Classification and Sedimentary Microfacies of Paleogene-Neogene Mixosedimentite in H Oilfield of Zagros Basin

Based B1 oil group of Asmari Formation in H oilfield of Zagros Basin in the Middle East develops a set of mixed siliciclastic-carbonate sediment in the marine-continental transitional zone. How to classify the mixosedimentite and study the sedimentary microfacies under the mixed sedimentary background is a difficult problem restricting the fine development of the oilfield. By using the two- endmember classification method, the mixosedimentite classification standard suitable for H oilfield is established. The mixosedimentite is divided into pure carbonate rock, mixed carbonate rock, highly mixed rock, mixed clastic rock, pure clastic rock and mudstone. For the study of sedimentary microfacies of mixosedimentite, the research process of sedimentary microfacies under mixed sedimentary background is clarified. Firstly, through the lithofacies “coarsening”, various lithofacies are simplified into three “large class of lithofacies”, then the one-to-one correspondence between sedimentary facies and “large class of lithofacies”is established.Secondly, the development range of different sedimentary facies is reasonably determined by the distribution of “large class of lithofacies”. Finally, according to the distribution of each lithofacies, the plane distribution of each microfacies in different sedimentary facies is determined. The results show that B1 oil group in H oilfield belongs to the carbonate platform model of gentle slope influenced by delta. When the sea level droped and the provenance supply of delta was strong, the delta expanded and H oilfield mainly developed delta front subfacies deposits, usually mixed platform facies was developed outside the front subfacies. When the sea level rose and the delta provenance supply was weak, the delta shrinked and H oilfield mainly developed mixed platform facies and carbonate platform facies deposits. The study of mixosedimentite classification and sedimentary microfacies under the background can provide guidance for the fine development of oil fields such as well pattern optimization and adjustment well deployment.