Sedimentary Characteristics and Differential Diagenetic Evolution of Restricted Platform in the Upper Member of M Formation in X Oilfield, Iraq

Based on the data of core, casting thin section, scanning electron microscope, whole rock analysis, trace elements and conventional physical properties, the sedimentary characteristics, differential diagenesis and the control mechanism of sedimentary and diagenesis on reservoir physical properties of the restricted platform in the upper member of M Formation in X oilfield in Iraq are studied. Three sedimentary subfacies of tidal flat, intra-platform shoal and intershoal are developed in the restricted platform of M Formation. The tidal flat can be further divided into two sedimentary microfacies, supratidal zone and intertidal zone, and tidal channel is existed in the intertidal zone. The vertical lithologic positive rhythm combination of tidal channel-intertidal zone-supratidal zone and the inverse rhythm combination of intershoal-intra-platform shoal are developed in the restricted platform. The content of bioclasts in the tidal flat is low, while the content of terrigenous minerals and trace elements is high. The diagenesis has the characteristics of medium dissolution and strong cementation, the mineral stabilization process is early, thus the content of dolomite is low. The supratidal zone is dominated by intercrystalline pores and micropores. The intertidal zone is dominated by intragranular pores, intercrystalline pores and micropores, and the intragranular pores and mould pores are developed in tidal channel. The intra-platform shoal has high bioclasts content, low terrigenous mineral and trace element content. Its diagenesis has the characteristics of strong dissolution and weak cementation, the mineral stabilization process is early, and the dolomite content is low. It is dominated by mould pores and intragranular pores. The intershoal has low bioclasts content, terrigenous mineral and trace element. The diagenesis has the characteristics of strong compaction and strong dolomitization. Its mineral stabilization process is late, therefore the content of dolomite is high, and the intragranular pores, dolomite intercrystalline pores and intracrystalline pores are more developed. The intra-platform shoal of the restricted platform is a high-quality reservoir, and the tidal channel is a relatively high-quality reservoir. This study clarifies the reservoir characteristics and its genesis of the restricted platform in the upper member of M Formation in X oilfield, which has certain guiding significance for the further deployment of development.