MICROFACIES DISTRIBUTION OF KHASIB FORMATION IN AMARA OIL FIELD, SOUTHERN IRAQ

Abstract

   The Khasib Formation Late Turonian – Lower Coniacian (Late Cretaceous) is an important reservoir rock in the Amara oil field. Hence, the importance of Petrographic study in this research of Khasib Formation is to know the facies distributions that are summarized in facies models and digenesis effected in the field. Through focusing in AM11, AM9, AM5, AM3, AM12, AM13 wells by using 33 thin sections, RG-log, density and sonic logs that used to the Layering models that have wide engineering applications.     The result shows that Khasib Formation consists of limestone and dolomitic limestone. The Khasib Formation has been divided into three microfacies that are deposited in pelagic deep marine environment (deep Cratonic water). The microfacies analysis of the Khasib Formation also is showing that the oil production units in Khasib Formation KA unit (upper part) is made up of Packstone and Grainstone carbonate, but KB unit (lower part) only from Grainstone. The skeletal grains of the Khasib Formation include variety of planktonic foraminifera, Calpionellids and bioclast. The bioclast consists of bivalved shells that belong to Mishrif Formation embedded in micrite and microspare groundmass. The Authogenic minerals consist of pyrite and iron oxide.    The rocks of the Formation are affected by diagenesis which have a significant impact on the reservoir architecture. The dolomitization is a very important factor to improve petrophysical properties and forming Intercrystalline pores in KA unit. Besides, dolomitization interprets the relatively height of the RG-log in the lower part of KA unit and BAR2. The dissolution has an important role in forming mold and vug pore space in KB unit and interparticle pores in KA unit.      The Cementation is forming impermeable rock (BAR1) in the upper part of the Globigerina Grainstone microfacies (GG3) through forming the granular cement. The chemical compaction has a negative role in petrophysics properties in Khasib units during reaching to the least contact phase and form sutured contacts, irregular stylolite and irregular parallel sutured of micro stylolite set.        The microfacies analysis also included oil show description that may be indicated to hydrocarbons concentration. The oil show is high in the upper part of KB unit and in the KA unit hydrocarbons concentrated in the medium and the lower part.    The dipocenter is located between AM11 and AM13 wells by the deep basin facies that is noted from facies models. The facies distributions in the sedimentary basin show that the Globigerina Grainstone microfacies is the main component of the Khasib Formation in the lower part. The Globigerina packstone microfacies and Calpionellids packstone microfacies are concentrated in the upper part of the Khasib Formation. Khasib reservoir has been divided into (45) layers depending on log behavior (RG-log, density and sonic) and petrophysical properties that are observed in the Layering model.   &nbsp