| The ramp deep-water carbonate rocks of the Upper Cretaceous Khasib Formation in the Middle East are
important oil producing strata. The Khasib Formation of H Oilfield in Iraq is divided into two sections of KB and KA and
six layers of KB3, KB2, KB1, KA2, KA1-2 and KA1-1 from bottom to top. The reservoir of Khasib Formation is
developed in KA1-2 layer and KB section. The reservoir heterogeneity of Khasib Formation is strong, and the reservoir
development characteristics, control factors and oil-gas distribution law are unclear, which restricts the next evaluation
and exploration. On the basis of regional geological investigation, based on core, petrographic thin section and logging
data, the lithofacies, sedimentary model, sedimentary microfacies and control factors of reservoir development of Khasib
Formation in H Oilfield are studied, and the following understandings are obtained: (1) Five rock types are developed in
the study area, including bioclastic grainstone, bioclastic packstone, bioclastic wackestone, micrite limestone and
calcareous mudstone. Bioclastic grainstone and bioclastic packstone are mainly developed in KA1-2 and KB, bioclastic
wackestone and micritic limestone are mainly developed in KA1-1 and KA2, and calcareous mudstone is developed at the
bottom of KA2. (2)Three types of non-gravity carbonate microfacies (bioclastic shoal, shoal flank and ramp mud) and one
type of gravity carbonate microfacies are developed in the transgressive system tract of middle ramp in the study area. KB
and KA1-2 mainly develop bioclastic shoal, shoal flank and ramp mud, KA2 and KA1-1 mainly develop ramp mud, and
calcareous mudstone deposited by gravity flow is developed at the bottom of KA2. (3) There developed bioturbation
including Teichichnus, Paleophycus, Chondrites, Thalassinoides and Planolites in KA1-2 and KB reservoir sections,
which make the carbonate rocks more heterogeneous. The permeability is positively correlated with the skeletal grain
content. The reservoir is mainly controlled by sedimentary microfacies, bioturbation and penecontemperaneous
dissolution. Finally, the ramp carbonate sedimentary model of shoreland-inner ramp-middle ramp-outer ramp from west
to east in Iraq is established, and the sedimentary microfacies evolution law of six layers in the study area is defined. The
research results have important guiding significance for the next exploration of the Upper Cretaceous in the study area,
which mainly develops deep-water carbonate rocks. At the same time, they provide a reference for expanding the oil and
gas exploration field in deep-water carbonate rocks in the three major marine basins of China and all over the world. |
