 11-4N Oilfield is realized by the combination of water injection and seawater softening treatment technology.