伊拉克南部白垩系Mishrif组碳酸盐缓坡潮道沉积特征

白垩系Mishrif组是伊拉克南部碳酸盐岩主力产层，属于典型的碳酸盐缓坡沉积，其中内缓坡高能滩相是优质储层最发育的部位。通过对伊拉克南部多个油田资料深入分析，发现Mishrif组中普遍存在有潮道沉积特征的优质储层，且多数潮道沉积在过去被当作另一种滩相沉积。笔者综合大量的岩心、铸体薄片、测井以及地震资料分析后，证实这部分储层为潟湖环境中潮道沉积，其分布广泛，是具有代表性的沉积亚相。潮道沉积岩石颗粒分选、磨圆较好，发育层理构造，粒级向上表现为正韵律或均质特征，对应为“钟形”或“箱形”测井响应特征以及弱波峰夹层地震响应特征，平面上呈北东-南西向条带状分布，整体上表现为由北东向南西迁移的特征。该研究说明碳酸盐岩地层中也发育成规模的潮道沉积，对缓坡背景下沉积模式研究是重要发现和补充。碳酸盐缓坡潮道的认识也为储层预测提供了新思路，进而为该类油藏开发方案设计与调整提供地质基础。

Depositional characteristics of tidal channel facies in carbonate ramp of the Cretaceous Mishrif Formation in southern Iraq

The Cretaceous Mishrif Formation is a major carbonate pay zone in southern Iraq and characterized by typical carbonate ramp deposition, in which high-energy deposits of shoal facies serve to develop the best reservoirs.Further analysis of data from oilfields in southern Iraq reveals high-quality reservoirs in tidal channels of the Mishrif Formation that were previously mistaken for shoal facies.An integrated analysis of cores, casting thin sections, log and seismic data confirms that these reservoirs are indeed of tidal channel facies in lagoon environment.The tidal channel facies is widely distributed as a representative sedimentary subfacies in the area.The sediments of the facies contain grains of good sorting and rounding, and well-developed beddings with grain size showing upward positive rhythmic or homogeneous characteristics, corresponding to "bell-" or "box-shaped" log and seismic responses of weak peak interlayer.On a map view, the facies shows a banded N-SW-trending distribution characterized by an overall shifting from northeast to southwest.This study reveals that large-scale deposits of tidal channel facies are also developed in carbonate strata, a new founding that may serve as an important supplement to the sedimentary model of carbonate ramps.The understanding of carbonate ramps of tidal channel facies also sheds light on reservoir prediction and thereby lays a geological foundation for the design and adjustment of development schemes.