Abstract: In order to study the pore throat structure characteristics of marine carbonate reservoir and its impact on water injection development, This paper is a case study of the M Formation in X oilfield in Iraq; comprehensively based on relevant data on core, casting thin section, high pressure mercury injection, nuclear magnetic resonance, three-dimensional CT, displacement experiment and production dynamics, a study is performed on the characteristics and genesis of the pore throat structure of carbonate reservoirs in the Middle East, and their influences on the water injection development of reservoirs, as well as relevant countermeasures. The results show that a variety of pores with different scales, such as matrix micropore, visceral foramen pore, mould pore, intergranular pore and intergranular dissolved pore, are developed in the study area; the radius of pore throat ranges from 0.01 to 100 μm, and micro pore throat, fine pore throat, medium pore throat and coarse pore throat coexist as a multimodal system, resulting in the poor correlation between porosity and permeability. The pore throat structure of carbonate reservoirs depends on the sedimentary environment and differential diagenesis. High-energy deposition and medium-energy deposition have the diagenetic characteristics of "medium-strong dissolution, medium-weak cementation and medium-weak compaction", while low-energy deposition has the diagenetic characteristics of "weak dissolution, medium-strong cementation, strong compaction and medium-strong dolomitization", thus forming Type Ⅰ to Ⅵ pore throat structures. The difference of pore throat structures leads to the poor effect of water flooding development. At the macro level, the reserves produced degree is uneven, and the reservoirs with Type Ⅰ or Type Ⅱ pore throat structure serve as the main contribution to horizontal and vertical well productivity; at the micro level, oil displacement efficiency is not high, and the oil is mainly produced from large pore throats. In the development process, the development mode and production pressure difference should be optimized according to the types of pore throat structure, so as to release the potential of reservoirs with medium or low permeability, and improve the reserves produced degree. In addition, low salinity and mild water injection should be ensured to change the wettability of reservoir rocks, and crude oil should be produced from medium and small pore throats to improve the efficiency of water flooding.

Key words: Middle East, carbonate reservoir, pore throat structure, water injection, development countermeasure

摘要： 为研究海相碳酸盐岩油藏孔喉结构特征及其对注水开发的影响,综合利用岩心、铸体薄片、高压压汞、核磁共振、三维CT、驱替实验和生产动态等资料,以伊拉克X油田M组为例,开展碳酸盐岩储层孔喉结构特征及成因、及其对油藏注水开发的影响和对策研究。研究结果表明:研究区发育基质微孔、体腔孔、铸模孔、粒间孔和粒间溶孔等多种不同尺度的孔隙,孔喉半径分布区间为0.01~100 μm,微孔喉、细孔喉、中孔喉和粗孔喉等多重孔喉体系共存,呈多模态特征,造成储层孔渗相关性差。碳酸盐岩孔喉结构依赖于沉积环境和差异成岩作用,高能沉积和中能沉积为"中强溶蚀、中弱胶结、中弱压实作用"的成岩特征,低能沉积为"弱溶蚀、中强胶结、强压实、中强白云石化作用"的成岩特征,形成了Ⅰ型—Ⅵ型的孔喉结构。孔喉结构差异导致油藏注水开发效果不佳,宏观上储量动用程度不均衡,Ⅰ型和Ⅱ型孔喉结构储层是平面和纵向产能的主要贡献者;微观上驱油效率不高,主要采出的是大孔喉内的原油。在开发过程中,应基于储层孔喉结构类型优化开发方式和生产压差,释放中—低渗储层潜力,提高储量动用程度;并采用低矿化度温和注水,改变油藏岩石的润湿性,动用中、小孔喉内的原油,改善水驱油效率。

关键词: 中东地区, 碳酸盐岩储层, 孔喉结构, 注水开发, 开发对策