伊拉克哈勒法耶油田塞迪组碳酸盐岩储层特征及高孔低渗成因分析

通过岩心观察、薄片鉴定、物性测试及实验压汞数据等资料,对伊拉克哈勒法耶(Halfaya)油田塞迪(Sa'di)组以生物体腔孔为主的高孔低渗生物灰岩储层进行了研究。该类储层岩石类型包括颗粒灰岩、泥粒灰岩、粒泥灰岩和泥(晶)灰岩,其中颗粒灰岩分为鲕粒灰岩和生物灰岩。塞迪组以缓坡相为主,发育内缓坡和外缓坡2个亚相,下段储层各项物性参数均好于上段。储层优势孔隙类型为体腔孔和粒内溶孔,压汞数据反映出排驱压力较高、喉道半径小,渗流能力差。储层主要受沉积相控制,不同微相储层特征差异较大,成岩改造作用对次生孔隙的形成有建设性作用,整体胶结作用较弱。生物体腔孔发育,连通性较差;沉积环境水动力条件较弱,被改造程度差;储层受沉积过程控制,成岩改造很弱;孔隙类型多样,但优势孔隙类型对渗透率贡献低是导致储层高孔低渗成因的关键因素。

Characteristics and origin of high porosity and low permeability carbonate reservoirs in the Sa'di Formation,Halfaya Oil Field,Iraq

The high-porosity and low-permeability reservoir in the Sa'di Formation of the Halfaya oil field in Iraq makes this a special oil and gas reservoir in the Middle East. Reservoir characteristics and the origin of high porosity and low permeability were studied by core observation, cast thin sections, physical property testing and mercury injection experiments. Rocks in the reservoir include grained limestones (oolitic limestones and limestones), packstones, wackestones and micritic limestones. The Sa'di Formation is characterized by ramp facies, and develops inner ramp and outer ramp subfacies. The lower part of the formation has better physical properties than the upper part. Pores are mainly intrafossil and intragranular. Mercury injection experiments showed a high driving pressure, small throat radius and poor flowability. The reservoir is mainly controlled by sedimentary facies, and the reservoirs of different facies showed different properties. Diagenetic transformation has constructive effects on the formation of secondary pores, resulting in poor cementation. High porosity and low permeability of the reservoir can be explained by the following factors:(1) Intrafossil pores developed, yet were poorly connected. (2) Sedimentary environment was featured by poor hydrodynamic conditions, and was poorly reformed. (3) The reservoir was controlled by sedimentary process, and the digenesis impact was very weak. (4) Pore types varied, but had low contribution to permeability.