伊拉克A油田Asmari组膏岩特征及成因分析

The Study of Characteristic and Genetic Model for the Anhydrite in Asmari Formation in A Oilfield, Iraq

摘要: 伊拉克A油田Asmari组为半局限–局限台地沉积，岩性以灰岩和白云岩为主，含少量膏岩。根据岩心、薄片、常规测井及成像测井等资料，对研究区膏岩的岩石学特征、测井响应特征、分布规律及成因模式进行了研究。研究发现，Asmari组膏岩主要以硬石膏为主，与灰岩和白云岩相比，具有低自然伽马、高电阻和高密度的测井响应特征。研究区主要发育两种类型的膏岩，一种呈薄层状与白云岩互层分布，平面局部分布，为蒸发环境下原生沉积形成；另一种呈团块状夹杂在白云岩中，为上覆厚层盐膏层卤水下渗充填胶结在白云岩溶蚀孔隙中。膏岩的发育为白云石化作用提供了有利流体环境，促进了研究区白云岩的形成；并且对储层物性、油田开发水淹规律、剩余油分布等有一定的影响。

Abstract: The sedimentary of Asmari Formation in A oilfield in Iraq is semi restricted and restricted platform, and the lithology is mainly composed of limestone and dolomite, with a small amount of anhydrite. Based on the data of core, thin section, conventional logging and imaging logging, the petrological features, logging response characteristics, distribution and genetic models of anhydrite in the study area are studied. It is found that, compared with limestone and dolomite, the anhydrite in Asmari Formation has low natural gamma, high resistance and high density logging response characteristics. There are two types of anhydrite in the study area. One is interbedded with dolomite, which is formed in the evaporation environment. The other is filled in the dolomite stone locally with lumps and plaques feature, which is caused by the fluid containing calcium sulfate from upper thick salt and anhydrite formation to cement in the dissolution pore in dolomite. The development of anhydrite provides a favorable fluid environment for dolomitization, promoting the formation of dolomite in the study area. What’s more, the anhydrite has a certain influence on reservoir properties, water flooding law and distribution of remaining oil.